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  • 1. Aimable, Anne
    et al.
    Doubi, Herve Goure
    Stuer, Michael
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Bowen, Paul
    Synthesis and Sintering of ZnO Nanopowders2017Ingår i: TECHNOLOGIES, ISSN 2227-7080, Vol. 5, nr 2, artikel-id 28Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nanopowders are continuously under investigation as they open new perspectives in numerous fields. There are two main challenges to stimulating their development: sufficient low-cost, high throughput synthesis methods which lead to a production with well-defined and reproducible properties; and for ceramics specifically, the conservation of the powders' nanostructure after sintering. In this context, this paper presents the synthesis of a pure nanosized powder of ZnO (dv(50)similar to 60 nm, easily redispersable) by using a continuous Segmented Flow Tubular Reactor (SFTR), which has previously shown its versatility and its robustness, ensuring a high powder quality and reproducibility over time. A higher scale of production can be achieved based on a "scale-out" concept by replicating the tubular reactors. The sinterability of ZnO nanopowders synthesized by the SFTR was studied, by natural sintering at 900 degrees C and 1100 degrees C, and Spark Plasma Sintering (SPS) at 900 degrees C. The performance of the synthesized nanopowder was compared to a commercial ZnO nanopowder of high quality. The samples obtained from the synthesized nanopowder could not be densified at low temperature by traditional sintering, whereas SPS led to a fully dense material after only 5 min at 900 degrees C, while also limiting the grain growth, thus leading to a nanostructured material.

  • 2. Biendicho, J. J.
    et al.
    Shafeie, S.
    Frenck, L.
    Gavrilova, D.
    Boehme, S.
    Bettanini, A. M.
    Svedlindh, P.
    Hull, S.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Istomin, S. Ya.
    Grins, J.
    Svensson, G.
    Synthesis and characterization of perovskite-type Sr(x)Y1-xFeO(3-delta) (0.63 <= x < 1.0) and Sr0.75Y0.25Fe1-yMyO3-delta (M=Cr, Mn, Ni), (y=0.2, 0.33, 0.5)2013Ingår i: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 200, s. 30-38Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Oxygen-deficient ferrates with the cubic perovskite structure SrxY1-xFeO3-delta were prepared in air (0.71 <= x <= 0.91) as well as in N-2 (x=0.75 and 0.79) at 1573 K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3-delta=2.79(2) for x=0.75 to 3-delta=2.83(2) for x=0.91. Refinement of the crystal structure of Sr0.25Y0.25FeO2.29 using TOP neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and highresolution electron microscopy (HREM) studies of Sr0.75Y0.25FeO2.79 reveal a modulation along (1 0 0)(p) with G +/- similar to 0.4(1 0 0)(p) indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5-390 K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr0.75Y0.25Fe02.79 shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm/K in air at 298-673 K. At 773-1173 K TEC increases up to 17.2 ppm/K due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673 K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr0.75Y0.25Fe1-yMyO3-delta (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr0.75Y0.25Fe02.79. Only M=Ni has increased electrical conductivity compared to un-doped Sr0.75Y0.25Fe02.79.

  • 3.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär G.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Wang, Cao
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Novel BaZr0.5Ce0.3Y0.2O3-δ based proton conductors prepared by spark plasma sinteringManuskript (preprint) (Övrigt vetenskapligt)
  • 4.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär G.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    BaZr0.5Ce0.3Ln0.2O3-δ(Ln=Y, Sm, Gd, Dy) based electrolytes used for intermediate temperature solid oxide fuel cellsManuskript (preprint) (Övrigt vetenskapligt)
  • 5.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär G.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi. Shanghai Institute of Technology, China.
    Ionic conductivity of dense BaZr(0.5)Ce(0.3)Ln(0.2)O(3-delta) (Ln = Y, Sm, Gd, Dy) electrolytes2014Ingår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 272, s. 786-793Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BaZr(0.5)Ce(0.3)Ln(0.2)O(3-delta) (BZCLn532, Ln = Y, Sm, Gd, Dy) based electrolytes were successfully synthesized by a cost-effective solid-state reactive sintering (SSRS) method while using 1.0 wt.% NiO as a sintering aid. Dense pellets of BZCLn532 compounds can be prepared at sintering temperatures of 1600 degrees C (BZCY532) and 1400 degrees C (BZCS532, BZCG532 and BZCD532). The conductivities of the dense BZCLn532 ceramics were tested in dry and wet air at temperatures of 700 degrees C-200 degrees C. On the basis of the obtained results, it could be concluded that the BZCY532-based electrolyte show promise for use as oxygen-ion conductors and proton conductors in intermediate temperature solid oxide fuel cells (ITSOFCs).

  • 6.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär G.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Preparation of 30 mol.% Y-doped hafnia (Hf0.7Y0.3O2-delta) using a modified solid-state reaction method2015Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 41, nr 2, s. 2611-2615Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A pure and well-crystallized Hf0.7Y0.3O2-delta (YSH) powder was synthesized using a modified solid-state reaction method. Water-based milling and freeze drying process were implemented to facilitate powder synthesis and final densification process. The improved powder performance, in aspects of phase development and sintering behaviour, was investigated by systematic comparison between different powder processing procedures. Dense YSH ceramic material with a relative density of 0.975 was successfully obtained using conventional sintering at 1650 degrees C for 10 h. XRD, SEM and EDS were employed to characterize the synthesized powder and dense YSH ceramics. Dense YSH ceramic possesses a fluorite cubic structure with an a value of 5.1406 angstrom, and the ionic radius of Y3+ in YSH was determined to be 0.1006 nm.

  • 7.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär G.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi. Shanghai Institute of Technology, China .
    Sintering behaviour of the protonic conductors BaZr(x)Ce(0.8-x)Ln(0.2)O(3-delta) (x=0.8, 0.5, 0.1; Ln=Y, Sm, Gd, Dy) during the solid-state reactive-sintering process2015Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 41, nr 2, s. 2558-2564Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The protonic conductors BaZr(x)Ce(0.8-x)Ln(0.2)O(3-delta) (x=0.8, 0.5, 0.1; Ln=Y, Sm, Gd, Dy) were successfully prepared using a solid-state reactive-sintering method. NiO (1 wt.%) was added as a sintering aid, and it was proven that NiO produced tremendous enhancement in the densification process. The morphologies of the variously doped BaZr(0.8)Ln(0.2)O(3-delta), BaZr(0.5)Ce(0.3)Ln(0.2)O(3-delta) and BaZr(0.1)Ce(0.7)Ln(0.2)O(3-delta) ceramics, as well as their sintering behaviour, were investigated. The results show that the Ce content in the BaZr(0.8)Ln(0.2)O(3-delta), BaZr(0.5)Ce(0.3)Ln(0.2)O(3-delta) and BaZr(0.1)Ce(0.7)Ln(0.2)O(3-delta) compounds influences the sintering temperature significantly, and a larger Ce content will lead to a lower sintering temperature. In addition, ionic radii of the dopants that are similar to the ionic radii of the B-site will also result in a lowered sintering temperature. Based on the present study, NiO has no influence on the lattice parameters.

