Structural phase transition, ionic conductivity, and dielectric investigations in K3H(SO4)2 single crystals

Optical observation, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) measurements have been carried out on K3H(SO4)(2) crystal in the temperature range between 25 and 300 degreesC. Domain structures of K3H(SO4)(2) were observed at room temperature which are the same as those observed in other member of A(3)H(XO4)(2) which show ferroelasticity. Two endothermic peaks of DSC were found at around 206 and 269 degreesC. In this temperature range, the result of TGA indicate the loss of weight. It supports that partial dehydration is most probable. The first peak can be accounted for the dehydration reaction on the surface of crystals, and the second peak corresponds to the melting of the sample crystal. The impedance measurements were performed as a function of both temperature and frequency. The electrical conductivity increases with increasing temperature and the sample crystal becomes a fast ionic conductor at the temperatures above 206 degreesC. The high conductivity of the crystal is caused by the increases of the defects due to the dehydration. The dielectric properties of the sample crystal were studied by the impedance spectroscopy. (C) 2003 Elsevier Science Ltd. All rights reserved.