Investigation of mixed divalent cation phosphates:: synthesis and X-ray powder structure determination of CdBa2(P2O7)(HPO4)

Hydrothermal synthesis, characterization by X-ray diffraction, IR absorption, TGA and ab-initio crystal structure determination are reported for a new phosphate CdBa2(P2O7)(HPO4). It crystallizes in a monoclinic cell (space group Im, No. 8, Z = 2) with a = 11.9022(1) Angstrom, b = 5.5530(1) Angstrom, c = 7.3401(1) Angstrom, beta = 90.091(1)degrees. The X-ray powder diffraction pattern was fitted by the Rietveld method technique with reliability R-Bragg = 0.037. Hydrogen atoms could not be located. The crystal structure of CdBa2(P2O7)(HPO4) is built up from P2O7 diphosphate groups sharing four oxygen atoms with two CdO6 trigonal prisms. Each CdO6 trigonal prism shares one edge with the HPO4 unit. Such an arrangement builds up isolated infinite chains CdP3O11 running along the b axis. Ba2+ ions are inserted between these chains in the (b,c) plane. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved.