Pressure-induced phase transitions of TiO2 nanosheets with high reactive {001} facets

Abstract

The high pressure phase transition behaviors of anatase TiO₂ nanosheets with high reactive {001} facets were studied using in situ synchrotron X-ray diffraction and Raman spectroscopy. The phase transition from starting anatase phase to a low ordered baddeleyite structure was found upon compression. Upon decompression, the low ordered baddeleyite structure transforms into an α-PbO₂ phase. The obtained bulk modulus for TiO₂ nanosheets is 317 (10) GPa, which shows ultralow compressibility compared with those of nanoparticles and bulks. We suggest that the enhanced bulk modulus for the TiO₂ nanosheets can be attributed to their ultrafine thickness along the [001] direction with fewer “soft” empty O6 octahedra distributed in the TiO₂ nanosheets than in other nanostructures and bulks. TiO₂ nanosheets retain their original morphology after being released to ambient pressure. These results indicate that the sheet-like morphology with exposed {001} facets plays important roles in the high pressure phase transition of TiO₂ nanosheets.