Hydrothermal synthesis of vanadium dioxide nanoparticles and its applications

• Main Author: Liu, Guowei
• Other Authors: Long Yi
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Materials::Nanostructured materials
• Online Access: https://hdl.handle.net/10356/151086
• Institution: Nanyang Technological University

Vanadium dioxide (VO2), as the typical phase transition material, has drawn an intensive study including the fabrication, stimuli to trigger the transition as well as the high-performance devices based on VO2 with different applications. High-performance optical and electrical applications of VO2 require the synthesis of the VO2 nanoparticles (NPs)with pure phase, high crystallinity, as well as controlled morphology and facet. However, because the VO2 has multiple polymorphs and VO2(M) has higher formation energy than other polymorphs, the common products of the hydrothermal synthesis are metastable VO2(A) or VO2(B). To address the above problems, one-step hydrothermal synthesis of pure phase VO2(M) with high crystallinity has been successfully realized by systematically investigating the parameters of the hydrothermal process. A phase evolution mechanism has been proposed in the formation of the VO2(M), and the process-microstructure-property relationship has been established in the optical and electrical devices further. The obtained VO2(M) NPs have been coated to be used as a thermochromic smart window. It is observed that the particle size below 60 nm exhibits the best thermochromic properties, which exhibit comparable 11.8% solar modulation with 37.3 % visible transmittance. Such performance is also related to crystallinity doping level and preferred growth of VO2 NPs. Furthermore, the VO2(M) mesh structure was prepared via the self-assembly method. The mesh structure was further fabricated into the resistance switches device. The high transparency resistance switches exhibit up to 104 ON/OFF ratio with the visible transparency at 86%, which outperforms the reported devices.