Porous (Ba,Sr)TiO3 ceramics for tailoring dielectric and tunability properties: Modelling and experiment

3D Finite Element Method simulations were employed in order to describe tunability properties in anisotropic porous paraelectric structures. The simulations predicted that properties of a ceramic can be tailored by using various levels of porosity. Porous Ba0.6Sr0.4TiO3 (BST) ceramics have been studied in order to investigate the influence of porosity on their functional properties. The BST ceramics with various porosity levels have been obtained by solid-state reaction. Lamellar graphite in different concentration of 10, 20 and 35 vol.% was added as sacrificial pore forming agent. The structural, microstructural, dielectric and tunability properties were investigated. By comparison with dense BST ceramic, porous samples present a fracture mode transformation from intragranular to an intergranular fracture and a decrease of grain size. Lower dielectric constants, low dielectric losses, but higher values of tunability than in the dense material were obtained in the porous BST structures as a result of local field inhomogeneity generated by the presence of air pores-ceramic interfaces

Study of the role of porosity on the functional properties of (Ba,Sr)TiO<inf>3</inf> ceramics

The role of porosity on the low and high field dielectric properties was studied in Ba0.70Sr0.30TiO3 ceramics with various porosity levels obtained by using lamellar graphite as sacrificial template. The permittivity decreases with increasing porosity, from around ε ∼ 7690 (dense ceramic) down to 380 (ceramic with 29% porosity), while preserving the Curie temperature at about 35 °C. The effective permittivity was discussed by using Effective Medium Approximation and Finite Element Method approaches. The role of porosity and specific microstructural characteristics induced by the pore forming addition, from closed porosity (0–3) towards a combined (0–3, 2–2) with lamellar-type of microstructures for the most porous ceramics was taken into consideration. All the investigated ceramics preserve a high level of tunability as in the dense material, irrespective of the porosity level, while the zero field permittivity was decreased to a few hundreds