Dense, Fine-Grained Ba_1-xSr_xTiO₃ Ceramics Prepared by the Combination of Mechanosynthesized Nanopowders and Spark Plasma Sintering

Ba 1 - x Sr x TiO 3 ( x = 0, 0.25, 0.5, 0.75, and 1) nanocrystalline powders were prepared by mechanosynthesis in a planetary mill, from stoichiometric mixtures of BaO 2, SrO, and TiO 2 at room temperature. Evolution during the mechanical treatment and subsequent annealings was investigated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Formation of the solid solution between BaTiO 3 and SrTiO 3 was observed in the whole range of compositions. The spark plasma sintering (SPS) technique was used to prepare dense ceramics. Densification occurred within a very short time (about 10 min). The combination of mechanosynthesis and spark plasma sintering has been used for the first time to process ceramics of the Ba−Sr−Ti−O system with very high density and homogeneous microstructure, at a temperature 300−400 °C lower than the conventional sintering of Ba 1 - x Sr x TiO 3 phases obtained by solid-state reaction. This approach allows grain growth to be controlled and opens the possibility of processing fully dense nanostructured Ba 1 - x Sr x TiO 3 ceramics. Dielectric permittivity as a function of temperature was characterized for a series of samples across the solid solution and confirmed that dense, fine-grained ceramics can be processed by this novel approach for all compositions. Ferroelectric hysteresis loops were recorded for BaTiO 3 ceramics with decreasing grain size. The variations of remanent polarization and coercitive field are consistent with the transition from the lamellar 90° ferroelectric domain to grains with only 180° domains.