TERNARY CHLORIDES IN THE SYSTEMS ACL/GDCL3 (A = NA-CS)

The phase diagrams of the pseudobinary systems ACl/GdCl3 (A = Na-Cs) were investigated by DTA. Their powder diffractograms were indexed in analogy to known structure families. By solution calorimetry and measurements of e.m.f. = f(T) in galvanic cells for solid electrolytes the enthalpies DELTA-H0 and free enthalpies DELTA-G0 for the formation of the ternary chlorides from the compounds adjacent in the systems were determined. The systems with A = K, Rb, Cs are analogous to those with Sm3+ and Eu3+. There exist compounds A3GdCl6, A2GdCl5 and AGd2Cl7. Cs2GdCl5 is crystallysing in the Cs2DyCl5 type; the Rb- and K-compounds and also Na2GdCl5 have the K2PrCl5-structure. In the system NaCl/GdCl3 additionally the compounds NaGdCl4 and Na3GdCl6 were found. L-Na3GdCl6 is metastable compared with (NaCl + NaGdCl5); above 265-degrees-C stable H-Na3GdCl6 is existing (cryolite-structure).