Comparative Dielectric Response in CaTiO3 and CaAl1/2Nb1/2O3 From First Principles

Published

January 21, 2001

Author(s)

Eric J. Cockayne

Abstract

TiO3 (CT) and CaA11/2Nb1/2O3 (CAN) have similar structures but very different dielectric properties. For CT at room temperature, the relative permittivity 6 ~ 170 and the temperature coefficient of resonance frequency t ~ +900 ppm/K, but for CAN, 6 ~ 25; t ~ -87 ppm/K. We use first-principles density functional theory calculations to investigate the origin of the divergent behaviors. We find important differences between the two systems in both the frequencies and the eigenvectors of the low-frequency polar phonons. In CT, the frequencies are lower and the perovskite B site cations move against the surrounding oxygen octahedra; whereas in CAN, the frequencies are higher and the B site cations move with the oxygen octahedra. These two factors are equally important in explaining the differences in 6. We introduce and solve a decoupled quantum oscillator model for the temperature-dependent permittivity. This model predicts a large positive t for CT and a small t for CAN, in qualitative agreement with experiment. We relate the different dielectric behaviors to differences in the electronic structures.

Citation

Journal of Applied Physics

Volume

90

Pub Type

Journals

Keywords

Ab-initio calculations, anharmonic lattice dynamics, calcium aluminum niobate, calcium titanate, dielectric permittivity, microwave dielectrics, temperature coefficients

Citation

Cockayne, E. (2001), Comparative Dielectric Response in CaTiO₃ and CaAl_1/2Nb_1/2O₃ From First Principles, Journal of Applied Physics (Accessed December 26, 2024)