Authors: H J Seifert
Publish Date: 2006/02/24
Volume: 83, Issue: 2, Pages: 479-505
Abstract
A comprehensive review on phase diagrams crystal structures and thermodynamic properties of ternary chlorides formed in the systems ACl/LnCl3 A=Na K Rb Cs is presented It continues an earlier review with the same contents on the lanthanides from La to Gd 1 In both papers the authors own studies published since 1985 together with original papers from other scientists are treated With the three larger cations compounds of the composition A3LnCl6 A2LnCl5 ALn2Cl7 and beginning with holmium Cs3Ln2Cl9 are formed With sodium the compounds Na3Ln5Cl18 Ln=La to Sm and NaLnCl4 Ln=Eu to Lu also exist The stability of a ternary chloride in a system ACl/LnCl3 is given by the free enthalpy of synreaction the formation of a compound from its neighbour compounds in its system This
must be negative A surprising result is that the highest – melting compounds in the systems A3LnCl6 are formed from ACl and A2LnCl5 with a loss of lattice energy U They exist as hightemperature compounds due to a sufficiently high gain in entropy at temperatures where the entropy term TΔS compensates the endothermic ΔH
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