Phase equilibrium and growth of homogeneous crystals in the γLa2S3  γNd2S3 system

T-x diagram of the γLa₂S₃  γNd₂S₃ system was plotted for the temperature interval 1400–2100°C. γLa₂S₃ and γNd₂S₃ form unlimited solid solutions of the substitution type. Basing on this phase diagram the theoretical distribution curves of Nd₂S₃ along the ingot of length were calculated. The experimental distribution curves were determined by chemical and electron microprobe measurements of La and Nd content in γ(La,Nd)₂S₃ ingots directionally solidified from the melt of different composition. Character of the component distribution in the ingots shows that diffusion of neodymium and lanthanum is exeptionally fast at 1700–2000°C. This phenomenon is explained by vacancy diffusion mechanism in γLa₂S₃  γNd₂S₃ solid solutions. Crystal structure of these solid solutions belongs to Th₃P₄ type with high concentration of randomly distributed cation vacancies.