X-Ray Diffuse Scattering Study of Some (TMTSF)₂X and (TMTTF)₂X Salts

Abstract

Abstract X-ray diffuse scattering experiments on the superconducting salts (TMTSF)2X with X = PF6, AsF6 and ClO4 reveal no charge density wave instability, in contrast with the poorly conducting (TMTTF)2PF6 salt. New structural phase transitions coinciding with conductivity anomalies are found in (TMTSF)2NO3, (TMTSF)2ReO4, and (TMTTF)2ClO4. It is suggested that they correspond to order-disorder transitions involving the non-centrosymmetric counter ions. Relationships between these structural instabilities and superconductivity are also discussed.