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Issue 5, 2017
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Composition-dependent charge transfer and phase separation in the V1−xRexO2 solid solution

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Abstract

The substitution of vanadium in vanadium dioxide VO2 influences the critical temperatures of structural and metal-to-insulator transitions in different ways depending on the valence of the dopant. Rhenium adopts valence states between +4 and +7 in an octahedral oxygen surrounding and is particularly interesting in this context. Structural investigation of V1−xRexO2 solid solutions (0.01 ≤ x ≤ 0.30) between 80 and 1200 K using synchrotron X-ray powder diffraction revealed only two polymorphs that resemble VO2: the low-temperature monoclinic MoO2-type form (space group P21/c), and the tetragonal rutile-like form (space group P42/mnm). However, for compositions with 0.03 < x ≤ 0.15 a phase separation in the solid solution was observed below 1000 K upon cooling down from 1200 K, giving rise to two isostructural phases with slightly different lattice parameters. This is reflected in the appearance of two metal-to-insulator transition temperatures detected by magnetization and specific heat measurements. Comprehensive X-ray photoelectron spectroscopy studies showed that an increased amount of Re leads to a change in the Re valence state from solely Re6+ at a low doping level (≤3 at% Re) via mixed-valence states Re4+/Re6+ for at least 0.03 < x ≤ 0.10, up to nearly pure Re4+ in V0.70Re0.30O2. Thus, compositions V1−xRexO2 with only one valence state of Re in the material (Re6+ or Re4+) can be obtained as a single phase, while intermediate compositions are subjected to a phase separation, presumably due to different valence states of Re.

Graphical abstract: Composition-dependent charge transfer and phase separation in the V1−xRexO2 solid solution

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Publication details

The article was received on 18 Nov 2016, accepted on 23 Dec 2016, published on 23 Dec 2016 and first published online on 23 Dec 2016


Article type: Paper
DOI: 10.1039/C6DT04389E
Citation: Dalton Trans., 2017,46, 1606-1617
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    Composition-dependent charge transfer and phase separation in the V1−xRexO2 solid solution

    D. Mikhailova, N. N. Kuratieva, Y. Utsumi, A. A. Tsirlin, A. M. Abakumov, M. Schmidt, S. Oswald, H. Fuess and H. Ehrenberg, Dalton Trans., 2017, 46, 1606
    DOI: 10.1039/C6DT04389E

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