Influence of Core-Shell Grains on the Internal Stress State and Permittivity Response of Zirconia Modified Barium Titanate
Abstract
Ceramic multilayer capacitor formulations based on BaTiO3 can be chemically or physically modified to exhibit temperature-stable dielectric behavior over the temperature range -55C to 125C. The stability can result either from chemical substitution in the ceramic, from a small-grained microstructure, or from the presence of core-shell grains which may result from chemical inhomogeneities. Heywang, described the basic structure of these latter materials as being comprised of a microstructure made up of biphasic grains (i. e., core-shell grains). BaTiO3 modified with grain boundary resident ZrO2 results in substantial inhomogeneities in the microstructure when sintered at 1320C for 2h. These inhomogeneous regions were seen as core-shell grains in the microstructure and were accompanied by an increase in the internal stress level. The shells had a variable composition (BaTi1-xZrxO3) and a tetragonal structure. An expansion mismatch between the core and the shell placed the core in compression resulting in a decrease in the c lattice parameter and a pseudo- cubic structure. The combination of core-shell grains and increased internal stress resulted in an essentially flat permittivity response with temperature, a condition consistent with a distribution of Curie points within the ceramic. Keywords: Ceramics; Dielectrics.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1989
- Accession Number
- ADA211245
Entities
People
- R. C. Buchanan
- T. R. Armstrong
Organizations
- University of Illinois Urbana–Champaign