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

Reduction of metal-insulator transition temperature (BMIT) 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 BMIT. 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 BMIT 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 BMIT and enhanced luminance transmittance (Tlum) 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 ff* bands and adjusting BMIT. These findings demonstrate an additional degree of freedom to manipulate the phase transition of VO2 through lattice stress engineering.