Nuclear magnetic relaxation study of protonic motion in hydronium beta″-aluminas

Abstract

The temperature dependence of proton T 1 and T 2 was measured at 20 MHz for polycrystalline hydronium beta″-alumina, its partially dehydrated phase, and potassium-hydronium beta″-aluminas. The protonic diffusion was recognized by motional narrowing of T 2 data for all samples. The activation energies of the diffusion are 19 and 24.5 kJ/mol for the fully hydrated and partially dehydrated hydronium beta″-alumina, respectively, indicating that the protonic translation becomes slower on dehydration. The proton relaxational behavior in potassium-hydronium beta″-alumina is similar to that of the hydronium analog, but its large activation energy (24 kJ/mol), suggests that the potassium ion on the conduction plane decreases the proton conductivity by acting as a blocking ion.