STRUCTURAL RELAXATION IN (NH4)(4)LIH3(SO4)(4) SUPERIONIC SINGLE-CRYSTALS

The results of electric conductivity study both on heating and cooling are presented for (NH4)(4)LiH3(SO4)(4) (ALHS) single crystal. At T-s approximate to 415 K the first order transition to the high conducting phase is observed. The electric conductivity curve sigma(1/T) at the first heating reveals high values of activation energy E both above an d below T-s. In the consecutive temperature cycles E is much lower, es pecially in the high conducting phase, and sigma(1/T) in practice ceas es changing after the second heating/cooling cycle. After the first he ating run ALHS becomes a superionic conductor and the resulting struct ure changes originating during the heating, which appear as a mosaic s tructure in X-ray study, are irreversible. The changes are the probabl e reason of vanishing of sigma anisotropy after the first heating run. (C) 1998 Elsevier Science B.V. All rights reserved.