Abstract

Electrical Impedance Spectroscopy (EIS) was used to study the electrical properties of the (1 - x)CsHSeO4-xKHSeO(4) binary system with concentrations x = 0.0 and 0.1. The results show a higher proton-conduction phase above 80 degrees C for both concentrations, however, while DC conductivity of CsHSeO4 shows a gradual change to higher values in the 80-118 degrees C temperature range, the 0.9CsHSeO(4)-0.1KHSeO(4) concentration reveals an abrupt change at about 80 degrees C to an intermediate temperature phase. The observed behavior for the doped sample was modeled using a trial free-energy density, based on the concentration of mobile ions, that takes into account the formation of defects, configurational and phonon entropies, and defect-defect interactions. By minimising the free-energy density one obtains two roots for the carrier concentration at a given temperature, which corresponds to a stable and metastable configuration. It is possible to characterise the phase behavior of the system by means of temperature and two model parameters, which depend on the crystalline properties of the system, but not on temperature. One can successfully explain the conductivity behavior of the system by changing the model parameters if it is assumed that its variations are due to the carriers density.