Phase Equilibria in the Cu2Se–Cu3AsSe4–Se System and Thermodynamic Properties of Cu3AsSe4

Abstract

The Cu₂Se–Cu₃AsSe₄–Se system has been studied using differential thermal analysis, X-ray diffraction, and emf measurements on concentration cells using Cu₄RbCl₃I₂ as a solid electrolyte. We have constructed a number of vertical sections through the phase diagram, the room-temperature solid-state phase compatibility diagram, and a projection of the liquidus surface. The primary crystallization fields of the phases present and the types and coordinates of in- and univariant equilibria in the system have been identified. The system has been shown to contain a broad liquid–liquid immiscibility region. Using emf data, we evaluated the standard thermodynamic functions of formation and standard entropy of the Cu₃AsSe₄ compound.