The modulation of metal–insulator transition temperature of vanadium dioxide: a density functional theory study

Abstract

The modulation of metal–insulator transition (MIT) temperature and phase stability of thermochromic materials based on all the transition metal doped VO₂ were systematically studied using density functional theory (DFT) calculations. The free energies, formation enthalpies, and Fermi energies of transition metal doped VO₂ were evaluated from DFT calculations; the cell volumes and bulk moduli were obtained by fitting the free energies to the Birch–Murnaghan equation of states; and the decomposition enthalpies and entropies of the transition metal doped VO₂ were calculated using both experimental data and DFT calculations. Based on these results, the MIT temperature was associated with lattice distortion of VO₂ (M₁) upon doping, the expansion of cell volume and the decrease in β-angle were associated with the decrease in MIT temperature, and the shrinkage of cell volume and the increase in β-angle were associated with the increase in MIT temperature. And it was also concluded that VO₂ (M₁) doped with high valence cations is more stable than those doped with low valence cations. These conclusions are consistent with experimental facts that W-, Mo-, and Re- are the most studied and the most effective dopants for the reduction of MIT temperature, and La-, Hg-, and Ag-doped VO₂ undergoes phase separation. In addition, DFT calculations without spin-polarization were also carried out, and the influence of spin-polarization was evaluated. Finally, scandium was proposed as a potential dopant for VO₂ in view of balanced comprehensive performance.