Internal Friction and Sodium Transport in Beta Alumina

Internal friction peaks near 100 K were observed for melt-grown single-crystal sodium β-alumina with a stress at 12 and 16 kHz. These data, combined with those of Barmatz and Farrow, produced limiting values for the activation energy and preexponential factor for the relaxation time, viz. 20 kJ/mol and 5.6×10−16 s and 23 kJ/mol and 7.4×10−18 s. Split-interstitial Na+ions on mid-oxygen sites could produce these peaks, but not simple interstitials on anti-Beevers-Ross sites. A relaxation mode calculation is given for the relaxation frequency in the internal friction experiment and for the electrical conductivity in the conducting plane for the split interstitial model.