Crystal structure evolution behavior and phase transformation mechanism of Gd and F doped vanadium dioxide
Vanadium dioxide(VO2)is a thermally induced phase change material,the high phase change tem-perature restricts its potential application.Elemental doping can cause the changes in the properties of VO2 such as band structure,state density,bond length and cell volume,resulting in the change of phase transition behav-ior.Using Materials Studio software,based on first principles and molecular orbital theory,the crystal structure evolution and phase transformation mechanism of Gd and F doped VO2 were studied,it was found that no matter F doping in the middle O position of VO2(M)or O position on both sides,the doping will cause O—O bond to contract,V—V bond to growth,β Angle to increase,system Helmholm self-energy to increase,band gap to be relative reduction,F on both sides of the doping effect is the best.With the decrease of V4+—V4+ unipolar bonding,the phase transition temperature reaches the lowest at 1at％ F doping.When Gd is doped in V position in VO2(M)at 0-1.8at％,O—O bond and V—V bond shrink,β Angle decreases,Helmholm self-energy in-creases,band gap decreases,and Gd 4f state coincides with tⅡ orbital,so that the phase transition energy barrier becomes lower and the phase transition temperature decreases significantly.The phase transition mechanism of gadolinium and fluorine doped VO2 is more consistent with Peierls-Mott synergistic phase transition.
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