X-ray scattering evidence for dimerization (4 kF) and spin-Peierls distortion (2 kF) in silver salts of dicyanoquinodiimine (2,5 MR-DCNQI )2 Ag (R = CH3, Cl or Br, M = CH3)

TLDR: In this article, structural instabilities of 2,5(MR-DCNQI) 2 Ag (R=CH 3, Cl or Br, M=CH3 ) using low-temperature X-ray diffuse scattering and diffraction techniques were studied.

Abstract: We have studied the structural instabilities of 2,5(MR-DCNQI) 2 Ag (R=CH 3 , Cl or Br, M=CH 3 ) using low-temperature X-ray diffuse scattering and diffraction techniques. In (DM-DCNQI) 2 Ag (DM=dimethyl) we observe quasi-1D 4k F diffuse scattering at room temperature which transforms into satellite reflections at Q 4kF =(0,0, 1/2) below T 4kF =(0,0, 1/2) below T 4kF ≃100 K. A second transition with limited quasi-1D precursor scattering occurs at T 2kF ≃100 K. A second transition with limited quasi-1D precursor scattering occurs at T 2kF ≃83 K with satellite reflections at Q 2kF ≃83 K with satellite reflections at Q 2kF =(0,0, 1/4). In relation with the transport and magnetic properties it is suggested that the upper transition localizes the charge carriers while the lower one leads to a spin-Peierls ground state. In (MCl-DCNQI) 2 =(0,0, 1/4). In relation with the transport and magnetic properties it is suggested that the upper transition localizes the charge carriers while the lower one leads to a spin-Peierls ground state. In (MCl-DCNQI) 2 Ag and (MBr-DCNQI) 2 Ag the quasi-1D 4K F and 2K f diffuse scatterings do not condense and there is not transition, probably because of the inherent disorder caused by the MCl and MBr substituents. Supplementary diffuse scattering features and irradiation effects are also reported Etude des instabilites structurales de ces composes par diffraction de rayons X et diffusion en diffraction. Pour M,R=CH 3 , observation d'une diffusion diffuse quasi-1D a 4 k F des la temperature ambiante, avec des satellites a Q 4 kF =(0,0,1/2) au-dessous de T 2kF =(0,0,1/2) au-dessous de T 2kF =100 K, et d'une 2eme transition, avec de faibles effets precurseurs quasi-1D a T 2kF =100 K, et d'une 2eme transition, avec de faibles effets precurseurs quasi-1D a T 2kF =83 K avec des satellites Q 2kF =83 K avec des satellites Q 2kF =(0,0,1/4). En relation avec les proprietes electriques et magnetiques, attribution de la 1ere transition a la localisation des porteurs et la 2eme a un etat fondamental de type spin-Peierls. Pour les composes avec M=CH 3 =(0,0,1/4). En relation avec les proprietes electriques et magnetiques, attribution de la 1ere transition a la localisation des porteurs et la 2eme a un etat fondamental de type spin-Peierls. Pour les composes avec M=CH 3 , R=Cl ou Br, absence de condensation a 4k F et 2k F et de transitions, probablement du fait du desordre inherent aux substituants Cl et Br