COPPER(2-ANION SALTS() STATES AS MEDIATORS FOR METALLIC CONDUCTIVITY IN DCNQI RADICAL)

By conductivity, ESR, and susceptibility measurements on fully and par tially deuterated dimethyl-DCNQI (2,5-Me(2)DCNQI, DCNQI = N,N'-dicyana quinonediimine) radical ion salts with copper as counterions, we have found giant phase transitions from a metallic to a semiconducting stat e at T-c approximate to 70 K which are accompanied by a steplike incre ase in the susceptibility and a change from a Pauli- to a Curie-Weiss behavior. Concomitantly, below T-c a narrow ESR signal of CU2+ spins o ccurs which is absent in the metallic range. Approaching a 3d-antiferr omagnetic transition at 7 K, the ESR line broadens and is lost. We exp lain the peculiarities of these copper salts via the coexistence of co nducting and relaxed areas. In the relaxed areas the previously fluctu ating CU2+ states are localized and ordered, suppressing the conductiv ity. The coincidence (in temperature) of charge ordering and the devel oping of a charge density wave are responsible for the giant changes i n sigma and chi in the deuterated salts.