Large-scale modelling of the phase transitions in KTa1-xNbxO3 perovskite solid solutions

R. I. Eglitis; D. Fuks; S. Dorfman; E. A. Kotomin; G. Borstel

doi:10.1016/S1369-8001(02)00097-5

Large-scale modelling of the phase transitions in KTa_1-xNb_xO₃ perovskite solid solutions

R. I. Eglitis, D. Fuks, S. Dorfman, E. A. Kotomin, G. Borstel

Department of Materials Engineering

Research output: Contribution to journal › Article › peer-review

10 Scopus citations

Abstract

We use quantum chemical method of the intermediate neglect of the differential overlap (INDO) based on the Hartree-Fock formalism for a large-scale modelling of the atomic and electronic structure of KNb_xTa_1-xO₃ (KTN) perovskite solid solutions. Results for periodic defect models (large unit cell) of 40 and 320 atoms are compared with 135-atom INDO cluster calculations. Periodic Nb impurities in KTaO₃ reveal clear off-center displacement beginning with the smallest calculated concentrations, so does an isolated Nb impurity in a cluster INDO calculation. The magnitude of Nb off-center displacement is close to the X-ray-absorption fine-structure observation (0.27 a.u.). In contrast, Ta impurities in KNbO₃ always remain on-center, due to higher ionicity of Ta as compared to Nb atom. Using the calculated energy gain due to the off-center displacements of Nb atoms for several concentrations of Nb in KTN, we construct the non-empirical Ginzburg-Landau-type functional for the excess energy. The coefficients of this functional are concentration dependent. This dependence allows to define the type of the concentration-induced phase transition in KTaO₃ alloyed by Nb.

Original language	English
Pages (from-to)	153-157
Number of pages	5
Journal	Materials Science in Semiconductor Processing
Volume	5
Issue number	2-3
DOIs	https://doi.org/10.1016/S1369-8001(02)00097-5
State	Published - 1 Apr 2002

Keywords

ABO perovskites
INDO method
KTN solid solutions

ASJC Scopus subject areas

General Materials Science
Condensed Matter Physics
Mechanics of Materials
Mechanical Engineering

Access to Document

10.1016/S1369-8001(02)00097-5

Cite this

@article{4f6bf458e85c4b58bdfd8947b1febc57,

title = "Large-scale modelling of the phase transitions in KTa1-xNbxO3 perovskite solid solutions",

abstract = "We use quantum chemical method of the intermediate neglect of the differential overlap (INDO) based on the Hartree-Fock formalism for a large-scale modelling of the atomic and electronic structure of KNbxTa1-xO3 (KTN) perovskite solid solutions. Results for periodic defect models (large unit cell) of 40 and 320 atoms are compared with 135-atom INDO cluster calculations. Periodic Nb impurities in KTaO3 reveal clear off-center displacement beginning with the smallest calculated concentrations, so does an isolated Nb impurity in a cluster INDO calculation. The magnitude of Nb off-center displacement is close to the X-ray-absorption fine-structure observation (0.27 a.u.). In contrast, Ta impurities in KNbO3 always remain on-center, due to higher ionicity of Ta as compared to Nb atom. Using the calculated energy gain due to the off-center displacements of Nb atoms for several concentrations of Nb in KTN, we construct the non-empirical Ginzburg-Landau-type functional for the excess energy. The coefficients of this functional are concentration dependent. This dependence allows to define the type of the concentration-induced phase transition in KTaO3 alloyed by Nb.",

keywords = "ABO perovskites, INDO method, KTN solid solutions",

author = "Eglitis, {R. I.} and D. Fuks and S. Dorfman and Kotomin, {E. A.} and G. Borstel",

note = "Funding Information: Authors are indebted to A.V. Postnikov and V. Vikhnin for many stimulating discussions. This study is supported in part by DFG, by NATO (grant PST.CLG. 977561) and by European Center of Excellence in Advanced Materials Research and Technology in Riga, Latvia. This research also was supported in part by the Niedersachsen Ministry of Science and Art and in part by the KAMEA program.",

year = "2002",

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doi = "10.1016/S1369-8001(02)00097-5",

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T1 - Large-scale modelling of the phase transitions in KTa1-xNbxO3 perovskite solid solutions

AU - Eglitis, R. I.

AU - Fuks, D.

AU - Dorfman, S.

AU - Kotomin, E. A.

AU - Borstel, G.

N1 - Funding Information: Authors are indebted to A.V. Postnikov and V. Vikhnin for many stimulating discussions. This study is supported in part by DFG, by NATO (grant PST.CLG. 977561) and by European Center of Excellence in Advanced Materials Research and Technology in Riga, Latvia. This research also was supported in part by the Niedersachsen Ministry of Science and Art and in part by the KAMEA program.

PY - 2002/4/1

Y1 - 2002/4/1

N2 - We use quantum chemical method of the intermediate neglect of the differential overlap (INDO) based on the Hartree-Fock formalism for a large-scale modelling of the atomic and electronic structure of KNbxTa1-xO3 (KTN) perovskite solid solutions. Results for periodic defect models (large unit cell) of 40 and 320 atoms are compared with 135-atom INDO cluster calculations. Periodic Nb impurities in KTaO3 reveal clear off-center displacement beginning with the smallest calculated concentrations, so does an isolated Nb impurity in a cluster INDO calculation. The magnitude of Nb off-center displacement is close to the X-ray-absorption fine-structure observation (0.27 a.u.). In contrast, Ta impurities in KNbO3 always remain on-center, due to higher ionicity of Ta as compared to Nb atom. Using the calculated energy gain due to the off-center displacements of Nb atoms for several concentrations of Nb in KTN, we construct the non-empirical Ginzburg-Landau-type functional for the excess energy. The coefficients of this functional are concentration dependent. This dependence allows to define the type of the concentration-induced phase transition in KTaO3 alloyed by Nb.

AB - We use quantum chemical method of the intermediate neglect of the differential overlap (INDO) based on the Hartree-Fock formalism for a large-scale modelling of the atomic and electronic structure of KNbxTa1-xO3 (KTN) perovskite solid solutions. Results for periodic defect models (large unit cell) of 40 and 320 atoms are compared with 135-atom INDO cluster calculations. Periodic Nb impurities in KTaO3 reveal clear off-center displacement beginning with the smallest calculated concentrations, so does an isolated Nb impurity in a cluster INDO calculation. The magnitude of Nb off-center displacement is close to the X-ray-absorption fine-structure observation (0.27 a.u.). In contrast, Ta impurities in KNbO3 always remain on-center, due to higher ionicity of Ta as compared to Nb atom. Using the calculated energy gain due to the off-center displacements of Nb atoms for several concentrations of Nb in KTN, we construct the non-empirical Ginzburg-Landau-type functional for the excess energy. The coefficients of this functional are concentration dependent. This dependence allows to define the type of the concentration-induced phase transition in KTaO3 alloyed by Nb.

KW - ABO perovskites

KW - INDO method

KW - KTN solid solutions

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