Phase equilibria in the BaS-Ln2S3 systems

A survey of available data for the BaS₂-Ln₂S₃ systems shows that the very light lanthanon systems form no intermediate phases but have extensive terminal solid solubilities of BaS in γ-Ln₂S₃ extending to near 50 mol.% BaS. For Ln=Nd and for all heavier lanthanons (smaller ionic radii, r _Ln ³⁺ ), an intermediate phase with stoichiometry of BaLn₂S₄ is formed. BaLn₂S₄ decomposes peritectoidally for Ln=Nd but melts congruently for Ln=Sm and for all heavier lanthanons. A second intermediate phase of stoichiometry, Ba₃Ln₂S₆, forms for Ln=Tb and for all heavier lanthanons (smaller ionic radii). For Ln=Lu, a third phase is formed at BaLu₈S₁₃. In all cases, Ba₃Ln₂S₆ melts peritectically, but BaLu₈S₁₃ melts congruently. The present article discusses: (1) three different techniques for synthesizing the intermediate phases; (2) the systems for Ln=Pr, Tb, and Y; and (3) a computer model for interpolating through the available data for the phase relationships in the nine systems that have been investigated to predict the phase diagrams for the seven systems for which there are limited or no data.