The Two-Component System CCl4 + CBrCl3. Inference of the Lattice Symmetry of Phase II of CBrCl3

Abstract

The phase diagram of the two-component system between two halomethanes, carbon tetrachloride (CCl4) and bromotrichloromethane (CBrCl3) has been determined by means of X-ray powder diffraction and thermal analysis techniques from 200 K to the liquid state. From the continuous series of mixed crystals, three relations of isomorphism have been evidenced: (i) between the stable low-temperature monoclinic (M) phases, (ii) between the stable orientationally disordered (OD) rhombohedral (R) phases, and (iii) between the stable OD face-centered cubic (FCC) of CBrCl3 and the metastable FCC phase of CCl4. The existence of such a metastable phase gives rise to the appearance, for a large range of composition, of metastable FCC mixed crystals that behave monotropically with respect to the R mixed crystals accordingly with the well-known monotropic character of the R to FCC phase transition of the CCl4. The isomorphism relationships i and ii enable us to validate the previously proposed structure of the monoclinic ph...