Ag₅Pd₂O₄, a New Subvalent Silver Oxide, Obtained from Ag₂PdO₂ via a High-pressure Synthesis

Subvalent silver oxides, where silver exhibits an oxidation state between 0 and + 1, have traditionally been discovered serendipitously due to a lack of systematic synthesis methods and understanding of their bonding schemes. This study presents a novel, purposeful approach to synthesizing multinary subvalent silver oxides through high-pressure techniques. By subjecting the monovalent silver oxide Ag₂PdO₂ to hydrostatic pressure of ∼30 GPa and laser heating at 1500 K, subvalent Ag₅Pd₂O₄ forms besides PdO. The crystal structure of Ag₅Pd₂O₄, determined via in situ single-crystal X-ray diffraction, reveals distinct layers of cationic silver aggregates and anionic oxopalladate units. Electronic structure calculations confirm the subvalent nature of silver in Ag₅Pd₂O₄, showing a vanished band gap and increased electron density on silver atoms. The findings pave the way for developing materials with rich magneto-electronic functionalities, owing to the interplay between subvalent silver and transition metal cations.