Porous ceramic structures are a relatively young research field, with the first patent on porous ceramics issued in 1963 and several methods proposed to reach high porosity levels. The amount and morphology (shape, connectivity, alignment) of the pores play an important role in determining the effective properties of porous ceramics. In recent years, an increasing interest on the effect of porosity on the properties of functional ceramics, such as dielectric permittivity, dielectric tunability, thermal conductivity and piezoelectric coefficients, is testified by several explorative papers. This work is aimed at understanding how the pore morphology affects the dielectric properties of porous ferroelectric barium titanate - BaTiO3 - ceramics.
Porous ceramics with controlled porosity, i.e. amount, size and shape of the pores were fabricated by using the sacrificial template method, in which porosity is obtained by the thermal treatment of a mixture of the ceramic powder and suitable pore former materials, which burn leaving pores. Porous BaTiO3 ceramics were fabricated using corn starch and/or graphite as pore formers (30 and 50 vol.%). The ceramics were prepared using the conventional solid-state route, with a step at intermediate temperature for pore former burnout during the sintering process, which leads to micro and macropores distributed in the ceramic body. The pore shape depends on the inclusion nature: mainly spherical for corn starch and elongated for graphite. Microstructural investigation of the ceramics was performed in 2D by scanning electron microscopy and also in 3D by micro X-ray computed tomography (μ-XCT), to determine porosity, pore distribution and connectivity. Dielectric characterization (permittivity and loss tangent) was carried out at 10–106 Hz in the temperatures range of 25–150 °C. Finally, the dielectric properties and pore shapes are discussed within a simple model.
Acknowledgements. This work was carried out in the framework of a Project funded by the JECS Trust.