Temperatures and enthalpies of melting of Ln2S3 (Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) compounds

Samples of Ln(2)S(3) (Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) polymorphs were prepared from Ln(2)O(3) in a CS2 + H2S flow at 1050-1150 degrees C. DSC melting traces were recorded for Ln(2)S(3) compounds of yttrium lanthanides for the first time. Samples for DSC were prepared by melting and then recrystallizing polycrystalline samples in crucibles of the DSC setup. The melting peak shapes and melting ranges signified the congruent melting of Ln(2)S(3) compounds. The temperatures and enthalpies of melting were determined for the prepared Ln(2)S(3) polymorphs: gamma-Gd2S3 (t(m) = 1794 degrees C; Delta H = 56.3 kJ mol(-1)), gamma-Tb2S3 (t(m) = 1753 degrees C; Delta H = 55.8 kJ mol(-1)), gamma-Dy2S3 (t(m) = 1698 degrees C; Delta H = 57 kJ mol(-1)), delta-Ho2S3 (t(m) = 1697 degrees C; Delta H = 47.7 kJ mol(-1)), delta-Er2S3 (t(m) = 1662 degrees C; Delta H = 42.2 kJ mol(-1)), delta-Tm2S3 (t(m) = 1665 degrees C; Delta H = 46.9 kJ mol(-1)), and epsilon-Lu2S3 (t(m) = 1755 degrees C; Delta H = 53.6 kJ mol(-1)). The Ln(2)S(3) samples experienced thermal dissociation near their melting temperatures; the relevant mass losses were 0.1-0.24 mass%. After DSC, the samples remained single phases; their concentration changed to Gd2S2.98, Tb2S2.99, Dy2S2.98, Ho2S2.97, Er2S2.97, and Lu2S2.98. A delta-Tm2S3 sample experienced a greater mass loss (0.77 mass%) at 1500-1670 degrees C to acquire the concentration Tm2S2.91. epsilon-Yb2S3 decomposed to YbS at temperatures above 1500 degrees C. The melting temperatures show an inner periodicity, and the enthalpies of melting of Ln(2)S(3) show the tetrad effect as a function of rLn(+3).