Thermochemical studies on the systems ABr-LaBr3 (A ≡ Na, K, Rb, Cs)

Article abstract of DOI:10.1016/0022-5088(91)90059-D

The pseudo-binary systems ABr-LaBr₃ (A ≡ Na-Cs) were investigated by means of differential thermal analysis and X-ray diffraction of crystal powders. The system NaBr/LaBr₃ is eutectic: in all other systems the compounds A₂LaBr₅(K₂PrCl₅-type) exist. Additional compounds A₃LaBr₆, stable only at high temperature, are formed with RbBr and CsBr. They have the elpasolite-structure; modifications, metastable at ambient temperature, crystallize into the K₃MoCl₆-type. A further high-temperature compound, CsLa₂Br₇, has the same structure as RbDy₂Cl₇. The thermodynamic functions of the ternary bromides were determined using solution calorimetry and e.m.f. vs. T measurements in galvanic cells for solid electrolytes. These were then compared with those of the LaCl₃ system. The main result is that, except for the halide ion, the A₂LaX₅ compounds are formed from adjacent compounds in the systems with a resulting gain in lattice enthalpy. All other compounds have less favourable structures: a loss of lattice enthalpy is compensated for by a gain in entropy at sufficiently high temperatures.

Full text of DOI:10.1016/0022-5088(91)90059-D

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Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.

Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.