Characterization and Properties of Novel Oxygen Contained Hollandite VO1.52(OH)0.77 Nanorods Synthesized by Nonaqueous Sol-Gel Route

author: Igor Djerdj, Department of Materials, ETH Zurich
published: Jan. 18, 2008,   recorded: October 2007,   views: 4125


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Using the nonaqueous sol-gel route based on benzyl alcohol pathway, a new compound VO1.52(OH)0.77 in the form of nanorods has been synthesized. Comprehensive structural investigations have been carried out using complementary neutron and synchrotron powder X-ray diffraction as well as different electron microscopy techniques: SEM, (HR)TEM, EDX, SAED, EELS for determination of material's morphology, crystallinity and oxidation state of vanadium. The data show that the structure can be described as hollandite-type containing only oxygen in the 2×2 channels along the c-axis, with hydrogen attached to the one octahedral-coordinating oxygen, forming thus OH− group. The nanorods are single-crystalline, up to 500 nm long and 105 nm in diameter with the growth direction along the axis. The shape of OK edge and L3/L2 white-line ratio confirmed that the vanadium oxidation state is between 3+ and 4+ which is also deduced from the charge neutrality analysis being +3.81. Temperature dependent DC conductivity measurement evidenced Arrhenius behavior and semiconducting ground state with a band gap of 0.64 eV (cooling mode). Ab initio density-functional calculations with local spin density approximation including orbital potential (LSDA+U) predicts a direct band gap of 0.64 eV and a high degree of hybridization between O 2p and V 3d orbitals. The temperature dependence of magnetic susceptibility follows the Curie-Weiss law above 150 K. The extracted effective magnetic moment per vanadium of 1.95 B is consistent with the mixture of 3+ and 4+ oxidation states with predominant fraction of 4+.

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