Ternary Chlorides in the Systems ACl/TbCl3 (A = K, Rb, Cs)

Unusual nature of lanthanide chloride–alkali metal chloride M3LnCl6 compounds in the solid state

“…It is a cubic, elpasolite-type crystal structure. The thermal effect at about 650-680 K for the M 3 LnCl 6 compounds in the second group also corresponds to a solid-solid phase transition [10][11][12][13][14][15], from low-temperature modification (monoclinic, Cs 3 BiCl 6 -type) to hightemperature (cubic, elpasolite-type) modification. This structural phase transition was described as a "non-reconstructive phase transition".…”

“…The enthalpy data related to the phase transition clearly split into two groups characterized by unusually large values (group 1: 45-55 kJ mol −1 -K 3 CeCl 6 , K 3 PrCl 6 , K 3 NdCl 6 and Rb 3 LaCl 6 ), on the one hand, and by noticeably smaller values (group 2: only 7-9 kJ mol −1 -K 3 TbCl 6 , Rb 3 CeCl 6 , Rb 3 PrCl 6 , Rb 3 NdCl 6 , Rb 3 TbCl 6 and all the Cs 3 LnCl 6 compounds), on the other [2,8,9]. According to literature information [10][11][12][13][14][15], the large enthalpy effect in the first group corresponds to formation of M 3 LnCl 6 compounds from MCl and M 2 LnCl 5 and is described as a "reconstructive phase transition". The M 3 LnCl 6 compounds in this group have a single, high-temperature crystal modification.…”

Thermodynamic assessment of LiCl–NdCl3 and LiCl–PrCl3 quasi-binary systems

“…According to the unpublished work of Sun and Qiao [31] on molten salt phase diagram evaluation by pattern recognition, the existence of the compound LiNd 2 Cl 7 in the LiCl-NdCl 3 system was strongly supported. It is intriguing that the compound LiNd 2 Cl 7 reported by Kim and Okamoto [19] and Sun and Qiao [31] was not confirmed by XRD or even not detected by other experimental researchers [17,18,[20][21][22][23][24][25][26][27][28][29][30]. Two probable reasons may be provided: one is that the compound only exists in a very limited temperature range, the phase transition should have occurred during the quenching of the XRD sample.…”

“…In the systematic phase diagram investigations of MCl-LnCl 3 binary systems by Differential Thermal Analysis (DTA) combined with high temperature X-ray analysis and e.m.f. measurements [20][21][22][23][24][25][26][27][28][29][30], Seifert and co-workers set up a series of phase diagrams for the MX-LnX 3 (M = Alkali metal, Ln = Rare earth metal, X = halide) binary systems and detected the CsLn 2 Cl 7 in all the chloride systems from cerium chloride (CeCl 3 ), the RbLn 2 Cl 7 starting from samarium chloride (SmCl 3 ) and KLn 2 Cl 7 from europium chloride (EuCl 3 ). According to this systematic trend, i.e., the smaller atomic number of alkali and lanthanide, the more difficult for MLn 2 Cl 7 to form in the corresponding system, LiLn 2 Cl 7 should not exist before europium chloride (EuCl 3 ).…”

Instrumentation and calibration of the Calvet calorimeter

“…The enthalpies of formation have been obtained from equation [6]: where D f H is enthalpy of formation, D sol H is enthalpy of solution, and m1 and m2 are the stoichiometry coefficients.…”