Proton jump diffusion dynamics in hydrated barium zirconates studied by high-resolution neutron backscattering spectroscopy

Abstract

We report results from high-resolution neutron backscattering experiments on hydrated samples of the proton conducting perovskite BaZr_1−xM_xO_3−x/2 with M = Sc and Y for x = 0.1, and M = In for x = 0.1, 0.2 and 0.25. The sampled wave vector range of up to 1.9 Å⁻¹ and energy resolution of less than 1 μeV allowed the identification of a jump diffusion process of protons in the samples. By monitoring the intensity of elastically scattered neutrons S(Q, ℏω = 0) upon heating the samples from base temperature 2 K up to about 550 K the onset temperature T_c of the diffusive process was established. Thereby characteristic dependences of T_c on the type of dopant atom M and on the dopant level x were found with T_c increasing along the sequence of x from less than 200 K in M = Sc, Y and In with x = 0.1 up to about 320 K in M = In with x = 0.25. The formfactor of the diffusive process was examined on one hand by monitoring the intensity of neutrons scattered inelastically with a fixed energy of 2 μeV as S(Q, ℏω = 2 μeV), and on the other, by monitoring the dynamic structure factor S(Q, ℏω) within the dynamic range of ±25 μeV. We have successfully approximated the data by established models of jump diffusion with a preference for the Chudley–Elliot model [C. T. Chudley, R. J. Elliot, Proc. Phys. Soc., 77, 353, (1961)]. Any of the applied models featured a characteristic jump distance of about 3 Å. Diffusion constants D and activation energies E_a were computed from temperature scans of the moderately In-doped compounds (x = 0.1 and 0.2). D takes on values within the range 1–5 × 10⁻⁷ cm² s⁻¹ at the highest applied T of about 550 K and E_a increases from about 40 to 120 meV along the sequence of x.