The Ru-doped VO₂ films fabricated by rapid thermal annealing of V–Ru co-sputtered alloy films with lowered phase transition temperature and narrowed hysteresis for smart windows

Vanadium dioxide (VO₂), a current favorite in the field of smart windows as a thermochromic material, faces limitations in practical application due to its high phase transition temperature (T_t, ~ 68 ℃) and wide hysteresis curve (ΔT). In this study, Ru-doped VO₂ thin films with reduced T_t and narrower ΔT were prepared through co-sputtering tetravalent metal Ru and V using magnetron sputtering to form alloy thin films, followed by rapid thermal annealing. Compared with pure VO₂ thin films, at the Ru doping concentration of 4.98 at%, the T_t was lowered from 59.6 °C to 35.8 °C, and the ΔT was reduced from 10.5 °C to 2.8 °C, primarily due to the structural similarity between RuO₂ and rutile phase VO₂, smaller grain size, and greater grain uniformity. The optical properties of Ru-doped VO₂ thin films had also been discussed, revealing only minor reductions in luminous transmittance (T_lum) and the solar modulation ability (ΔT_sol) when the T_t decreased to 35.8 °C. This methodology offers a viable path for applying VO₂ in smart windows, providing effective reductions in T_t and ΔT with minimal impact on optical performance.