Computer Modeling of Point Defects, Impurity Self-Ordering Effects and Surfaces in Advanced Perovskite Ferroelectrics
G. Borstela, E.A. Kotomina,b, R.I. Eglitisa and E. Heifetsc
aUniversität Osnabrück, Fachbereich Physik, 49069 Osnabrück, Germany
bInstitute of Solid State Physics, University of Latvia Kengaraga str. 8, Riga 1063, Latvia
cMaterials and Processes Simulation Center, Beckman Institute Caltech, Pasadena, CA 91125, USA
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The calculated optical properties of basic point defects - F-type centers and hole polarons - in KNbO3 perovskite crystals are used for the interpretation of available experimental data. The results of quantum chemical calculations for perovskite KNbxTa1-xO3 solid solutions are presented for x=0, 0.125, 0.25, 0.75, and 1. An analysis of the optimized atomic and electronic structure clearly demonstrates that several nearest Nb atoms substituting for Ta in KTaO3 - unlike Ta impurities in KNbO3 - reveal a self-ordering effect, which probably triggers the ferroelectricity observed in KNbxTa1-xO3. Lastly, the (110) surface relaxations are calculated for SrTiO3 and BaTiO3 perovskites. The positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized using the classical shell model. Strong surface rumpling and surface-induced dipole moments perpendicular to the surface are predicted for both the O-terminated and Ti-terminated surfaces.
DOI: 10.12693/APhysPolA.98.469
PACS numbers: 61.72.-y, 68.35.-p, 71.15.-m