Structure and proton conduction in CsDSO4

Caesium hydrogen sulphate is one of the most extensively studied superproto nic conductors with hydrogen bonds. A first order phase transition, from th e low conductivity to the high conductivity phase, takes place at 414 K. Th e crystallographic structure of both phases has been established using high -resolution neutron powder diffraction. Quasielastic neutron scattering has provided information about the spatial and temporal characteristics of pro ton transport. In the present paper we report the results of reverse Monte Carlo modelling of neutron diffraction (total scattering) data which makes it possible to obtain the diffusion pathways for protons. The results are i n good agreement with the qualitative model for proton transport proposed p reviously; in particular we show clearly that the proton motion is highly c orrelated with the rotation of the sulphate groups. In the low temperature phase we identify a weak correlation between protons and oxygens on the nex t-nearest-neighbour sulphate group which increases with temperature and pro bably drives the phase transition. (C) 1999 Elsevier Science B.V. All right s reserved.