Hydrothermal synthesis and thermochromism effects in Eu-doped VO₂ polycrystalline materials

M phase Eu-doped VO₂ powders were prepared by a hydrothermal method followed by post annealing. The semiconductor–metal transition (MIT) properties of the produced samples were studied by Raman spectroscopy, infrared transmittance and resistance measurements. The results indicated that a low dose of Eu doping in VO₂ induces an enhanced switching ability of its infrared transmittance as the MIT occurs, and the ∆T_r is 48% at 1000 cm⁻¹ when the dose of Eu doping is 6%. Moreover, a low dose of Eu doping in VO₂ results a better crystal quality. While a high dose of Eu doping induces enhanced tensile stress in VO₂, resulting in the formation of the M₂ phase of VO₂ at room temperature. These results suggested that Eu is a particularly effective dopant in the synthesis of high-quality M phase VO₂. Thus, Eu doping in VO₂ is a distinctive strategy for realizing M phase VO₂ materials that have extensive applications in the construction of smart window coatings. Possible mechanisms of Eu doping in VO₂ are discussed.