Study of molecular motion by1H NMR relaxation in ferroelectric LiH3(SeO3)2, Li2SO4·H2O, and LiN2H5SO4single crystals

The proton NMR line widths and spin-lattice relaxation rates, T₁⁻¹ , of ferroelectric LiH₃(SeO₃)₂ , Li₂SO₄·H₂O , and LiN₂H₅SO₄ single crystals were measured as a function of temperature. The line width measurements reveal rigid lattice behavior of all the crystals at low temperatures and line narrowing due to molecular motion at higher temperatures. The temperature dependences of the proton T₁⁻¹ for these crystals exhibit maxima, which are attributed to the effects of molecular motion by the Bloembergen - Purcell - Pound theory. The activation energies for the molecular motions of ¹H in these crystals were obtained. From these analysis, ¹H in LiH₃(SeO₃)₂ undergoes molecular motion more easily than ¹H in LiN₂H₅SO₄ and Li₂SO₄·H₂O crystals.