Speaker
Description
Solid-state phase-change materials (PCMs) are of considerable interest as alternatives to conventional solid--liquid systems because they can provide a thermal response while mitigating issues such as leakage and large volume changes. VO$_2$ is particularly attractive in this regard because it exhibits a metal--insulator transition (MIT) near room temperature, accompanied by pronounced structural, electrical, magnetic, and thermal changes. Here, we investigate the composition-dependent evolution of the MIT in W-doped VO$_2$ powders, with particular emphasis on the associated thermodynamic response relevant to functionalities based on a solid-state phase change. Structural, magnetic, electrical, and thermal properties were characterized by X-ray diffraction, magnetization, electrical resistivity, and differential scanning calorimetry, respectively. The transition temperature decreases systematically from approximately 340~K for undoped VO$_2$ to about 299~K for the highest-W-content sample (1.239~at\%). Despite this substantial suppression of the transition temperature, the volumetric latent heat remains relatively large, decreasing from 237.3 to 161.8~kJ\,L$^{-1}$, which is higher than those of representative solid--solid PCMs such as NiTi and neopentyl glycol. Meanwhile, the corresponding transition entropy change ($\Delta S$) decreases from 1.52 to 1.18~$k_{\mathrm{B}}$/VO$_2$ (from 12.64 to 9.81~J\,mol$^{-1}$\,K$^{-1}$). Compared with representative phase-change materials, VO$_2$ occupies a distinctive region that combines near-room-temperature operation and relatively high thermal conductivity, giving rise to the practical advantages of utilizing a solid-state transition. These results demonstrate that W doping enables effective tuning of the MIT temperature while retaining a substantial intrinsic thermodynamic response, underscoring the promise of VO$_2$ as a viable solid-state phase-change material.
