Proton dynamics in hydrogen-bonded systems studied by neutron incoherent scattering

Abstract

The dynamical properties of protons in the hydrogen-bonded ferroelectrics are studied by neutron incoherent scattering technique. In particular, attentions are focused on the so-called ‘‘zero-dimensional'’ hydrogen-bonded systems where the crystals are constructed of isolated dimers containing single hydrogen bond. A model is proposed to describe the dynamics of a single dimer embedded on a phonon sea. The ground state is characterized by the proton self-trapped state or protonic polaron. The low-energy fluctuations of the ground state is identified as phonon-assisted tunneling process of the proton. Neutron scattering function from the protonic polarons undergoing phonon-assisted tunneling is formulated and compared with the experimental results. The possible origin of the large isotope effect is discussed in connection with the proposed model.

Keywords:

• Neutron incoherent scattering
• proton self-trapped state
• protonic polaron
• phonon-assisted tunneling
• hydrogen-bonded ferroelectrics