高温无铅PTCR陶瓷晶界特性及导电机理研究

PTCR ceramics have been widely used in the electrical communications, aerospace, automotive and other fields due to their nonlinearly electrical resistivity. At present, the commercial high Tc PTCR materials contain Pb, which is prohibited in the electronic ceramics from the viewpoint of environmental protection. Therefore, it is necessary to develop high Tc lead-free materials to substitute Pb-containing ones. It is noted that the investigation of PTCR ceramics is mainly focuses on the composition and preparation, and until now, the conduction mechanism of PTCR effect was not still well understood. This project aims at BaTiO3-Bi0.5Na0.5TiO3 ceramics and focuses on two key scientific problems, namely, “grainboundary characteristics” and “formation mechanism of grainboundary barrier as well as calculation of barrier height”. The grainboundary characteristics are studied using XRD, TEM and AFM; Influences of microstructures on the PTCR properties are studied by ac impedance spectroscopy; Formation mechanism of grainboundary barrier is investigated; Finally, the barrier height is calculated by two different methods; The relationship between the barrier height and the grainboundary characteristics is also studied; Thus, conduction mechanism of high temperature lead-free PTCR ceramics will be grasped. Through the above research, it would provide both technical and theoretical support for development of high Tc lead-free PTCR materials.

PTCR陶瓷具有电阻非线性效应，广泛应用于电子通讯、航天、汽车、家电等领域。目前，可实用化的高温PTCR材料均含铅，而铅的挥发会造成环境污染，因此，研究高温无铅PTCR材料具有重要意义。国内外对无铅PTCR材料的研究，主要是组成配方和制备工艺的研究，然而迄今为止，高温无铅PTCR材料的导电机理仍不清楚。本项目以BaTiO3-(Bi0.5Na0.5)TiO3为研究对象，针对“晶界特性”、“晶界势垒形成机制及势垒高度的计算”两个关键科学问题开展研究。采用XRD、TEM、AFM等研究材料的晶界特性；通过阻抗分析材料的微观结构对宏观电学性能的影响；研究材料晶界势垒产生机制；通过两种不同方法计算晶界势垒高度；并且研究晶界势垒和晶界特性之间的关系；揭示材料PTCR效应的导电机理。通过上述研究，为我国高温无铅PTCR材料的发展提供技术支持和理论保障。

PTCR陶瓷具有电阻非线性效应，广泛应用于电子通讯、航空航天、汽车、家电等领域。目前，可实用化的高温PTCR材料均含铅，而铅的挥发会造成环境污染，因此，研究高温无铅PTCR材料具有重要意义。.项目采用化学法制备了La-Mn共掺杂的0.97BaTiO3-0.03(Bi0.5Na0.5)TiO3 PTCR陶瓷 (xLa-yMn-BBNT3)。XRD表明所有样品形成了纯的四方钙钛矿结构，当La掺杂x=0.002时，材料的室温电阻率大约为103 Ω•cm，电阻突跳比约3个数量级，电阻突变温度140℃。为进一步提高材料的电阻突跳比，当Mn受主掺杂y=0.0015时，电阻突跳比增大到4.4个数量级。同样，用化学法制备了Y掺杂的 BBNTx(x=1,2,3,4,5)PTCR陶瓷，0.2 mol% Y掺杂BBNT1陶瓷，室温电阻率为500 Ω•cm，电阻突跳比为2.7个数量级，电阻突变温度约130℃。随着BNT的增加，BBNT5的居里温度增大到145℃。同时，利用阻抗和介电频谱等研究方法，研究了不同温度下材料的晶粒晶界结构对宏观电性能的影响，表明材料的PTC效应主要是晶界的贡献，晶粒贡献可以忽略不计，从而初步揭示了材料PTC效应的导电机理。