High temperature structural and thermal expansion behavior of pyrochlore-type praseodymium zirconate

In this communication we report the high temperature structural details of pyrochlore-type Pr2Zr2O7, a potential mixed electronic and ionic conducting material, as observed from the in situ variable temperature powder neutron diffraction in vacuum. The evolution of structural parameters with temperature revealed a smooth expansion of the lattice while a feeble decreasing trend in the oxygen parameters of pyrochlore structure. The analyses of the structural parameters further indicate a larger expansion of the Pr–O bonds (α = 11.32 × 10−6 K−1) compared to that of Zr–O bonds (α = 8.83 × 10−6 K−1). The temperature dependent unit cell parameters measured under vacuum deviates from those measured in air and the coefficient of axial thermal expansion (αa) of Pr2Zr2O7 lattice is 10.18 × 10−6 K−1 (in vacuum). The analyses of structural parameters indicated a larger distortion in PrO8 polyhedra compared to ZrO6 octahedra of the Pr2Zr2O7. The differences in high temperature behaviour in air and vacuum have been explained by the contributions of oxidation of Pr3+ to Pr4+.