NMR and impedance study of H⁺-ion irradiated TlH ₂PO₄

The H⁺-ion treatment effect on TlH₂PO₄, a KH₂PO₄ (KDP)-type ferroelectrics, was studied by nuclear magnetic resonance (NMR) and AC dielectric measurements. A sample of TlH ₂PO₄ was irradiated by 1-MeV H⁺ ion beams to a dose of 10¹⁵ ions/cm². The irradiation changed the hydrogen-bond geometry, presumably affecting the order-disorder proton dynamics. The deformation of the PO₄ tetrahedra was identified by the isotropic chemical shift and the full width at half maximum (FWHM) of the high-resolution ³¹P NMR spectra. A prominent decrease in the dielectric constant was also observed after the irradiation. The macroscopic and microscopic changes due to the irradiation are discussed in the light of the proton dynamics.