The influence of different additives and the mode of their addition on thesintering behavior and the properties of semiconducting barium titanate ceramics

The influence of different additives (TiO2, TiO2/SiO2, CaO/TiO2/SiO2, CaO/T iO2/2SiO(2)) and the mode of their incorporation (spray drying: series 1; m ixed-oxide method: series 2) on the sintering behavior and the microstructu ral and electrical properties of n-doped BaTiO3, ceramics has been investig ated. The incorporation of the additives from their aqueous solution by spr ay drying produces a homogeneous distribution of the additive in the BaTiO3 , matrix powder by coating the BaTiO3, particles. This homogeneous distribu tion significantly lowers the activation energy for the densification proce ss compared with that of the powders of series 2. Dynamic and isothermal di latometric measurements revealed that the sintering process is considered a s a classical solid phase sintering followed by recrystallization of the Ba TiO3 matrix particles by a eutectic melt. The densification process is domi nated by sliding processes. These sliding processes are caused by the amorp hous layer of the additive and by the defect-rich grain boundary layers of the BaTiO3, grains generated intermediately by diffusion processes and reac tions of the matrix material with the additive forming the secondary phases Ba2TiSi2O8 and Ba4Ti13O30, respectively. In series 1, ceramics with a homo geneous microstructure and useful electrical properties (e.g, low resistivi ty at room temperature) were already produced at a sintering temperature of 1280 degrees C (with SiO2-containing additives) due to the homogeneous dis tribution of the additive. The ceramics of series 2 sintered at the same te mperature could only be obtained in poor quality. At higher sintering tempe ratures the differences between the two series vanished. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved.