Pressure-induced structural and valence transition in AgO

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Chemistry

Background:

• Silver oxide (AgO) exhibits complex crystal structures and electronic properties.
• Understanding AgO's behavior under pressure is crucial for materials science applications.

Purpose of the Study:

• Investigate the pressure-induced evolution of AgO crystal structures.
• Analyze the changes in the oxygen environment around silver (Ag) atoms under varying pressures.
• Determine the pressure at which AgO undergoes a semiconductor-to-metal transition.

Main Methods:

• Density functional theory (DFT) with a hybrid functional.
• Structure prediction methods.
• Analysis of coordination environment and valence states of Ag atoms.

Main Results:

• Under ambient conditions, AgO displays two distinct Ag sites (Ag1 and Ag2) with different oxygen coordination and mixed-valence states.
• Increasing pressure causes the Ag1 site's coordination and valence state to converge towards those of the Ag2 site.
• A significant decrease in the band gap leads to a semiconductor-to-metal transition at approximately 75 GPa.
• A structural phase transition from monoclinic (P21/c) to trigonal (R3[combining macron]m) occurs around 77 GPa, accompanied by a valence state change.

Conclusions:

• Pressure significantly alters AgO's crystal structure, Ag atom coordination, and valence states.
• AgO transitions from a semiconductor to a metal above 75 GPa.
• The study reveals pressure-driven phase and electronic transitions in AgO.