Abstract
Vanadium dioxide (VO2) is a strongly correlated electronic material with a metal-insulator transition (MIT) near room temperature. Ion-doping to VO2 dramatically alters its transport properties and the MIT temperature. Recently, insulating hydrogenated VO2 (HVO2) accompanied by a crystal structure transformation from VO2 was experimentally observed. Despite the important steps taken towards realizing novel applications, essential physics such as the diffusion constant of intercalated protons and the crystal transformation energy between VO2 and HVO2 are still lacking. In this work, we investigated the physical parameters of proton diffusion constants accompanied by VO2 to HVO2 crystal transformation with temperature variation and their transformation energies. It was found that protons could propagate several micrometers with a crystal transformation between VO2 and HVO2. The proton diffusion speed from HVO2 to VO2 was approximately two orders higher than that from VO2 to HVO2. The long-range propagation of protons leads to the possibility of realizing novel iontronic applications and energy devices.
Highlights
Vanadium dioxide (VO2) is a strongly correlated electronic material with a metal-insulator transition (MIT) near room temperature
These results indicate that the VO2 microwires become fully hydrogenated VO2 in the 4 μm gap between the Pt source and drain catalytic electrodes
We estimated the activation energy (EHVO2) for the structural transformation from VO2 to hydrogenated VO2 (HVO2) using the experimental results of the 4-μm-length VO2 wire and simulation fittings
Summary
Vanadium dioxide (VO2) is a strongly correlated electronic material with a metal-insulator transition (MIT) near room temperature. Doping has an impact on 3d-band filling, which often results in dramatic modification of the orbital states This results in large changes of electronic properties, such as the metal-insulator transition (MIT). A shift of the MIT temperature (TMI) of VO2 via doping with a variety of elements, such as W, Mo, and Nb has been reported[1,2,3,4,5,6,7,8] This is caused by charge transfer from the impurity ions to the vanadium ions through the oxygen ions, which displaces an integral number of 3d1 electrons in V4+ that are Mott insulating states to 3d1+δ, resulting in the formation of more stable metallic states. We demonstrated the long-range propagation of protons in VO2 This was accomplished by investigating the transient electronic transport properties during proton intercalation in VO2 and the associated structural transformation to HVO2 under H2 + Ar gas atmosphere. The results showed that the diffusion constants and crystal transformation energies differed for the two states
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