  • 8.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär G.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    The effect of NiO on the conductivities of BaZr0.5Ce0.3Y0.2O3-δ based electrolytesManuskript (preprint) (Övrigt vetenskapligt)
  • 9.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär G.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Yttrium doped hafnium oxide Hf0.69Y0.31O2-δ used for solid oxide fuel cell electrolytes and electronic materialsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    An Yttrium doped hafnium oxide Hf0.69Y0.31O2-δ (YSH orYDH) is obtained by a modified solid state reactionmethod, where freeze drying is implemented to reduce theagglomeration. Refinement result shows that YSH is influorite cubic crystal with lattice parameter a = b = c =5.140674 Å (Figure 1). Based on this, the ionic radius ofY3+ in YSH for 8 coordination is 0.1006 nm, confirms theprevious prediction that it should be smaller than 0.1015nm. The YSH ceramic material with relative density of>97.5% can be obtained by conventional sintering at 1650℃ for 10hrs. Its conductivity is only 3.65×10-5 s cm-1 at700 ℃ (Figure 2), which is too low for solid oxide fuelcell application. However, its high dielectric constant22.03 (Figure 3a, average value, which is 1.4 times largerthan the pure Hafnia) and low dielectric loss over a widefrequency range and DC potential make it very promisingfor the microelectronic device application.

  • 10.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär Göran
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Shanghai Institute of Technology, China.
    Dense and translucent BaZrxCe0.8-xY0.2O3-delta (x=0.5, 0.6, 0.7) proton conductors prepared by spark plasma sintering2015Ingår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 107, s. 145-148Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dense and translucent BaZrxCe0.8-xY0.2O3-delta (x = 0.5, 0.6, 0.7) proton conductors were firstly and successfully prepared by Spark Plasma Sintering (SPS) at a temperature of 1350 degrees C without sintering aids' addition. XRD, SEM and EDS were applied to determine the phase purity, morphology and element composition of prepared pellets, respectively. Moreover, the sintering behaviors of these proton conductors were monitored and analyzed through the on-line sintering curves. The obtained results indicate that a lowered sintering temperature (<1400 degrees C) and a fast cooling rate (>= 200 degrees C/min) represent two key parameters to prepare dense Ce-containing BaZrO3-BaCeO3 based proton conductors.

  • 11.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jönsson, Pär Göran
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Shanghai Institute of Technology, China.
    Electrical conductivities of translucent BaZr(X)Ce0.8-XY0.2O3-delta (x=0.5, 0.6, 0.7) ceramics2016Ingår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 115, s. 87-90Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The electrical conductivities of translucent BaZr0.5Ce0.3Y0.2O3-delta (x = 0.5, BZCY532), BaZr0.6Ce0.2Y0.2O3-delta (x = 0.6, BZCY622) and BaZr0.7Ce0.1Y0.2O3-delta(x = 0.7, BZCY712) proton conductors were investigated systematically in different atmospheres and also at different oxygen partial pressures. The obtained results indicate that translucent BZCY532, BZCY622 and BZCY712 ceramics are pure oxygen-ion and proton conductors without unfavorable electronic conduction. In addition, they represent promising proton conductors to be used as intermediate temperature solid oxide fuel cell electrolytes.

  • 12.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jönsson, Pär Göran
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    The effect of NiO on the conductivity of BaZr0.5Ce0.3Y0.2O3-delta based electrolytes2016Ingår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, nr 67, s. 62368-62377Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effects of NiO on the sintering behaviors, morphologies and conductivities of BaZr0.5Ce0.3Y0.2O3-delta (BZCY532) based electrolytes were systematically investigated. 1 wt% NiO powder was added by different methods during the sample preparation: (i) added during ball-milling before a powder mixture calcination (named BZCY(Ni) 532), (ii) no NiO addition in the whole preparation procedure (named BZCY532) and (iii) added after a powder mixture calcination (named BZCY532(Ni)). The conductivities of these three kinds of dense BZCY532 ceramics were investigated in dry air, wet N-2 and wet H-2 atmospheres, respectively. Moreover, the electronic contributions to the total conductivities were also identified in a broad oxygen partial pressure range. According to the achieved results, it can be concluded that the dense BZCY(Ni) 532 ceramics showed the best enhanced oxygen and proton conductivities, followed by the BZCY532(Ni) and BZCY532 ceramics. Furthermore, the BZCY(Ni) 532 and BZCY532 ceramics showed a tiny electronic conductivity, when the testing temperatures were lower than 800 degrees C. However, the BZCY532(Ni) ceramics revealed an obvious electronic conduction when they were tested at temperatures of 600-800 degrees C. Therefore, it is preferable to add the NiO during powder preparation, which can lower the sintering temperature and also increase the conductivity of BZCY532-based electrolytes.

  • 13.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jönsson, Pär Göran
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Shanghai Institute of Technology, China.
    Transport properties of BaZr0.5Ce0.3Y0.2O3-delta proton conductor prepared by spark plasma sintering2016Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 42, nr 3, s. 4393-4399Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dense BaZr0.5Ce0.3Y0.2O3-delta (BZCY532) proton conductors were prepared by a spark plasma sintering method. Their conductivities were determined in different atmospheres: dry air, wet N-2 and wet H-2. Moreover, the potential electronic conductivity contribution to the total conductivity was also identified by testing their total conductivities at different oxygen partial pressures (1-10(-24) atm) in combination with an XPS analysis. It is found that the prepared dense BZCY532 ceramics are good proton conductors at 600 degrees C. In addition, the Ce3+ concentration in the dense BZCY532 ceramics is around 3.5 atm% of the total Ce element, and the electronic contribution to the total conductivity can be neglected after a postheat treatment.

  • 14.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi. Department of Materials Science and Engineering, Shanghai Institute of Technology, China.
    Preparation of Potential Protonic Conductor Yttria Doped Hafnia by Using the Modified Solid State Reaction Method2014Ingår i: ECS Transactions, 2014, Vol. 59 (1), s. 315-320Konferensbidrag (Refereegranskat)
    Abstract [en]

    A pure and well crystalized yttrium doped hafnium oxide Hf0.69Y0.31O2-δ (YSH) is obtained by using a modified solid state reaction method, where a water-based milling medium and freeze drying are implemented to reduce the agglomeration. The mean sizes of the YSH powder, which is obtained through a traditional alcohol-based milling method, is more than 1 um. However, the powder size can be reduced to 100 nm by using the water-based milling method. In addition, the calcination temperature can be lowered 200 °C to get a pure phase by using the water-based milling method, compared to the alcohol-based milling method. The relative density of YSH ceramic materials can reach to 97.5% by conventional sintering at 1650 °C after during 10 h.

