Pressure and temperature-dependent optical properties of TiTa 2 O 7 .

Polycrystalline TiTa 2 O 7 was synthesized directly by solid-state reaction methods. The structures were determined by using X-ray diffraction (XRD). The high-pressure Raman and UV-vis absorption spectra of TiTa 2 O 7 were obtained up to 25 GPa in a diamond anvil cell (DAC) at room temperature. The Raman scattering results reveal that a pressure-induced amorphization occurs above 10.5 GPa. An inflection point was also observed at 11 GPa in the pressure-dependent bandgap energy spectra, which agrees well with the amorphization point found in Raman spectra. The temperature-dependent Raman and photoluminescence (PL) spectra of TiTa 2 O 7 were also measured. The PL mechanism for TiTa 2 O 7 was studied. It is worth noting that the Raman vibrations attributing to the bending vibration of the Ta (Ti)-O octahedron exhibit anomalous frequency shifts in both the high-pressure and temperature-dependent Raman spectra.