Physical properties and lattice dynamics of bixbyite-type V 2 O 3

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istian Schwickert Institut für Anorganische und Analytische Chemie, Universität Münster, 84149 Münster, Germany

Anatoliy Senyshyn Heinz Maier-Leibnitz Zentrum, Technische Universität München, 85748 Garching, Germany

Martin Lerch Institut für Chemie, Tecnische Universität Berlin, 10623 Berlin, Germany

Rainer Pöttgen Institut für Anorganische und Analytische Chemie, Universität Münster, 84149 Münster, Germany (Received 8 December 2016; accepted 30 March 2017)

Some time ago, we reported the synthesis of bixbyite-type V2O3, a new metastable polymorph of vanadium sesquioxide. Since, a number of investigations followed, dealing with different aspects like electronic and magnetic properties of the material, the deviation from ideal stoichiometry or the preparation of nanocrystals as oxygen storage material. However, most of the physical properties were only evaluated on a theoretical basis. Here, we report the lattice dynamics and physical properties of bixbyite-type V2O3 bulk material, which we acquired from physical property measurements and neutron diffraction experiments over a wide temperature range. Besides attributing different possible orientations of the magnetic moments for V1 and V2 to the identified antiferromagnetic (AFM) ground state with a Néel temperature of 38.1(5) K, we use a first order Grüneisen approximation to determine lattice-dependent parameters for the relatively stiff cubic lattice, and, amongst others identify the Debye temperature to be as low as 350 6 65 K.

I. INTRODUCTION

Because of their structural diversity, abundant physical and chemical properties, and numerous potential applications, vanadium-based materials hold an exceptional position amongst transition metal-based compounds. Besides their use in electronic and optical devices,1 chemical sensors,2 as catalysts,3,4 and as cathode materials for high energy density lithium ion batteries,5–7 even binary vanadium oxides, due to their unique behavior, have been subject to various investigations. In particular, a large number of experimental and theoretical studies have already been conducted on the thermodynamically stable vanadium sesquioxide, as it presents a model system for a Mott–Hubbard transition.8–10 At low temperatures, this polymorph of V2O3 is an antiferromagnetic (AFM) insulator, crystallizing in a monoclinic structure (M1). At around 170 K it transforms into a paramagnetic conductor, undergoing a structural phase transition to the well-known rhombohedral corundumtype structure with a notably large c/a ratio of 2.823.9–14 Contributing Editor: Michael E. McHenry a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.144

Regarding the inimitable characteristics of thermodynamically stable V2O3, the investigation of the physical properties of additional polymorphs of V2O3 is of fundamental interest. A few years ago, we synthesized a new metastable polymorph of vanadium sesquioxide that crystallizes in the bixbyite-type structure (space group Ia 3).15 This polymorph o