Duanwei He1 and Yusheng Zhao1, Huifeng Xu2 and Yingbing Zhang2, Zhenxian Liu3, Ho-kwang. Mao3, Jinfu Shu3, Jingchu Hu3, and Russell J. Hemley3,
1LANSCE, Los Alamos National Laboratory, Los Alamos, New Mexico 87545
2Department of Earth & Planetary Sciences, University of New Mexico
3Geophysical Laboratory, Carnegie Institution of Washington
dwhe@lanl.gov
NSLS-U2 (DAC)
Titanium dioxide (TiO2) in the macrocrystalline and nanocrystalline forms is an important material with several known and potential industrial applications such as pigments, plastics, cosmetics, electronics, and catalysts. It has also served mineral physicists as a model system in the study of pressure-induced structural phase transition of oxides relevant to the Earth's mantle and size-dependent phase transition behavior of nanoscale oxides in terrestrial environments. However, the study of the properties and phase stability of TiO2 nanotubes under high pressure has not been reported. Recently, we investigated the behaviour of TiO2 nanotubes at high pressures up to 50 GPa using in situ Raman and x-ray diffraction techniques. The starting multi-wall (~ 4 layers) TiO2 nanotubes have an inner diameter of ~ 6 nm, outer diameter of ~ 9 nm and averaged length of ~ 1 micron. The high pressure, in situ Raman experiment was performed at U2 beam line at NSLS of Brookhaven National Laboratory. The Raman spectra showed that intensities of the initial relative sharp peaks from TiO2 nanotubes decreased with increasing pressure and almost disappeared at about 15 GPa that implies a collapse of the nanotubes around this pressure region. Moreover, this transformation is irreversible when pressure was released up to ambient pressure. The phase stability of TiO2 nanotubes at high pressure was also investigated using diamond anvil cell technique and energy dispersive X-ray diffraction (EDXRD) at X-17C of NSLS. We used the bulk metallic glass as gasket to avoid the interference of gasket XRD peaks with samples? pattern. Similar to the Raman observation, the XRD peaks of TiO2 nanotubes become broader and weaker as pressure increased, and finally transferred into an amorphous state at around 20 GPa. The multi-wall carbon nanotubes were also reported to be in amorphous at 10- 20 GPa by in situ XRD observation. This might demonstrate that the TiO2 nanotubes are as strong as carbon nanotubes. Interestingly, theTiO2 nanotubes kept in an amorphous state with further compressed to 50 GPa according to the XRD observation. It was reported that the microparticle and nanocrystalline anatase (TiO2 ) started to transfer to the baddeleyite structure at ~12-18 GPa. As it is known, the external pressure can depress the atomic diffusion, thus kinetically hinder the recrystallization of high pressure TiO2 phases after the nanotubes were crushed in our experiments.