Processing of submicrometric CaTi0.8Fe0.2O3-d ceramics by mechanical activation

Effects of mechanical activation of precursors in order to obtain CaTi0.8Fe0.2O3-d are reported. Mixtures of CaCO3, TiO2 and Fe2O3 were dry-grinded in Teflon or zirconia containers using planetary ballmills 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.