Dynamical Properties of Protons in KH₂PO₄ Studied by Incoherent Neutron Scattering

Abstract

Neutron incoherent scattering experiments covering wide energy-momentum space were carried out by utilizing both pulsed neutron source and steady neutron source, in order to elucidate the dynamical properties of the protons in KDP (KH₂PO₄). In the paraelectric phase, no inelastic peaks corresponding to the excitation of the proton tunneling mode was observed within the limit of the instrumental resolution. Instead, strong quasi-elastic scattering was observed extending in a wide energy-momentum space. The experimental results are analyzed consistently based on the `order-disorder' model throughout T_c. However, in order to get reasonable fit for the energy spectra in the paraelectric phase, we have to assume an extraordinary value for the relaxation time of the proton hopping motion as 3× 10^-13, sec, which is of the order of the inverse of the averaged phonon frequency.