Morphology-Tuned Phase Transitions of Anatase TiO$_{2}$ Nanowires under High Pressure

The phase transitions of one-dimensional (1D) anatase TiO$_{2}$ nanowires were studied by in situ high pressure synchrotron X-ray diffraction (XRD) and Raman scattering. A direct anatase-to-baddeleyite transformation was observed at $\sim$9 GPa, which is clearly different from the size-dependent phase transition behaviors for nanocrystalline TiO$_{2}$. We found the higher compressibility in the c-axis compared to the a-axis for anatase nanowires which may be attributed to both the crystal structural feature and the growth direction of the nanowires. This phase transition of the TiO$_{2}$ nanowires shows obvious morphology-tuned behaviors. Upon decompression, the baddeleyite phase transformed into $\alpha $-PbO$_{2}$ phase. The morphology of the TiO$_{2}$ nanowires shows excellent stability and TiO$_{2}$ nanowires with $\alpha $-PbO$_{2}$ phase were obtained at ambient conditions through a compression-decompression cycle. These results indicate that the nanoscale quasi-1D structure of TiO$_{2}$ nanowires may contribute to the high pressure phase transitions showing unique morphology-tuned behaviors.