Micro-structure, optical properties and ac conductivity of rare earth double perovskite oxides: Sr2ErNbO6

A polycrystalline rare earth double perovskite oxide strontium erbium niobate, Sr2ErNbO6 (SEN) is synthesized by the solid state reaction technique. Rietveld analysis of X-ray diffraction pattern reveals that SEN has monoclinic phase with space group P21/n. Fourier transform infrared spectrum shows two phonon modes of the sample due to the antisymmetric NbO6 stretching vibration. The compound shows significant frequency dispersion in its dielectric properties. The frequency dependent ac conductivity spectra follow the Jonscher's universal power law. The conductivity at 100 Hz varies from 1.38×10−6 Sm−1 to 2.34×10−4 Sm−1 with the increase of temperature from 303 K to 653 K respectively. The increase of conductivity can be explained from the Correlated barrier hopping (CBH) model. The relaxation mechanism of the sample in the framework of electric modulus formalism is modelled by Davidson–Cole equation. The activation energy of the sample, calculated from both conductivity and modulus spectra is found to be~0.8 eV which indicates that the conduction mechanism for SEN is due to ion hopping. The scaling behavior of imaginary electric modulus suggests that the relaxation describes the same mechanism at various temperatures.