From core-shell particles to functional ceramics and composites

Core-shell particles represent an alternative to the conventional mechanical mixing method for the preparation of functional ceramics with local graded structure and composites with 0-3 connectivity. Ferroelectric, antiferroelectric, paraelectric and magnetic compounds can be combined together to obtain new or improved functionalities, including flat temperature dependence of permittivity, tunability, multiferroic behaviour, etc. The final microstructure and properties are strongly determined by the extent of interdiffusion between core and shell and the possible formation of intermediate compounds at the phase boundary. To better preserve the core-shell structure in the final material and minimize interface reactions, densification is often performed by spark-plasma sintering or similar field-assisted sintering methods. These rapid densification techniques offer the possibility to fabricate non-equilibrium or metastable structures and composites. The presentation will be focused on some representative examples about the synthesis of core-shell particles such as BaTiO3@Fe2O3, SrTiO3@BaTiO3, (Pb,La)(Zr,Ti)O3@BaTiO3 as well as the microstructure and properties of the final ceramics and composites. It will be shown that the composites obtained from the core-shell powders have distinct properties in comparison to the parent phases and materials obtained by mechanically mixed powders.