The conduction behavior of Pr3+ ion-exchanged Na+-”- crystals, with various degrees of exchange, was investigated by means of impedance spectroscopy at temperatures ranging from 300 to 1000K. The Arrhenius plots exhibited a curvature, at about 560K, towards higher activation energies. This was attributed to the onset of lanthanide ion motion. With increasing degree of Pr3+ exchange, the ionic conductivity decreased and the activation energy increased. For a given degree of exchange, the conductivity exhibited a scatter of one or two orders of magnitude and the activation energy was between 0.15 and 0.2eV. These changes were explained in terms of the variable composition, which affected the thickness of the conduction slabs and the ionic distributions. A lower in-plane cation concentration, for a given degree of exchange, led to widened conduction channels and resulted in an increased conductivity and reduced activation energy.

J.Köhler, W.Urland: Journal of Solid State Chemistry, 1996, 127[1], 161-8