Metallic Re₃O₂ with mixed-valence states.

Area of Science:

• Solid State Chemistry
• Materials Science
• Computational Materials Discovery

Background:

• Rhenium (Re) exhibits diverse valence states (+2 to +7) in compounds.
• Mixed-valence states in rhenium compounds have not been previously reported.
• Understanding high-pressure phase diagrams is crucial for discovering new materials.

Purpose of the Study:

• To explore the Rhenium-Oxygen (Re-O) phase diagram under high pressure.
• To identify novel Re-O compounds and their properties.
• To investigate the possibility of mixed-valence states in rhenium compounds.

Main Methods:

• First-principles structural search calculations were employed.
• Exploration of a wide range of stoichiometric compositions under high pressure.
• Electronic structure calculations to determine material properties.

Main Results:

• Identification of two novel high-pressure phases: ReO2 and ReO3.
• Discovery of two new Re-O compounds: Re3O2 (Re-rich) and ReO4 (O-rich).
• Re3O2 exhibits the first known mixed-valence states in Re-based compounds due to inequivalent coordination environments.
• All four discovered Re-O phases display metallicity originating from Re 5d electrons.
• ReO3 shows a predicted superconducting critical temperature of up to 12 K at 50 GPa.

Conclusions:

• This study successfully identified novel Re-O phases, including the first mixed-valence rhenium compound.
• The discovered materials exhibit metallicity and potential for superconductivity.
• Opens new avenues for discovering novel transition metal compounds with mixed-valence states.