Characterization of Grain Boundaries by IS

While high-resolution transmission electron miCToscopy (TEM) is a powerful technique, it samples only a tiny fraction of the grain boundary area, potentially allowing some grain boundary defects to be missed. A definitive statement as to the absence of grain boundary phases cannot be made—the phases could be too thin or too sparse to detect. For electrically conducting materials, IS averages over the entire sample and thus provides a valuable complement to TEM. 

Further indirect information about the topology of the grain boundary phases can be obtained from the temperature dependence of the quantities and r i,. In crystalline ionic conductors in the extrinsic region, the conductivity is thermally activated and described by  

The error introduced by this assumption is smaller than the spread in the distribution of grain size, that is, about a factor of two. 

Effect of Anisotropy in Grain Shape and Conductivity. In the ceramics discussed so far, the shape and conductivity of the grains were isotropic. This, is not, however, a rule for ceramics. Two examples are given of materials whose conduction or grain structure are anisotropic. 

The experimental conditions were chosen to allow resolution of the grain interior arc over the widest possible temperature range. The conductivity of 5 x 10 Scm at ambient temperature coresponds to a relaxation frequency of the order of 10 Hz. 

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