PTCR MECHANISM IN NEWLY DEVELOPED Bi_4Ti_3O_<12> CERAMIC HEATER

新开发的Bi_4Ti_3O_<12>陶瓷加热器中的PTCR机制

• 批准号: 05650666
• 负责人: OKADA Masuo
• 金额: $ 1.41万
• 依托单位: TOHOKU UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (C)
• 财政年份: 1993
• 资助国家: 日本
• 起止时间: 1993 至 1994
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-05650666/
• 关键词: PTC THERMISTOR; CERAMIC HEATER; Bi_4Ti_3O_<12> CERAMIC; PTCR MECHANISM

The purpose of the present studies is to establish the preparataion techniques of Bi_4Ti_3O_<12> ceramics (Tc=675ﾟC) as PTC thermistors, and to clarify the PTCR mechanisms.As a result, Bi_4Ti_3O_<12> ceramics with 5mol%Nb as semiconducting element show the rapid resistivity increase (PTCR properties) with high-order of magnitude of 3-4 at 270ﾟC.The temperature coefficient of resistivity is by 10-1000 times higher than that of BaTiO_3 presently used thermistor. But the PTCR temperature does not correspond to their Curie temperature. Then the proposed Heywang model for BaTiO_3 ceramic is unable to apply to the system.The microstructure of the sample which shows PTCR properties are such that surface of the sample consists of TiO_2 and Bi_2Ti_4O_<11>, and the Bi metals are dispersed inside the sample of several mum. The size of Bi metals have a lager size at outer of the sample and finer size at inside. The impedance analysis indicates that the permittivity decreases rapidly at 270ﾟC,which corresponds to the melting temperature (Tm) of Bi metals. Therefore, the mechanism of the appearance of PTCR properties are such that existence of Bi metals forms the low resistivity electrical circult below the melting temperature of Bi metals, but it changes to high electrical circuit above Tm. Then the total resistivity of the sample is subject to the matrix phase of SrBi_4Ti_4O_<15>.It is also found that the addition of Sr oxides improved stabilities of PTCR properties.

本研究的目的是建立Bi_4Ti_3O_<12>陶瓷（Tc=675 C）作为PTC热敏电阻的制备工艺，并阐明PTCR的机理。结果表明，以5mol%Nb为半导体元素的Bi_4Ti_3O_<12>陶瓷在270℃时电阻率快速提高（PTCR性能），达到3 ~ 4个数量级。电阻率温度系数比目前使用的BaTiO_3热敏电阻高10-1000倍。但PTCR温度并不符合它们的居里温度。因此提出的BaTiO_3陶瓷的Heywang模型无法应用于该系统。样品的微观结构表现为表面由TiO_2和Bi_2Ti_4O_<11>组成，Bi金属分散在若干个金属的样品内部。铋金属样品的外粒径较大，内粒径较小。阻抗分析表明，在270℃时介电常数迅速减小，对应于Bi金属的熔化温度（Tm）。因此，PTCR性能出现的机制是：Bi金属的存在在Bi金属熔化温度以下形成低电阻率电回路，而在Tm以上变为高电阻率电回路。试样的总电阻率受SrBi_4Ti_4O_<15>的基体相约束。同时发现Sr氧化物的加入提高了PTCR性能的稳定性。