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, rLn3+), 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.