Dynamic disorders and its relaxation in organic superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

In this paper, we report direct evidence of dynamic structural disorders introduced by quenching a crystal of charge transfer salt kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br superconductor from high temperatures to 77 K. The sample quenched from different high temperatures relaxes to an equilibrium state with a single relaxation time constant. The magnitude of the relaxation amplitude is dependent on the quenching temperature up to 140 K, above which all relaxation curves overlap with each other. The results suggest strongly that the 140 K is associated with the onset temperature of the order-disorder transition of ethylene groups and the transition is responsible for the anomalous lattice expansion observed at this temperature. (C) 1998 Elsevier Science Ltd. All rights reserved.