Comparative study of the metal insulator transition of a VO2 film with simultaneous infrared thermography and electric measurements

Baoshun Liu,Jun Zhang,Xiujian Zhao,Mengtao Gong,Shouqin Tian

doi:10.1063/5.0036756

Abstract

Metal–insulator transition (MIT) of a polycrystalline VO2 film was studied with simultaneous electric resistance and infrared thermographic measurements. The apparent temperatures (Tapp,s) determined from infrared thermography show an obvious thermal hysteresis over the MIT that could match with the electric resistance very well. The dynamic change in the emissivity (ε) over the MIT was obtained from the Tapp,s hysteresis. The MIT parameters, including the critical phase transition temperature, thermal hysteresis width, and transition sharpness, could be obtained from the ε thermal hysteresis, which are in good accordance with those obtained from the electric resistance hysteresis. The temperature coefficient of ε (TCE) was defined, and the TCE change over the MIT was also obtained from ε thermal hysteresis. Based on the effective medium approximation, the fraction of the metallic phase during the MIT was estimated from the ε thermal hysteresis; this is also consistent with that calculated from the electric resistance hysteresis. Our results showed that the infrared thermographic measurement could be a simple and reliable method to study the MIT of VO2 materials.

Highlights

Vanadium dioxide (VO2) can undergo a metal–insulator transition (MIT) under the stimuli of heat, pressure, electric field, and light,1–3 which will result in a great change in optical, thermal, and electric properties
The thermal hysteresis features of the polycrystalline VO2 film deposited on a quartz substrate over the MIT were studied with simultaneous infrared thermography and electric resistances
The Tapps determined from the infrared thermography showed a good thermal hysteresis across the MIT of the VO2 film, which could well match the resistance measurement

Summary

Introduction

Vanadium dioxide (VO2) can undergo a metal–insulator transition (MIT) under the stimuli of heat, pressure, electric field, and light, which will result in a great change in optical, thermal, and electric properties. For single-crystalline VO2, the electric conductance can be changed by five orders of magnitude during the MIT. The MIT are of great interest in the applications of potential optics, sensing, micromechanics, and high-density memories. VO2 films are extensively studied as functional candidate materials for smartly solar-controllable glazes.11–13M-phase VO2 is insulating and R-phase VO2 is metallic, so structural phase transition (SPT) between them is a main reason causing the MIT. The critical temperature (Tc) of SPT for the bulk perfect VO2 crystal is ∼68 ○C.15 In the course of the SPT of VO2, the low temperature insulating phase can exist above Tc as a metastable phase, and the high-temperature metallic phase can exist below Tc. Super-heating and super-cooling are needed to obtain the SPT; this leads to a neat heat hysteresis during the MIT, a typical feature of VO2 materials. Vanadium dioxide (VO2) can undergo a metal–insulator transition (MIT) under the stimuli of heat, pressure, electric field, and light, which will result in a great change in optical, thermal, and electric properties.. The MIT are of great interest in the applications of potential optics, sensing, micromechanics, and high-density memories.. VO2 films are extensively studied as functional candidate materials for smartly solar-controllable glazes.. M-phase VO2 is insulating and R-phase VO2 is metallic, so structural phase transition (SPT) between them is a main reason causing the MIT.. The MIT of VO2 crystals has a hysteresis of 1–3 K, while that of polycrystalline films is much larger (10–40 K), depending on material structures.. Studying and controlling the hysteresis loops is meaningful for both mechanisms and applications of the MIT for VO2 materials Thermal hysteresis of the MIT was found to be sensitive to the grain size, boundaries, defects, and dopants. studying and controlling the hysteresis loops is meaningful for both mechanisms and applications of the MIT for VO2 materials

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Results

Conclusion