Suppression of Pressure-Induced Phase Transitions in a Monoclinically Distorted LiNbO₃-Type CuNbO₃ by Preference for a CuO₃ Triangular Coordination Environment

Abstract

Pressure-induced phase transitions in a monoclinically distorted LiNbO 3 -type CuNbO 3 with triangularly coordinated Cu and octahedrally coordinated Nb were experimentally and computationally investigated. Phase transitions into GdFeO 3 -type or NaIO 3 -type structures generally observed in LiNbO 3 -type compounds below 30 GPa were not detected in CuNbO 3 even at the maximum experimental pressure, 32.4 GPa. Our density functional theory calculations revealed that the phase transition is suppressed by the preference for the CuO 3 triangular coordination environment, which reduces the total internal energy. This study clarifies that the change in the coordination environment of given ions can affect the pressure-induced phase transition.