Unraveling Mechanism on Reducing Thermal Hysteresis Width of VO2 by Ti Doping: A Joint Experimental and Theoretical Study

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• 作者：Shi Chen ; Jianjun Liu ; Lihua Wang ; Hongjie Luo ; Yanfeng Gao
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：August 21, 2014
• 年：2014
• 卷：118
• 期：33
• 页码：18938-18944
• 全文大小：417K
• ISSN：1932-7455

文摘

Tailoring effectively the hysteresis loop width of VO₂ semiconductor-metal transition (SMT) is crucial to develop thermal sensor devices. The Ti-doping is known as the most effective method to reduce 螖T_c and has been considered as the prototypical model in understanding the mechanism by which the 螖T_c of VO₂ MST could be manipulated. Here we present a joint experimental and first-principles computational study on nondoped and Ti-doped VO₂ to clarify the mechanism of Ti-doping on narrowing the hysteresis loop width of VO₂. On the basis of the analyses of differential scanning calorimetry (DSC), we found that phase transition temperatures in the cooling circle increase faster than those in the heating circle with increasing Ti concentrations, exhibiting a hysteresis width reduction at 2 掳C per Ti at. %. First-principles calculations reveal that dopant Ti atoms break the octahedral symmetry of local structure in VO₂ (R) phase. This distortion is propagated in anisotropy and exhibits an obvious nonlocal effect. In contrast, the Ti-doping-induced structural change in VO₂ (M) phase is only constrained in Ti-involved chain along the a-axis. The calculated energy profiles for Ti_xV_1鈥?i>xO₂ phase transition shows that structural stability and activation energies increased with the increase of Ti concentration. The activation barriers in Ti-doped VO₂ (R) phases are increased more remarkably than that in Ti-doped VO₂ (M) phases, which is consistent with experimental observation of concentration-dependent reduction of thermal hysteresis width.