(Ba-Sr)TiO_3基PTC陶瓷材料第二相结晶对半导化性能的影响

Effect of Secondary Phase Crystallization on Semiconduction of PTC Ceramics Based on (Ba-Sr)TiO_3

调整 Al_2O_3、SiO_2烧结添加剂比例,采用常规的混合氧化物制备工艺,可使施主钛酸钡陶瓷第二相形成针状或柱状莫来石微晶体。莫来石第二相的生成,改善了用低纯原料制备的 PTC 材料半导化性能。本文从莫来石对杂质离子的固溶作用方面,探讨了这一影响。莫来石对半导化有害的 Fe^(3+)、Mg^(2+)杂质具有较大的固溶作用,纯化了(Ba-Sr)TiO_3基主晶格,使主晶相中施主物提供的“多余”电子被更多的 Ti^(4+)所俘获,形成Ti^(3+),从而降低了 PTC 材料室温电阻率。实验结果还表明,当 Al_2O_3、SiO_2比例适宜生成莫来石时,用低纯原料制备的 PTC 材料室温电阻率具有较好的一致性和重复性。

Needle and column types of mullite crystallites can be formed as the secondphase in the BaTiO_3 ceramics,doped with Al_2O_3 and SiO_2 additives by a commonprocessing technique,as well as mixing oxides and adjusting Al_2O_3/SiO_2 ratios.Itsformation can improve semiconductive properties of PTC ceramics prepared withraw materials of lower purity,Mullite can solubilize more impurities of Fe^(3+) andMg^(2+),which are harmful to semiconduction of PTC materials,so it can purify themain lattice of (Ba-Sr) TiO_3 matrix.The excessive electrons provided by donor inthe main lattice can be captured by more Ti^(4+) forming Ti^(3+),as a result,the speci-fic resistance at room temperature of the PTC material can be lowered.The experi-mental results show that the specific resistance at room temperature of the PTCceramics even prepared with raw materials of lower purity has a better uniformityand repeativity,when the ratio of Al_2O_3/SiO_2 added is optimized for forming mul-lite.