  • 15.
    Bu, Junfu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Jönsson, Pär
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Preparation of Protonic Conductor BaZr0.5Ce0.3Ln0.2O3-δ (Ln = Y, Sm, Gd, Dy) by using a Solid State Reactive Sintering Method2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    A pure and well crystalized yttrium doped hafnium oxide Hf0.69Y0.31O2-δ (YSH) is obtained by using a modified solid state reaction method, where a water-based milling medium and freeze drying are implemented to reduce the agglomeration. The mean sizes of the YSH powder, which is obtained through a traditional alcohol-based milling method, is more than 1 um. However, the powder size can be reduced to 100 nm by using the water-based milling method. In addition, the calcination temperature can be lowered 200 ℃ to get a pure phase by using the water-based milling method, compared to the alcohol-based milling method. The relative density of YSH ceramic materials can reach to 97.5% by conventional sintering at 1650 ℃ after during 10 h.

  • 16. Buscaglia, M. T.
    et al.
    Buscaglia, V.
    Viviani, M.
    Petzelt, J.
    Savinov, M.
    Mitoseriu, L.
    Testino, A.
    Nanni, P.
    Harnagea, C.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Nygren, M.
    Ferroelectric properties of dense nanocrystalline BaTiO3 ceramics2004Ingår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 15, nr 9, s. 1113-1117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dense BaTiO3 ceramics with 50 nm average grain size obtained by spark plasma sintering were investigated. The dielectric data show a broad ferro-para phase transition with a maximum permittivity of approximate to1100 at 390 K and 1 kHz. The local ferroelectric switching behaviour was investigated by piezoresponse force microscopy. Typical piezoelectric hysteresis loops were recorded at different positions of the sample. The present results provide experimental evidence for polarization switching at the local scale, indicating that the critical grain size for the disappearance of ferroelectric behaviour in dense, bulk BaTiO3 nanocrystalline ceramics is below 50 nm.

  • 17. Buscaglia, M. T.
    et al.
    Viviani, M.
    Buscaglia, V.
    Mitoseriu, L.
    Testino, A.
    Nanni, P.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Nygren, M.
    Harnagea, C.
    Piazza, D.
    Galassi, C.
    High dielectric constant and frozen macroscopic polarization in dense nanocrystalline BaTiO3 ceramics2006Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 73, nr 6Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Theoretical models for small ferroelectric particles predict a progressive decrease of the Curie temperature, spontaneous lattice strain, and polarization until the critical size corresponding to transition to the cubic phase and disappearance of ferroelectricity is reached. In contrast, the behavior of nanocrystalline BaTiO3 ceramics with a grain size of approximate to 30 nm is dominated by extrinsic effects related to the grain boundaries which mask the expected downscaling of properties. While the noncubic crystal structure, the high dielectric constant (approximate to 1600) and the variation of permittivity with temperature suggest a ferroelectric behavior, very slim, and nearly linear polarization hysteresis loops are observed. Evidence for the existence of a ferroelectric domain structure with domains extending over several grains and of polarization switching at local scale is given by piezoresponse force microscopy. The suppression of macroscopic ferroelectric hysteresis and switching originates from a frozen domain structure stable under an external field owing to the effects exerted by the grain boundaries, such as the clamping of the domain walls and the hindrance of polarization switching. Furthermore, the depolarization field originated by the low-permittivity nonferroelectric grain boundaries can cause a significant reduction of polarization. If the grain size is small enough, the ceramic is expected to undergo a "phase transition" to a polar phase with nonswitchable polarization. The BaTiO3 ceramics with grain size of 30 nm investigated in the present study are deemed to be close to this transition.

  • 18. Buscaglia, M. T.
    et al.
    Viviani, M.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Buscaglia, V.
    Nanni, P.
    Synthesis of BaTiO3 core-shell particles and fabrication of dielectric ceramics with local graded structure2006Ingår i: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 18, nr 17, s. 4002-4010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The coating of BaTiO3 particles with a different perovskite and the subsequent consolidation to dense ceramics retaining a radial composition gradient within the single grains are presented and discussed. A shell of SrTiO3 or BaZrO3 was directly grown on the surface of BaTiO3 spherical templates suspended in aqueous solution by means of a precipitation process making use of inorganic precursors. The overall composition and the particle size can be tailored over a wide range. Densification of the resulting core-shell particles was realized using spark plasma sintering or conventional sintering. Dense ceramics with locally graded structure can be only obtained by a careful choice of the sintering conditions, that is, controlling the interdiffusion between core and shell. The final materials show strongly modified dielectric properties in comparison to both the parent compounds and the homogeneous solid solutions. The proposed approach is generic and suggests a new avenue to create functional and structural polycrystalline materials with locally graded structure by the controlled sintering of core-shell particles.

  • 19.
    Buscaglia, Maria Teresa
    et al.
    IENI-CNR.
    Buscaglia, Vincenzo
    IENI-CNR.
    Curecheriu, Lavinia
    Alexandru Ioan Cuza University.
    Postolache, Petronel
    Polytechnic University of Bucharest.
    Mitoseriu, Liliana
    Polytechnic University of Bucharest.
    Ianculeschu, A.C
    Vasile, B.S
    Zhao, Zhe
    Department of Materials and Environmental Chemistry, Stockholm University.
    Nanni, Paolo
    University of Genoa.
    Fe2O3@BaTiO3 Core−Shell Particles as Reactive Precursors for the Preparation of Multifunctional Composites Containing Different Magnetic Phases2010Ingår i: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 22, nr 16, s. 4740-4748Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Well-designed reactive precursors and templates allow for careful control of solid-state reactions at the nanoscale level, thus enabling the fabrication of materials with specific microstructures and properties. In this study, Fe2O3@BaTiO3 core−shell particles have been used as precursors for the in situ fabrication of multifunctional composites containing a dielectric/ferroelectric phase and two magnetic phases with contrasting coercivities (Fe2O3/Fe3O4, BaFe12O19/Ba12Fe28Ti15O84). The formation of new magnetic phases occurs during sintering or post-annealing via reaction between BaTiO3 and Fe2O3. The starting powders have been prepared using a multistep process that combines colloidal chemistry methods and a solid-state reaction. The nature and the amount of the magnetic phases and, consequently, the final magnetic properties of the composite can be controlled by varying the relative amount of Fe2O3 (30 or 50 vol %), the densification method (conventional or spark plasma sintering), and the processing temperature. The composites show constricted magnetic hysteresis loops with a coercivity of 0.1−2.5 kOe and a saturation magnetization of 5−16 emu/g. Composites obtained from powders containing 30 vol % Fe2O3 show, at temperatures of 20−80 °C and frequencies between 10 kHz and 1 MHz, a relative dielectric constant of 50 and dielectric losses of <10%.

