Achieving room-temperature M_(2)-phase VO_(2) nanowires for superior thermal actuation

摘要

Vanadium dioxide (VO_(2)) has emerged as a promising micro-actuator material for its large amplitude and high work density across the transition between the insulating (M_(1) and M_(2)) and metallic (R) phase. Even though M_(2)–R transition offers about 70% higher transformation stress than M_(1)–R structural phase transition, the application of the M_(2) phase in the micro-actuators is hindered by the fact that previously, M_(2) phase can only stay stable under tensile stress. In this work, we propose and verify that by synthesizing the VO_(2) nanowires under optimized oxygen-rich conditions, stoichiometry change can be introduced into the nanowires (NWs) which in turn yield a large number free-standing single-crystalline M_(2)-phase NWs stable at room temperature. In addition, we demonstrate that the output stress of the M_(2)-phase NWs is about 65% higher than that of the M_(1)-phase NWs during their transition to R phase, quite close to the theoretical prediction. Our findings open new avenues towards enhancing the performance of VO_(2)-based actuators by using M_(2)–R transition.