Processing of submicrometric CaTi_0.8Fe_0.2O_3-δ ceramics by mechanical activation

Effects of mechanical activation of precursors in order to obtain CaTi_0.8Fe_0.2O_3-δ are reported. Mixtures of CaCO₃, TiO₂ and Fe₂O₃ were dry-grinded in Teflon or zirconia containers using planetary ball-mills at different rotations (200, 300 and 500 rpm) and for various periods of time. The perovskite is not formed just by milling and a subsequent heat treatment at 800–1,000 °C was necessary. This still represents a significant advantage over the classical ceramic route as a result of the improved reaction kinetics due to the smaller grain size (<100 nm) of the activated powders and a modification of the thermodynamic initial state. Dense ceramic samples showing a bimodal submicrometric grain-size distribution (100–200 and 250–500 nm) were obtained after sintering the activated powders at 1,150 °C TEM revealed homogeneous samples, free from inhomogeneities such as core-shell grains typically observed in ceramics obtained from non-activated precursors sintered at 1,320–1,350 °C.