Microscopic study of superionic transition

Abstract

The mechanism of superionic transition is discussed both phenomenologically and microscopically in the framework of the ``chemical bond peculiarities'' approach which was originally proposed by Phillips. The proximity of p-halogen and d-metal electronic levels is proved to be a critical prerequisite to the formation of a local additional minimum of crystalline potential. The fold coordination number change involved in the transition is regarded as a redistribution of ionic occupancies, rendering this additional minimum absolute. The low-energy excitations are ascribed to the ionic motion between the local and absolute potential minima, with their consequent appearance both at temperatures below and above the phase transition. \textcopyright{} 1996 The American Physical Society.