| dc.description.abstract | Vanadium dioxide (VO2) is a kind of transition metal oxide with phase change properties. Therefore, when metal-insulator transformation (MIT) occurs, the monoclinic VO2 will transform to the tetragonal rutile phase. At this time, the physical properties will also undergo mutations, such as 2 to 5 orders of magnitude mutations in resistance, accompanied by changes in magnetic and optical properties. Because the phase transition temperature (about 68 °C) of VO2 is close to room temperature, it has a great potential in the field of functional materials.
The purpose of this research was to directly deposit W-doped vanadium dioxide on substrates by hydrothermal method, and performed post-annealing treatment. We explored its microstructure and crystalline phase, and tried to optimize the phase transition temperature (resistance mutation temperature) .
The experimental results showed that when the precursor ratio (vanadium pentoxide: oxalic acid) was 3:5, the best substrate coverage could be obtained after the reaction and the formation of impurity V3O7 could be avoided. The pure vanadium dioxide B phase nanostructure could be successfully prepared through hydrothermal method at 180 °C for 4 hr.
In addition, the Tc of the undoped VO2 structure was about 68 °C, and the resistance dropped by about 3 orders, which was roughly the same as the commonly known Tc of undoped VO2. When W content increased to 2 at%, the lowest Tc was 53 °C. The electrical resistance change was one order. The Tc did not decrease significantly when the doping amount was increased, and the M-phase characteristic peak of the X-ray diffraction pattern was also not shifted. However, the M phase characteristic peak displacement of the X-ray diffraction pattern of the tungsten-doped vanadium dioxide powder synthesized under the same experimental conditions increased with the increase of the doping amount. It was speculated that the doped vanadium dioxide tended to form homogeneous nucleation rather than heterogeneous nucleation, so only a small part of the structure could be deposited on the surface of the sapphire substrate. | en_US |