Interplay between the Charge Transport Phenomena and the Charge-Transfer Phase Transition in RbxMn[Fe(CN)6]y•zH2O

Charge transport and dielectric measurements were carried out on compacted powder and single-crystal samples of bistable RbxMn[Fe(CN)(6)](y)center dot zH(2)O in the two valence-tautomeric forms ((MnFeIII)-Fe-II and (MnFeII)-Fe-III) as a function of temperature (120-350 K) and frequency (10(-2)-10(6) Hz). The complex conductivity data reveal universal conductivity behavior and obey the Barton-Nakajima-Namikawa relationship. The charge transport is accompanied by dielectric relaxation that displays the same thermal activation energy as the conductivity. Surprisingly, the activation energy of the conductivity was found very similar in the two valence-tautomeric forms (similar to 0.55 eV), and the conductivity change between the two phases is governed mainly by the variation of the preexponential factor in each sample. The phase transition is accompanied by a large thermal hysteresis of the conductivity and the dielectric constant. In the hysteresis region, however, a crossover occurs in the charge transport mechanism at T < similar to 220 K from an Arrhenius-type to a varying activation energy behavior, conferring an unusual double-loop shape to the hysteresis.