Fine grained Ba0.75Sr0.25TiO3 (BST) ceramics were prepared via spark plasma sintering technique. BST nano-powders freshly prepared by a low-temperature direct solution synthesis technique were used as starting materials. X-ray diffraction measurements indicated that the ceramics had a pure perovskite phase and the observation under scanning electron microscope revealed that the ceramic had a grain size in the range of 50 to 300 nm. The dielectric properties of the fine-grained BST ceramics were determined at different temperatures and frequencies. At room temperature, the ceramics exhibited a moderate dielectric constant (3962±10), a good dielectric tunability (53.84% under a dc bias of 19.72 kV/cm). The highest tunability and figure of merit (FOM) values are 83.27% at 50.2 °C and 289.28 at 62.3 °C, respectively. These results suggested that the BST ceramics are suitable for use in tunable microwave devices.
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