Structural phase transition and disorder in tetrathiafulvalenium chloride [(TTF)Clx]

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Abstract
(TTF)Clx, x=0.67 and 0.70, is a quasi‐one‐dimensional organic conductor with a room temperature conductivity of ∼ 150 Ω−1 cm−1. At room temperature the structure is tetragonal and consists of chains of uniformly spaced, eclipsed TTF molecules surrounding channels occupied by chloride ions, which form a disordered structure. The chloride substructure becomes ordered and the TTF substructure undergoes a phase transition from tetragonal to monoclinic symmetry at ∼250 °K. The angle β of the monoclinic phase increases continuously as the temperature is decreased from 245 ° to 19 °K. The electrical conductivity shows a sharp decrease at the phase transition which is suggestive of the formation of commensurate charge density waves in the monoclinic phase.