Metallization without Charge Transfer in CuReO₄ Perrhenate under Pressure

Area of Science:

• Materials Science
• Solid-State Chemistry
• High-Pressure Physics

Background:

• Copper rhenium oxide (CuReO₄) exhibits complex structural behavior under varying conditions.
• Understanding pressure-induced phase transitions is crucial for designing novel materials.

Purpose of the Study:

• To elucidate the sequence of pressure-induced structural transformations in CuReO₄.
• To investigate the electronic properties of CuReO₄ at high pressures.

Main Methods:

• High-pressure synchrotron X-ray diffraction.
• Raman spectroscopy.
• Density-functional theory calculations.

Main Results:

• Two first-order phase transitions observed at 1.5 GPa and 7 GPa.
• Structural changes involve transformation from ReO₄ tetrahedra to ReO₆ octahedra, forming chains and then a NbO₂-type structure.
• A significant volume reduction of 7% and 14% accompanies the transitions.
• The high-pressure phase exhibits metallicity, evidenced by Raman signal disappearance and calculations.

Conclusions:

• CuReO₄ undergoes distinct structural and electronic changes under high pressure.
• The metallization is attributed to the broadening of Cu 3d and Re 5d bands.
• The material shows negative thermal expansion along the c-axis at ambient pressure.