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  • 1.
    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 strategy2012Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 32, nr 10, s. 2325-2331Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 2.
    Li, Shuai
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Preparation and characterization of perovskite structure lanthanum gallate and lanthanum aluminate based oxides2009Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The present work was initiated to study the synthesis and properties of lanthanum gallate based oxides as intermediate temperature electrolyte for solid oxide fuel cells. The wet chemical method, polymer complexing route, was used to prepare the precursor powders. To further investigate the polymer complexing method, it was also applied to the preparation of lanthanum aluminate based oxides.

     

    Single perovskite phase La0.8Sr0.2Ga0.83Mg0.17O2.815 can be prepared by the polymer complexing method using PVA as complexing agent. The thermal decomposition of the precursor powder undergoes three stages. While complete decomposition of the precursor is obtained at 1000°C. Further investigation of LaGaO3 doped with various amounts Sr or/and Mg was conducted. Three secondary phases were identified by X-ray diffraction, e.g. LaSrGaO4, LaSrGa3O7 and La4Ga2O9. The relative amount of these secondary phases depends on the doping compositions. Sr doping produced more Sr rich secondary phases with increasing content, while enhanced solid solubility was observed with Mg addition. Sintered samples showed dense microstructures with well-developed equiaxed grains, and the secondary phases were mainly in the grain boundaries. The oxygen ionic conductivity was enhanced by doping with Sr and Mg. Mg doping showed the increased activation energy of conductivity.

     

    Preliminary study showed that the lanthanum gallate and ceria composite electrolyte is mainly fluorite CeO2 phase after sintering. The minority secondary phase, Sm3Ga5O12, was also detected by XRD. The composite electrolyte showed superior electrical performance. It exhibited the highest conductivity in the temperature range of 250–600°C, compared with lanthanum gallate and ceria specimens.

     

    The phase pure perovskite La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 powders can easily be obtained by the polymer method using PVA as complexing agent. No secondary phase was detected after calcination at various temperatures (500–1100°C). The fully crystallized LaAlO3 phase was prepared after calcination at 900°C. Meanwhile the secondary phases were difficult to eliminate in the Sr- and Mg- doped LaGaO3 powder prepared by the same polymer method. It is thus concluded that the polymer, PVA in this work, provides more homogeneous mixing for cations of lanthanum aluminate based oxides, compared with the one for doped lanthanum gallate.

     

    The influence of different complexing agents, e.g. PVA and PEG, was investigated in the synthesis of lanthanum aluminate powders. Minority impurity La2O3 existed in the PEG powder, but it could be eliminated after sintering at high temperatures. Although the pure phase LaAlO3 can be easily obtained in PVA powders calcined at 950°C, more seriously aggregated particles existed. PEG showed advantages over PVA in terms of better densification and microstructure control in the sintered products. To select proper polymers in complex oxide synthesis, the agglomeration and morphology of the powder are the most important factors to be considered.

     

  • 3.
    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.
    Doping effect on secondary phases, microstructure and electrical conductivities of LaGaO3 based perovskites2009Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 29, nr 6, s. 1139-1146Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The intermediate temperature electrolytes La1-xSrxGa1-yMgyO3-delta (LSGM, where delta=(x+y)/2) with perovskite structure were prepared using a poly(vinyl alcohol) (PVA) solution polymerization method. Three secondary phases were identified by X-ray diffraction, LaSrGaO4, LaSrGa3O7 and La4Ga2O9. The relative amount of these secondary phases depended on the doping compositions. Sr doping produced more Sr rich secondary phases with increasing content, while enhanced solid solubility was observed with Mg addition. Sintered samples showed dense microstructures with well-developed equiaxed grains, and the secondary phases were mainly in the grain boundaries. LaSrGaO4 could not be detected by SEM for the sintered pellets. The oxygen ionic conductivity was enhanced by doping with Sr and Mg. Mg doping showed the increased conductivity activation energy. La0.8Sr0.2Ga0.9Mg0.1O2.85 had the highest ionic conductivity sigma = 0.128 S/cm at 800 degrees C in this work.

