Phenomenological Theory of High Permittivity in Fine‐Grained Barium Titanate

Abstract

The anomalously high permittivity in fine‐grained ceramic barium titanate is explained by the absence of 90° twinning within the grains, giving rise to internal stresses as the ceramic cools below the Curie temperature. Using the Devonshire phenomenological thermodynamic method and a simplified model, the stresses involved are calculated. At these stresses levels, the reduced strain calculated on this model agrees well with X‐ray data for the fine‐grained material. The limitations and possible developments of the proposed model are discussed.