Electronic structure and total energy of SrBi2Ta2O9 by first-principles calculations

摘要

The results of first-principles calculations of the electronicnstructure and the total energy in strontium bismuth tantalate,nSrBi2Ta2O9 (SBT), with respect to Tanion displacements, are reported. In pseudotetragonal SBT and its solidnsolutions, bismuth oxide, [(Bi2O2)2+],nlayers alternate with double strontium tantalate,n[(Sr2Ta2O7)2-], perovskitenlayers. The dual crystal chemistries give rise to dual electronic andndielectric properties that are anisotropic. The calculated electronicnstructure of SBT indicates that the absence of an energy gap in thenvicinity of the Fermi level stems from lowering of the Sr orbitalnenergies due to its lower electronegativity relative to Ta and Bi ions,nand significant hybridization between Sr, Ta, Bi and O ions. Althoughncharge carriers in the “semimetallic”n(Sr2Ta2O7)2$sublattice havena large effective mass, the (Bi2O2)2+nsublattice is insulating. The calculated partial and total densities ofnstates provide alternative but plausible explanations to the reportednspectroscopic data. The total energy anisotropy indicates that multiplenphase transformations, and anisotropies in the polarization retentionnand coercive field (Ec), are expected. Explanations of thenfatigue-free behavior and leakage current (JL) and itsnanisotropy of SBT, and comments on optical transparency and calculatingnmethods for band structure of SBT are forwarded