Here, we report an irreversible cubic-to-monoclinic structural transition in cubic cSc2O3 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 mSc2O3 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 cSc2O3 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.

Yongtao Zou, Mu Li, Wei Zhang, Cangtao Zhou, Tony Yu, Hongbin Zhuo, Yanbin Wang, Yusheng Zhao, Shuangchen Ruan, Baosheng Li, “Unraveling microstrain-promoted structural evolution and thermally driven phase transition in c-Sc2O3 nanocrystals at high pressure”, Phys. Rev. B 102, 214115, abstract