Growth, characterization, and Raman spectra of the 1T phases of TiTe₂, TiSe₂, and TiS₂

High-quality large 1T phase of TiX_2 (X =\rm Te, Se, and S) single crystals have been grown by chemical vapor transport using iodine as a transport agent. The samples are characterized by compositional and structural analyses, and their properties are investigated by Raman spectroscopy. Several phonon modes have been observed, including the widely reported A_1g and E_g modes, the rarely reported E_u mode (\sim183 cm^-1 for TiTe_2, and \sim185 cm^-1 for TiS_2), and even the unexpected K mode (\sim85 cm^-1) of TiTe_2. Most phonons harden with the decrease of temperature, except that the K mode of TiTe_2 and the E_u and "A_2u/Sh" modes of TiS_2 soften with the decrease of temperature. In addition, we also found phonon changes in TiSe_2 that may be related to charge density wave phase transition. Our results on TiX_2 phonons will help to understand their charge density wave and superconductivity.