研究目的
To study the pressure dependence of structural and electronic properties of two TiO2 phases: the cotunnite-type and the Fe2P-type structure.
研究成果
The band gaps of both high-pressure phases of TiO2 are found to be unexpectedly robust across a broad range of pressures. The robustness originates from the synchronous change of valence band maximum and conduction band minimum with nearly identical rates of changes. Such unusual properties may have potential applications for optical devices operating at extreme conditions.
研究不足
The study is limited to theoretical calculations and does not include experimental validation. The pressure range considered is up to 260 GPa, which may not cover all possible high-pressure scenarios.
1：Experimental Design and Method Selection:
First-principles calculations were carried out by the Vienna ab initio simulation package (VASP), based on density functional theory (DFT). The exchange-correlation interactions of electrons are described by the generalized gradient approximation (GGA) within the PBE formalism. The band gaps are calculated using DFT with GGA, as well as the many-body perturbation theory with the GW approximation.
2：Sample Selection and Data Sources:
The study focuses on two TiO2 phases: the cotunnite-type and the Fe2P-type structure.
3：List of Experimental Equipment and Materials:
Vienna ab initio simulation package (VASP), projector-augmented-wave potentials, energy cut-off for plane waves is 600 eV.
4：Experimental Procedures and Operational Workflow:
Structural optimization and total energy calculations were performed with specific k-mesh for sampling the Brillouin zone (BZ) of the cotunnite-type and Fe2P-type structure. GW calculations were performed to estimate the band gap values.
5：Data Analysis Methods:
The pressure dependence of the band gaps is analyzed using a modified form of a quadratic polynomial equation. The pressure coefficients are calculated as the first derivative of the band gap with respect to pressure.
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