title: Composition-dependent charge transfer and phase separation in the V1-xRexO2solid solution.
abstract: The substitution of vanadium in vanadium dioxide VO2influences 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-xRexO2solid 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-xRexO2with 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.
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany. daria.mikhailova@kit.edu and Institute for Complex Materials, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden, Germany and Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, D-01187 Dresden, Germany. yuki.utsumi@synchrotron-soleil.fr.
authors.forename: D
authors.identifier: http://orcid.org/0000-0002-8197-1807
authors.initials: D
authors.lastname: Mikhailova
authors.affiliation: Institute of Inorganic Chemistry SB Russian Academy of Science, Acad. Lavrentiev Avenue 3, Novosibirsk, 630090, Russia.
authors.forename: N N
authors.initials: NN
authors.lastname: Kuratieva
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, D-01187 Dresden, Germany. yuki.utsumi@synchrotron-soleil.fr.
authors.forename: Y
authors.initials: Y
authors.lastname: Utsumi
authors.affiliation: National Institute of Chemical Physics and Biophysics, Akadeemia tee 23, 12618 Tallinn, Estonia and Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, D-86159 Augsburg, Germany.
authors.forename: A A
authors.initials: AA
authors.lastname: Tsirlin
authors.affiliation: Skoltech Center for Electrochemical Energy Storage, Skolkovo Institute of Science and Technology, 143026 Moscow, Russia and Chemistry Department, Moscow State University, 119991, Moscow, Russia and EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: A M
authors.initials: AM
authors.lastname: Abakumov
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, D-01187 Dresden, Germany. yuki.utsumi@synchrotron-soleil.fr.
authors.forename: M
authors.initials: M
authors.lastname: Schmidt
authors.affiliation: Institute for Complex Materials, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Oswald
authors.affiliation: Institute for Materials Science, Darmstadt University for Technology, Alarich Weiss-Straße 2, D-64287, Darmstadt, Germany.
authors.forename: H
authors.initials: H
authors.lastname: Fuess
authors.affiliation: Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany. daria.mikhailova@kit.edu.
authors.forename: H
authors.initials: H
authors.lastname: Ehrenberg