LI Qiaohui, ZHOU Jian, LU Jinshan
(School of Materials Science and Engineering, Nanchang Hangkong University, Nanchang 330063, Jiangxi, China)
Abstract: VO2powders and VO2/graphene composite powders were prepared by using hydrothermal reaction and thermal treatment with vanadyl oxalate solution as the vanadium source, sodium tungstate as the dopant and graphene oxide as the additive. With the assistance of XRD, DSC and TEM analyses, the effects of hydrothermal reaction conditions, doping amount and graphene oxide addition on structure and morphology, phase transition temperature and thermochromic properties the powders were systematically studied. Within the experimental temperature range, property of the hydrothermal reaction product is independent on the hydrothermal temperature, but is directly related to the hydrothermal time. The phase transitions of VO2(D) and VO2(B) to VO2(M) during the thermal treatment occurred at 300 ℃ and 550 ℃, respectively. Tungsten doping resulted in reduction in thermochromic temperature and thermal hysteresis temperature difference of the VO2 powders. With increasing content of graphene oxide, the thermochromic temperature first decreased and then increased, while the variation trend of thermal hysteresis temperature difference is the opposite. With the doping concentration of 9 at.% and graphene oxide content of 1 wt.%, the doped VO2/graphene composite powder exhibited a thermochromic temperature of 34.5 ℃ and a thermal hysteresis temperature difference of 7.7 ℃.
Key words: VO2; graphene; hydrothermal reaction; phase transition temperature; thermochromic property