晶格畸变对VO2相变温度的影响

Influence of Lattice Distortion on the Metal-Insulator Transition Temperature of VO2

采用高功率脉冲磁控溅射在石英玻璃基片上成功制备了具有明显金属-绝缘体转变特性的多晶VO2薄膜,其最低相变温度仅为32℃。X射线衍射结果表明沉积薄膜的晶体结构均为存在明显晶格畸变的VO2(M),且薄膜(011)晶面间距越接近相变后VO2(R)(110)晶面的晶面间距,相变温度越低。根据试验结果,利用从头算分子动力学分别对VO2金属-绝缘体相变过程的晶体结构与态密度演化规律进行了研究。结果表明:随计算温度升高,不同(011)晶面间距绝缘态超胞的晶体结构均逐渐由VO2(M)向VO2(R)转变,同时伴随着禁带宽度的逐渐降低,最终转变为费米能级完全被电子占据的金属态;初始VO2(M)超胞(011)面的晶面间距与相变后VO2(R)(110)面的晶面间距之差越小,费米能级附近的禁带宽度也越小,这可能是导致VO2金属-绝缘体转变温度降低的本质物理原因。

In this work,VO2 thin films were prepared on the quartz glass substrates by using high power impulse magnetron sputtering.As-deposited films had a typical metal-insulator transition(MIT)and the lowest phase transition temperature was only 32℃.The X-ray diffraction patterns revealed that the lattice distortions in the as-deposited VO2(M)films were different,and the MIT temperature decreased with the interplanar spa-cing difference between the VO2(M)(011)and standard VO2(R)(110).According to the experimental results,the crystal structure and density of states in MIT of the VO2 were studied by the ab initio molecular dynamics to evaluate the influence of the lattice distortion on the MIT temperature.The results showed that the crystal structure in the MIT was gradually transformed from initial VO2(M)to the VO2(R)with the increase of the temperature,coupled with the decrease of the band gap near the Fermi energy.In the end,VO2 supercells were completely transformed into the metallic state,in which the Fermi energy is occupied by electrons.Furthermore,the MIT temperature was also related to the difference in the interplanar spacing between the initial VO2(M)(011)and standard VO2(R)(110),and the less the difference in the interplanar spacing,the lower the MIT temperature,which might be the nature resulting in the reduction of the MIT temperature.