Investigations on the bismuth rare-earth oxyhalides Bi2REO4X (X = Cl, Br, I)

Compounds of the composition of Bi2REO4X (RE = Y, La-Lu; X = Cl, Br, I) hav e been prepared by solid state reaction of stoichiometric mixtures of BiOX, Bi2O3, and RE2O3. They were characterized by X-ray powder diffraction, IR spectroscopy, mass spectrometry and DTA/TG measurements as well. The crysta l structure (tetragonal, P4/mmm, a approximate to 3.9 Angstrom, c approxima te to 9 Angstrom) was determined by the Rietveld method. In the structure [ M3O4](+) layers are interleaved by single halogen layers. Rare-earth and bi smuth atoms in Bi2REO4X are 8-coordinated, The structure can be derived fro m the LiBi3O4Cl2 type structure. The enthalpies of formation are derived fr om heats of solution. The standard entropies were calculated from low-tempe rature measurements of the specific heat capacities.