STRUCTURAL INVESTIGATION OF THE POTASSIUM VANADOMOLYBDATE CRYSTAL

摘要

Potassium vanadomolybdate KVMoO6 crystallizes in the orthorhombic system (space group Pnma, a=10.3478(1) angstroms, b=3.6967(1) angstroms, c=13.3769(2) angstroms, Z=4). With an powder XRD technique, its structure was solved and refined by direct and Rietveld methods, respp. (RF=3.33, RI=4.70, Rwp=12.44). The crystals are isostructural with PbV2O6. Octahedra of two types build chains parallel to the b direction; there is disorder in the octahedra described by different occupation numbers of V and Mo atoms: 0.721(4) and 0.279(4), respp. K atoms occupy the space between the octahedra chains. They play a decisive role, due to the large ionic radius, in generating both KVMoO6 and pseudobrannerite, KxVxMo2-xO6 (0.76 less than or equal to x less than or equal to 0.82) structures, contrary to other alkali-metal vanadomolybdates of the brannerite structure type. The melting point of KVMoO6 was detected at 480 C using the DTA method. 18 refs.