A novel route to realize controllable phases in an aluminum (Al3+)-doped VO2 system and the metal–insulator transition modulation

• The controllable phases of Al3+-doped VO2 were achieved through a hydrothermal method and subsequent annealing treatment.
• The Al3+ dopants and the Ar flux rates in the annealing process play the important roles in formation of stable M2 phase.
• Phase transition behavior of Al-doped VO2 showed the important role of phase structure on tuning TC.

The controllable M1 or M2 phases of Al3+-doped VO2 were successfully achieved through an effective and economical route, which combines a hydrothermal method and subsequent annealing treatment. The crystalline structure and the valence states of as-prepared samples were characterized by XRD, TEM, and XANES spectroscopy. Experiments showed that the Al3+ dopants and the Ar flux rates in an annealing process played the important roles in the formation of stable M2 phase. Microstructural characterizations by SEM indicated that the size of Al-doped VO2 particles gradually reduced with increasing Al concentration. The phase transition property measured by DSC revealed that the metal–insulator transition temperature (TC) could be tuned by the Al-doping concentration only in the formation of M2 phase.