  • 20. Buscaglia, V.
    et al.
    Buscaglia, M. T.
    Viviani, M.
    Ostapchuk, T.
    Gregora, I.
    Petzelt, J.
    Mitoseriu, L.
    Nanni, P.
    Testino, A.
    Calderone, R.
    Harnagea, C.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Nygren, M.
    Raman and AFM piezoresponse study of dense BaTiO3 nanocrystalline ceramics2005Ingår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 25, nr 12, s. 3059-3062Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dense nanocrystalline BaTiO3 (BT) ceramics with grain sizes (GSs) below 100 nm obtained by spark plasma sintering (SPS), were investigated by micro-Raman spectroscopy in order to obtain information about the changes in the local order induced by size effects. The obtained spectra in the range 80-700 K showed the presence of all the crystalline phases of BaTiO3, even in the finest structure (50 nm grain size ceramic), with particularities attributed to the high density of non-ferroelectric grain boundaries. The AFM piezoresponse study incontestably proved the ferroelectric switching at local scale in nanocrystalline BaTiO3 ceramics at room temperature.

  • 21. Buscaglia, V.
    et al.
    Viviani, M.
    Buscaglia, M. T.
    Nanni, P.
    Mitoseriu, L.
    Testino, A.
    Stytsenko, E.
    Daglish, M.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Nygren, M.
    Nanostructured barium titanate ceramics2004Ingår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 148, nr 1, s. 24-27Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dense nanocrystalline ceramics can be obtained starting from non-agglomerated nanopowders and using low-temperature sintering processes. The preparation and the properties of Barium Titanate (BaTiO3) ceramics and thick films are reported: ceramics were prepared by Spark Plasma Sintering (SPS) at 800 degreesC of nanopowders produced by a wet chemical process, while films were fabricated by airflow deposition (AD) of mixed fine and coarse powders at room temperature followed by isothermal firing. Ferroelectric ordering was found in both the ceramics and the sintered films by a.c. impedance. The transition from ferroelectric to paraelectric state was broadened over a wide temperature range with Curie-Weiss parameters strongly depressed in comparison to coarse-grained ceramics.

  • 22.
    Cheng, Yajuan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jönsson, Pär Göran
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Controllable fabrication of large-area 2D colloidal crystal masks with large size defect-free domains based on statistical experimental design2014Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 313, s. 144-151Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A large-area hexagonal packed monolayer of silica spheres with consistent defect-free domains of a size larger than 3000 mu m(2) was prepared by spin coating on glass substrates with the assistance of experimental design and statistical analysis. The ratio of the defect-free monolayer area to the square of sphere diameter is nearly two times of the previously reported maximum values. Several parameters involved in the spin coating systems were investigated. The results indicated that the relative humidity and the rotational speed of the first step of the spin coating had the most important impact on the ordering degree of the prepared monolayer. Furthermore, the ordering degree of the obtained monolayer increased with a decreased relative humidity. In addition, it reached an optimal value when the first rotational speed during spin coating reached a value of 1000 rpm. From this study, it can be concluded that statistical experimental design is an efficient strategy, especially for multi-factor phenomenon studies.

  • 23.
    Cheng, Yajuan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jösson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Fabrication of large size defect-free domains of 2D colloidal crystal monolayer withassistance of statistical experimental designManuskript (preprint) (Övrigt vetenskapligt)
  • 24.
    Cheng, Yajuan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jösson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Optimization of synthesizing upright ZnO rod arrays with large diameters through response surface methodologyManuskript (preprint) (Övrigt vetenskapligt)
  • 25.
    Cheng, Yajuan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Wang, Jing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jönsson, Pär Göran
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Optimization of high-quality vertically aligned ZnO rod arrays by the response surface methodology2015Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 626, s. 180-188Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optimization of the deposition parameters was conducted by the response surface methodology to synthesize high-quality ZnO rod arrays with a high texture coefficient, a large aspect ratio and a narrow bandgap. In addition, mathematical models based on statistical analysis were also developed to predict the texture coefficient, aspect ratio and bandgap of the ZnO rod arrays. With the optimized parameters, all of the three involved responses obtained the desired optimum values. The results show that the texture coefficient can be elevated up to a value of 0.998, which represents an almost perfect value. Moreover, wide range of aspect ratios was obtained for various applications and the obtained maximum value of 21.3 is relatively high value by wet chemical method, especially when no capping agent and no refreshing growth solution in a nearly neutral solution is used.

  • 26.
    Cheng, Yajuan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Wang, Jing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jösson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Improvement and optimization of the growth quality of upright ZnOrod arrays by the response surface methodology2015Ingår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 351, s. 451-459Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Response surface methodology was employed to guide the growth of ZnO rod arrays. With its assistance, the growth quality of the obtained samples was improved dramatically. The morphologies evolved from sparsely, randomly oriented rods to dense and upright rod arrays. Moreover, the significant parameters for ZnO rod arrays growth and their optimal regions were also determined. Furthermore, with the optimized parameters, the obtained aspect ratio of the vertically aligned ZnO rod arrays reached a value of 31. This is relatively a high value of ZnO rod arrays synthesized by wet chemical methods without capping agents in neutral solutions.

  • 27. Cheng, Z.
    et al.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Tianjin University, Tianjin, China.
    Ink-jet printed BNT thin films with improved ferroelectric properties via annealing in wet air2018Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 44, nr 9, s. 10700-10707Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, an ink-jet printing process based on the sol-gel route was applied to prepare lead-free ferroelectric Na0.5Bi0.5TiO3(BNT) thin films for the first time. Dense and crack-free films with perovskite structure were obtained from a modified precursor solution through multiple printing and pyrolysis processes. The ferroelectric, dielectric and electrical properties were significantly affected by the annealing temperature and atmosphere. The film annealed at 670 °C in wet air showed a high remnant polarization of 24.7 μC/cm2 with a low coercive field of 263 kV/cm, the dielectric constant and loss were 185 and 0.1 at 10 kHz, respectively. It was found that wet air was an alternative to reduce oxygen vacancies and enhance properties of ferroelectric films, which can be explained by the defect chemical reaction between water and oxygen vacancies. X-ray photoelectron spectroscopy(XPS) confirmed the decrease of oxygen vacancies after annealing with water presence, with a formation of Ohmic conduction mechanism dominated by charged hydroxyl groups.

  • 28.
    Curecheriu, Lavinia
    et al.
    Alexandru Ioan Cuza University.
    Buscaglia, Maria Teresa
    IENI-CNR.
    Buscaglia, Vincenzo
    IENI-CNR.
    Zhao, Zhe
    Department of Materials and Environmental Chemistry, University of Stockholm.
    Mitoseriu, Liliana
    Polytechnic University of Bucharest.
    Grain size effect on the nonlinear dielectric properties of barium titanate ceramics2010Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 97, nr 24Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The nonlinear dielectric properties of dense BaTiO(3) ceramics with grain size of 1 mu m-90 nm were investigated. In the finest ceramics, the permittivity reduces below 1000 and a remarkable nonhysteretic linear dc-tunability [epsilon(E)] is obtained at high field, above 40 kV/cm. The observed behavior was explained by considering the nanostructured ceramic as a composite formed by ferroelectric grains, whose nonlinearity is reducing, and by low-permittivity nonferroelectric grain boundaries, whose volume fraction increases when decreasing the grain size. Reducing the grain size in ferroelectric dense materials is an alternative route to accomplish the application requirements: nonhysteretic tunability and permittivity below 1000.

