High-pressure structural stability of compositionally complex pyrochlore oxides

Abstract

Compositionally complex oxides (CCOs) present immense potential for tailoring physical properties across a broad compositional landscape. Understanding their structural stability and tunability, particularly under external pressure, is crucial for advancing their functional applications. In this study, we investigate the impact of hydrostatic pressure on the crystal structure and cation ordering of three partially ordered transition metal and rare-earth-based CCO compositions, all stabilized in the pyrochlore structure-type. Using in situ high-pressure synchrotron x-ray powder diffraction (SXRD) and Raman spectroscopy, conducted with the diamond anvil cell (DAC) technique, we found that the pyrochlore phase remains stable up to pressures of 17–20 GPa at room temperature. The isothermal bulk moduli, determined by fitting the pressure–volume data to a third-order Birch–Murnaghan equation of state, range from 168 to 179 GPa. Raman spectroscopy results corroborate the SXRD findings, further confirming the structural robustness of the pyrochlore phase under high pressures. Moreover, analysis of the pressure-dependent relative intensities of selected Raman modes offers insights into pressure-induced modifications in cation ordering within these compounds.