Diffuse X-ray scattering in the metallic state of TSeF-TCNQ and HMTSeF-TCNQ

Abstract

Some results of a X-ray diffuse scattering investigation on the charge transfer compounds TSeFTCNQ and HMTSeF-TCNQ are reported. In the metallic region the results show the formation of a 1-D distortion or a Kohn anomaly in the phonon spectrum. For TSeFTCNQ this is observed below T ∼ 238 K and corresponds to a periodicity of (3.15 ± 0.05) | b| along the chain axis. For HMTSeFTCNQ the distortion was detected even at room temperature and has a period of (2.7 ± 0.1) | b|. In both materials the distortion has both transverse components in contrast to TTFTCNQ. In the insulating state of TSeF-TCNQ below 29 K the 1-D distortions on each stack are correlated to form a 3-D superlattice.