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Nonthermal phase transitions in irradiated oxides.
1Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 182 21 Prague 8, Czech Republic.
Summary
Ultrafast electronic excitation induces nonthermal phase transitions in oxides like alumina and magnesia. Expansion affects damage thresholds, with TiO2 showing increased resistance, unlike other oxides.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Physical Chemistry
Background:
- Oxides exhibit complex responses to high-energy stimuli.
- Understanding ultrafast electronic excitation effects is crucial for materials science.
Purpose of the Study:
- To theoretically investigate nonthermal phase transitions in oxides (Al2O3, MgO, SiO2, TiO2) under ultrafast electronic excitation.
- To analyze the influence of sample size and expansion on material response and damage thresholds.
Main Methods:
- Theoretical prediction of material behavior under ultrafast excitation.
- Analysis of phase transitions including superionic, disordering, and solid-solid transitions.
- Comparison of simulation results with and without the Born-Oppenheimer approximation.
Main Results:
- Al2O3 forms a superionic phase; MgO and SiO2 disorder; TiO2 undergoes solid-solid transition, while others may melt.
- Finite-size effects and surface regions alter transition pathways for MgO.
- Expansion lowers damage thresholds for most oxides, but increases it for TiO2 by preventing solid-solid transitions.
Conclusions:
- Nonthermal phase transition is a general response of oxides to high ultrafast electronic excitation.
- The Born-Oppenheimer approximation can overestimate damage thresholds and miss phase transitions.
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