Spark plasma sintering (SPS) is an efficient tool to obtain highly densified ferroelectric-dielectric ceramic composites with clean interfaces and tunable properties. Dielectric MgO and ferroelectric ${\mathrm{Ba}}_{0.6}{\mathrm{Sr}}_{0.4}\mathrm{Ti}{\mathrm{O}}_3$ (BST) were combined in two-dimensional multilayer and three-dimensional random powders design. Their unmodified BST Curie temperature proves the suppression of interdiffusion while dielectric losses are below 0.5% and the tunability is 40% at room temperature. The composites and pure BST with similar densities $(>95\%)$ were obtained, owing reliable comparison of their dielectric properties. Such SPS ceramics can be used as experimental input for simulation and are potential candidates for high frequency applications.

Supercapacitor behavior has been reported in a number of oxides including reduced BaTiO3 ferroelectric ceramics. These so-called giant properties are however not easily controlled. We show here that the continuous coating of individual BaTiO3 grains by a silica shell in combination with spark plasma sintering is a way to process bulk composites having supercapacitor features with low dielectric losses and temperature stability. The silica shell acts both as an oxidation barrier during the processing and as a dielectric barrier in the final composite.

Spray-drying technique is used to fabricate spherical microparticles out of dissolved TiO2 nanoparticles. We show both experimentally and through numerical calculations that the microspheres support a Mie resonance, leading to an effective magnetic response. For this purpose, nearly single layers of microspheres were prepared and characterized by time-domain terahertz spectroscopy. We developed an experimental approach allowing simultaneous measurement of complex transmittance and reflectance of a thin layer, which in turn enables evaluation of its effective dielectric permittivity and effective magnetic permeability. Numerical finite-element-method calculations of the electromagnetic response show that the prepared microparticles are suitable for preparing a metamaterial with negative effective magnetic permeability.