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In this article, anatase Titanium dioxide (TiO2) nanowires were synthesized via hydrothermal method, and its grain and grain boundary behaviors and electrical properties were investigated by AC impedance method under high pressure (up to 34.0 GPa). The research results indicate that, from the relationship between the frequency dependence of impedance Z'' and pressure, the transmission mechanism of anatase phase TiO2 nanowires in test pressure range is electronic conductivity. It should be noted that, the characteristic?peaks of Z'' move toward to high frequency region as the pressure increasing, demonstrating the effect of grain internal on impedance is becoming increasingly?apparent. Additionally, the overall variation?trends?of grain and grain boundary resistance are downward with increase in pressure, and the descent rates of grain boundary are larger than those of grain before and after phase transition. However, in the range of phase transition (8.2 ~ 11.2 GPa, from anatase to baddeleyite phase), grain boundary resistance shows a discontinuously change (increased to 11.2 GPa and then decreased). Based on the different variation trends of grain and grain boundary resistance, it becomes obvious that the phase transition from anatase to baddeleyite phase occurred at the surface of grain firstly, and then extended to the interior of grain gradually. Also, as an intrinsic characteristic, relaxation frequency is independent of the geometrical parameters. The pressure dependence of activation energy is obtained by fitting the pressure dependence of relaxation frequency. The activation energies of grain and grain boundary decreased with pressure increasing, implying the contribution of pressure on the conductivity of sample is positive. Furthermore, the space charge potential for the whole test pressure range is positive, which is determined by the relation between pressure and relaxation frequency. This fact illustrates that the anion defects are easily formed in the space charge region, and the oxygen defects are the main inducement for TiO2 phase transformation.

Grain and Grain boundary behaviors and electrical transport properties of TiO2 Nanowires Under High Pressure