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Phase Diagram of the TbBr₃−RbBr Binary System: Thermodynamic and Transport Properties of the Rb₃TbBr₆ Compound

Leszek Rycerz^†^‡ and Marcelle Gaune-Escard*^†

Ecole Polytechnique Universitaire de Marseille, CNRS-UMR 6595, Technopole de Chateau Gombert, 5 rue Enrico Fermi, 13453 Marseille Cedex 13, France, and Chemical Metallurgy Group, Department of Chemistry, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland

Inorg. Chem., 2007, 46 (6), pp 2299–2306

DOI: 10.1021/ic0615978

Publication Date (Web): February 21, 2007

†

Ecole Polytechnique.

‡

Wroclaw University of Technology.

To whom correspondence should be addressed. E-mail: Marcelle.Gaune-Escard@polytech.univ-mrs.fr.

Abstract

Phase equilibria in the TbBr₃−RbBr binary system were established from differential scanning calorimetry (DSC) measurements. This binary system is characterized by two compounds, namely Rb₃TbBr₆ and RbTb₂Br₇, and two eutectics located at the TbBr₃ mole fractions, x = 0.117 (728 K) and x = 0.449 (718 K), respectively. Rb₃TbBr₆ undergoes a solid−solid phase transition at 728 K and melts congruently at 1047 K with the related enthalpies 7.8 and 58.7 kJ mol^-¹, respectively. RbTb₂Br₇ melts incongruently at 803 K. It undergoes also a solid−solid phase transition at 712 K, a temperature very close to that (718 K) of the second eutectic, and much attention was paid in evidencing and separating these transition and eutectic effects. Separate investigations of the thermodynamic and transport properties were performed on the Rb₃TbBr₆ compound. These heat capacity and electrical conductivity experimental results suggest an order−disorder mechanism in the alkali-metal cation sublattice whereas the TbBr₆ octahedra, forming the anionic sublattice, retain their normal lattice positions.