Phase Diagram and Electrical Conductivity of CeBr₃-KBr

Abstract

This paper continues our research program on lanthanide halide-alkali metal halide systems. Differential scanning calorimetry (DSC) was used to investigate the phase equilibria of the CeBr 3 -KBr system. This system is characterized by the two congruently melting compounds K 3 CeBr 6 and K 2 CeBr 5 and the three eutectics located at the CeBr 3 mole fractions 0.193 (837 K), 0.295 (855 K) and 0.555 (766 K). K 3 CeBr 6 forms at 775 K and melts congruently at 879 K with the related enthalpies 54.5 and 41.7 kJ mol −1 , respectively. K 2 CeBr 5 melts congruently at 874 K with the enthalpy 82.4 kJ mol −1 . The electrical conductivity was measured of all CeBr 3 -KBr mixtures and of the pure components down to temperatures below solidification. The experimental determinations were conducted over the entire composition range in steps of about 10 mol%. The specific electrical conductivity decrease with increasing CeBr 3 concentration, with significantly larger conductivity changes in the potassium bromide-rich region. The results are discussed in terms of possible complex formation.

Thermodynamic Functions of Congruently Melting Compounds Formed in the CeBr3−KBr Binary System

“…Enthalpy of Fusion and Heat Capacity of K 3 CeBr 6 . K 3 CeBr 6 forms at 775 K from KBr and K 2 CeBr 5 and melts congruently at 879 K with the related enthalpies 54.5 ± 0.5 and 41.7 ± 0.3 kJ·mol -1 , respectively . Our experimental heat capacity data on K 3 CeBr 6 , obtained for the first time, are plotted against temperature in Figure .…”

“…Phase equilibria in lanthanide halide−alkali metal halide systems are generally complex and characterized by the existence of several stoichiometric compounds. The stability of these compounds depends on the nature both of the cations (lanthanide, Ln; alkali, M) and of the halide X. − Two congruently melting compounds, namely, K 3 CeBr 6 and K 2 CeBr 5 , have been observed in the CeBr 3 −KBr system …”

Compound formation in lanthanide–alkali metal halide systems

“…This classification was tested on the CeBr 3 –MBr binary systems (M = Li, Na, K, Rb, Cs), still unknown at the time it was established. Further experimental investigations validated that CeBr 3 –LiBr and CeBr 3 –NaBr are simple eutectic systems (Ingier-Stocka et al , 2008) (IP M+ /IP Ce3+ = 0⋅465 and 0⋅366, respectively), whereas two congruently melting compounds, namely K 3 CeBr 6 and K 2 CeBr 5 , exist in the CeBr 3 –KBr system (Rycerz et al , 2007), as expected from the corresponding ionic potential ratio (IP K+ /IP Ce3+ = 0⋅249). The CeBr 3 –RbBr (Rycerz et al , 2008b) and CeBr 3 –CsBr (Rycerz et al ., 2009) systems (IP Rb+ /IP Ce3+ = 0⋅231 and IP Cs+ /IP Ce3+ = 0⋅202, respectively) follow the predicted pattern.…”

Thermodynamic Functions of CeBr3 and Congruently Melting M3CeBr6 Compounds (M = Rb, Cs)

“…The stability of these compounds depends on the nature both of the cations (lanthanide Ln, alkali M) and of the halide X. – We have paid much attention to the M 3 LnX 6 stoichiometric compounds that exist in most of the LnX 3 −MX systems and have a more extended stability range than those of different stoichiometry. These congruently melting compounds were found – to exist also in the CeBr 3 −MBr systems (M = K, Rb, and Cs). The thermodynamic properties of the K 3 CeBr 6 potassium compound have been characterized previously .…”