Diffusion and conductivity in Na+Cd2+ β alumina
The diffusion coefficient for Na+ at 335°C in single crystals of beta alumina has been measured as a function of increasing divalent cadmium concentration. The conductivities of the same compositions were determined over the temperature range of 25–400°C. The results reveal that the conductivity in these mixed crystals actually increases when small (<20%) concentrations of the sodium ions are exchanged for cadmium. The data are consistent with the expected interstitialcy mechanism for sodium ion diffusion when the concentration of ions is greater than 1/Beevers-Ross site and a vacancy mechanism when the concentration of ions is less than 1/Beevers-Ross site.