AgCu₃V₄O₁₂: A novel perovskite containing mixed-valence silver ions

A novel silver-containing perovskite, AgCu₃V₄O ₁₂, was synthesized under high-pressure and high-temperature conditions. It crystallizes in an A-site-ordered perovskite structure (space group Im3Ì...), in which silver ions occupy the 12-coordinated A sites forming regular icosahedra, and exhibits metallic behavior. Bond-valence-sum calculations and X-ray photoemission spectroscopy reveal that Ag ions are present in the mixed-valence state, most likely attributable to the coexistence of Ag⁺ and Ag³⁺, unlike the case of well-known perovskite-type AgNbO₃ and AgTaO₃ containing only Ag ⁺ ions. We discuss metallic conduction in relation to electronic structure calculations.