IONIC-CONDUCTIVITY IN NA+ PR3+-BETA''-AL2O3 CRYSTALS/

The conduction behaviour of Pr3+ ion-exchanged Na+-beta ''-Al2O3 cryst als varying in degree of exchange (xi) has been investigated by impeda nce spectroscopy in the temperature range 300-1000 K. The Arrhenius pl ots show a curvature at about 560 K to higher activation energies expl ainable by the beginning of lanthanide ion motion. With growing Pr3+ e xchange, the ionic conductivity (sigma) is lowered combined with an in creasing activation energy (E(a)). For a given degree of exchange, sig ma scatters about one to two orders of magnitude and E(a) within 0.15- 0.2 eV. These deviations can be understood by the different crystal co mpositions influencing the thickness of the conduction slabs and the i onic distributions. A lower in-plane cation concentration (for a given xi) induces widened conduction channels, resulting in an increased co nductivity and reduced activation energies. (C) 1996 Academic Press.