Lattice stress engineering induced by rare-earth ion in regulating phase transition and thermochromic properties of VO₂ films

Reduction of metal-insulator transition temperature (θ_MIT) of VO₂ has been a key topic in turning its potential into practical applications. Electron injection as induced by high-valence ions’ doping of W, Mo and Nb has been studied extensively due to its high efficiency in declining θ_MIT. However, little attention has been given to the impact of lattice stress/strain caused by larger radius ions on the phase transition and thermochromic properties of VO₂. Herein, we investigate the dependence of θ_MIT on lattice stress by varying the radius of rare-earth (RE) ions in RE-Mo co-doped VO₂ films. As the radius of the RE ion increases, the lattice stress gradually intensifies, resulting in a lower θ_MIT and enhanced luminance transmittance (T_lum) at the same doping concentration. The TEM results reveal that the apical V–O bond length of the VO₆ octahedron is significantly influenced by the radius of the RE ion, thereby altering the energy gap between the d_// and π^∗ bands and adjusting θ_MIT. These findings demonstrate an additional degree of freedom to manipulate the phase transition of VO₂ through lattice stress engineering.