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Žguns, P., Ruban, A. V. & Skorodumova, N. (2019). Influence of composition and oxygen-vacancy ordering on lattice parameter and elastic moduli of Ce1-xGdxO2-x/2: A theoretical study. Scripta Materialia, 158, 126-130
Open this publication in new window or tab >>Influence of composition and oxygen-vacancy ordering on lattice parameter and elastic moduli of Ce1-xGdxO2-x/2: A theoretical study
2019 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 158, p. 126-130Article in journal (Refereed) Published
Abstract [en]

We study the behaviour of the lattice parameter and elastic moduli of Ce1-xGdxO2-x/2 for the random (fluoritelike) and C-type ordered oxygen-vacancy configurations [Zguns et al., PCCP 20 (2018) 11805-11818]. For the fluorite phase, elastic moduli decrease linearly with Gd concentration. For the C-type phase, the bulk, shear and Young moduli are found to be systematically larger and the lattice parameter smaller than those for disordered fluorite phase. Essentially the linear behaviour of the bulk modulus and lattice parameter depending on the degree of the C-type order is found. Our findings explain the experimentally observed elastic moduli of Ce1-xGdxO2-x/2.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Structure-property relation, Gd-doped ceria, Ordering, Elastic moduli, DFT
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-238105 (URN)10.1016/j.scriptamat.2018.08.034 (DOI)000447094500027 ()2-s2.0-85052894758 (Scopus ID)
Note

QC 20190111

Available from: 2019-01-11 Created: 2019-01-11 Last updated: 2019-05-20Bibliographically approved
Schönfeld, B., Sax, C. R., Zemp, J., Engelke, M., Boesecke, P., Kresse, T., . . . Ruban, A. V. (2019). Local order in Cr-Fe-Co-Ni: Experiment and electronic structure calculations. Physical Review B, 99(1), Article ID 014206.
Open this publication in new window or tab >>Local order in Cr-Fe-Co-Ni: Experiment and electronic structure calculations
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 1, article id 014206Article in journal (Refereed) Published
Abstract [en]

A quenched-in state of thermal equilibrium (at 723 K) in a single crystal of Cr-Fe-Co-Ni close to equal atomic percent was studied. Atom probe tomography revealed a single-phase state with no signs of long-range order. The presence of short-range order (SRO) was established by diffuse x-ray scattering exploiting the variation in scattering contrast close to the absorption edges of the constituents: At the incoming photon energies of 5969, 7092, and 8313 eV, SRO maxima that result from the linear superposition of the six partial SRO scattering patterns, were always found at X position. Electronic structure calculations showed that this type of maximum stems from the strong Cr-Ni and Cr-Co pair correlations, that are furthermore connected with the largest scattering contrast at 5969 eV. The calculated effective pair interaction parameters revealed an order-disorder transition at approximately 500 K to a L12-type (Fe,Co,Ni)3Cr structure. The calculated magnetic exchange interactions were dominantly of the antiferromagnetic type between Cr and any other alloy component and ferromagnetic between Fe, Co, and Ni. They yielded a Curie temperature (TC) of 120 K, close to experimental findings. Despite the low value of TC, the global magnetic state strongly affects chemical and elastic interactions in this system. In particular, it significantly increases the ordering tendency in the ferromagnetic state compared to the paramagnetic one.

Place, publisher, year, edition, pages
American Physical Society, 2019
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-248271 (URN)10.1103/PhysRevB.99.014206 (DOI)000456028800001 ()2-s2.0-85060376483 (Scopus ID)
Note

QC 20190408

Available from: 2019-04-08 Created: 2019-04-08 Last updated: 2019-04-08Bibliographically approved
Ponomareva, A. V., Ruban, A. V., Mukhamedov, B. O. & Abrikosov, I. A. (2018). Effect of multicomponent alloying with Ni, Mn and Mo on phase stability of bcc Fe-Cr alloys. Acta Materialia, 150, 117-129
Open this publication in new window or tab >>Effect of multicomponent alloying with Ni, Mn and Mo on phase stability of bcc Fe-Cr alloys
2018 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 150, p. 117-129Article in journal (Refereed) Published
Abstract [en]

