Suppression of Pressure-Induced Phase Transitions in a Monoclinically Distorted LiNbO-Type CuNbO by Preference for a CuO Triangular Coordination Environment.

Pressure-induced phase transitions in a monoclinically distorted LiNbO-type CuNbO with triangularly coordinated Cu and octahedrally coordinated Nb were experimentally and computationally investigated. Phase transitions into GdFeO-type or NaIO-type structures generally observed in LiNbO-type compounds below 30 GPa were not detected in CuNbO 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 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.