  • 29. Dahl, P.
    et al.
    Kaus, I.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Johnsson, M.
    Nygren, M.
    Wiik, K.
    Grande, T.
    Einarsrud, M. A.
    Densification and properties of zirconia prepared by three different sintering techniques2007Ingår i: Ceramics International, ISSN 0272-8842, E-ISSN 1873-3956, Vol. 33, nr 8, s. 1603-1610Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Densification of nanocrystalline yttria stabilized zirconia (YSZ) powder with 8 mol% Y2O3, prepared by a glycine/nitrate smoldering combustion method, was investigated by spark plasma sintering, hot pressing and conventional sintering. The spark plasma sintering technique was shown to be superior to the other methods giving dense materials (>= 96%) with uniform morphology at lower temperatures and shorter sintering time. The grain size of the materials was 0.21, 0.37 and 12 mu m after spark plasma sintering, hot pressing and conventional sintering, respectively. Total electrical conductivity of the materials showed no clear correlation with the grain size, but the activation energy for spark plasma sintered materials was slightly higher than for materials prepared by the two other densification methods. The hardness, measured by the Vickers indentation method, was found to be independent on grain size while fracture toughness, derived by the indentation method, was slightly decreasing with increasing grain size.

  • 30. Dong, H.
    et al.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. School of Materials Science and Engineering, Shanghai Institute of Technology, Shanghai, 201418, China.
    Wang, C.
    Effect of powder characteristics on the thermal conductivity and mechanical properties of Si 3 N 4 ceramics sintered by Spark plasma sintering2019Ingår i: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 30, nr 8, s. 7590-7599Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of powder characteristics on the thermal conductivity and mechanical properties of silicon nitride (Si 3 N 4 ) ceramics were investigated systematically by using two α-Si 3 N 4 powders as raw materials and using MgSiN 2 or MgO + Y 2 O 3 as sintering additives. The Si 3 N 4 ceramics with a higher density were obtained by α-Si 3 N 4 powders with lower oxygen content and impurities and using none-oxide sintering additive MgSiN 2 . The α–β phase transformation completely taken place in all the specimen at 1750 °C. The specimens sintered by powders with lower levels of oxygen and impurities show higher mechanical properties than other specimens. The Y 2 O 3 and MgO sintering additives lead to higher flexural strength and fracture toughness than MgSiN 2 . The Vickers’ hardness is just the opposite. The thermal conductivity value of powders with lower oxygen content is higher than that of the materials prepared by the other type of powder at the same conditions. The effects of the Si 3 N 4 particle size, native oxygen and impurities on the thermal conductivity of resultant materials were discussed in detail. This work demonstrates that the improvement in thermal conductivity of Si 3 N 4 can be obtained by using none-oxide sintering additive MgSiN 2 and the Si 3 N 4 powder with lower oxygen content, and impurities.

  • 31.
    Gao, Zhan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Liu, Xingmin
    Bergman, Bill
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Comparative study of Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) electrolyte synthesized by different routes2011Ingår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 509, nr 35, s. 8720-8727Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, four different methods, including polyvinyl alcohol (PVA)-assisted sol-gel process, polyethylene glycol (PEG)-assisted sol-gel process, citrate sol-gel process and oxalate coprecipitation process (OCP) are employed to synthesize the Sm and Nd co-doped ceria electrolyte with the composition of Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) (SNDC). The phase structure of the powders can be well indexed with the fluorite-type CeO(2) structure. The morphology of sintered samples indicates that the ceramics can be highly densified. The relative density and the average grain size vary with the synthesis processes and the sintering temperatures. The bulk conductivities are quite close and the OCP-SNDC yields highest grain-boundary conductivities and total conductivities. The results indicate that the OCP process for the powder synthesis results in higher relative density and conductivities, lower grain-boundary resistance and activation energy. Grain-boundary space charge potentials for different specimens are calculated based on the Mott-Schottky model. The synthesis process and sintering temperature have significant effect on the space charge potential and the specific grain-boundary conductivity. (C) 2011 Elsevier B.V. All rights reserved.

  • 32.
    Gao, Zhan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Liu, Xingmin
    Bergman, Bill
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Electrical properties of ceria co-doped with Sm3+ and Lu3+electrolyte materialsArtikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Sm and Lu co-doped ceria with compositions of Ce1-x(Sm3Lu2)x/5O2-δ (SLDC, x=0.05, 0.1, 0.15, 0.2) are investigated to validate the concept of critical dopant ionic radius ( rc ), where the number-average dopant ionic radius is designed tomatch the critical dopant ionic radius ( c r ). A variety of techniques including X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to characterize the SLDC powders and the sintered pellets. Electrical properties of different specimens are investigated by using the impedance spectroscopy. The result sdemonstrated that the critical dopant ionic radius concept is not totally valid for Sm-Lu co-doping strategy, even that the co-doping with appropriate chemicalcomposition, Ce0.85(Sm3Lu2)0.03O2-δ, yields higher total conductivity than either Smor Lu-doped ceria. More co-doping strategies need to be studied to test the critical dopant ionic radius concept.

  • 33.
    Gao, Zhan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Liu, Xingmin
    Bergman, Bill
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Enhanced ionic conductivity of Ce0.8Sm0.2O2-delta by Sr addition2012Ingår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 208, s. 225-231Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sm and Sr co-doped ceria-based electrolyte with compositions of Ce-0.8(Sm1-xSrx)(0.2)O2-delta (x = 0, 0.3, 0.5, 0.7) are synthesized and investigated with the aim of improving the electrical properties of Ce0.8Sm0.2O2-delta. X-ray diffraction (XRD) and electron microscope (SEM and TEM) techniques are employed to characterize the microstructure of powders and sintered pellets. The ionic conductivity has been examined by the A.C. impedance spectroscopy in air. The Ce-0.8(Sm0.7Sr0.3)(0.2)O2-delta exhibits the highest bulk conductivity among the series, which can be mainly ascribed to the increase of oxygen vacancy concentration. The specific grain-boundary conductivities are observed to increase with the Sr doping content up to x = 0.5. Further increase in Sr concentration will lead to reduced specific grain-boundary conductivities. The total conductivities of all Sm and Sr co-doped ceria are higher than that of Ce0.8Sm0.2O1.9. The results indicate that Sr co-doping opens a new avenue to improve ionic conductivity in Ce0.8Sm0.2O1.9.