Fe-Cr system attracts lot of attention in condensed matter physics due to its technological importance and extraordinary physics related to a non-trivial interplay between magnetic and chemical interactions. However, the effect of multicomponent alloying on the properties of Fe-Cr alloys are less studied. We have calculated the mixing enthalpy, magnetic moments, effective chemical, strain-induced and magnetic exchange interactions to investigate the alloying effect of Ni, Mn, Mo on the phase stability of the ferromagnetic bcc Fe−Cr system at zero K. We demonstrate that the alloying reduces the stability of Fe-Cr alloys and expands the region of spinodal decomposition. At the same time, the mixing enthalpy in ternary Fe100-≿-05Cr≿Ni05 alloys indicates a stability of solid solution phase up to 6 at. % Cr. In Fe100-≿-07Cr≿Ni05Mn01Mo01 alloys, we did not find any alloy composition that has negative enthalpy of formation. Analyzing magnetic and electronic properties of the alloys and investigating magnetic, chemical and strain-induced interactions in the studied systems, we provide physically transparent picture of the main factors leading to the destabilization of the Fe-Cr solid solutions by the multicomponent alloying with Ni, Mn, Mo.

Place, publisher, year, edition, pages
Acta Materialia Inc, 2018
Keywords
Fe-Cr system, First-principles calculations, Mixing enthalpy, Multicomponent alloying, Phase stability, Spinodal decompositon
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-227570 (URN)10.1016/j.actamat.2018.02.007 (DOI)000433272400011 ()2-s2.0-85045886801 (Scopus ID)
Note

QC 20180516

Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2018-06-27Bibliographically approved
Ehteshami, H. & Ruban, A. V. (2018). High-temperature thermophysical properties of gamma- and delta-Mn from first principles. PHYSICAL REVIEW MATERIALS, 2(3), Article ID 034405.
Open this publication in new window or tab >>High-temperature thermophysical properties of gamma- and delta-Mn from first principles
2018 (English)In: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 2, no 3, article id 034405Article in journal (Refereed) Published
Abstract [en]

Thermophysical properties of gamma-and delta-Mn phases have been investigated using first-principles calculations in their thermodynamically stable temperature range. An adiabatic approximation is used for partitioning of the Helmholtz free energy into electronic, magnetic, and vibrational contributions from the corresponding temperature induced excitations, where the fastest degree of freedom has been included in the slower ones. Namely, electronic excitations (on a one-electron level) have been included directly in the first-principles calculations at the corresponding temperatures. Magnetic excitations in the paramagnetic state then have been taken into consideration in the two opposite limits: localized, considering only transverse spin fluctuations (TSF), and itinerant, allowing for the full coupling of transverse and longitudinal spin fluctuations (LSF). Magnetic contribution to the free energy has been included in the calculations of the vibrational one, which has been obtained within the Debye-Gruneisen model. The calculated thermophysical properties such as lattice constance, thermal lattice expansion, and heat capacity are in good agreement with available experimental data, especially in the case when the itinerant magnetic model is chosen. We also present our results for elastic properties at high temperatures.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-228153 (URN)10.1103/PhysRevMaterials.2.034405 (DOI)000428785600002 ()2-s2.0-85059613698 (Scopus ID)
Note

QC 20180521

Available from: 2018-05-21 Created: 2018-05-21 Last updated: 2019-05-07Bibliographically approved
Ruban, A. V. & Peil, O. E. (2018). Impact of thermal atomic displacements on the Curie temperature of 3d transition metals. Physical Review B, 97(17), Article ID 174426.
Open this publication in new window or tab >>Impact of thermal atomic displacements on the Curie temperature of 3d transition metals
2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 17, article id 174426Article in journal (Refereed) Published
Abstract [en]

