非化学计量比CaCu₃Ti₄O₁₂陶瓷及掺杂特性研究

【作者】 梁桃华；

【导师】 杨仕清；

【作者基本信息】 电子科技大学 ， 材料科学与工程， 2010， 硕士

【摘要】 CaCu3Ti4O12(CCTO)陶瓷材料由于其高介电常数、高温度稳定性在大容量电容器、动态随机存储器等领域有着广泛的应用前景。但目前CCTO陶瓷材料主要存在两方面的问题:一方面,CCTO陶瓷的介电常数随配方及工艺差别较大,甚至可达数量级的差异,可重复性差;另一方面,CCTO的介电损耗较大。因此,提高CCTO的介电常数和可重复性,同时降低其介电损耗非常必要。在提高CCTO的介电常数和可重复性方面,本文拟通过在固相球磨时改变Ca、Cu、Ti元素的不同配比,首先找出单一元素偏离化学计量比对CCTO介电性能的影响规律,进而找出Ca和Ti、Ca和Cu、Cu和Ti同时偏离化学计量比对CCTO介电性能的影响规律。研究表明,Ca、Cu和Ti偏离化学计量比对CCTO的介电性能影响规律不同,Cu不足以及Ti不足时都存在介电常数的反常现象。研究结果还表明,当Ca、Cu、Ti的原子摩尔比为1.08:3.00:4.44时,其相对介电常数在1KHz下达到4×105,介电常数比标准化学计量比的CCTO陶瓷提高了一个数量级。其高介电常数来源于大的颗粒尺度和薄的晶界层的贡献,支持IBLC(internal barrier layer capacitance )模型。在降低CCTO的介电损耗方面,本文通过在获得特高介电常数成分配方及烧成工艺的基础上,对非化学计量比的CCTO陶瓷的晶界及颗粒边界掺杂不同剂量的高绝缘LTCC玻璃以及纳米SiO2粉,研究其对降低介电损耗特别是漏导损耗的影响。研究表明,高绝缘玻璃掺杂不仅有助于加快固相反应,降低烧结温度,而且,明显有助于提高晶界和颗粒边界电阻,降低漏导损耗。研究结果还表明,当CCTO原料偏离化学计量比且CuO微过量时掺杂某一剂量的纳米SiO2粉,获得的CCTO陶瓷观察到负电容效应。研究表明,CCTO陶瓷中的负电容效应与Sandoval等在发光二极管中P-N结上观察到的负电容效应有本质不同。其负电容效应并不是来自于电流-电压的相位变化,而是来自于电容谐振。特别地,CCTO在低频段发现的负电容效应,为我们在特定频段利用电容代替电感提供了可能。更多还原

【Abstract】 CCTO ceramic has broad application prospects in the large-capacity capacitors, dynamic random access memory and other fields, because of its high dielectric constant and temperature stability. But CCTO ceramic has mainly problems in two aspects: on the one hand, its dielectric constant varys greatly owing to different compositions and processes, even up to one magnitude differences, poor reproducibility; on the other hand, its dielectric loss is large. Therefore, it is necessary to improve its dielectric constant and reproducible, while reduce its dielectric loss.To improve its dielectric constant and repeatability, this paper was proposed to change Ca, Cu, Ti elements in different proportions by the solid state technique, and to find the regular pattern that the non-stoichiometry single element impacts on its dielectric properties, and then to find the regular pattern that the non-stoichiometry Ca and Ti, Ca and Cu, Cu and Ti impact on its dielectric properties. The results showed that the non-stoichiometry Ca, Cu, or Ti element impacted differently on its dielectric properties, and that the abnormal dielectric constant existed owing to the deficiency of Cu and Ti. The results also showed that when Ca, Cu, Ti atomic molar ratio was 1.08:3.00:4.44, its relative dielectric constant reached 4×105 at 1KHz , and its dielectric constant improved one magnitude than the standard stoichiometry CCTO ceramics. Its high dielectric constant derived from the larger particle size and the thinner boundary layer, and supported IBLC model.On the basis of ultra-high dielectric constant components in the formula and the firing process, the paper was proposed to doping the high insulation LTCC glass and nano-SiO2 powder at grain boundary of the non-stoichiometry CCTO ceramic in order to reduce its dielectric loss especially the leakage loss. The results showed that CCTO ceramics doped with the high insulation glass would not only speed up the reaction and lower sintering temperature, but also increase significantly the grain boundary resistance and reduce its leakage loss. The results also showed that the negative capacitance effect was firstly observed when the non-stoichiometry CCTO material excessed with a slight CuO and doped with nano-SiO2 powder. It was essentially different with the negative capacitance observed in the P-N junction in the light-emitting diode. The negative capacitance effect was not from the phase of the current - voltage change, but from the capacitor resonant. In particular, this found that the negative capacitance effect at some frequency provides us with the possibility to use capacitor instead of inductance in some frequency band.更多还原