Metal-ceramic composites (cermets) are currently used in electronics, aerospace applications and other fields, due to their adjustable electrical properties, high hardness and superior thermostability. The presence of metal components into the ceramic matrix provides interesting electromagnetic properties, making them attractive for microwave absorption, electromagnetic shielding, filters and capacitors. The present work aimed to investigate xAg – (1-x) BaTiO₃ cermets in searching for compositional and microstructural optimisation to provide either giant permittivity below the percolation limit or metacomposite properties (e.g. negative permittivity).
Finite element calculations demonstrated that dielectric, ferroelectric and tunability properties can be tuned through inhomogeneous field distributions at the interfaces between metal-ferroelectric by creating regions subjected to high fields and generating enhanced electrical responses [1].
The Ag-BaTiO₃ composite powders have been prepared either by simple mixing of BaTiO₃ and Ag micropowders or by precipitation of Ag nanoparticles from AgNO₃ directly onto BaTiO₃ grains in order to provide different types of final microstructures after sintering. The powders have been sintered at temperatures around and above the silver melting point (900°C – 1300°C/2h) in open atmosphere. The resulting ceramics have relative densities of 76% – 96%, with ceramic grain sizes in the range of 350 nm - 3mm and bi-modal distribution of silver filler, with both fine Ag inclusions and large agglomerates embedded into the ceramic matrix. The frequency and temperature dependence of the dielectric, conductive and electromagnetic properties have been investigated and discussed as a function of Ag filler addition and resulted microstructures.
 
 
[1]. I. Turcan et al., J. Eur. Ceram. Soc. 38, 5420-5429 (2018)
 
Acknowledgements: This work was supported by the Romanian UEFISCDI PN-III-P4-ID-PCE-2020-1988 grant.