Grain size effects on activation energy and conductivity: Na-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"><mml:mrow><mml:mi>β</mml:mi></mml:mrow></mml:math>″-alumina ceramics and ion conductors with highly resistive grain boundary phases

Abstract As for many ion conductors, the electrical conductivity of polycrystalline Na- β ″-alumina reported in literature varies by over two decades at a given temperature. This is often ascribed to combination variable effects related grain size, composition, phase content, porosity and impurities, but dominating factors are rarely identified. Based on an extensive set Li2O-stabilized ”-alumina ceramics sintered different conditions, we evaluate sample series with constant composition content conductivity. The total samples features pronounced non-Arrhenius temperature dependence. To explain this effect, present simple microstructural model describing influence size Arrhenius-type conductors highly resistive boundaries as second phase. We show that further predicts linear relationship between effective activation energy temperature, which also observe experimentally. this, able identify extent variations data may be explained only. same relates fundamental transport properties corresponding boundary phases experimentally observed relationship, discuss how these parameters can extracted, e.g. taking into account determined data. Comparison indicates additional such changes percolation coarse grains relevant properties. Our findings relation applicable general.