Dielectric and AC ionic conductivity investigations in K3H(SeO4)2 single crystal

Optical observation under the polarizing microscope and DSC measurements on K3H(SeO4)(2) single crystal have been carried out in the temperature range 25-200degreesC. It reveals a high-temperature structural phase transition at around 110degreesC. The crystal system transformed from monoclinic to trigonal. Electrical impedance measurements of K3H(SeO4)(2) were performed as a function of both temperature and frequency. The electrical conduction and dielectric relaxation have been studied. The temperature dependence of electrical conductivity indicates that the sample crystal became a fast ionic conductor in the high-temperature phase. The frequency dependence of conductivity follows the Jonscher's universal dynamic law with the relation sigma(omega) = sigma(0) + Aomega(n), where omega is the frequency of the AC field, and n is the exponent. The obtained n values decrease from 1.2 to 0.1 from the room temperature phase to fast ionic phase. The high ionic conductivity in the high-temperature phase is explained by the dynamical disordering of protons between the neighboring SeO4 groups, which provide more vacant sites in the crystal. (C) 2002 Elsevier Science Ltd. All rights reserved.