Dielectric relaxation and electronic structure of BaAl 1/2Nb 1/2O 3: X-ray photoemission and nuclear magnetic resonance studies

Abstract

The frequency-dependent dielectric relaxation in barium-aluminium-niobate, BaAl1/2Nb1/2O3 ( BAN), at low temperatures (103-443 K) is investigated by alternating-current impedance spectroscopy in the framework of conductivity and electric modulus formalisms. The Havriliak-Negami expression is used to analyse the electric modulus data. The scaling behaviour of the imaginary part of the electric modulus suggests that the relaxation describes the same mechanism at various temperatures. The frequency-dependent conductivity spectra follow the power law. The electronic structure of BAN is studied using x-ray photoemission spectroscopy (XPS). The XPS data are analysed by the first-principles full potential linearized augmented-plane-wave method using density functional theory under the generalized gradient approximation. The electronic structure calculation reveals that the electrical properties of BAN are dominated by the interaction between niobium d-states and oxygen p-states. The Al-27 and Nb-93 nuclear magnetic resonance (NMR) studies of the sample are performed at 78 and 73 MHz, respectively, in the temperature range 4-295 K to understand the transport properties of charge carriers in terms of their dynamics on a microscopic level. The description of the NMR lineshape is given on the basis of analytical formulae. The NMR investigation confirms the chemical ordering of 1:1 Al/Nb in BAN.