It is demonstrated that thermally induced atomic displacements from ideal lattice positions can produce considerable effect on magnetic exchange interactions and, consequently, on the Curie temperature of Fe. Thermal lattice distortion should, therefore, be accounted for in quantitatively accurate theoretical modeling of the magnetic phase transition. At the same time, this effect seems to be not very important for magnetic exchange interactions and the Curie temperature of Co and Ni.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-230429 (URN)10.1103/PhysRevB.97.174426 (DOI)000433061200002 ()2-s2.0-85047726355 (Scopus ID)
Note

QC 20180618

Available from: 2018-06-18 Created: 2018-06-18 Last updated: 2018-11-13Bibliographically approved
Zguns, P. A., Ruban, A. V. & Skorodumova, N. V. (2018). Phase diagram and oxygen-vacancy ordering in the CeO2-Gd2O3 system: a theoretical study. Physical Chemistry, Chemical Physics - PCCP, 20(17), 11805-11818
Open this publication in new window or tab >>Phase diagram and oxygen-vacancy ordering in the CeO2-Gd2O3 system: a theoretical study
2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 17, p. 11805-11818Article in journal (Refereed) Published
Abstract [en]

We present the phase diagram of Ce1-xGdxO2-x/2 (CGO), calculated by means of a combined Density Functional Theory (DFT), cluster expansion and lattice Monte Carlo approach. We show that this methodology gives reliable results for the whole range of concentrations (x x(Gd) <= 1). In the thermodynamic equilibrium, we observe two transitions: the onset of oxygen-vacancy (O-Va) ordering at ca. 1200-3300 K for concentrations x(Gd) = 0.3-1, and a phase separation into CeO2 and C-type Gd2O3 occurring below ca. 1000 K for all concentrations. We also model 'quenched' systems, with cations immobile below 1500 K, and observe that the presence of random-like cation configurations does not prevent C-type vacancy ordering. The obtained transition temperatures for Va ordering agree rather well with existing experimental data. We analyse the effect of vacancy ordering and composition on the lattice parameters and relaxation pattern of cations.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-230525 (URN)10.1039/c8cp01029c (DOI)000431824000034 ()29658037 (PubMedID)2-s2.0-85046640148 (Scopus ID)
Funder
Swedish Research Council, VR 348-2012-6196 2015-05538 VR 348-2012-6196 2015-05538EU, European Research CouncilVINNOVA
Note

QC 20180723

Available from: 2018-07-23 Created: 2018-07-23 Last updated: 2018-07-23Bibliographically approved
Zhang, X., Grabowski, B., Koermann, F., Ruban, A. V., Gong, Y., Reed, R. C., . . . Neugebauer, J. (2018). Temperature dependence of the stacking-fault Gibbs energy for Al, Cu, and Ni. Paper presented at AREBRO.LM, 1967, CANADIAN JOURNAL OF PHYSICS, V45, P1135, EMENT N, 1974, PHILOSOPHICAL MAGAZINE, V30, P663 ao Shijun, 2017, ACTA MATERIALIA, V134, P334. PHYSICAL REVIEW B, 98(22), Article ID 224106.
Open this publication in new window or tab >>Temperature dependence of the stacking-fault Gibbs energy for Al, Cu, and Ni
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2018 (English)In: PHYSICAL REVIEW B, Vol. 98, no 22, article id 224106Article in journal (Refereed) Published
Abstract [en]

