Dielectric relaxation and electronic structure ofBaAl1/2Nb1/2O3: 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 impedancespectroscopy in the framework of conductivity and electric modulus formalisms. TheHavriliak–Negami expression is used to analyse the electric modulus data. The scalingbehaviour of the imaginary part of the electric modulus suggests that the relaxationdescribes the same mechanism at various temperatures. The frequency-dependentconductivity spectra follow the power law. The electronic structure of BAN is studiedusing x-ray photoemission spectroscopy (XPS). The XPS data are analysed bythe first-principles full potential linearized augmented-plane-wave method usingdensity functional theory under the generalized gradient approximation. Theelectronic structure calculation reveals that the electrical properties of BAN aredominated by the interaction between niobium d-states and oxygen p-states. The27Al and 93Nb nuclear magnetic resonance (NMR) studies of the sample are performed at 78and 73 MHz, respectively, in the temperature range 4–295 K to understandthe transport properties of charge carriers in terms of their dynamics on amicroscopic level. The description of the NMR lineshape is given on the basis ofanalytical formulae. The NMR investigation confirms the chemical ordering of 1:1Al/Nb in BAN.