Synthesis of mercury rare earth ternary sulfides

Three new mercury rare earth sulfides have been synthesized by heating a mixture of the sesquisulfide of rare earth and cinnabar at 800°c for 25 h in an evacuated (10^?4 Torr) sealed quartz tube. Their general formula, Ln₄HgS₇ (Ln = Tm, Yb and Lu), was determined by chemical analysis. These sulfides are tetragonal. Lattice parameters for Ln = Tm, Yb and Lu are: a = 11.09(2), 11.07(3) and 11.03(2)Å, c = 8.38(5), 8.35(2) and 8.33(2)Å respectively. These compounds are stable toward air and moisture at room temperature, but are oxidized slowly at elevated temperature. Thermogravimetric curves show that Tm₄HgS₇, Yb₄HgS, and Lu₄HgS₇ are decomposed and oxidized at 500°, 650° and 450°C respectively.