INFLUENCES OF SIO_2 CONTENT ON THE PTC PROPERTIES IN N-BATIO_3 CERAMICS

摘要

In the composition of Positive Temperature Coefficient (PTC) ceramics during the early stage, in most cases, small quantities of Al_2O_3, SiO_2 and TiO_2 (AST) are added to form liquid glass phase in the course of sintering. This kind of glass phase is helpful to dissolve the harmful acceptor impurities, and to minimize the grain size. Recently, in the prescription of PTC ceramics, especially in those with lower room temperature resistance, and higher resistance temperature coefficient, since the enhanced purity of raw materials, there is a tendence of not doping Al_2O_3. The reason is mainly due to the appearance of Al~(3+) ions will not favor for enhancing resistivity temperature coefficient, lowering room temperature resistivity and minimizing the grain sizes. However, the dopant of SiO_2 can not be cancelled, otherwise the density of ceramics and voltage withstanding ability will be very low. Here, we shall discuss the influences of SiO_2 content on the PTC characteristics in the case of not doping Al_2O_3.