It is predicted theoretically that various oxides (Al2O3, MgO, SiO2and TiO2) under ultrafast excitation of the electronic system exhibit nonthermal phase transitions. In the bulk, Al2O3transiently forms a superionic phase via nonthermal phase transition, MgO and SiO2disorder, TiO2experiences solid-solid phase transition while thermal effects lead to melting. In the finite-size samples and near-surface regions, MgO undergoes solid-solid phase transition at lower doses than those required for atomic disorder. All studied oxides but TiO2, if allowed to expand, exhibit a lower damage threshold, whereas in TiO2expansion releases the stress and prevents solid-solid phase transition thereby increasing the damage threshold up to the melting one. The results suggest that a nonthermal phase transition is a general response of oxides to sufficiently high ultrafast electronic excitation. A comparison with nonadiabatic simulations demonstrates that Born-Oppenheimer approximation systematically overestimates damage thresholds, and in some cases misses a phase transition entirely.

中文翻译：

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辐照氧化物中的非热相变


理论上预测，各种氧化物（Al2O3、MgO、SiO2和TiO2）在电子系统的超快激发下会表现出非热相变。在本体中，Al2O3通过非热相变、MgO和SiO2无序暂时形成超离子相，TiO2经历固-固相变，而热效应导致熔化。在有限尺寸的样品和近表面区域，MgO 在比原子无序所需的剂量更低的剂量下经历固-固相变。除 TiO2 外，所有研究的氧化物如果允许膨胀，都会表现出较低的损伤阈值，而 TiO2 膨胀会释放应力并防止固-固相变，从而将损伤阈值提高到熔化阈值。结果表明，非热相变是氧化物对足够高的超快电子激发的一般响应。与非绝热模拟的比较表明，玻恩-奥本海默近似系统地高估了损伤阈值，并且在某些情况下完全错过了相变。