Polarizability Enhancement of Ionic Conductivity for A1+ in A1+M2X6 Series

The ionic conductivity of A1+ is studied in the isostructural series of the general formula A1+M2X6 where A1+ is Rb, Cs, or Tl; M is Ta, Nb, or W; and X is O or F. High polarizability of either A1+ or the (M2X6)1- framework enhances the ionic mobility of A1+. Thus although Tl1+ is essentially the same size as Rb1+, the mobility of Tl1+ is much higher in a given (M2X6)1- framework. This is attributed to the higher polarizability of Tl1+. The polarizability of the (M2X6)1- framework is related to the polarizability of M—X bonds. The influence of polarizability in β-alumina and anion conductors is also discussed.