Abstract
Microstructural features such as pores, secondary phases and inclusions can significantly alter the electrical response of ceramics. Here we present a morphological finite element approach to better understand the effect of such microstructural defects on the behaviour of electroceramics. We generate irregular three-dimensional geometric models with realistic features and controllable parameters providing a method of characterising their morphology using sphericity, signifying irregularity, and projected area. The inclusion models are solved for their electrical response for changes in the material properties, making the feature either insulating or conductive in relation to the surrounding material. The electric field distribution analysis indicates the irregularity has a significant effect on the electric response, increasing the field concentration up to 12 times more than the applied field. Plotting the electric field distribution using a Weibull cumulative Probability Distribution Function we have also estimated the breakdown strength of the material. This shows that a material's breakdown strength can be reduced to 55% for an 87.5% dense sample if the inclusion is insulative and has a low sphericity or high projected area. This can be further reduced to only 40% if the feature is more conductive than the ceramic.
Highlights
Due to excellent dielectric properties and high thermal stability, granular electro-ceramics are employed in the fabrication of devices such as multilayer ceramic capacitors, positive temperature coefficient of resistance thermistors, piezoelectric sensors and transducers [1,2]
To highlight the complexity in the microstructural features that can be formed in ceramic materials during processing [6] we look at the SEM images of Yttria-stabilized zirconia (YSZ) processed at 1350 °C as a case study
A computer-aided approach was used to replicate the irregular geometry of single intra-grain inclusion for electroceramics
Summary
Due to excellent dielectric properties and high thermal stability, granular electro-ceramics are employed in the fabrication of devices such as multilayer ceramic capacitors, positive temperature coefficient of resistance thermistors, piezoelectric sensors and transducers [1,2]. The critical threshold value is determined by the average electric field within upper 30% of all the electric fields measured in the ceramic layer This is obtained from a probability distribution function and the reciprocal of this value can be linked to the breakdown strength of the material. Accurate imitation of these features will improve our ability to predict the electrical behaviour. The electric field distributions obtained from solving them through finite element analysis are statically analysed to achieve a comprehensive understanding of the field enhancement generated by irregular shaped features and their influence on the breakdown strength
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