Phonons of Phase-Change Materials

Phase-change materials (PCMs) undergo a reversible transition from a semiconducting to a metallic state, nicely termed "incipient metal." This transition is driven by a Peierls distortion. A model of covalent bonding is developed in a tight-binding scheme that accounts for the drastic evolution of some properties of PCMs, among which the Gruneisen parameter. The original vibrational properties of PCM and related Peierls distorted materials are analyzed. A three-body covalent interaction describes the PCM properties. It explains the simultaneous softening of the optical phonons and the hardening of the acoustic phonons upon crystallization of the PCMs.