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Investigation of the Vanadyl Bond Ordering and Analysis of the Spin Exchange Interactions in Pb2V3O9 and Pb2As2VO9

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posted on 2008-11-25, 00:00 authored by O. Mentré, H.-J. Koo, M.-H. Whangbo
The structures of Pb2V3O9 and Pb2As2VO9 were determined by X-ray diffraction to settle the issue concerning whether the arrangement of the V4+O vanadyl bonds is ordered or disordered. The new crystal structure of Pb2V3O9 refined by using a twinned crystal differs from the previous structure, determined from a combined use of powder X-ray and neutron diffraction data, and suggests an ordered Ferro arrangement of the V4+O vanadyl bonds as does the Antiferro crystal structure of the new Pb2As2VO9. In Pb2V3O9, a triclinic → monoclinic transition is observed at 400 °C, and the corresponding high temperature form was structurally characterized. The spin exchange interactions of Pb2V3O9 and Pb2As2VO9 were evaluated by performing qualitative spin dimer analysis based on tight binding calculations, and those of Pb2V3O9 were also examined by quantitative mapping analysis based on density functional theory calculations. To a first approximation, the spin−lattice of Pb2V3O9 is described by an alternating antiferromagnetic chain model, which is made up of the super-superexchange interactions mediated by VO4 tetrahedra between adjacent chains of corner-sharing V4+O6 octahedra. The magnetic property of Pb2As2VO9 is predicted to be paramagnetic, in agreement with experiment.