Phase diagram of the TbBr₃-CsBr binary system. Thermodynamic and transport properties of the Cs₃TbBr₆ compound

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• 作者：Leszek Rycerz^a ; ^{leszek.rycerz@pwr.wroc.pl} ; Ida Chojnacka^a ; Jan Kapala^a ; Marcelle Gaune-Escard^b
• 关键词：Terbium(III) bromide ; Cesium bromide ; Phase diagram ; Differential scanning calorimetry ; Heat capacity ; Electrical conductivity
• 刊名：Calphad
• 出版年：2012
• 期刊代码：8_03645916
• 类别：ms
• 出版时间：June, 2012
• 卷：37
• 期：Complete
• 页码：108-115
• 文件大小：782 K

摘要

Phase equilibria in the TbBr₃-CsBr binary system were established from Differential Scanning Calorimetry (DSC) measurements. This binary system is characterized by three compounds, namely Cs₃TbBr₆, Cs₃Tb₂Br₉ and CsTb₂Br₇, and two eutectics located at the TbBr₃ mole fraction, (865聽K) and (808聽K), respectively. Cs₃TbBr₆ undergoes a solid-solid phase transition at 728聽K and melts congruently at 1083聽K with the related enthalpies 8.4 and 60.6聽kJ聽mol^鈭?, respectively. Cs₃Tb₂Br₉, decomposes peritectically at 879聽K, whereas CsTb₂Br₉ forms from Cs₃Tb₂Br₉ and TbBr₃ at 776聽K and melts incongruently at 846 K. It undergoes also a solid-solid phase transition at 805聽K, temperature very close to that (808聽K) of the Cs₃Tb₂Br₉-CsTb₂Br₇ eutectic. Separate investigations of the thermodynamic and transport properties were performed on the Cs₃TbBr₆ 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. Compatibility of the experimental data was tested by the CALPHAD method. The entropy of mixing and Gibbs energies of formation of solid compounds were calculated. The temperature range of Cs₃TbBr₆ existence was discussed.