On phase diagrams of rare earth trichlorides/MCl2 (rare earth = La, Sm, Gd, Yb; M = Sr, Ba)

The systems LaCl3(SmCl3, GdCl3, YbCl3)-SrCl2(BaCl2) were determined by difference thermal analysis. The phase diagrams contain compounds of the formula BaLnCl5, M2LnCl7, Ba3LnCl9 and probably Sr4LnCl11, which decompose peritectoidally, resp. peritectically. Sr2SmCl7 and Sr2GdCl7 are isotypic, and as indicated by the very similar reflection patterns of the Guinier photographs related to the structure of the compound Sm3Cl7. The phase diagrams are comparable to the systems LnCl3-LnCl2 with similar radii quotients of the cations. The enthalpies of mixing of the systems LaCl3(GdCl3, YbCl3)-SrCl2 were measured calorimetrically. The values are exothermic, the minima were found at approximately 65 mol-% SrCl2. (author)