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.

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