研究目的
Analyzing the bulk phase transitions of titanium dioxide polymorphs (anatase, rutile, and brookite) in thermodynamical equilibrium and after ultrafast laser excitation to understand their energy barriers and transition pathways.
研究成果
The anatase-rutile and brookite-rutile phase transitions have lower energy barriers than the anatase-brookite transition, both in thermal equilibrium and upon laser excitation. Laser excitation stabilizes the rutile phase without significantly altering the transition pathways. The study suggests extending calculations to the nanoparticle regime for more practical insights.
研究不足
The study focuses on bulk material, neglecting surface effects and particle size dependencies, which are crucial in real-world applications. The energy relation between polymorphs is not corrected, and the phase transitions are modeled as collective transformations, which may not fully represent real nucleation processes.
1：Experimental Design and Method Selection:
The study uses the generalized solid-state nudged elastic band (G-SSNEB) method for analyzing phase transitions, with forces and stresses calculated using electronic-temperature dependent density functional theory (DFT).
2：Sample Selection and Data Sources:
The study focuses on bulk titanium dioxide polymorphs (anatase, rutile, and brookite) to avoid surface effects, using periodic boundary conditions and a supercell with 48 atoms.
3：List of Experimental Equipment and Materials:
The in-house Code for Highly excIted Valence Electron Systems (CHIVES) is used for DFT calculations, with a 2 × 2 × 2 k grid for bulk properties.
4：Experimental Procedures and Operational Workflow:
The G-SSNEB method is applied to find minimal energy pathways (MEPs) between polymorphs, with atomic positions and lattice parameters optimized using the FIRE algorithm.
5：Data Analysis Methods:
The energy barriers and threshold temperatures for phase transitions are calculated, and the influence of laser excitation on the phase transitions is analyzed.
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