  • 34.
    Gao, Zhan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Liu, Xingmin
    Bergman, Bill
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Investigation of oxygen reduction reaction kinetics on Sm(0.5)Sr(0.5)CoO(3-delta) cathode supported on Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) electrolyte2011Ingår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 196, nr 22, s. 9195-9203Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Sm(0.5)Sr(0.5)CoO(3-delta) (SSC) cathode prepared by a glycine-nitrate process (GNP) is investigated for solid oxide fuel cells (SOFCs) based on Ce(0.85)Sm(0.075)Nd(0.075)O(2-delta) (SNDC) electrolyte. SSC forms cubic perovskite structure after being annealed at 1100 degrees C for 5 h. SSC cathode and SNDC electrolyte can retain their own structure and there is no reaction between the two compositions. The microstructure of the cathode and the interfaces between cathodes and SNDC electrolytes are studied by scanning electron microscopy (SEM) after sintering at various temperatures. Impedance spectroscopy measurements reveal that area specific resistances (ASRs) of SSC-SNDC30 cathode are much lower than those of SSC cathode. Kinetics of oxygen reduction reaction (ORR) on porous SSC cathode is investigated by analysis of impedance spectra. Medium-frequency conductivities show no dependency on oxygen partial pressure (Po(2)), which can be attributed to the oxygen ions transfer across the electrode/electrolyte interface. The dependencies of low-frequency conductivities on oxygen partial pressure (Po(2)) vary in the range from ca. 0.31 to ca. 0.34 and increase with the increasing temperatures. The low-frequency electrode process is a mixing process involving oxygen reduction reaction related to atomic oxygen and oxygen ions conduction step together with total charge-transfer step. IR-compensated current density (i)-overpotential (eta) relationship is established and the exchange current densities i(0) originated from high-field approximations are much higher than those of low-field approximations and a.c. impedance data under OCV state. It demonstrates the polarization overpotential has great effect on the kinetics of ORR. The polarization current is observed to increase with time in the long-term stability measurement, which can be ascribed to the propagation process of oxygen vacancies.

  • 35.
    Gao, Zhan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Liu, Xingmin
    Bergman, Bill
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Mao, Zongqiang
    Novel BaZr0.1Ce0.7Y0.2O3-δ (BZCYO)-Ce0.8Y0.2O2-δ (YDC) composite ceramic electrolyte for low-temperature SOFCsArtikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Novel BaZr0.1Ce0.7Y0.2O3-δ (BZCYO)-Ce0.8Y0.2O2-δ (YDC) composite ceramic electrolyte possessing both proton and oxygen ion vacancies conduction was first reported. There are no chemical reactions between the two compositions. The composite ceramic electrolyte shows excellent chemical stability to reduction. BZCYO2-YDC8 exhibits the highest bulk ionic conductivities in the temperature range of 450 oC to 650 oC and total ionic conductivities when the temperatures are higher than 550 oC. The conductivity enhancement mechanism has been discussed. BZCYO-YDC composite ceramics may be promising electrolytes in low-temperature solid oxide fuel cells.a)

  • 36. Gebauer, D.
    et al.
    Liu, X.
    Aziz, B.
    Hedin, N.
    Zhao, Zhe
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Porous tablets of crystalline calcium carbonate via sintering of amorphous nanoparticles2013Ingår i: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 15, nr 6, s. 1257-1263Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Porous tablets of crystalline calcium carbonate were formed upon sintering of a precursor powder of amorphous calcium carbonate (ACC) under compressive stress (20 MPa) at relatively low temperatures (120-400 °C), induced by pulsed direct currents. Infrared spectroscopy ascertained the amorphous nature of the precursor powders. At temperatures of 120-350 °C and rates of temperature increase of 20-100 °C min-1, the nanoparticles of ACC transformed into crystallites of mainly aragonite, which is generally difficult to achieve using wet-chemicals under kinetic control. The amorphous precursor particles (∼10 nm) transformed into crystallites (∼30-50 nm) during sintering. Consistently, the specific surface areas of 140-160 m2 g-1 for the precursor particles were reduced to 10-20 m2 g-1 for the porous tablets. The porous network within the tablets consisted of fused aragonite and vaterite particles in a ratio of ∼80:20. The fraction of aragonite to vaterite was invariant to the temperature and rate of temperature change used. The particle size increased only to a small amount on an increased rate of temperature change. At temperatures above 400 °C, porous tablets of calcite formed. The later transformation was under thermodynamic control, and led to a minor reduction of the specific surface area. The size of the crystallites remained small and the transformation to calcite appeared to be a solid-state transformation. Porous, template- and binder-free tablets of calcium carbonate could find applications in for example, biology or water treatment.

  • 37. Ha, Minh Ngoc
    et al.
    Zhu, Feng
    Liu, Zhifu
    Wang, Lichao
    Liu, Linyan
    Lu, Guanzhong
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Shanghai Institute of Technology, China.
    Morphology-controlled synthesis of SrTiO3/TiO2 heterostructures and their photocatalytic performance for water splitting2016Ingår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, nr 25, s. 21111-21118Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Different morphologies of SrTiO3/TiO2 heterostructures like nanocubes, nanoparticles, nanospheres, and nanofibers were synthesized via a facile hydrothermal process using TiO2 as both a template and precursor in Sr(OH)(2) solution. Their structure, interface and composition can be rationally tailored by simply adjusting the Sr(OH)(2)/TiO2 (Sr/Ti) mole ratios and the morphology of SrTiO3/TiO2 heterostructures can be controlled easily using TiO2 with different morphologies. A SrTiO3 crystal thin layer was grown on an anatase TiO2 substrate to fabricate a heterostructure interface contact between SrTiO3 and TiO2 and the lattice mismatch had an effect on the electrical transport properties. The SrTiO3/TiO2 heterostructures are beneficial for the fast separation of photogenerated electrons and holes so as to suppress the recombination of photogenerated electrons and holes at the interface of SrTiO3 and TiO2. Besides this, the different morphologies of the SrTiO3/TiO2 heterostructures allowing facile electron transfer, the hierarchical structure promoting mass transfer and allowing more light reflection and absorption, and the large specific surface area providing more reaction sites to facilitate the reactants to the desired oxidation places all together create a synergistic effect to improve the photocatalytic activity of the hierarchical SrTiO3/TiO2 heterostructures. Under the irradiation of UV light, in a water/methanol sacrificial reagent system, the SrTiO3/TiO2 NP heterostructures at a Sr/Ti mole ratio of 40% with the highest BET and smallest crystallite size achieve the highest photocatalytic activity generating 0.731 mmol of H-2. The SrTiO3/TiO2 heterostructures exhibit better photocatalytic activity by generating three times more H-2 than bare TiO2 and pure SrTiO3.

  • 38.
    Lapina, Alberto
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Li, Shuai
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Bergman, Bill
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 powder by gel combustion route with two-step doping strategy2012Ingår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 32, nr 10, s. 2325-2331Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A two-step doping strategy was applied to the synthesis of La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 (LSGM1020) powder by a gel combustion method. The Mg-doped LaGaO 3 powder was prepared in the first step, and Sr incorporation in the Mg-doped LaGaO 3 powder was done in the second step to obtain the final LSGM1020 powder. The two-step procedure is effective in preparing higher purity powders than the traditional one-step procedure. Rietveld refinement of X-ray powder diffraction (XRD) patterns shows that incorporation of Mg in LaGaO 3 in the first step enlarges the LaGaO 3 lattice: this facilitates the incorporation of Sr in the second doping step and thus high purity powder is obtained. Relatively phase pure LSGM1020 powder with only 3.1% of LaSrGaO 4 was obtained after calcination at 1300°C for 5h. Therefore, the two-step doping strategy is an effective procedure for the preparation of LSGM powders with high Sr- and Mg-doping levels.

