The conductivity was measured in moist air or in H atmospheres, and the ionic transport number was estimated by using a steam concentration cell, a H permeation cell and a fuel cell. It was found that the temperature dependence of the conductivity in moist air differed from that in a moist H atmosphere. The conductivity under reducing conditions increased with time in parallel with a structural change in Ba(Pr0.6Gd0.4)O3, due to O loss from the lattice site. Under moist air conditions, the main conducting species were holes. However, the species changed to protons, oxide ions and holes following structural changes in a reducing atmosphere. It was concluded that ionic conduction occurred due to the change in crystal structure. It was suggested that this peculiarity of the conductivity affected the non-stoichiometric behaviour of Pr in the crystal structure.

Ionic Conductivity of Gadolinium-Doped Barium Praseodymium Oxide. T.Fukui, S.Ohara, S.Kawatsu: Solid State Ionics, 1999, 116[3-4], 331-7