RANDOM DISORDER AND STRUCTURAL INSTABILITIES IN (TMTSF)2X-(TMTTF)2Y SOLID-SOLUTIONS AND (TMDTDSF)2X SERIES OF ORGANIC CONDUCTORS

Substitutional and orientational disorders in some of the title compou nds have been characterized by simulations of the X-ray diffuse scatte ring pattern. It is found that in most of the cases the disorder is ra ndom but accompanied by molecular displacements (size effect). The inf luence of a random disorder on the 2k(F) charge density wave (CDW), sp in Peierls (SP) and on the anion ordering (AO) instabilities is analyz ed. The smoothening and even the complete suppression of the AO transi tion is discussed in term of random interactions and random fields act ing on the Ising orientational order parameter of the anions. Random i nteractions are relevant in the (TMTSF)2(ReO4)1-x(ClO4)x solid solutio n while the effect of random fields is pertinent in the (TMDTDSF)2X se ries and in the [(TMTSF)1-x(TMTSF)x]2ClO4 solid solutiOn.