The present paper reports the dependence of dielectric, ferroelectric and piezoelectric properties on the porosity level in BaZr_0.15Ti_0.85O₃ ceramics with porosity from 5% to 21%. Microporosity with 0–3 connectivity has been produced using PMMA microspheres as a sacrificial template. The functional properties (dielectric, ferroelectric and piezoelectric effect) are mostly affected by the “dilution effect”: permittivity decreases by 40% when porosity increases by 21%, and P_max decreases from 13 to 5 µC/cm² while the P_rem is in the range of (2–8) µC/cm². However, the reduction of the zero-field permittivity and hysteretic behaviour of ε(E) while the tunability level is still high makes from porous ceramics interesting materials for tunability application.

Tunable microwave devices are widely used in radar, telecommunication and radio frequency measurement systems. In recent years, a promising technology for tunable microwave devices, which combines the advantages of using the magnetic and electrical properties of materials as well as their magnetoelectric coupling, has been developed. In the present work, x MnFe ₂ O ₄ -(1 − x )Pb _0.988 (Zr _0.52 Ti _0.48 ) _0.976 Nb _0.024 O ₃ ferrite-ferroelectric composites have been prepared and their functional properties were investigated, in order to be designed as components in tunable microwave devices. Structural, microstructural, dielectric and magnetic investigations confirmed the formation of composite ceramics with valuable dielectric and magnetic properties at room temperature. The complex permittivity and permeability of the investigated magnetoelectric ceramics, measured in the frequency range of 1 MHz to 1 GHz, show as a combination of the properties of Pb(Zr,Ti)NbO ₃ ferroelectric and magnetic MnFe ₂ O ₄ phases. Experimental measurements and the numerical simulations were done using a high frequency structure simulator (HFSS) which revealed that the investigated composite disk placed on a microstrip line acts as an electromagnetic resonator and it could be consider as a filter with tunable stop-band capabilities controlled by an external magnetic field. It was found that the central stop-band frequency of the designed filter can be tuned with 18 MHz by changing the magnetic field from 0 to 2 kOe.

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.