INFLUENCES OF THALLIUM-DOPING ON THE PHASE TRANSITION AND RAMAN SPECTRA OF BLUE MOLYBDENUM BRONZES IN CHARGE-DENSITY-WAVE STATE

Abstract

Temperature dependencies of the Raman spectra of pure K 0.3 MoO 3 and thallium-doped K 0.15 Tl 0.15 MoO 3 blue bronzes are reported. The results showed that in pure bronze the commensurate domains separated by discommensurations occur below 100 K, perhaps as a result of the influence of the commensurate potentials of the undistorted alkaline sublattice. The disorder Tl-impurities may destroy the commensurate domains and lead to complete incommensuration in Tl-doped blue bronze below 100 K. The tremendous critical fluctuations and impurity-induced lack of long-range order of incommensurate CDW would lead to the spectral continuum or its disappearing. The weak softening of the amplitude mode is about 11%, which is similar to previous report. We were also the first to observe two strong new modes at about 76 cm −1 and 86 cm −1 in the distorted CDW state and attributed them to zone center excitations of the phonon branches at zone boundary due to CDW-induced collapse of the Brillouin zone at T p .