Comparative computational study of antiferromagnetic and mixed-valent diamagnetic phase of AgF2: Crystal, electronic and phonon structure and p-T phase diagram

Abstract

Crystal and electronic structure, lattice dynamics and thermodynamic stability of little known mixed-valent diamagnetic Ag1+Ag3+F4β form of AgF2 is thoroughly examined for the first time and compared with well-known antiferromagnetic Ag2+F2α form within the framework of Density Functional Theory based methods, phonon direct method and quasiharmonic approximation. Computed equations of state, bulk moduli, electronic densities of states, electronic and phonon band structures including analysis of optically active modes and p–T phase diagram of the α–β system are presented. This study demonstrates that α is thermodynamically preferred over β at all temperatures and pressures of its existence but simultaneously β is dynamically stable in much broader pressure range. The β phase is discussed in broader context of isostructural ternary metal fluorides and isoelectronic oxides including NaCuO2 – the reference Cu3+ compound corresponding to fully overdoped high-temperature oxocuprate superconductor.