New functional properties driven by nanoscale interface reactions in magnetoelectric ceramics produced from core-shell Fe2O3 and BaTiO3 powders

The nanoscale coating of particles of a material with a dissimilar compound is an effective tool to engineer its surface, microstructural characteristics and functional properties. The method of using core-shell powders followed by an appropriate method of sintering is a very successfull route to obtain desired microstructures with various degrees of connectivity in ceramic composites. Core-shell multiferroic nanocomposites formed by a magnetic core ( -Fe2O3) and BaTiO3 ferroelectric shell were prepared and then densified either by classical sintering at various temperatures (10500C- 11500C) or by spark plasma sintering [1]. By employing various sintering strategies, dense and homogeneous ceramics were produced with: (ii) di-phase compositions with fully isolated hematite regions within a BaTiO3 matrix (0-3 connectivity), (ii) multi-phase compositions, as result of the interface reactions between constituents. Besides the properties of the parent materials Fe2O3 and BaTiO3, variable amounts of secondary phases (Fe3O4, BaFe12O19 and Ba12Fe28Ti15O84) have driven to new functional properties in the ceramic composites. Dielectric, tunability and magnetic properties were determined and discussed in correlation with the sample microstructures, composition and degree of connectivity. The ceramics show interesting dielectric characteristics, with dielectric constant of 100-300 and low losses by comparison with BaTiO3-based magnetoelectric composites produced by other methods and reduced hoping conductivity contribution due to the isolation of the low-resistivity magnetic phase [2]. In addition, dielectric tunability was determined for the best dielectric composites and multipolar contributions to the dielectric non-linearity were found. Peculiar magnetic properties, including "wasp-waisted" constricted M(H) loops were determined as result of the formation of magnetic phases with contrasting magnetic coercivities (hard and soft phases). The present results demonstrate the usefulnessof the core-shell approach in driving new functional properties in multifunctionalcomposites by an appropriate control of the in situ solid-state nanoscale interface reactions. Acknowledgements: This work was supported by the Romanian CNCSISPCCEID-76 grant under the RAMTECH centre. References: [1] M.T. Buscaglia et al., Chem. Mater. 22, 4740-4748 (2010) [2] L.P. Curecheriu et al., J. Appl. Phys.107, 104106 (2010) [3] A. Stancu et al., Appl. Phys. Lett. 83, 3767-3669 (2003).