First-principles electronic structure and lattice dynamics of the giant dielectric compoundNa0.5Bi0.5Cu3Ti4O12

Abstract

We report the results of an ab initio study of electronic, dielectric, and latticedynamical properties of high dielectric constant perovskite-derived oxideNa1/2Bi1/2Cu3Ti4O12. The calculations have been carried out within the local spin density functionalapproximation using norm-conserving pseudopotentials and a plane-wave basis. The groundstate is found to be an antiferromagnetic direct band gap semiconductor. Latticedynamical properties, such as Born effective charge tensors, dielectric permittivitytensors, and phonon frequencies at the Brillouin zone center were calculated usingdensity functional perturbation theory and found to be similar to the more studiedCaCu3Ti4O12 and CdCu3Ti4O12 compounds. The calculated electronic () and static (ϵ0≈150) dielectric constants indicate that the observed high dielectric constant is extrinsic in origin.The main contribution to the static dielectric constant is found to be due to a low frequency(50 cm−1) infrared-active mode which has a large mode effective charge.