Structural Investigation of the Potassium Vanadomolybdate Crystal

Potassium vanadomolybdate KVMoO6 crystallizes in the orthorhombic system (space group Pnma, a=10.3478(1) ?, b= 3.6967(1) ?, c=13.3769(2) ?, Z=4). With an X-ray powder diffraction technique, its structure was solved and refined by direct and Rietveld methods, respectively (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), respectively. Potassium 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