Phase Relationships in CaS-Rare Earth Sulfide Systems

Phase relationships in the CaS-Y2Sa, CaS-Dy2S3, CaS-Er~Ss, and CaS-Yb2S3 systems have been determined between 800 ~ and 1200 ~ at Ps2---- 3 X 10-6 atm. All four dopants how significant solid solubility in CaS (15-30 m/o at 1200 ~ Approximate Ps2/Po2 ratios required to avoid oxygen contamina-tion of the mixed sulfides are derived. Variation of the lattice parameter of the CaS phase with dopant content indicates an increase in size of the dopant ion upon dissolution. The x-ray diffraction pattern of monoclinic fl-CaY2S4 has been determined. The;~-phase may be regarded as a slight distortion of the orthorhombic low temperature a phase. Calcium sulfide doped with a rare earth sesqui-sulfide such as Y2S8 has been proposed as a solid electrolyte system for sensing of sulfur activities by Worrell (1, 2). The dopant cation on a Ca site is effectively positively charged (e.g., Yca'), and is com