Polymeric synthesis and conventional versus laser sintering of CaCu3Ti4O12 electroceramics: (micro)structures, phase development and dielectric properties

Abstract

CaCu3Ti4O12 (CCTO) powder was synthesized in this work by applying a modified polymeric precursor method, followed by calcination at 700–800 °C for 2 h, and, then, conventional as well as laser sintering. Dense and homogeneous microstructures were achieved, with observation of an increase in average grain size with raising sintering temperature or laser power density. The grain size in the laser sintering revealed smaller than in conventional sintering, because the former involved very high heating rates coupled with lower annealing time. Moreover, sintering toward high temperatures or laser power densities resulted in CCTO containing traces of CuO- and TiO2-like phases. This result is promoted by a thermally-assisted migration of Cu2+ to the interfaces (grain boundaries and sample surfaces), toward which Cu2+ is proposed to reduce in air to Cu+. Because involving as well very high cooling rates, laser sintering had the effect of inhibiting Cu+ re-oxidation to Cu2+, accounting for Cu2O stabilization instead of the CuO phase identified in conventional sintering. The dielectric responses of the ceramics showed to be strongly dependent on the processing method through the (micro)strutural characteristics achieved during sintering. This complex dependence is discussed in terms of the effects expected from bulk versus grain boundaries in such materials.