Polarized Raman scattering study of blue bronze Tl_(0.3)MoO _3

摘要

Temperature dependent polarized Raman spectra of quasi-one dimensional blue bronze Tl_(0.3)MoO_3 are reported on a frequency range 1001100 cm~(-1). Frequency shift and splitting in some modes were observed, revealing the role of the alkali atom. Many new modes emerge at 170 K accompanied by charge density wave (CDW) formation, and show gradual temperature dependent intensity and line-width, implying the second order nature of CDW transition. A frequency "jump" is found for many Raman vibrational modes in Tl_(0.3)MoO_3 near 110 K, confirming that the transition from an incommensurate to commensurate state occurs around this temperature. In addition, only three stretching vibration modes of terminal MoO bonds are observed for (xx) polarizations from 800 to 1100 cm~(-1) at 300 K; new modes appear only when the temperature drops below 110 K and are ascribed to the splitting of the mode at 931 cm~(-1) due to commensurate state formation.