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

High-quality large 1 T phase of Ti X 2 ( X = 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 1 g and E g modes, the rarely reported E u mode (∼183 cm −1 for TiTe 2 , and ∼185 cm −1 for TiS 2 ), and even the unexpected K mode (∼85 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 2 u /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 Ti X 2 phonons will help to understand their charge density wave and superconductivity.