Sm_2O_3掺杂的BaTiO_3陶瓷的PTCR效应

Positive Temperature Coefficient Resistivity Effect in Sm_2O_3-doped BaTiO_3 Semiconducting Ceramics

施主浓度与 PTCR效应的关系 ,一方面受各种杂质乃至助烧剂影响而变得复杂化 ;另一方面也被很多作者所忽视。然而 ,这一关系可以在一定程度上映射出 PTCR效应的本质。海望曾指出 ,在 Ba Ti O3材料中 ,晶界上过剩施主的堆集 ,能够形成晶界层中高浓度的表面受主态 ,从而使材料 PTCR效应迅速提高。尽管海望的表面受主态模型被广为接受 ,然而 ,我们研究了 Sm2 O3掺杂的 Ba Ti O3陶瓷中掺杂浓度与 PTCR效应的关系 ,结果表明 :随着稀土掺杂量的提高 ,材料的升阻比降低。采用其他稀土元素 ,也得到相同的结果。因此 ,PTCR效应应当来源于在铁电相变点 ,晶界层中电子陷阱中性钡缺位被激活俘获自由电子 ;过剩施主的增加只能增加材料的室温电阻率 ,而不能提高

The relationship of donor concentration to PTCR effect in BaTiO 3 ceramics is not clear;it is so complicated that such as impurities,even sintering aids can make it changed.The intrinsic nature of PTCR effect can be revealed in a certain extent by this relationship,but many authors ignored it.Heywang previously presumed that the PTCR effect can be greatly enhanced by the existence of high concentration of acceptor levels at grain boundary layers,which can be formed by the piling up of excess donors at grain boundary or by the addition of some acceptors.In this paper,it results in a contradiction to Heywang’s presumption by studying the influence of Sm 2O 3 concentrations on PTCR effect.With the rising of Sm 2O 3 concentration,the PTCR effect of the BaTiO 3 samples was decreased.Thus,excess donor can not enhance the PTCR effect;it can only increase the room temperature resistance.Here,another model in which the neutral barium vacancy would be responsible for the PTCR effect is more possible than Heywang’s model,which was accepted widely.