Structure, thermal and electrical properties of calcium doped pyrochlore type praseodymium zirconate

Abstract

Herein we report the structure, thermal and electrical properties of pyrochlore type Pr2−xCaxZr2O7 (x = 0.00, 0.10 and 0.20) compositions. These compounds have been prepared by gel combustion method followed by heating in reducing (Argon/Hydrogen) atmosphere and characterized by powder X-ray diffraction, Raman spectroscopy and ac-impedance studies. The powder XRD and Raman spectroscopic studies revealed the retention of the parent cubic pyrochlore type structure up to the compositions with x = 0.10. The thermal stabilities of the compositions have been investigated by in situ high temperature powder XRD and thermogravimetric studies. A maximum of about 1.25% weight gain due to oxidation of Pr3+ is observed in all the samples. The typical axial thermal expansion coefficients (αa) for the compositions with x = 0.00, 0.10 and 0.20 are 8.40 × 10−6, 11.29 × 10−6 and 11.67 × 10−6 K−1, respectively. The analyses of impedance and admittance spectra revealed maximum conductivity at x = 0.10, while the activation energy increases with Ca2+ content. At around 770 K, the conductivities of the compositions with x = 0.00, 0.10 and 0.20 are 2.26 × 10−5 S/cm, 1.88 × 10−4 S/cm and 1.23 × 10−4 S/cm, respectively. The activation energy for electronic conductivity for the composition with x = 0.00 and 0.10 are 0.42 and 0.63 eV, respectively. The temperature dependent conductivity of the composition with x = 0.20 composition revealed a deviation around 700 K where the aviation energy decreased from 0.97 eV to 0.38 eV. The electrical properties Pr2−xCaxZr2O7 have been correlated with structural parameters and explained by the coexisting electronic and ionic conductivities.