We compare first-principles (FP) calculations of the ionic effective charges, phonon frequencies, and static dielectric permittivities ks of several perovskite-type materials. Transition metal ions have anomalously large effective charges, though in the double perovskite CaAll/2Nbl/203 (CAN), the effective charge of Nb is significantly lower than in the simple pervoskite KnbO3, showing different Nb-0 bonding chemistry. Tolerance factors, cation chemistry, and structure phase transitions all affect the nature of the softest phonons in perovskites. For the solid solution (CaAll/2Nbl/203)1-x(CaTiO3)x (CAN-CT), ks is modeled via a cluster expansion, with the parameters determined from FP. In pure CAN, ks is found to increase when cation order increases, in agreement with experimental results on analogous systems. The dielectric constant of CAN-CT increases nonlinearly with x, in agreement with experiment.
Proceedings Title: Proceedings Issue of the MMA 2002 Meeting
Issue: No. 14
Conference Dates: August 31-September 4, 2002
Conference Location: York, UK
Conference Title: Journal of the European Ceramic Society
Pub Type: Conferences
dielectric properties, first-principles calculations, perovskites