研究目的
Investigating the phase transition systematics in BiVO4 under high-pressure and high-temperature conditions using Raman experiments and ab initio calculations.
研究成果
The behavior of the fergusonite phase is decisively affected by anharmonic effects, evidenced by the sign of their pressure and temperature coefficients. The introduction of a critical temperature depending both on temperature and pressure allows the description of the results of all the experiments in a unified way. The fergusonite-to-scheelite phase transition is reversible and second-order, while the zircon-to-scheelite transition is first-order and irreversible.
研究不足
The destabilization of the scheelite phase is observed at lower pressures if less hydrostatic pressure transmitting media are used. The changes observed are irreversible since the spectrum recovered from 17.8 GPa is different from the initial fergusonite phase.
1：Experimental Design and Method Selection:
High-pressure–high-temperature Raman experiments were performed on BiVO4 to characterize the fergusonite, scheelite, and zircon phases. The experimental results were supported by ab initio calculations providing vibrational patterns.
2：Sample Selection and Data Sources:
Samples included fergusonite and scheelite phases (powder and single crystal) and zircon polymorph (nanopowder).
3：List of Experimental Equipment and Materials:
Diamond anvil cell with a 16:3:1 methanol-ethanol-water mixture or Ne as pressure-transmitting medium, 632.8-nm He-Ne laser, Jobin-Yvon spectrometer, thermoelectric-cooled multichannel CCD detector.
4：8-nm He-Ne laser, Jobin-Yvon spectrometer, thermoelectric-cooled multichannel CCD detector.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Raman spectra were collected in backscattering geometry. Pressure was determined using ruby luminescence. High-temperature experiments were conducted in an air atmosphere.
5：Data Analysis Methods:
The anharmonic contribution to the wave-number shift was analyzed using an order parameter. The results were interpreted with the aid of ab initio calculations.
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