Structural and proton-dynamical effects in a proton-irradiated KH2 PO4 single crystal

A KH2 PO4 (KDP) crystal, irradiated by a 1 MeV hydrogen ion beam to a dose of 1015 ions/cm2, was studied by means of x-ray diffraction (XRD), H1 nuclear magnetic resonance (NMR), and dielectric constant measurements. The XRD pattern for the a -cut KDP crystal revealed a decrease in the lattice constant along the a axis after the proton irradiation. According to the H1 NMR spin-lattice relaxation rate measurements, the proton irradiation gave rise to reduction in the activation energy in the paraelectric phase, from 0.42 to 0.28 eV, in agreement with the temperature dependent second moment measurements indicating the proton motion is more activated after the proton irradiation. Besides, analysis of the temperature-dependent dielectric constants using a mean-field approximation revealed a change in the hydrogen bond induced by the proton irradiation.