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.

The purpose of the present studies is to establish the preparation techniques of Bi_4Ti_3O_<12> ceramics (Tc=675ﾟC) as PTC thermos, and to clarify the PTCR mechanisms.As a result, Bi_4Ti_3O_<12> ceramics with 5mol%Nb as semiconducting element show the rapid resistant increase (PTCR properties) with high-order of magnitude of 3-4 at 270 ﾟC。抗性的温度系数比提出的二手热水瓶的BATIO_3高10-1000倍。但是PTCR温度与其居里温度不符。然后，提出的BATIO_3陶瓷的Heywang模型无法应用于系统。样品的微观结构表明PTCR性质的样品表面由TIO_2和BI_2TI_4OO__ <11>组成，并且BI Metals在几个MUM的样品中分散了BI Metals。 BI金属的尺寸在样品的外部具有啤酒尺寸，内部尺寸更细。阻抗分析表明，在270°C下介电常数迅速降低，这对应于BI金属的熔化温度（TM）。因此，PTCR特性出现的机理使得BI金属的存在形成低于BI金属熔化温度以下的低抗性电路，但它会变为TM上方的高电路。然后，样品的总抗性受SRBI_4TI_4O__ <15>的矩阵相位，也发现添加SR氧化物改进的PTCR性能系统。