Dense, Fine-Grained Ba₁_-<i>_x</i>Sr<i>_x</i>TiO₃ Ceramics Prepared by the Combination of Mechanosynthesized Nanopowders and Spark Plasma Sintering

Abstract

Ba1-xSrxTiO3 (x = 0, 0.25, 0.5, 0.75, and 1) nanocrystalline powders were prepared by mechanosynthesis in a planetary mill, from stoichiometric mixtures of BaO2, SrO, and TiO2 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 BaTiO3 and SrTiO3 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 Ba1-xSrxTiO3 phases obtained by solid-state reaction. This approach allows grain growth to be controlled and opens the possibility of processing fully dense nanostructured Ba1-xSrxTiO3 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 BaTiO3 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.