Superprotonic conduction and ferroelectricity in addition cesium sulfate tellurate Cs2SO4.Te(OH)6

Dielectric investigations in the temperature and frequency ranges 300-600 K and 10(2) - 1.3 x 10(7) Hz, respectively, show that cesium sulfate tellurate Cs2SO4. Te(OH)(6) (CsSTe) exhibits two phase transitions at 490 and 500 K. The a.c. complex impedance measurements performed on CsSTe material show an important level of conductivity at high temperature, attributed to the motion of H+ proton. This behavior is in agreement with the presence of a superionic protonic phase transition in CsSTe material at 500 K. This assignment was confirmed by the analysis of the M " /M " (max) spectra. The temperature dependence of is an element of (')(r) and tan delta indicates that the anomaly at 490 K is attributed to a ferroelectric-paraelectric phase transition. Crystallographic studies show that this material presents a non-centrosymmetric space group at room temperature which is in agreement with our last deduction. (C) 2001 Elsevier Science Ltd. All rights reserved.