G. Borstel et al., Computer modeling of point defects, impurity self-ordering effects and surfaces in advanced perovskite ferroelectrics, ACT PHY P A, 98(5), 2000, pp. 469-481
The calculated optical properties of basic point defects - F-type centers a
nd hole polarons - in KNnO(3) perovskite crystals are used for the interpre
tation of available experimental data. The results of quantum chemical calc
ulations 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 electro
nic structure clearly demonstrates that several nearest Nb atoms substituti
ng for Ta in KTaO3 - unlike Ta impurities in KNbO3 - reveal a self-ordering
effect, which probably triggers the ferroelectricity observed in KNbxTa1-x
O3. Lastly, the (110) surface relaxations are calculated for SrTiO3 and BaT
iO3 perovskites. The positions of atoms in 16 near-surface layers placed at
op a slab of rigid ions are optimized using the classical shell model. Stro
ng surface rumpling and surface-induced dipole moments perpendicular to the
surface are predicted for both the O-terminated and Ti-terminated surfaces
.