The temperature-dependent intrinsic stacking fault Gibbs energy is computed based on highly converged density-functional-theory (DFT) calculations for the three prototype face-centered cubic metals Al, Cu, and Ni. All relevant temperature-dependent contributions are considered including electronic, vibrational, magnetic, and explicit anharmonic Gibbs energy contributions as well as coupling terms employing state-of-the-art statistical sampling techniques. Particular emphasis is put on a careful comparison of different theoretical concepts to derive the stacking fault energy such as the axial-next-nearest-neighbor-Ising (ANNNI) model or the vacuum-slab approach. Our theoretical results are compared with an extensive set of previous theoretical and experimental data. Large uncertainties in the experimental data highlight the necessity of complementary parameter-free calculations. Specifically, the temperature dependence is experimentally unknown and poorly described by thermodynamic databases. Whereas CALPHAD derived data shows an increase of the stacking fault energy with temperature for two of the systems (Cu and Ni), our results predict a decrease for all studied systems. For Ni, the temperature induced change is in fact so strong that in the temperature interval relevant for super-alloy applications the stacking fault energy falls below one third of the low temperature value. Such large changes clearly call for a revision of the stacking fault energy when modeling or designing alloys based on such elements.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
Keywords
NTENEER PJH, 1991, SOLID STATE COMMUNICATIONS, V78, P857, NTENEER PJH, 1987, JOURNAL OF PHYSICS C-SOLID STATE PHYSICS, V20, PL883, NTENEER PJH, 1991, JOURNAL OF PHYSICS-CONDENSED MATTER, V3, P8777 Yue, 2007, PHYSICAL REVIEW B, V75, abowski B., 2009, PHYSICAL REVIEW B, V79, hnatek Michal, 2009, PHYSICAL REVIEW B, V79, ermann F., 2009, PHYSICAL REVIEW B, V79, andl C., 2007, PHYSICAL REVIEW B, V76, ang S. L., 2012, JOURNAL OF PHYSICS-CONDENSED MATTER, V24, ban A. V., 2007, PHYSICAL REVIEW B, V75, ermann F., 2012, PHYSICAL REVIEW B, V85, tta Aditi, 2009, SCRIPTA MATERIALIA, V60, P124 abowski B., 2011, PHYSICAL REVIEW B, V84, Campos M. F., 2008, Advanced Powder Technology VI6th International Latin American Conference on Power Technology, NOV 07-10, 2007, Buzios, BRAZIL, V591-593, P708 tta A., 2011, COMPUTATIONAL MATERIALS SCIENCE, V50, P3342 andran Mahesh, 2011, JOURNAL OF APPLIED PHYSICS, V109, ermann F., 2011, PHYSICAL REVIEW B, V83, basi Afshin, 2011, ACTA MATERIALIA, V59, P3041 zyk M., 2011, SCRIPTA MATERIALIA, V64, P916
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-241198 (URN)10.1103/PhysRevB.98.224106 (DOI)000454421700006 ()2-s2.0-85059512701 (Scopus ID)
Conference
AREBRO.LM, 1967, CANADIAN JOURNAL OF PHYSICS, V45, P1135, EMENT N, 1974, PHILOSOPHICAL MAGAZINE, V30, P663 ao Shijun, 2017, ACTA MATERIALIA, V134, P334
Note

QC 20190121

Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2019-01-21Bibliographically approved
Tian, Y., Gorbatov, O. I., Borgenstam, A., Ruban, A. V. & Hedström, P. (2017). Deformation Microstructure and Deformation-Induced Martensite in Austenitic Fe-Cr-Ni Alloys Depending on Stacking Fault Energy. Metallurgical and Materials Transactions. A, 48A(1), 1-7
Open this publication in new window or tab >>Deformation Microstructure and Deformation-Induced Martensite in Austenitic Fe-Cr-Ni Alloys Depending on Stacking Fault Energy
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2017 (English)In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 1, p. 1-7Article in journal (Refereed) Published
Abstract [en]

The deformation microstructure of austenitic Fe-18Cr-(10-12)Ni (wt pct) alloys with low stacking fault energies, estimated by first-principles calculations, was investigated after cold rolling. The E >-martensite was found to play a key role in the nucleation of alpha'-martensite, and at low SFE, E > formation is frequent and facilitates nucleation of alpha' at individual shear bands, whereas shear band intersections become the dominant nucleation sites for alpha' when SFE increases and mechanical twinning becomes frequent.

