DISORDER IN SOLID CBR2CL2 AND CBRCL3

The low-temperature structures of CBr2Cl2 and CBrCl3 have been determi ned using powder neutron diffraction. The two phases are isostructural with one another, CBr4 and CCl4, belonging to the C 2/c space group w ith 32 molecules per unit cell. A preliminary discussion of the high-T phases of these molecules is presented. The high-T phases show patter ns consistent with an orientationally disordered (plastic) crystalline phase, consisting of rotating pseudospheres on an FCC lattice. A seco nd disordered phase, between the other two phases, has also been obser ved in CBrCl3. It is still under investigation. (C) 1998 Elsevier Scie nce B.V. All rights reserved.