ROCK-SALT DEFECT STRUCTURES IN THE SYSTEMS LIBR-MBR2 (WHERE M IS MG, MN)

The phase diagrams of the systems LiBr-MgBr2 and LiBr-MnBr2 have been studied by high temperature X-ray powder diffraction and differential scanning calorimetry measurements. At elevated temperatures, complete series of solid solutions between NaCl-type LiBr and CdCl2-type MBr2 are formed. On cooling to ambient temperature, these solid solutions decompose to LiBr, CdI2-type MBr2, and the ternary compounds Li6MBr8 (Suzuki type) and Li2MBr4 (SnMn2S4 type). The structures of the ternary bromides can be characterized by different ordering schemes of the metal ions and vacancies on the octahedral sites of the cubic close-packed bromide ions. The symmetry relations to the aristotype NaCl structure and the Coulomb parts of the cohesive energies are given.