Preparation of Ca0.8Sr0.2Ti1−xFexO3−δ (x = 0.1–0.3) nanoparticles using a flow supercritical reaction system

Perovskite oxide Ca0.8Sr0.2Ti1−xFexO3−δ (CTO) nanoparticles, in which Ca and Ti sites are partially doped by Sr and Fe atoms, were synthesized using a flow supercritical reaction system. Effect of synthetic parameters such as pH, Fe content x, and temperature were investigated on (1) production of single-phase CTO and (2) particle size control. Products were characterized using X-ray diffraction, elemental analysis, transmission electron microscopy, and BET surface area. A single-phase CTO was obtained at 673 K, 30 MPa. The pH of the mixed salt solution affected the single-phase CTO production. High pH was necessary to obtain single-phase CTO and the required pH increased with an increase in Fe content x. In addition, homogeneous fine particles (ca. 20 nm) were achieved at high pH. The BET surface areas of the hydrothermal products were much higher, about 70–90 m2/g, compared with that of the conventional sol–gel product (<5 m2/g). Supercritical conditions were essential to prepare single phase CTO nanoparticles, whereas CTO nanoparticles with lower Fe content (x = 0.1) could be synthesized under subcritical conditions.