Kernresonanz-und leitfähigkeitsmessungen zu diffusion und fehlordnung in LiBr

Electrical conductivity and nuclear magnetic relaxation rates were measured with pure and doped LiBr between 400 K and the melting point (824 K). Prevalent intrinsinc disorder was observed down to 470 K. The degree of thermal disorder is 5.10⁻⁷ at 470 K and 5.10⁻³ at the melting point. From the relaxation rates of ⁷Li, which are caused by Li-diffusion and nuclear dipole interaction, mean jump frequencies of the cations are derived. Conductivities calculated from these frequencies for a jump process via neighbouing cation vacancies are in perfect agreement with directly measured conductivities. From relaxation rates of ⁸¹Br with MgBr₂-doped crystals jump frequencies of vacancies were obtained which are again in good agreement with those derived from the conductivity data. The energies resulting from the measurements are (0.43 ± 0.03) eV for migration of cation vacancies and (1.46 ± 0.05) eV for thermal disorder. From motional narrowing of the ⁸¹Br absorption line the jump frequency of the anions is obtained, which is much smaller than for the cations. Since this motional narrowing is not influenced by any doping, it is concluded that anion transport mainly occurs via pairs of cation and anion vacancies.