Raman studies on the structures and properties of the compounds formed in the CdCl2CsCl binary system

Abstract

AbstractRaman spectra were obtained for the solid phases formed from binary mixtures of the CdCl2 and CsCl salts. Five compounds were identified, three congruent (Cs3CdCl5, Cs2CdCl4 and CsCdCl3) and two incongrnent (Cs3Cd2Cl7 and CsCd5Cl11). Unlike the potassium and rubidium systems, there was no evidence to suggest the formation of a solid with a discrete octahedrally coordinated species as has been found in K4CdCl6 and Rb4CdCl6. Cs3CdCl5 is isostructural with Cs3CoCl5, space group I 4/mcm (D), and contains the discrete CdCl; it forms from the melt and is thermodynamically stable only above 390°C. Below 390°C Cs3CdCl5 normally decomposes into a mixture of Cs2CdCl4 and CsCl, but the sample may be quenched to room temperature to give metastable Cs3CdCl5, which converts to Cs2CdCl4 and CsCl when warmed to 200°C. Cs2CdCl4 has the K2NiF4 structure in the lowtemperature phase, space group I4/mmm (D), but this salt undergoes a phase transition at a β‐K2SO4‐type high temperature phase, space group P nma (D) with discrete CdCl. The transition occurs over the temperature range 370–460°C. A dynamic equilibrium between the two solid phases within the temperature range has been inferred. Cs3Cd2Cl7 has been reported to be isostructural with Rb3Mn2Cl7 at room temperature but it decomposes into CsCdCI3 and Cs2CdCl4 at temperatures above 450°C. The structure of CsCd5Cl11 is not yet known but the Raman spectrum suggested that the Cd atoms have octahedral coordination within a network structure. CsCdCl3 is hexagonal, space group P63/mmc, and the Raman studies indicated that there was no structural phase transition from 25°C to the melting point.