Composition-induced phase-transition splitting in cuprous selenide

The nature of the phase transition to the superionic phase of cuprous selenide has been investigated by measuring thermal expansion, electron diffraction, and electronic conductivity. The degenerate nature of the transition has been demonstrated by introducing controlled deviations from stoichiometry. The origin of this first-order phase transition is interpreted in terms of the formation of a modulated ion distribution along the [111] cubic axis.