Unraveling microstrain-promoted structural evolution and thermally driven phase transition in c-Sc2 O3 nanocrystals at high pressure

Here, we report an irreversible cubic-to-monoclinic structural transition in cubic c-Sc2O3 nanocrystals which occur at pressures above ∼8.9GPa upon nonhydrostatic compression in association with a pronounced volume collapse. This phase-transition-induced anomaly is further confirmed by our experimental Raman spectroscopy measurements and theoretical predictions. After annealing, however, this high-pressure monoclinic m-Sc2O3 phase undergoes a reversible back-transformation to the cubic counterpart at ∼1123K and 9.0 GPa. Our observed transition pressure of ∼8.9GPa for the cubic-to-monoclinic structural evolution is significantly lower than that from the previously diamond-anvil-cell-based hydrostatic x-ray experiments because of the existence of internal microscopic stress and/or high-stress concentration in the specimen caused by grain-to-grain contacts upon nonhydrostatic compression, which promoted the cubic-to-monoclinic structural transition. Moreover, we have reported new thermoelastic properties of c-Sc2O3 nanocrystals at simultaneous high-pressure and high-temperature conditions. These findings/results may have significant implications for the design of phase-switching devices and for the exploration of the structural relationship among sesquioxides for their uses in extreme environments.