Core-Shell-Structures in Multiphase Dielectric Ceramics

Abstract

Developments in the field of multilayer capacitors (MLC) still require investigations of the micro‐structure‐property relationships of the dielectric materials. Multiphase ceramic dielectrics with “core‐shell” micro‐structure obviously are best suited for a “flat”, i.e. nearly constant temperature behavior of the dielectric constant (DC), which is of the order of 2000—4000. A general demand is that the DC‐reduction within the temperature range —55 °C to +125 °C should be less than 15% (X7R classification). In addition to this, the sintering temperature should not exceed 1120 °C. The kind of structure, which is finally obtained is influenced by several factors: the composition of the precursor materials, the mixing procedure, the temperature‐time regime during the firing process, and eventually the final annealing treatment. Using barium titanate as core material and mixing it with different perovskite compounds we adopted two different methods of production of the dielectrics, here investigated. They resulted in two different structure forming mechanisms, leading to different micro‐structures.