A role of B-site cation on structural and transport properties of La2BMnO6 (B= Cr, Fe, Co, Ni, Cu, Zn) double perovskites

Structural, dielectric and electrical properties of polycrystalline double perovskite oxides La2BMnO6 (Where B= Cr, Fe, Co, Ni, Cu, Zn) were prepared by auto combustion sol-gel method. The characterization of samples via X-ray reflects single phase in present series. X-ray diffraction pattern of all samples reveal monoclinic structure with space group P2(1)/n except Cu which shows orthorhombic symmetry with Pbnm space group. The crystallite size (D) was calculated by Scherrer formula and Williamson hall analysis. Frequency dependent dielectric properties measured at various temperatures. Dielectric constant (epsilon') and loss tan decreases with frequency. AC conductivity (sigma(ac)) increases as function of frequency shows semiconducting nature. I-V characteristic curve shows increase in current with rise in temperature. The DC resistivity (rho(dc)) shows negative temperature coefficient behaviour. It is confirmed that results in case of copper and chromium fitted well by small polaron hopping (SPH) model and for cobalt variable range hopping (VRH) of small polaron was observed whereas for Zn, Ni and Fe follows variable range hopping model.