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

• Published in: Physical review. B 2020-12, Vol.102 (21), p.1
• Main Authors: Zou, Yongtao, Li, Mu, Zhang, Wei, Zhou, Cangtao, Yu, Tony, Zhuo, Hongbin, Wang, Yanbin, Zhao, Yusheng, Ruan, Shuangchen, Li, Baosheng
• Format: Article
• Language: English
• Subjects: Contact stresses; Diamonds; Evolution; Extreme environments; High temperature; Microstrain; Nanocrystals; Phase transitions; Raman spectroscopy; Sesquioxides; Stress concentration; Thermoelastic properties; Transition pressure
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.102.214115

Here, we report an irreversible cubic-to-monoclinic structural transition in cubic c − Sc2 O3 nanocrystals which occur at pressures above ∼ 8.9 GPa 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 − Sc2 O3 phase undergoes a reversible back-transformation to the cubic counterpart at ∼ 1123 K and 9.0 GPa. Our observed transition pressure of ∼ 8.9 GPa 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 − Sc2 O3 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.