Correlation between impedance spectra of bulk ceramics and films with in-plane configuration

Strontium titanate is an interesting model electroceramics with grain boundary controlled properties. However, the relative role of grain boundaries may be significantly different in bulk ceramics and in films. Under oxidising conditions, impedance response of bulk ceramics can be described by series association of bulk and grain boundary contributions, which are distinguished based on major differences in relaxation frequencies. This allows de-convolution over relatively wide temperature ranges with standard impedance meters. In this case, one finds reasonably good correlations between microstructural effects and grain boundary behaviour. However, one finds major differences between those spectra and corresponding impedance spectra obtained for in-plane measurements of films. This may be partially accounted for by major increase in the equivalent thickness/area ratio as well as microstructural changes. In addition, the substrate may affect the results by significant leakage, and by stray capacitance effects exerted by a combination of substrate and experimental equipment.