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) Å, b=5.5530(1) Å, c=7.3401(1) Å, β=90.091(1)°. 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.