  • 39.
    Li, Shuai
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Bergman, Bill
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Synthesis and characterization of lanthanum aluminate powders via a polymer complexing plus combustion route2012Ingår i: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 132, nr 2-3, s. 309-315Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Lanthanum aluminate powders were prepared by a simple polymer complexing plus combustion method using PVA or PEG as complexing agent and fuel. The influence of different polymers on phase purity, powder morphology and sintering performance were investigated. Trace amount impurity La 23 exists in the PEG powder, but it could be eliminated after high temperature sintering. The pure phase LaAlO 3 can be easily obtained in PVA powders calcined at 950 °C even severe aggregation always exists. PEG shows advantages over PVA in terms of the densification and microstructure control during sintering process. The high relative density of 97.0% and homogeneous fine microstructure with grain size < 3 μm can be obtained in the PEG-derived sample sintered at 1600 °C for 5 h. To obtain better quality LaAlO 3 powders through combustion route, PEG is preferred over PVA.

  • 40. Liang, Yujie
    et al.
    Liu, Zhifu
    Cheng, Yao
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Seeded growth of WO3 film on FTO substrate with tunable structures for stable electrochromic performance2016Ingår i: Integrated Ferroelectrics, ISSN 1058-4587, E-ISSN 1607-8489, Vol. 173, nr 1, s. 109-116Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, tungsten trioxide (WO3) film was prepared on FTO-coated glass substrates using a facile hydrothermal method. Detailed studies revealed that a variety of WO3 nanostructures-including nanosheets, nanoflakes, nanocuboids and 3D nanowire flowers could be obtained by tuning the composition of the precursor solution, where the additive ((NH4)(2)C2O4 and CO(NH2)(2)-(NH4)(2)C2O4)) content and solvent composition played important roles in controlling the shape and size of the WO3. These nanostructure films exhibited good electrochromic performance. The transmittance spectra showed that WO3 film displayed 50% and 70% in the range of visible light at the colored and bleached states (S2) and a potential of +/- 1.0V. There is no significant degradation of the electrochromic properties after 1000 continuous coloration/bleaching cycles, making it attractive for practical applications.

  • 41. Liu, Linyan
    et al.
    Cheng, Yao
    Liu, Zhifu
    Ha, Minh Ngoc
    Guo, Qiangsheng
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Thermochemical conversion of CO2 into CH4 using oxygen deficient NiFe2O4-delta with unique selectivity2016Ingår i: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 6, nr 87, s. 83814-83819Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    NiFe2O4 nanoparticles with a high concentration of oxygen vacancies were synthesized via a solvothermal route. The morphology and oxygen vacancies of the catalyst was changed by adjusting the ratio of ethylene glycol (EG) in the mixture solvent. Water was used as a hydrogen source, the thermal catalytic performance of NiFe2O4 was up to 357.6 mu mol g(-1) of CH4 evolution under low temperature conditions. These findings may further broaden the horizon for CO2 reduction using the oxygen nonstoichiometry strategy.

  • 42. Mitoseriu, L.
    et al.
    Harnagea, C.
    Nanni, P.
    Testino, A.
    Buscaglia, M. T.
    Buscaglia, V.
    Viviani, M.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Nygren, M.
    Local switching properties of dense nanocrystalline BaTiO3 ceramics2004Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 84, nr 13, s. 2418-2420Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The switching properties of dense BaTiO3 ceramics with 50 nm average grain size were investigated at local scale by piezoresponse force microscopy. Large areas with low piezoelectrical activity beside islands with strong piezoresponse were found. The application of electric fields induces stable domain structures and changes in the polarization state far away from the probing area, probably via trans-granular dipole interactions. Piezoelectric hysteresis loops were recorded on various positions, even in regions with initial zero piezoresponse, which possibly showed a superparaelectric behavior. The results are incontestable proof that 50 nm BaTiO3 ceramics retain ferroelectricity at a local scale.

  • 43. Petkov, V.
    et al.
    Buscaglia, V.
    Buscaglia, M. T.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Ren, Y.
    Structural coherence and ferroelectricity decay in submicron- and nano-sized perovskites2008Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, nr 5Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Understanding the loss of ferroelectricity in submicron- and nano-sized perovskites is an issue that has been debated for decades. Here we report results from a high-energy x-ray diffraction (XRD) study on a prime example of the perovskite's family, BaTiO(3) ceramics with a grain size ranging from 1200 to 5 nm. We find that the loss of ferroelectricity in submicron- and nano-sized BaTiO(3) has an intrinsic origin related to the increased atomic positional disorder in spatially confined physical systems. Our results imply that no particular critical size at which ferroelectricity in BaTO(3), in particular, and perovskites, in general, is completely lost exists. Rather it weakens exponentially with the decreasing of their physical size. Smart technological solutions are needed to bring it back.

  • 44.
    Ren, Yanan
    et al.
    Shanghai Inst Technol, Sch Mat Sci & Engn, Shanghai 201418, Peoples R China..
    Zheng, Dongmei
    Shanghai Inst Technol, Sch Mat Sci & Engn, Shanghai 201418, Peoples R China..
    Liu, Linyan
    Shanghai Inst Technol, Sch Mat Sci & Engn, Shanghai 201418, Peoples R China..
    Guo, Qiangsheng
    Shanghai Insititute Technol, Sch Chem & Environm Engn, Shanghai 201418, Peoples R China..
    Sha, Na
    Shanghai Insititute Technol, Sch Chem & Environm Engn, Shanghai 201418, Peoples R China..
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Shanghai Inst Technol, Sch Mat Sci & Engn, Shanghai 201418, Peoples R China..
    3DOM-NiFe2O4 as an effective catalyst for turning CO2 and H2O into fuel (CH4)2018Ingår i: Journal of Sol-Gel Science and Technology, ISSN 0928-0707, E-ISSN 1573-4846, Vol. 88, nr 3, s. 489-496Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Three-dimensional ordered macroporous NiFe2O4 (3DOM-NFO) powder was synthesized through the direct templating method combined with the sol-gel combustion technique. Polymethyl methacrylate (PMMA) spheres with different sizes were used as the hard templates. In order to understand the effect of PMMA spheres mean size on the structure and catalytic activity of synthesized 3DOM-NFO, the detailed characterization of the material was carried out by XRD, SEM, BET, XPS, UV-VIS, and DRS techniques. Direct hydrogeneration production of CH4 from CO2 and H2O was used to evaluate the catalysis performance of 3DOM-NFOs. The production of CH4 evolution can reach 1040.8mol/g at 350 degrees C and ambient pressure when 300nm template was used. It was concluded that the specific surface area and moderate concentration of oxygen vacancies are the crucial factors affecting the catalysis properties. Reasonably high turnover number of 0.244 and high CH4 conversion efficiency of 0.897% were obtained in this study. 3DOM-NFO can be a promising catalyst for hydrocarbon fuel production by directly using CO2 and H2O as the safe and cheap feedstocks. [GRAPHICS] .

