Influence of inter-chain correlations on proton ordering in MeHXO4 protonic conductors

Energy spectrum and thermodynamics of the proton subsystem of the crystal with chains of hydrogen bonds are investigated. The consideration is based on the orientational-tunneling model, which includes two types of proton transfer. The strong short-range interactions and the influence of the internal ordering field arising due to the inter-chain correlations are taken into account. It is shown that under certain conditions the uniform proton distribution along the chain becomes unstable. A possible explanation of the precursor effect observed in the CsDSO4 crystal at temperatures below the superionic transition point is proposed.