Neutron scattering study of the dynamics of hydronium lion in (H3O)Zr2(PO4)3 nasicon across the order-disorder transition

Neutron incoherent scattering measurements were performed on (H3O)Zr-2(PO4)(3) Nasicon by the quasi-elastic spectrometer IN13 (ILL, Grenoble), to characterize the slow proton dynamics of the H3O+ ion in this compound. Both quasi-elastic and elastic data were collected at temperatures above and below the order-disorder phase transition (T-c = 177 K). Quasi-elastic contributions with peak full widths at half-maximum of 12 and 33 mueV (corresponding to proton jumping times of 110 and 40 ps) were determined at 150 and 200 K, respectively. This supports a confined proton motion both above (faster) and below (slower) the transition temperature, consistent with the full and partial disorder of the hydronium ion found in the high-T rhombohedral and low-T monoclinic phase, respectively, by previous neutron diffraction experiments. Results of the elastic scans vs momentum transfer and temperature are analyzed and discussed.