SUPERIONIC PHASE-TRANSITION IN RB4LIH3(SEO4)4 SINGLE-CRYSTALS

Derivatographic, dielectric and complex impedance studies of Rb4LiH3(S eO4)4 crystals revealed a superionic phase transition at T(s) almost-e qual-to 448 K. The bulk conductivity rises from 10(-6) to 10(-4) (OMEG Am)-1 at T(s), and the activation energy of conductivity in the direct ion of crystal axes a and b (where a = b for tetragonal symmetry) W(a) = W(b) decreases from 0.94 eV in the low temperature phase to the val ue of 0.27 eV at T > T(s). The analysis of the results of X-ray studie s at room temperature and at 450 K indicates that the fast ion transpo rt, characterized by low activation energy, is related to the delocali zation of the H2 protons in the O(12)-H2-O(24) bonds linking the Se(1) O4 and Se(2)O4 tetrahedra. The ''cogwheel'' mechanism is suggested to be involved in the fast proton transport.