Charge Density Wave States and Structural Transition in Layered Chalcogenide TaSe2−xTex

The structural features and three-dimensional nature of the charge density wave (CDW) state of the layered chalcogenide 1T-TaSe2 - x Te-x (0 <= x <= 2.0) are characterized by Cs-corrected transmission electron microscopy measurements. Notable changes of both average structure and the CDW state arising from Te substitution for Se are clearly demonstrated in samples with x > 0.3. The commensurate CDW state characterized by the known star-of-David clustering in the 1T-TaSe2 crystal becomes visibly unstable with Te substitution and vanishes when x = 0.3. The 1T-TaSe2 (- x) Te-x (0.3 <= x <= 1.3) samples generally adopt a remarkable incommensurate CDW state with monoclinic distortion, which could be fundamentally in correlation with the strong d-dependent electron-phonon coupling-induced period-lattice-distortion as identified in TaTe2. Systematic analysis demonstrates that the occurrence of superconductivity is related to the suppression of the commensurate CDW phase and the presence of discommensuration is an evident structural feature observed in the superconducting samples.