Study of Na + motions in βAl 2O 3 by quasi-elastic neutron scattering

Abstract

The commom non stoichiometric Al 11O 17+x/2 Na 1+x (x = 0.25) Alumina in the powder state has been studied by quasi elastic neutron scattering at -196, 44, 200, 300 and 400°C using incident wave lengths of 4.1 and 5.1 Å, the time of flight spectra have been corrected in S(Q,W) quasi elastic spectra and inelastic frequency distribution P(Q,W)(Q→O) in the energy range 1–80 meV (8–650 cm −1). Quasi elastic contribution is clearly evidenced above room temperature; it has been fitted with different jump models based on structural data. It is shown that even at 400°C, only 15 % Na cations are mobile on the time scale of IN6 (τ < 10 −10 s). Two kinds of motions have been characterized : localized jumps (τ ∼ 10 −12 s, activation energy ∼ 0.050 eV) and long range diffusion (D ∼ 0.005 eV, activation energy 0.25 eV).