A Comprehensive Review on Synthesis, Phase Transition, and Applications of VO₂

The first-order reversible phase transition in vanadium dioxide (VO₂), popularly coined as metal-insulator transition (MIT), is a matter of significant interest since its genesis in the late 1950s. VO₂ in its bulk form exhibits MIT at a transition temperature (T_t) of 340 K. Below T_t, VO₂ crystallizes in the monoclinic insulting phase while above T_t, the crystal structure transforms into a more symmetrical tetragonal-rutile phase which is conducting. Such a structural phase transformation (SPT) draws attention to several oxides of vanadium. Vanadate has been a subject of specific correlated compounds where numerous attempts have been made to develop a single theory that can fully define the peculiar nature of phase transition. Two major models namely Peierls and Mott have been proposed to understand the phase transitions. The structural modification in VO₂ is responsible for several applications such as thermochromism, Mott-based transistors, bimorph actuators, hydrogen storage capability, microbolometers, and so on. Ferromagnetism (FM) in the doped VO₂ films would enhance the data storage capacity. This review focuses on the systematic advancement in the thin films and nanostructures of VO₂ over the past decades and the comprehensive understanding between MIT and SPT for advanced applications. A brief account is also given on various methods of synthesis of these oxides.