Phase Behavior of Ag2CrO4 under Compression: Structural, Vibrational, and Optical Properties

• Published in: Journal of physical chemistry. C 2013-06, Vol.117 (23), p.12239-12248
• Main Authors: Santamaría-Pérez, David, Bandiello, Enrico, Errandonea, Daniel, Ruiz-Fuertes, Javier, Gomis, Oscar, Sans, Juan Angel, Manjón, Francisco Javier, Rodríguez-Hernández, Plácida, Muñoz, Alfonso
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electron states; Exact sciences and technology; Methods of electronic structure calculations; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp401524s

We have performed an experimental study of the crystal structure, lattice dynamics, and optical properties of silver chromate (Ag2CrO4) at ambient temperature and high pressures. In particular, the crystal structure, Raman-active phonons, and electronic band gap have been accurately determined. When the initial orthorhombic Pnma Ag2CrO4 structure (phase I) is compressed up to 4.5 GPa, a previously undetected phase (phase II) has been observed with a 0.95% volume collapse. The structure of phase II can be indexed to a similar orthorhombic cell as phase I, and the transition can be considered to be an isostructural transition. This collapse is mainly due to the drastic contraction of the a axis (1.3%). A second phase transition to phase III occurs at 13 GPa to a structure not yet determined. First-principles calculations have been unable to reproduce the isostructural phase transition, but they propose the stabilization of a spinel-type structure at 11 GPa. This phase is not detected in experiments probably because of the presence of kinetic barriers. Experiments and calculations therefore seem to indicate that a new structural and electronic description is required to model the properties of silver chromate.