高精度高比容独石电容器用瓷料研究及其介电常数的计算

首先利用蒙特卡罗有限元法在分析陶瓷材料内电场分布的基础上 ,对微粒混合陶瓷材料的介电常数与各成分含量及其介电常数之间的关系进行了探讨。研究表明 ,由于介质极化的原因 ,在陶瓷材料内部 ,等势线的分布将主要集中于低介电常数成分所占的区域 ,并且 ,微粒混合陶瓷材料各成分的含量及其介电常数都会对陶瓷材料内电场的分布产生重要影响 ,并使陶瓷材料的宏观介电常数发生变化。当陶瓷材料中含有与其他成分介电常数差别相当大的成分时 ,利用蒙特卡罗有限元法可获得较其他传统方法更为准确的结果系统地研究了钡钛钕系统陶瓷的介电性能。研究结果表明 ,Ba Ti O3中掺入极少量的 Nd2 O3(例如摩尔分数 x为 0 .1% )时 ,材料呈半导性 ,电阻率呈明显的 PTCR效应。Ba Ti O3中掺入少量的 Nd2 O3(x≥ 0 .2 % )时 ,材料呈绝缘性 ,且随着 Nd2 O3掺入量的增加 ,材料的平均晶粒尺寸不断减小 ,居里峰向负温方向移动 ,居里峰不断降低。Ba Ti O3中掺入少量 Nd2 O3· 2 Ti O2时 ,随着掺入量的增加 ,居里峰向负温方向移动 ,晶粒尺寸不断增大 ;Ba Ti O3中掺入较多的 Nd2 O3· 2 Ti O2 时 ,随着掺入量的增加 ,介电常数不断减小 ,介电常数的温度特性曲线的非线性程度不断减小 ,并且 ,当 Ba Ti O3与 Nd2 O3· 2 Ti O2 的摩尔比?

Study on the Ceramics for MLCC of High Accuracy and Specific Capacity and the Calculation of Its Dielectric Constant

Firstly, the relations between dielectric constant of ceramic composed of several compositions and content or dielectric constant of the compositions are studied on the basis of analysis of inner electric field distribution in ceramic using Monte Carlo Finite Element Method in this paper. The results show that, in ceramic, the contour lines of voltage mainly concentrate in the field of composition with low dielectric constant because of the polarization of dielectric. The content and dielectric constant of composition in the ceramic will all affect inner electric field distribution, and thus make the macroscopical dielectric constant of the ceramic different. More accurate results can be gained using Monte Carlo Finite Element Method than other traditional methods when there is a composition which dielectric constant is much different from the other's in ceramic. 　　Dielectric properties of ceramic in barium, titanium and neodymium system are synthetically studied. The results show that, material will be semiconductive, and resistivity shows obviously PTCR effect when little amount of Nd2O3 (for example 0.1mol%) doped into BaTiO3. Material will be insulating when a little amount of Nd2O3 (≥0.2mol%) doped into BaTiO3, and with the increase of doping amount of Nd2O3, the average grain size decreases, the Curie point shifts to minus temperature, the Curie summit reduces constantly. When a little amount of Nd2O3.2TiO2 is doped into BaTiO3, with the increase of doping amount, Curie point shifts to minus temperature, and the average grain size increases constantly. When much Nd2O3.2TiO2 is doped into BaTiO3, with the increase of doping amount, dielectric constant decreases, nonlinear extent of temperature characteristic curve of dielectric constant reduces, and when the mole ratio of BaTiO3 and Nd2O3*2TiO2 is equal, the main phase will change from BaTiO3 to BaNd2Ti3O10. In barium, titanium and neodymium system, when the ratio of BaO, Nd2O3 and TiO2 is different, compositions of BaNd2Ti5O14, BaTiO3, Nd2Ti2O7, dissociative TiO2、BaTi4O9、Ba2Ti9O20, and et al. can be obtained, and ceramic will show different dielectric properties. Perfect dielectric properties can be obtained near BaO.Nd2O3.5TiO2, the main phase now will be BaNd2Ti5O14. Quinary ceramic system is constructed when PbO and Bi2O3 is added into barium, titanium and neodymium system. The adding of PbO or Bi2O3 can all increase dielectric constant of the material, and commonly move temperature coefficient to positive value. 　　In the quinary system of barium, titanium, neodymium, lead and bismuth, adding of calcined SrO*TiO2 can increase dielectric constant of the material and move temperature coefficient to minus value; adding of calcined 2Bi2O3*3TiO2 can increase dielectric constant of the material and move temperature coefficient of positive value; adding of glass can reduce the sinter temperature of the material, decrease dielectric constant and move temperature coefficient to minus value. Doping of a little of Al2O3 can decrease the dielectric loss of the material in the quinary system of barium, titanium, neodymium, lead and bismuth added simultaneously with calcined SrO*TiO2, 2Bi2O3*3TiO2 and glass. 　　Composing ceramic of the quinary system of barium, titanium, neodymium, lead and bismuth, and adding proper amount of calcined SrO.TiO2, 2Bi2O3.3TiO2 glass and a little Al2O3, ceramic of high precise and high volume capacitance for MLC sintered at intermediate temperature is successfully obtained, dielectric properties are list as below: 　　Dielectric constant εr: 99.10 　　Temperature coefficient αε : -13×10－6℃－1 　　Dielectric loss tgδ: 2.6×10-4 　　Resistivity　ρv: ≥1013 Ω.cm 　　Break-down electric field strength Eb: ＞10 MV/m 　　Dielectric properties of MLC produced with such ceramic are list as below: 　　Capacitance C: ≥250 nF 　　Temperature coefficient αC: -(90～80)×10－6℃－1 　　Dielectric loss tgδ:(10～12)×10-4 　　Resistance Ri: ≥1012 Ω 　　Break-down voltage: ＞triple working voltage 　　Sintering temperature: 1 150℃ 　　Matching with Ag (70)-Pd (30) inner electrode. 　　Finally, dielectric constant of ceramic for MLC of high precise and high volume capacitance sintered at intermediate temperature is calculated using Monte Carlo Finite Element Method. The results show that, the value calculated using Monte Carlo Finite Element Method is more close to the practical test value than the one calculated using traditional Lichedonich Logarithm Rule. This proves that this method is effective for the calculation of the dielectric constant of ceramic composed of several compositions.