Sharp Phase Transition by the Enhanced Lattice Stability of Low‐Temperature Phase of Cr‐Doped VO₂

Abstract

We have prepared Cr‐doped VO2 film (V1−xCrxO2, 0 ≤ x ≤ 0.15) on a c‐cut sapphire plate (0001). The insulator to metal transition (IMT) behavior of the VO2 was observed by the resistance and transmittance measurements near the phase transition point (Tc ~ 340 K). Whereas the starting point of metal to insulator transition (THE) was nearly constant at 350 K (x ≤ 0.03), the starting point of the insulator to metal transition (THS) was shifted from 308 K (x = 0) to 326 K (x = 0.05), suggesting that the Cr‐doped VO2 lattice is significantly stabilized below Tc of the VO2. The difference between THS and THE and the gap between thermal cycles (hysteresis gap), which reflect the sharpness of the phase transition, were minimal at x = 0.03–0.05 in V1−xCrxO2. This sudden phase transition of Cr‐doped VO2 is expected to be uniquely advantageous for sensitive on–off applications.

Element doping: a marvelous strategy for pioneering the smart applications of VO2

“…Chromium can effectively stabilize the room temperature phase and thus raise the T MIT . 89–91 With Cr content increasing from 3.5% to 10%, T MIT is significantly raised from 80.8 to 111.5 °C (Fig. 4e).…”

“…The results of many studies have shown that external atoms generally reduce the phase transition amplitude of VO 2 by 1-2 orders of magnitude. 13,23,29,56,77,94,[101][102][103] Especially, for some elements, such as Cr, 91,101 H, 29 Ni, 103 and N, 76 a high doping level can even lead to the disappearance of the switch effects.…”

“…Element doping can greatly reduce the hysteresis width of VO 2 . 29,91,93,[101][102][103]114 Currently, the mechanism of tailoring hysteresis by doping is still an open issue, but some factors have been reported to affect the thermal hysteresis behavior, such as the grain size, 99 nucleation defects, 115 crystallinity, 116 and orientation of grain boundaries. 99 In addition, the oxygen stoichiometry is found to influence the hysteresis width; small oxygen depletions lower the transitions up to 8 °C, while oxygen-rich sample will reduce ΔT to 2 °C.…”

“…In general, dopants reduce the size of VO 2 particles, which is accompanied by decreased surface roughness, and the extent of size reduction is negatively correlated with external atom concentration. 22,27,29,42,56,91,114,115 Fig. 8a shows the relationship between grain size and Ta concentration.…”

Structural and electrical properties of high-performance vanadium dioxide thin layers obtained by reactive magnetron sputtering

“…The large scale and successful integration of VO2 for most of these applications require good control of the MIT characteristics (either electrical or optical) in one or more of its specific parameters: transition speed, magnitude, hysteresis width, and transition temperature value. These parameters can also be modified by doping the vanadium with metal atoms such as tungsten [16], magnesium [17], molybdenum [18], chromium [19], niobium [20] which results in a modulation of the Tc or a modification in a controlled way of the electrical or optical hysteresis shape. Thus, the material's properties can be adapted to a specific domain of applications requiring lower or higher transition temperatures, a precise hysteresis width, or particular electrical/optical properties in a specific state.…”