New Ternary Phases in Some Alkaline-Earth Rare-Earth Sulfide Systems

New ternary alkaline-earth rare-earth sulfide phases of composition MLn2S7 where M = Ca or Sr and Ln = La, Nd, or Gd have been formed by open-system reactions in flowing H2S. The phases have been characterized by X-ray powder diffraction and electron microprobe analysis. These compounds form as low-melting (Tm approximately 1100°C) products when refractory compounds along the MS-Ln2S3 join are oxidized at high sulfur fugacities.