The dielectric constants of a ferroelectric ceramic

Publisher Website
Google Scholar
Abstract
The problem of estimating the dielectric constants of a ferroelectric ceramic from those of the single crystal is tackled theoretically. It is pointed out that conventional formulae, such as those that average the dielectric constant or its inverse, presuppose particular microscopic geometries and lead to great inaccuracies in the case of ferroelectrics. A variational theory is used which gives upper and lower bounds to the ceramic dielectric constants; this being the maximum information obtainable without a detailed knowledge of the microstructure. The results are compared with experiments on tri-glycine sulphate (TGS) and barium titanate. Agreement is good for TGS; but for BaTiO3, which has a very large anisotropy, the bounds are rather wide. Also it is concluded that piezoelectric interactions need to be included to improve the accuracy of the theory.