Zur Stabilität von Doppelchloriden in den Systemen ACI/PrCl₃(A  NaCs)

Abstract

Die pseudobinären Systeme ACl/PrCl3(A = NaCs) wurden mittels DTA neu untersucht. Folgende Verbindungen wurden gefunden (erstmalig nachgewiesene Verbindungen sind unterstrichen) \documentclass{article}\pagestyle{empty}\begin{document}$ \underline {{\rm Na}_{\rm 2} {\rm Pr}_{\rm 5} {\rm Cl}_{{\rm 18}} } $\end{document} K3PrCl6; K2PrCl5; \documentclass{article}\pagestyle{empty}\begin{document}$ \underline {{\rm Rb}_{\rm 3} {\rm Pr} {\rm Cl}_{{\rm 6}} } $\end{document} Rb2PrCl5, \documentclass{article}\pagestyle{empty}\begin{document}$ \underline {{\rm Rb} {\rm Pr}_{\rm 2} {\rm Cl}_{{\rm 7}} } $\end{document} Cs3PrCl6, \documentclass{article}\pagestyle{empty}\begin{document}$ \underline {{\rm Cs}_{\rm 3} {\rm Pr} {\rm Cl}_{{\rm 5}} } $\end{document}, CsPr2Cl7. Messungen der Lösungsenthalpien, der freien Enthalpien für die Bildung aus ACl und den PrCl3‐reicheren Nachbarverbindungen mittels einer galvanischen Zelle für feste Elektrolyte sowie die Berechnung der freien Enthalpien für die Synproportionierung aus den Nachbarverbindungen im Zustandsdiagramm ergaben, daß nur die Chloride A2PrCl5 bei Raumtemperatur stabil sind; alle anderen sind Hochtemperaturphasen. Strukturuntersuchungen an Kristallpulvern ergaben Isotypie mit den entsprechenden La‐ und Ce‐Verbindungen. Magnetische Suszeptibilitäten nach der Gouy‐Methode im Bereich 80—300 K zeigen die erwarteten Werte.

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 ).…”

Ternäre Chloride in den Systemen ACl/YCl3 (A = Cs, Rb, K, Na)

“…EMK-Messungen. Ûber die Durchfu È hrung der EMK-Messungen sei auf fru È here Vero È ffentlichungen verwiesen [10,11]. Fu È r die YCl 3 -a È rmsten Verbindungen in den Systemen war der Elektrodenraum wie folgt aufgebaut:…”