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Ba 0.75 Sr 0.25 TiO 3 -Mg 0.9 Zn 0.1 O (BST-MZO) composite ceramics were prepared by sintering core-shell structured nano-powders at 1200°C via a spark plasma sintering (SPS) process. X-ray diffraction measurements revealed the coexistence of two phases (BST and MZO). Scanning electron microscope analysis indicated that the ceramic had a pore-free microstructure and an average grain size of ~400 nm. The dielectric constant and loss tangent of the ceramic were 607 and 1.2×10 -4 at 10 kHz at room temperature, respectively. A good dielectric tunability was observed in the ceramic. At room temperature, the tunability and the figure of merit of the ceramic were 65.78% and 300 (under a dc bias of 19.27 kV/cm), suggesting that the ceramic is a good candidate for tunable microwave devices.

Lead-free piezoelectric ceramics based on bismuth sodium titanate (BNT) -barium hafnate titanate (BHT) were prepared by a two-step synthesis process. The final BNT-BHT ceramics sintered at 1180oC for 2 h in air showed a perovskite structure with high density. The morphotropic phase boundaries (MPB) were found in BNT based piezoelectric ceramics with 8~10 wt% BHT in composites. In the case of Bi0.5Na0.5TiO3-0.08BaHf0.05Ti0.95O3 ceramics, a maximum piezoelectric coefficient d33 of 122.6 pC/N was obtained. The remnant polarization (Pr) and coercive field (Ec) were measured and the relationship between ferroelectricity and the BHT fraction in the compounds was investigated. The BNT-BHT ceramics were expected to be a new and promising candidate for lead-free piezoelectric device applications.