Temperature dependence of oxygen ion transport in Sr plus Mg-substituted LaGaO3 (LSGM) with varying grain sizes

The conductivity of La0.90Sr0.10Ga0.90Mg0.10O2.90 (LS10GM10) was measured from 1430 K to room temperature by combining four-point van der Pauw measurements (high temperatures) with two-point impedance spectroscopy (intermediate and low temperatures). At intermediate and low temperatures, samples with different grain sizes were studied in order to look for fast conduction in the gain boundaries (in parallel). No fast grain boundary transport was, however, detected. The conductivity data were modeled well by a defect association model involving Mg dopant-oxygen vacancy clusters. The derived entropy and enthalpy of association were -73 J (K mol)(-1) and -80 kJ mol(-1) for this association pair and the enthalpy of migration of the unassociated oxygen vacancies was 58 kJ mol(-1). The model was tested on measured high to intermediate temperature conductivities of LaGaO3 with lower dopant concentrations. The model was found to describe the conductivity of La0.95Sr0.05Ga0.95Mg0.05O2.95 (LS5GM5) well, but it failed to describe the intermediate temperature conductivities of our sample of La0.99Sr0.01Ga0.99Mg0.01O2.99 (LS1GM1). The influence of phase transitions on the temperature dependency of the conductivity is discussed. (C) 2004 Elsevier B.V. All rights reserved.