Uncovering the distinctive phase transition characteristics and thermochromic performance of VO2 with different N-doping sites
Yibei Xue, Lei Miao, Takuya Hasegawa, Ayahisa Okawa, Shunya Yoshino, Hideki Kato, Masato Kakihana, Shu Yin
Abstract
Nitrogen is a rare dopant that can not only enter the interstitial sites (Ni) but also oxygen substitutional sites (Ns) of vanadium dioxide (VO2). The incorporation of the N atom has been demonstrated to modulate the phase transition behavior of VO2. However, a deep understanding of the effect of N doping sites on the phase transition and thermochromic properties of VO2 remains lacking. Here, we prepare N-doped VO2 with tunable doping sites. Ni demonstrates the ability to slightly increase phase transformation temperature (Tc), while greatly improving the visible light transmittance and near-infrared (NIR) modulation performance by 5 % and 44 %, respectively. Interestingly, the introduction of Ns reduces the Tc of N-doped VO2 with double doping sites (interstitial and O substitution sites, Ni,s), from 65.2 to 60.6 °C. More attractively, the thermal hysteresis width of the phase transition is reduced to near zero (0.2 °C). This is of great interest for the precise regulation of the VO2 phase transition. These distinctions are attributed to the differences in the effects of N-doping sites on the lattice and energy band structure of VO2. Ns injects hole carriers into the d// band raising the valence band maximum and thus narrowing the band gap. The point defect-induced nucleation mechanism supports a narrow hysteresis width in the combination effect of oxygen vacancies and N impurities.