Porosity-dependent properties of Nb-doped Pb(Zr,Ti)O3 ceramics

In the present work, it is shown how the controlled porosity can be exploited to obtain a compromise between a reduced permittivity down to a few hundreds and maintaining a high tunability level as in the dense material, to fulfill requirements for tunable applications. Nb-doped Pb(Zr,Ti)O-3 ceramics with porosity in the range 5%-30% have been prepared by direct sintering method. X-ray diffraction analysis and Rietveld refinement indicated a co-existence of tetragonal and monoclinic phases in the porous ceramics. Dielectric properties revealed a gradual reduction in permittivity when increasing the porosity level, while maintaining low dielectric losses below 3%. The ferroelectric switching behavior is also influenced by the porosity level: a continuous reduction in the saturation and remnant polarization is observed with increasing porosity. The nonlinear dielectric properties of all the investigated ceramics preserve a high level of tunability in comparison with one of the dense material, irrespective of the porosity level, while zero field permittivity was decreased below 1000. An optimum behavior is found for the ceramic sample with 25% porosity, which shows a high tunability, smaller losses, and moderate dielectric constant (epsilon similar to 600).