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采用高压原位阻抗谱测量技术对锐钛矿TiO 2多晶的电输运性质进行了系统研究. 在6.4, 11.5和24.6 GPa压力处发现了晶粒和晶界的电阻、参数因子和弛豫频率的反常变化行为. 研究分析表明: 6.4和11.5 GPa压力点分别对应着TiO 2由锐钛矿转变为α-PbO 2, 再转变为斜锆石的结构相变, 当压力高于24.6 GPa时, TiO 2完全转变为斜锆石相. 通过分析晶粒和晶界电阻在压力作用下的变化行为可知, 本征缺陷的存在对TiO 2高压下电输运性质的变化起着关键的作用. 在6.4 GPa压力处, 相变的发生导致缺陷的作用发生了变化, 由作为复合中心的深能级缺陷转变为向导带和价带提供载流子的浅能级缺陷, 并且作为浅能级缺陷存在至实验最高压力点38.9 GPa, 浅能级缺陷在能带中的位置也随着相变发生而改变. 晶粒和晶界的激活能随着压力升高而降低, 表明高压下载流子在晶粒和晶界的输运变得更加容易. 此外, TiO 2晶粒和晶界的弛豫频率比值随压力的升高而不断减小, 高压下的晶界效应不明显.The electrical transport properties of anatase TiO 2polycrystalline have been systematically investigated by using high pressure in-situimpedance spectroscopy measurements. The anomalous behaviors of resistance, parameter factor and relaxation frequency of grain and grain boundary can be found at 6.4, 11.5 and 24.6 GPa. The results indicate that the first two discontinuous points (6.4 and 11.5 GPa) correspond to the phase transitions of TiO 2from anatase to α-PbO 2and then to baddeleyite, respectively. Above 24.6 GPa, TiO 2completely transforms into the baddeleyite phase. Based on the change of grain resistance and grain boundary resistance under pressure, intrinsic defects play a crucial effect in the electrical transport properties of TiO 2at high pressures. At 6.4 GPa, the occurrence of phase transition gives rise to the variation of defects’ role, from a deep energy level defect (as a recombination centre) changes into a shallow energy level defect (providing carriers for the conduction and valence bands). In addition, the position of defect in energy band changes with pressure increasing. The phase transition of TiO 2at 6.4 GPa is the rearrangement of TiO 6octahedron, while the other one at 11.5 GPa can be attributed to the migration of oxygen Schottky defects from inner to surface. Combining the packing factor and relaxation frequency, the electrical transport properties of TiO 2under pressure are revealed, the packing factor and the relaxation frequency are closely related to the mobility and the carrier concentration, respectively. The activation energy of grain and grain boundary decrease with the pressure elevating, indicating that the transport of carriers in grain and grain boundary become easier under pressure, and the former is smoother than the latter owing to the activation energy of grain being smaller than that of grain boundary in the same pressure range. Moreover, the relaxation frequency ratio of TiO 2grain and TiO 2grain boundary decreases with pressure increasing, and the grain boundary effect under high pressure is not obvious.
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Keywords:
- high pressure/
- TiO2/
- defects/
- grain boundary
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Pressure region/GPa dE/dP/(meV·GPa–1) Grain Grain boundary 0—6.4 –11.51 –22.79 6.4—11.5 –7.59 –9.33 11.5—24.6 –6.16 –6.82 24.6—38.9 –3.54 –4.91 
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