Thermal Expansion and Defect Chemistry of MgO-Doped Sm2Zr2O7

Abstract

A series of solid solutions of (Sm2 - xMgx)Zr2O7 - x/2 pyrochlores were prepared by a solid-state reaction and characterized by X-ray diffraction, high-temperature dilatometry, Raman spectroscopy, and X-ray photoelectron spectroscopy. X-ray diffraction and Raman spectroscopy reveal that MgO doping does not break down the pyrochlore structure of Sm2Zr2O7 for all of the samples, though it increases the degree of structure disorder. However, the thermal expansion coefficient is remarkably increased through doping up to x = 0.075 with a maximum value around 11.94 × 10-6 K-1 (room temperature to 1000 °C), which can mitigate the mismatches of thermal expansion in the high-temperature applications of Sm2Zr2O7. A new solid−solution mechanism that is different from previous research was proposed and confirmed by analyzing the variation of the lattice parameters, experimental density, and X-ray photoelectron spectroscopy of samples. It involves the transformation of the solid−solution model about Mg2+ interstitial and substitution with a turning point at composition point x = 0.075. This transformation and consequently the variation of lattice energy may be responsible for the variation of the thermal expansion coefficient.