Abstract
Al2O3/graphene and BaTiO3/graphene composites with different concentrations of the conductive second phase, both below and above the percolation threshold, were prepared by the traditional ceramic processing route followed by spark plasma sintering. It is shown that the addition of graphene pins the grain growth of the ceramic matrix grains, leading to a change of the microstructure at low filler concentrations. As a consequence, the composites exhibit two percolation thresholds and their dielectric properties are not only determined by the dielectric properties of the constituents and their relative fractions but also the microstructure of the composite must be considered. Additionally, a giant increase of the dielectric constant has been found around the percolation thresholds in barium titanate–graphene composites. In particular, values of the dielectric constant up to 45,000 and 15,000 were found at 1 kHz in composites containing 0.4 and 0.6 wt. % graphene, respectively.
Highlights
It is increasingly being recognized that new applications for materials require functions and properties that are not achievable with monolithic materials
We report how the dielectric properties of ceramic matrix composites are determined by the changes in the microstructure due to the introduction of a conductive second phase of graphene
In summary, it has been shown that low concentrations of the filler produce a strong change in the microstructure of the ceramic matrix composites, on the average grain size of the ceramic matrix
Summary
It is increasingly being recognized that new applications for materials require functions and properties that are not achievable with monolithic materials. The dielectric properties of insulator–conductor materials, such as conductivity and permittivity, show a critical behavior when the fraction of the conductive phase reaches the percolation threshold [6, 7], which has been the subject of interest of many studies [8,9,10]. It has Fernández-García et al Nanoscale Research Letters (2015) 10:216
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