Behavior of strontium titanate ceramics in reducing conditions suggesting enhanced conductivity along grain contacts

In reducing conditions the resistance of dense strontium titanate ceramic samples decreases markedly with decreasing average grain size. This trend is interpreted on assuming enhanced conductivity along grain contacts in parallel with a RC bulk term. The temperature dependence is consistent with this model and indicates that the bulk may still control the overall behavior at sufficiently high temperatures (typically for T>700 °C). The resistivity of fine grained porous samples is intermediate between the results obtained for fine grained dense samples and dense samples with large average grain size. An extended model is thus proposed to describe the behavior of porous samples by assuming a series association of isolated channels connected by the interior of adjacent grains.