Synthesis, structure and magnetic properties of V4O9—A missing link in binary vanadium oxides

V4O9: A missing link of Wadsley phases has been successfully synthesized by using sulfur as a reducing agent at a low temperature and its structure has been determined by combining electron, X-ray and neutron diffractions. V4O9 has an orthorhombic Cmcm structure and the lattice parameters are a=10.356(2) Å, b=8.174(1) Å and c=16.559(3) Å at room temperature. The structure is composed of shared edges and corners of three types of polyhedra; a VO6 distorted octahedron, a VO5 pyramid and a VO4 tetrahedron. The structure of V4O9 is very similar to that of vanadyl pyrophosphate (VO)2P2O7 which has PO4 tetrahedra instead of VO4 tetrahedra. This indicates that V4O9 is a salt of pyro-ion [V2O7]4-; (VO)2V2O7. The magnetic properties of V4O9 have been investigated by magnetic susceptibility, high-field magnetization and inelastic neutron scattering measurements. V4O9 is a quantum spin system with a spin-gapped ground state. The excitation gap between the singlet ground state and the excited triplet state is approximately 73 K. The magnetic susceptibility behavior suggests that V4O9 is a spin-1/2 dimer system with significant interdimer interactions, as opposed to (VO)2P2O7, which is an alternating spin-1/2 chain system. This difference is thought to be due to the fact that VO4-mediated interactions are considerably weaker than PO4-mediated interactions.

Graphical abstractTemperature dependence of magnetic susceptibility (χraw) measured at 0.1 T for V4O9. The intrinsic d-spin susceptibility (χspin) of V4O9 after subtracting the Curie tail and the temperature-independent term is shown by the solid line. V4O9 is a spin-1/2 1D antiferromagnetic quantum spin system with a spin-gapped ground state. The structure of V4O9 is constructed from distorted VO6 octahedra and VO4 tetrahedra, similar to the structure of (VO)2P2O7 with PO4 tetrahedra instead of VO4 tetrahedra.Figure optionsDownload full-size imageDownload as PowerPoint slide