Pressure-induced transformations of Ag II F2—towards an 'infinite layer' d 9 material

The enthalpy of seven polymorphs of AgF2 has been scrutinized up to 50 GPa using density functional theory (DFT) calculations. We show that α-Ag II F2 (Pbca, with its puckered-sheet structure and an elongated octahedral 4 + 2 coordination of Ag) transforms above 15 GPa into a layered polymorph δ (Abma). The Jahn–Teller effect persists and the coordination of Ag(II) is of the 4 + 4 type; the Ag–F–Ag bridges are bent. Cubic γ structure of the CaF2 type (Fm¯ 3m), and its Pa 3v ariant(η), rutile (ζ ), and tetragonal ‘infinite chain’ P4mm structure related to AgFBF4 (e) are not preferred in the entire pressure window that was investigated. Electronic structure of high-pressure δ-Ag II F2 form shows features that are characteristic for two-dimensional (2D) materials, a prerequisite for high-TC superconductivity.