Pressure-induced structural transformations and new polymorphs in BiVO₄.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Bismuth vanadate (BiVO4) is recognized for its photocatalytic and dielectric properties.
• Its properties are highly sensitive to crystalline phase, necessitating control over phase stability.
• Understanding phase transitions is key to tailoring BiVO4 for specific applications.

Purpose of the Study:

• To investigate the phase stability and vibrational properties of fergusonite- and zircon-type BiVO4 under high pressure.
• To elucidate the structural transformations and reversibility of BiVO4 phases up to 41.6 GPa.
• To computationally predict new BiVO4 phases at elevated pressures.

Main Methods:

• In situ synchrotron X-ray diffraction (XRD) for structural analysis.
• Raman spectroscopy to probe vibrational properties.
• First principles calculations for theoretical predictions and structural determination.

Main Results:

• Both fergusonite- and zircon-type BiVO4 transform to scheelite and subsequently to β-fergusonite structures under compression.
• The β-fergusonite structure of BiVO4 was determined for the first time using computational methods and XRD refinement.
• A new BiVO4 phase was theoretically predicted at higher pressures, with reversible fergusonite-scheelite and scheelite-β-fergusonite transitions observed.
• Irreversible zircon-to-scheelite transition and significant volume collapses were noted during phase transitions.

Conclusions:

• Compression induces sequential phase transitions in BiVO4, leading to the formation of scheelite and β-fergusonite structures.
• The study provides the first computational determination of the β-fergusonite structure in BiVO4.
• Reversibility and irreversibility of transitions, along with volume changes, offer critical insights into BiVO4 phase behavior and structure-property relationships.