Effect of conventional and laser sintering on the (micro)structural and dielectric properties of Bi2/3Cu3Ti4O12 synthesized through a polymeric precursor route

Abstract

This work explores a polymeric synthesis route for Bi2/3Cu3Ti4O12 (BCTO) and analyses the effect of both conventional and laser sintering on the (micro)structural and dielectric properties of the processed ceramics. The physico-chemical reactions taking place during the heat treatment of BCTO powders were investigated through differential thermal analysis (DTA), in which an endothermic event (at about 990 °C) was identified and ascribed to a liquid phase formation. Dense ceramics were achieved, with the observation of a slight increase in average grain size (AGS) from 1.1 μm to 2.1 μm while raising the sintering temperature from 960 °C to 1000 °C. The laser-sintered ceramics presented an AGS of 1.0 μm, which is comparable to that found for the ceramic conventionally sintered at 960 °C. It is shown, using energy dispersive analysis of X-rays (EDAX), that a Cu-rich phase segregates at the grain boundaries in BCTO ceramics, irrespective of the considered sintering technique. The dielectric response from such ceramics displays a remarkable dependence on the processing approach. We show that the grains of BCTO laser-sintered ceramics can be highly resistive, with room temperature (RT) resistivity of 2 MΩ cm and activation energy of 0.3 eV. In this case, a predominant bulk dielectric response (ε′ < 102) was verified at RT. When conventional sintering was applied, a semiconducting phase, with activation energy of 0.06 eV, develops into the grains (RT resistivity of 140 Ω cm) in agreement with the results typically reported in the literature. This latter electrical microstructure, which is consistent with the well-known internal barrier layer capacitance (IBLC) mechanism, results in the manifestation of interfacial polarization (grain-grain and material-electrode interfaces) effects at RT and, consequently, in a high effective permittivity (ε′ > 103).