Investigation of the ordered-disordered structural transition of (Nd1-xYx)2(Zr1-xCex)2O7 pyrochlore by X-ray diffraction, Raman spectroscopy, and Transmission electron microscopy

Abstract

In the current research, the equal molar Y and Ce co-doped (Nd1-xYx)2(Zr1-xCex)2O7 pyrochlore solid solution was prepared by solid-state method at 1500 °C. And the ordered-disordered structure of the as-prepared samples was investigated systematically by X-ray diffraction, Raman spectroscopy, and Transmission electron microscopy, respectively. The results showed that the lattice constants of ordered or disordered (Nd1-xYx)2(Zr1-xCex)2O7 solid solutions increase with increasing Y and Ce co-doping contents simultaneously from 0 to 1. The phase structure presents monophasic ordered pyrochlore (Fd3‾m space group, Z = 8) when Y and Ce contents are in the range of 0–0.15. While a biphasic region exists when contents of Y and Ce are 0.2, namely, there are ordered pyrochlore and disordered defect fluorite (Fm3‾m space group, Z = 4) structure coexisting in the (Nd0.8Y0.2)2(Zr0.8Ce0.2)2O7 solid solution. With the co-doping content of Y and Ce in the 0.3–1 range, the phase composition becomes monophasic disordered defect fluorite. Variation of the average rA/rB ratio value leads to the increase of the xO48f coordinate parameter from 0.3192 (0) to 0.3309 (0) when the phase structure of the sample present ordered pyrochlore. X-ray diffraction, Raman spectroscopy, and Transmission electron microscopy results confirm that the ordered-disordered transformation of (Nd1-xYx)2(Zr1-xCex)2O7 pyrochlore is related to the xO48f coordinate parameter.