High-pressure studies of titanium pyrophosphate by Raman scattering and infrared spectroscopy

High-pressure investigations of titanium pyrophosphate, TiP2O7, in diamond anvil cell have been performed at room temperature using in situ Raman scattering and Fourier transform infrared spectroscopy (FTIR). The endeavor was to acquire information on pressure-induced structural transformations such as phase transitions and amorphization occurring in the crystal lattice. The pressure-stimulated alterations in the spectral profile, the position, and the intensity of the stretching and bending modes of PO4 tetrahedral structural units have been investigated up to 42.8 and 49.4 GPa for Raman and infrared-active modes, respectively. The spectral changes pointed mostly to the densification and partial amorphization of the crystal lattice. FTIR spectra confirmed that the investigated compound, TiP2O7, compressed smoothly up to the highest investigated pressures. The spectroscopic studies did not indicate an unambiguous structural transformation matching to a pressure-driven phase transition. The reversibility to ambient pressure structure upon decompression was implied by FTIR but was not confirmed by Raman spectroscopy. The mode Grueneisen parameters were calculated for the various Raman and infrared-active vibrational modes. The results obtained are consistent with our previous high-pressure synchrotron radiation-based X-ray diffraction investigations