Phase relations in the CaAl2O4|CaGa2O4 system

The solid state reactions and the phase relations in the CaAl₂O₄|CaGa₂O₄ system, of which both end-members have the stuffed tridymite structure, were examined by using three kinds of starting materials; A (CaCO₃ + (Al,Ga)₂O₃), B (CaAl₂O₄ + CaGa₂O₄) and C (CaCO₃ + Al₂O₃ + Ga₂O₃). In the starting material B, a very low rate of solid state reaction between CaAl₂O₄ and CaGa₂O₄ was found, which seemed to be due to very slow interchange of Al³⁺ and Ga³⁺ located in tetrahedra of this structure. In order to obtain the probable equilibrium phase relations, it was necessary to use the starting material A. In the present system, a new phase was found in a wide range of composition as a stable phase, which was supposed to have the same structure as so-called metastable phase of CaGa₂O₄ and different array of tetrahedra from either CaAl₂O₄ or CaGa₂O₄|I.