Improving phase transition temperature of VO_(2) via Ge doping:a combined experimental and theoretical study

Enhancing the semiconductor-metal phase transition temperature(TSMT)of VO_(2) is of great consequence for further exploring the potential applications of VO_(2) at elevated temperatures.In this study,Ge^(4+)-doped VO_(2)(Ge_(x)V_(1-x)O_(2))samples were prepared by the hydrothermal and annealing approach.X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM),differential scanning calorimetry(DSC)and resistivity-temperature(R-T)analyses were used to investigate the influence of Ge doping on the lattice structures and phase transition properties of Ge_(x)V_(1-x)O_(2) samples.We found that the lattice parameter of Ge_(x)V_(1-x)O_(2) decreased with the Ge concentration increasing from 2 at%to 18 at%,which was further supported by density functional theory(DFT)-based first-principle simulations.TSMT firstly increased from 64.5 to 73.0℃ at 8 at% Ge and then decreased to 71.5℃ at higher Ge concentration.Furthermore,DFT analysis revealed that the impact of lattice distortion induced by Ge doping rather than the changes in electronic structure is more pronounced on modulating TSMT of Ge_(x)V_(1-x)O_(2).The present work has pointed out the direction that the TSMT could be enhanced and illustrated the physical reason behind the regulation of TSMT in ionsdoped VO_(2) systems.