Indirect correlation between superionc sodiums in $\beta $-alumina -First principles molecular dynamic study-

The atoms are ionized in the ion conductors like the atoms in the ionic crystals, yet either cations or anions are mobile under the electric field unlike the ions in the ionic crystals. The elucidation of the conduction mechanism is essential for the development of the secondary batteries which operate at low temperature. Since the Na-Na correlation peak in superionic $\beta $-alumina has been located at a well separated from the peak position arising from the commensurate sites, the analyses of the origin of the correlation peak allows us to give the nature of the conduction mechanism in conductors. The first principles molecular dynamic study shows that split-interstitial sodiums on mid-oxygen produce the correlation. This is an indirect correlation between the superionic sodiums and is consistent with low Haven's ratios in the $\beta $-alumina.