Dielectric relaxation in double-perovskite Ca2GdTaO6

The double perovskite oxide calcium gadolinium tantalate, Ca 2 GdTaO 6 (CGT) is synthesized by solid-state reaction technique. The Rietveld refinement of the X-ray diffraction pattern of the sample shows monoclinic phase at room temperature. Fourier transform infrared (FTIR) spectrum shows two primary vibrational modes of the sample at around 378 and 566 cm -1 . Dielectric spectroscopy is applied to investigate the ac electrical conductivity of CGT in the temperature range 303-673 K and frequency range 42 Hz-1 MHz. The modified Cole-Cole equation is used to describe the relaxation mechanism in CGT. The relaxation time corresponding to dielectric loss is found to obey the Arrhenius law with an activation energy of 0.26 eV. The impedance data has been modeled by an equivalent circuit consisting of two serially connected R-CPE units, one for the grain and the other for the grain boundary, each containing a resistor (R) and a constant phase element (CPE). The frequency dependent conductivity spectra follow the Jonscher power law.