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structure structure (solids and liquids) D 2000 -001Refinement of the CsYP2O7 Crystal Structure by the Rietveld Method.-The structure of the title compound, characterized by the powder XRD data, is refined by the Rietveld method. CsYP2O7, prepared from a stoichiometric mixture of Cs2CO3, Y2O3 and (NH4)2HPO4 at 740 • C, crystallizes in the monoclinic space group P21/c with Z = 4. The structure which is isotypic with M(I)M(III)P2O7 (M(I): K, Rb, Cs; M( III): Fe, V, Mo, Ti) consists of layers of M(III)P2O11 units, composed of diphosphate groups linked to M(III)O6 octahedra, forming a three-dimensional framework. The large size of the Cs+ and Y3+ cations has a significant influence on the distortions of the CsO10 and P2O7 polyhedra and thus explains the lower thermal stability of CsYP2O7 as compared to RbYP2O7. -(AKRIM, A.; ZAMBON, D.; METIN, J.; COUSSEINS, J.-C.; C. R.

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