  • 45. Stuer, Michael
    et al.
    Bowen, Paul
    Cantoni, Marco
    Pecharroman, Carlos
    Zhao, Zhe
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Nanopore Characterization and Optical Modeling of Transparent Polycrystalline Alumina2012Ingår i: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 22, nr 11, s. 2303-2309Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Production of transparent ceramics has become a topic of resurgent interest in recent years, with its promise of near-net shaping appealing to applications ranging from biomedicine to solar energy. However, the mechanisms governing ceramic transparency, translucency, and opaqueness are not entirely understood. Models of both grain boundary and pore scattering have been proposed, but too often without sufficient experimental corroboration. An extensive experimental analysis of transparent alumina samples is presented, establishing a first direct link between the observed transparency, defect size, and porosity. Given the unprecedented experimental detail from the full 3D pore reconstruction from the FIB tomography, how to correctly interpret the experimentally observed transparency is additionally shown. The unprecedented experimental and theoretical agreement for the first time identifies the relative contributions of different scattering mechanisms, thereby paving the way forward for microstructural tuning of transparent polycrystalline alumina.

  • 46. Stuer, Michael
    et al.
    Carry, Claude Paul
    Bowen, Paul
    Zhao, Zhe
    KTH, Skolan för kemivetenskap (CHE), Kemi. KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi. KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Comparison of apparent activation energies for densification of alumina powders by pulsed electric current sintering (spark plasma sintering) and conventional sintering-toward applications for transparent polycrystalline alumina2017Ingår i: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 32, nr 17, s. 3309-3318Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the quest for high real in-line transmittances for transparent polycrystalline alumina (PCA), we need defect free processing. One of the biggest advances in producing high density defect free ceramics over recent years has been the advent of spark plasma sintering (SPS) or pulsed electric current sintering. The production of PCA with high transmittances >60% has been demonstrated, but the mechanisms behind this fast, pressure aided sintering method are still much debated. Here, we investigate the sintering of doped a-alumina powders using traditional and pulsed electric current dilatometry. We demonstrate that at the final sintering stage, there is no major difference in the sintering mechanisms between conventional sintering and SPS sintering. High densification rates occurring in SPS are shown to be related to powder reorientation at the very early sintering stage and viscous-flow dominated densification in the intermediate sintering cycle. This paper clarifies what parameters in the processing-sintering domain have to be improved for even higher real in-line transmittances for PCA.

  • 47.
    Stuer, Michael
    et al.
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Aschauer, Ulrich
    EPFL.
    Bowen, Paul
    EPFL.
    Transparent polycrystalline alumina using spark plasma sintering: Effect of Mg, Y and La doping2010Ingår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 30, nr 6, s. 1335-1343Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transparent polycrystalline alumina (PCA) is a promising replacement for sapphire. Its optical properties however are highly dependent on the grain size and residual porosity which need to be controlled for real inline transmittances (RIT), that are high enough for possible applications. To achieve high RITs, doping as well as pressure assisted sintering is often used. In this study spark plasma sintering (SPS) and doping are investigated. A systematic experimental design is used to study the influence of Mg, Y and La single or co-doping (75-450 ppm) as well as the SPS sintering pressure and temperature on the RIT and grain size of PCA. Using optimized sintering parameters, RITs of >50% were attained in the visible wavelength (640 nm) for 0.8 mm thick samples for almost all doping strategies. The best RIT of 57% was for triple-doped samples at a total dopant level of 450 ppm. These results are significantly better than previously published SPS studies and illustrate that SPS sintered alumina can attain high and reproducible optical transmittances under various doping and sintering conditions.

  • 48.
    Suarez, M.
    et al.
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Fernandez, A.
    ITMA, Spain.
    Menendez, J. L.
    CSIC-CINN, Spain.
    Nygren, M.
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Torrecillas, R.
    CSIC-CINN, Spain.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Hot isostatic pressing of optically active Nd:YAG powders doped by a colloidal processing route2010Ingår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 30, nr 6, s. 1489-1494Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, 1 at.% Nd doped Yttrium Aluminum Garnet Y(3)Al(5)O(12) (YAG) nano-sized powder prepared by colloidal route was investigated thoroughly concerning agglomeration control and preparation of transparent ceramic by post-HIP. Electrostatic and mechanical deagglomeration process followed by freeze-drying turned out to be an effective method to alleviate agglomeration, yielding a powder with a homogeneous particle size distribution around 100 nm. Transparent Nd:YAG ceramic samples have been successfully prepared by post-HIP without the aid of sintering additives. The optical properties varied markedly with the sintering and hot isostatic pressing conditions used. In-fine transmittance values of 56% at 680 nm and close to 80% in the infrared region were recorded.

  • 49. Wang, C.
    et al.
    Zhao, Zhe
    Department of Physical Inorganic and Structural Chemistry, Stockholm University.
    Transparent MgAl2O4 ceramic produced by spark plasma sintering2009Ingår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 61, nr 2, s. 193-196Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A two-step pressure profile was used to prepare transparent MgAl(2)O(4) ceramic without sintering aids by spark plasma sintering (SPS) at 1300 degrees C for 3 min. The influence of the pressure profile was investigated systematically and the discoloration in the present study was attributed to the dislocation formed during the fast densification in SPS. At low pre-load pressure, 5 MPa, with the normal characteristic fast heating rate (100 degrees C min(-1)), high inline transmittance of 51% at 550 nm and 85% at 2000 nm can be achieved.

  • 50.
    Wang, Cao
    et al.
    Department of Materials and Environmental Chemistry,Stockholm University.
    Cheng, Laifei
    Northwest Polytechnical University, China.
    Zhao, Zhe
    Department of Materials and Environmental Chemistry, Stockholm University.
    FEM analysis of the temperature and stress distribution in spark plasma sintering: Modelling and experimental validation2010Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 49, nr 2, s. 351-362Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A fully thermal-electrical-mechanical coupled and dynamic finite element model (FEM) is implemented to analyze of the temperature and stress distribution in spark plasma sintering (SPS) process. The real densification behaviour is also integrated by the moving mesh technique. The simulation studies were conducted using COMSOL and a range of die sizes, heating rates and uniaxial stresses were considered. The further validation experiments are implemented to validate the simulation results. The detailed microstructure investigations generally demonstrate that the temperature and stress profile obtained in present model are correct. But further development of complicated models is still needed for more precise prediction of sintering condition and microstructure development in SPS.

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