The solid-solution region for the langasite-type Ca₃TaGa₃Si₂O₁₄ crystal as determined by a lever rule

A lever rule was applied to data concerning the compositions and proportions of secondary phases coexisting with a Ca₃TaGa₃Si₂O₁₄ (CTGS) matrix to determine the boundary compositions of the solid-solution region for CTGS at 1320 °C, as a means of ascertaining the solid-solution for the langasite-type phase in the quaternary CaO-Ta₂O₅-Ga₂O₃-SiO₂ system. The compositions and proportions of secondary phases were assessed by electron probe micro-analysis as well as through back-scattered electron images. The experimental results showed that the narrow solid-solution region for CTGS is located in a Ta-poor, Ga-poor and Si-rich region relative to its stoichiometric composition.