Structural Study of the Quantum-Spin Chain Compound (VO)2P2O7

The crystal structure of the quantum-spin chain compound (VO)2P2O7 was studied by electron, X-ray, and neutron diffraction. A polycrystalline sample which clearly exhibited a singlet ground state in magnetic susceptibility measurements was examined. Electron diffraction experiments revealed systematic extinctions which are consistent with an orthorhombic space group Pca21, in good agreement with previous studies. However, the recent single-crystal X-ray analysis by Nguyen et al. concluded that it is monoclinic with space group P21. This discrepancy may imply that (VO)2P2O7 crystallizes in two slightly different structures depending on preparation conditions. The structural parameters of orthorhombic (VO)2P2O7 were defined by Rietveld analyses of X-ray and neutron powder diffraction data; a=7.73808(7) ?, b=9.58698(8) ?, c=16.5895 (1) ?, and Z=8. Crystallographic disorder was also studied by high-resolution electron microscopy and discussed in terms of positional disorder in the arrangement of the P2O7 groups.