Influence of sintering condition on microstructure development of BaTiO3 based PTCR materials

The influence of sintering conditions on the microstructure development of the (Ba-Sr)TiO₃ system was studied. Experimental results show that the samples were densified at a rather low temperature without substantial grain growth. As the temperature increased, both discontinuous and continuous grain growth took place, depending mainly on the temperature range and heating rate of the sintering schedule, i.e., nucleation and grain growth processes. A good PTCR (positive temperature coefficient of resistivity) characteristic was observed for samples having a grain size of 5-10 μm. Compared to the normal process for the (Ba-Pb)TiO₃ system, sintering in nitrogen and cooling in air produces a finer grain microstructure, resulting in decreased resistivity and an improved PTCR characteristic. SIMS (secondary ion mass spectrometry) and EPMA (electron-probe microanalysis) indicated that the additive ions are mainly deposited at grain boundary and intragranular regions