Influence of stoichiometry and the nature of the spinel-block stabilizing element on proton transport behavior in solid electrolytes with the β″-alumina structure

Abstract

As an extension of prior work done in this laboratory on proton transport in NH + 4-H 3O + β″-alumina, we reported here new proton diffusion coefficient and conductivity measurements on: (a) magnesia-stabilized NH + 4-H 3O + β″-alumina crystals with a substantially different stoichiometry than that reported earlier; and (b) NH + 4-H 3O + β″-gallate crystals where stabilization of the as-grown crystal involves sodium substitution in the spinel block. Proton diffusion coefficients of both compounds were measured over the temperature range 300–450K with the aid of a pulsed field gradient NMR technique, whereas a complex admittance method was used to obtain the protonic conductivities reported here for the same temperature interval. In the light of the present and earlier observations of protonic transport behavior, ideas were discussed concerning; (a) possible mechanisms of proton transport and (b) the role played by stoichiometry and the type of spinel-block stabilizing element in these β″ materials.