Place, publisher, year, edition, pages
Springer, 2017
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-201245 (URN)10.1007/s11661-016-3839-2 (DOI)000391492200001 ()2-s2.0-84992754455 (Scopus ID)
Note

QC 20170216

Available from: 2017-02-16 Created: 2017-02-16 Last updated: 2018-05-16Bibliographically approved
Ruban, A. V. (2017). First-principles modeling of the Invar effect in Fe65Ni35 by the spin-wave method. Physical Review B, 95(17), Article ID 174432.
Open this publication in new window or tab >>First-principles modeling of the Invar effect in Fe65Ni35 by the spin-wave method
2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 17, article id 174432Article in journal (Refereed) Published
Abstract [en]

Thermal lattice expansion of the Invar Fe0.65Ni0.35 alloy is investigated in first-principles calculations using the spin-wave method, which is generalized here for the ferromagnetic state with short-range order. It is shown that magnetic short-range order effects make a substantial contribution to the equilibrium lattice constant and cannot be neglected in the accurate ab initio modeling of the thermal expansion in Fe-Ni alloys. We also demonstrate that at high temperatures, close to and above the magnetic transition, magnetic entropy associated with transverse and longitudinal spin fluctuations yields a noticeable contribution to the equilibrium lattice constant. The obtained theoretical results for the temperature dependent lattice constant are in semiquantitative agreement with the experimental data apart from the region close the magnetic transition.

Place, publisher, year, edition, pages
American Physical Society, 2017
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-208724 (URN)10.1103/PhysRevB.95.174432 (DOI)000401997600002 ()2-s2.0-85024397087 (Scopus ID)
Note

QC 2017-06-13

Available from: 2017-06-13 Created: 2017-06-13 Last updated: 2017-11-29Bibliographically approved
Zguns, P. A., Ruban, A. V. & Skorodumova, N. (2017). Ordering and phase separation in Gd-doped ceria: a combined DFT, cluster expansion and Monte Carlo study. Physical Chemistry, Chemical Physics - PCCP, 19(39), 26606-26620
Open this publication in new window or tab >>Ordering and phase separation in Gd-doped ceria: a combined DFT, cluster expansion and Monte Carlo study
2017 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 39, p. 26606-26620Article in journal (Refereed) Published
Abstract [en]

Ordering of dopants and oxygen vacancies is studied for Gd-doped ceria (x(Gd) <= 0.25) by means of a combined density functional theory (DFT) and cluster expansion approach, where the cluster interactions derived from DFT calculations are further used in Monte Carlo simulations. The methodology is meticulously tested and the stability of the obtained solutions with respect to the volume change, applied exchange-correlation approximation and other modelling parameters is carefully analysed. We study Gd and vacancy ordering in the case of thermodynamic equilibrium and vacancy ordering for quenched Gd configurations. We find that at the thermodynamic equilibrium there exists a transition temperature (T-C) below which phase separation into C-type Gd2O3 and pure CeO2 occurs. The phase separation is observed in the whole studied concentration range and the transition temperature increases with concentration from ca. 600 (x(Gd) = 0.03) to 1000 K (x(Gd) = 0.25). Above T-C the distribution of Gd is random, oxygen vacancies tend to cluster in the coordination shells along < 1, 1/2, 0 > and < 1, 1, 1 >, and the nearest neighbour position is preferred for Gd-vacancy. In the quenched Gd case, where Gd atoms are immobilised below 1500 K, the vacancy ordering is significantly frustrated. In fact, we observe an oxygen freezing transition below temperature T-F approximate to T-C - 350 K, which is close to temperatures at which a change in the conductivity slope is observed experimentally.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2017
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-217031 (URN)10.1039/c7cp04106c (DOI)000412763700014 ()28949350 (PubMedID)
Note

QC 20171124

Available from: 2017-11-24 Created: 2017-11-24 Last updated: 2018-03-12Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3880-0965

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