Charge carriers in grain boundaries of 0.5% Sr-doped LaNbO4

The grain boundary and grain interior conductivities of La0.995Sr0.005NbO4 − δ have been studied by means of impedance spectroscopy at 400 °C after quenching from different pH2O, pO2 and temperatures. Effects of H/D isotope shifts on the conductivity were, moreover, determined from 400 to 480 °C under isothermal conditions. The microstructure and composition were characterized by scanning electron microscopy and transmission electron microscopy. On basis of the effects of pH2O and H/D isotope exchange on the grain boundary and grain interior conductivities, it is concluded that protons are the major charge carrier and, furthermore, that they are relatively more predominating in the grain boundaries than in the grain interior. Ionic transport in the grain boundaries is discussed in terms of the grain boundary core–space charge layer model.