Structural, vibrational and electrical properties of ordered double perovskite oxide BaLaMnSbO6

BaLaMnSbO6 (BLMS) has been successfully synthesized by solid-state reaction technique. In contrast to earlier reports, Rietveld refinement of powder X-ray diffraction (XRD) data of BLMS shows tetragonal structure having space group I4/m. The octahedral tilt about the direction of the c-axis is found to be 8.99 degrees and the superlattice line (011) indicates the presence of cation ordering. FT-IR and Raman analysis as well as group theoretical investigation confirm the ordered tetragonal structure of BLMS with I4/m space group. The anti-phase distortions appear to be sufficiently large as detected by infrared and Raman spectroscopies, which give rise to the degeneracy and breaking of the symmetries of the normal modes. Impedance spectroscopy is used to investigate the dielectric relaxation and ac electrical conductivity in the temperature range of 303-403 K and in the frequency range of 0.1 kHz-1 MHz. Experimental electric modulus data are fitted to the Cole-Cole model in order to analyse the dielectric relaxation in BLMS. The frequency dependence ac electrical conductivity data are fitted to Jonscher's universal power law at various temperatures. The dc conductivity follows Arrhenius law with activation energy (E-a) 0.51 eV suggesting the polaron hopping. The complex impedance plane plots of BLMS indicate the presence of both grain and grain boundary effects and are analyzed by the electrical equivalent circuit consisting of a resistance and capacitance. (C) 2013 Elsevier B.V. All rights reserved.