Proton magnetic relaxation and ionic conductivity of ammonium hydronium β″-alumina

The protonic motion in NH⁺₄-H⁺(H₂O)_nβ″ -alumina wasstudied by measurements of proton spin-lattice and spin-spin relaxation times. The results show that two types of NH⁺₄ reorientation, that is, three-fold reorientation about its unique C₃ axis and tumbling motion as a whole, occur below room temperature. Above room temperature a fast proton translational diffusion was apparent, and its activation energy was estimated to be 36 kJ/mol. On the other hand, the conductivity measured on a pressed sample by an ac method is strongly humidity-sensitiveand changes by more than five orders from 0 to 100% relative humidity. The activation energy also may be humidity-sensitive. Its value was 73 kJ/mol for the sample equilibrated at 90°C in a dry nitrogen atmosphere.