Homogeneity and Primary Crystallization Polyhedra of Chalcopyrite in the Cd–Ge–Mn–As Tetrahedron

Resumo

Isotherms of the T–x–y–z projection of the p–T–x–y–z phase diagram for the system Cd–Ge–Mn–As have been constructed by a topologic representation of phase states using fragmentary experimental data. In the absence of melt (below 320°C), 18 stable equilibria involving four crystalline phases were found to exist. For limited chalcopyrite solid solutions (Cd,Ge,Mn)As₂, eight crystalline phases affecting its cationic composition have been isolated, namely, Cd₃As₂, CdAs₂, GeAs, GeAs₂, Ge, MnAs, MnGeAs₂, and As. The (Cd,Ge,Mn)As₂ homogeneity area has been shown to be a 14-vertex nonahedron, and the transformation of the (Cd,Ge,Mn)As₂ polyhedron upon the appearance of melt has been considered. A model of the primary crystallization polyhedron has been presented for limited solid solutions (Cd,Ge,Mn)As₂ in equilibrium with the saturated vapor.