AC conductivities at 5 Hz-10 kHz and 78 K up to room temperature of bis- (ethanolammonium) Co2X6, and bis- (ethanolammonium) Cu2X6, X=C1 and Br are reported. At high temperatures, band type conduction prevails for all dimers. In the low temperature range T< 200 K the (Co2Br6)-2 dimer conducts via small polarons and the other three dimers conduct via quantum mechanical tunneling. The obtained relaxation times for the different dimers were found to be 1.1 • 10-14 s. The frequency dependence follows the universal power law σac (ω) = Aωs. The exponent s and the pre-factor A were found to be very sensitive to the phase transitions, with 5 showing a minimum or maximum at the transition temperature. Changes in the conduction mechanism are reflected by abrupt changes in the variation of the pre-factor A vs 1/T relation. The conduction is found to depend on the type of the halide ion rather than on the transition metal ion.
PACS #76, 74.