  • 4.
    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, Keramteknologi.
    Zhao, Zhe
    A Polymer Complexing Route for Low Temperature Synthesis of Perovskite Lanthanum Aluminate Powder2010Inngår i: HIGH-PERFORMANCE CERAMICS VI  / [ed] Pan W; Gong J, 2010, Vol. 434-435, s. 863-867Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Lanthanum aluminate powders were prepared via a polymer complexing method by using PEG as complexing agent. The LaAlO3 powder was characterized by XRD and SEM. The influence of processing parameters such as molar ratio of PEG monomers to metal cations (PEG:Men+) and aging process on the phase purity and powder morphology were investigated. The calcined powder with the PEG:Me ratio larger than 2:1 may contain the secondary phase, namely La2O3. The formation of phase pure LaAlO3 powder occurs when the PEG:Men+ ratio is 1:1 or enough gelation time is involved. Although the phase pure powder is obtained by this PEG method, all the single phase LaAlO3 powders are found to have seriously aggregated particles. The weakly agglomerated powder morphology is only found in the powders which contain La2O3.

  • 5.
    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
    Preparation and characterisation of perovskite La0.8Sr0.2Ga0.83Mg0.17O2.815 electrolyte using a poly(vinyl alcohol) polymeric methodInngår i: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689Artikkel i tidsskrift (Annet vitenskapelig)
  • 6.
    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 route2012Inngår i: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 132, nr 2-3, s. 309-315Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 7.
    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
    Synthesis of La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 using a polymeric method2009Inngår i: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, ISSN 0955-2219, Vol. 29, nr 6, s. 1133-1138Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanocrystalline La0.9Sr0.1Al0.85Mg0.1Co0.05O2.875 (LSAMC) powders were synthesized via a polymeric method using poly(vinyl alcohol) (PVA). The effect of PVA content on the synthesized powders was studied. When the ratio of positively charged valences (Mn+) to hydroxyl groups (-OH) is 1.5:1, crystalline LaAlO3 could be obtained at such a low calcination temperature as 700 degrees C. While at 900 degrees C the ratio is of less importance, since pure LaAlO3 perovskite could be formed for all powders after calcination at 900 degrees C. Thermal analysis (TG/DTA) was utilized to characterize the thermal decomposition behaviour of precursor powders. The chemical structure of the calcined powder was studied by Fourier transform infrared (FTIR) spectroscopy. The powder morphology and microstructure were examined by SEM. Dense pellets with well-developed submicron microstructures could be formed after sintering at 1450 degrees C for 5 h. Compared with the solid-state reaction method, the sintering temperature is substantially lower for powder prepared by the PVA method. This is due to the ultrafine and highly reactive powder produced.

  • 8.
    Li, Shuai
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Li, Zhicheng
    Bergman, Bill
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Lanthanum gallate and ceria composite as electrolyte for solid oxide fuel cells2010Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, ISSN 0925-8388, Vol. 492, nr 1-2, s. 392-395Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The composite of doped lanthanum gallate (La(0.9)Sr(0.1)Ga(0.8)Mg(0.2)O(2.85), LSGM) and doped ceria (Ce(0.8)Sm(0.2)O(1.9), CSO) was investigated as an electrolyte for solid oxide fuel cell (SOFC). The LSGM-CSO composite was examined by X-ray diffraction (XRD) and impedance spectroscopy. It was found that the sintered LSGM-CSO composite contains mainly fluorite CeO(2) phase and a minority impurity phase, Sm(3)Ga(5)O(12). The LSGM-CSO composite electrolyte shows a small grain boundary response in the impedance spectroscopy as compared to LSGM and CSO pellets. The composite electrolyte exhibits the highest conductivity in the temperature range of 250-600 degrees C, compared to LSGM and CSO. The LSGM-CSO composite can be expected to be an attractive intermediate temperature electrolyte material for solid oxide fuel cells.

  • 9.
    Zhou, Jie
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Li, Shuai
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Soliman, Herrera M. A.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Toprak, Muhammet S.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Muhammed, Mamoun
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Platzek, D.
    Mueller, E.
    Seebeck coefficient of nanostructured phosphorus-alloyed bismuth telluride thick films2009Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 471, nr 1-2, s. 278-281Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanostructured phosphorous-alloyed Bi2Te3 thick films have been prepared by electrochemical deposition. The average grain size of the films was calculated to be 14-26nm based on Scherrer's equation. The effect of P on the Seebeck coefficient of the Bi2Te3 thick film was investigated. The results show that P-alloyed thick film has n-type conductivity with the Seebeck coefficient of -35 mu V/K. The correlation between P site occupancy in the crystal and the Seebeck coefficient was discussed.

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