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

High-quality large 1T phase of TiX2(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 proper-ties are investigated by Raman spectroscopy.Several phonon modes have been observed,including the widely reported A1g and Eg modes,the rarely reported Eu mode(～183 cm-1 for TiTe2,and～185 cm-1 for TiS2),and even the unexpected K mode(～85 cm-1)of TiTe2.Most phonons harden with the decrease of temperature,except that the K mode of TiTe2 and the Eu and"A2u/Sh"modes of TiS2 soften with the decrease of temperature.In addition,we also found phonon changes in TiSe2 that may be related to charge density wave phase transition.Our results on TiX2 phonons will help to understand their charge density wave and superconductivity.