Basic aspects of the metal–insulator transition in vanadium dioxide VO 2 : a critical review

Vanadium dioxide exhibits a first order metal to insulator transition (MIT) at 340 K (TMI) from a rutile (R) structure to a monoclinic (M1) structure. The mechanism of this transition interpreted as due either to a Peierls instability or to a Mott–Hubbard instability is controversial since half a century. However, in the last twenty years the study of chemical and physical properties of VO2 and of its alloys, benefits of a renewed interest due to possible applications coming from the realization of devices made of thin films. We describe in this review the structural, electronic and magnetic properties of the different metallic (R) and insulating (M1, T, M2) phases of VO2, of its solid solutions and under constraint. We present in a synthetic manner the various phase diagrams and their symmetry analysis. This work allows us to revisit older interpretation and to emphasize in particular the combined role of electron–electron interactions in the various phase of VO2 and of structural fluctuations in the MIT mechanism. In this framework we show that the phase transition is surprisingly announced by anisotropic one-dimensional (1D) structural fluctuations revealing chain like correlations between the V due to an incipient instability of the rutile structure. This leads to an unexpected critical dynamics of the order–disorder (or relaxation) type. We describe how the two-dimensional (2D) coupling between these 1D fluctuations, locally forming uniform V4+ zig-zag chains and V–V pairs, stabilizes the M2 and M1 insulating phases. These phases exhibit a 1D electronic anisotropy where substantial electron–electron correlations conduct to a spin–charge decoupling. The spin-Peierls ground state of M1 is analyzed via a mechanism of dimerization, in the T phase, of the spin 1/2 V 4+ zigzag Heisenberg chains formed in the M2 phase. This review summarizes in a critical manner the main results of the large literature on fundamental aspects of the MIT of VO2. It is completed by unpublished old results. Interpretations are also placed in a large conceptual frame which is also relevant to interpret physical properties of other classes of materials. Résumé. Le dioxyde de vanadium présente une transition métal–isolant (TMI) du premier ordre à 340 K (=TMI) d’une structure rutile (R) à une structure monoclinique (M1). Le mécanisme de cette transition interprétée comme étant due soit à une instabilité de Peierls soit à une instabilité de Mott–Hubbard reste très controversé depuis près d’un demi-siècle. Cependant depuis une vingtaine d’années l’étude des propriétés chimiques et physiques de VO2 et de ses alliages suscite un renouveau d’intérêt par la possibilité d’applications provenant de l’obtention de dispositifs s’appuyant sur la réalisation de films minces. Nous décrivons dans cette revue les propriétés structurales, électroniques et magnétiques des différentes phases métallique ISSN (electronic) : 1878-1535 https://comptes-rendus.academie-sciences.fr/physique/