Coupling between the protons and PO ₄ tetrahedra in H ⁺-ion-irradiated TlH ₂PO ₄

We studied hydrogen-bonded TlH ₂PO ₄ (TDP) ferroelectrics treated with proton-beam bombardment. The TDP material was irradiated with a 1-MeV proton beam at a dose of 10 ¹⁵/cm ². To analyze the local microscopic structure of TDP, we conducted ¹H combined rotation and multiple pulse spectroscopy (CRAMPS), nuclear magnetic resonance (NMR), and high-resolution ³¹P NMR measurements. The isotropic chemical shifts of hydrogen and phosphor nuclei exhibited displacive features throughout the antiferroelectric, ferroelastic, and paraelastic phases that were attributed to the interplay of PO ₄ lattice deformation and the microscopic hydrogen bond network. The temperature dependence of the isotropic chemical shift σ _iso in ¹H and high resolution ³¹P NMR revealed that the electronic charge redistribution was induced by proton-beam irradiation and the material's elastic properties. We examined the proton-lattice relationship in terms of the proton's location in a local double minimum well and the displacive character of the PO ₄ lattice.