Ionic conductivity of Na2SO4-Al2O3 composite electrolytes: Mechanism and the role of the preparatory parameters

A moderate increase in the electrical conductivity of sodium sulfate has been obtained by dispersing alumina particles. The largest enhancement in conductivity for furnace-cooled samples is observed for 5.5 and 35 m/o alpha-Al2O3 compositions. For 35 m/o composition, the conductivity increases by more than 1 order of magnitude at 400 degrees C and 2 orders of magnitude at 200 degrees C. In contrast to the understanding based on many composite electrolyte theories, 0.004 mu m alumina brings about the same or even lower enhancement in conductivity as 0.5 mu m alumina. Furthermore, contrary to expectations, negligible enhancement is observed when gamma-Al2O3 is employed. The maximum enhancement in this study is observed for the 4 m/o Al2O3 quenched sample: the conductivity increases by 2 orders for the high-temperature phase and by more than 3 orders for the low-temperature phase, (C) 200