SPECIFIC-HEAT OF TSEF-TCNQ

We have measured the specific heat of single crystals of TSeF-TCNQ. An omalies are observed at T-a = 28 K and T-b = 33 K, indicating that the re are two phase transitions, presumably reflecting the separate conde nsation of the charge-density-wave on the TSeF and TCNQ conducting cha ins. The total increase of the specific heat on cooling through both t ransitions is larger than the value estimated from mean-field theory, as expected for transitions in a quasi-one dimensional material, but, because of the proximity of the two transitions, it is not possible to unambiguously determine the specific heat baseline and hence the magn itude of the specific heat step. A sharp peak in specific heat is also observed at T-a; if the entropy contained in this peak is to be assoc iated with locking of the charge-density-wave phases on the two conduc ting chains, its large size implies a surprisingly small phase coheren t volume. (C) 1997 Elsevier Science Ltd.