INELASTIC NEUTRON-SCATTERING STUDY OF PROTON DYNAMICS IN BETA-ALUMINA

Inelastic neutron scattering (INS) spectra from similar to 20 to 3000 cm(-1) of proton containing beta-alumina samples at 20 K reveal well-defined bands below 2000 cm(-1). The spectra of the most hydrated (11Al(2)O(3)-5H(2)O) and less hydrated sample (11Al(2)O(3)-1.3(H3O+)(2)O) correspond to mixtures of two distinct entities. The dominant entity in the latter sample is hydrogen bond free oxonium (H3O+) with tetrahedral symmetry. The dominant entity in the most hydrated sample previously thought to be H5O2+, is better regarded as perturbed oxonium ion. A continuum of INS intensity is attributed to bare protons travelling almost freely along the conducting planes.