高比容的多层陶瓷电容器是一种重要的电子元件，铅基弛豫铁电陶瓷介电的广泛采用实现了高性能、低成本。为了适应对其电场下的可靠性、温度稳定性越来越高的发展要求，本文对弛豫铁电陶瓷介质在外电场下的介电响应以及温度稳定特性进行了研究。通过对PMN-PZN-PT系弛豫铁电陶瓷不同温度下介电常数随直流偏压变化情况的实验测定，总结出了弛豫铁电陶瓷的直流偏压特性规律。并与采用Monte Carlo方法模拟计算得到的弛豫铁电体的偏压特性进行了对比，进而采用了偶极子玻璃模型和多瘳态模型对弛豫铁电陶瓷的偏压特性的问题提出了自己的见解。分别采用PNN-PT及PMZNT陶瓷对弛豫铁电陶瓷在交流测试电场下介电特性进行了系统的分析。总结出了弛豫铁电陶瓷的介电常数、介电损耗随交流测试电场的变化规律。并分别应用畴壁动力学以及欧集资玻璃模型对增大电场与降低频率作用相似这一现象进行了定性分析。比较了直流偏压场及交流测试场对PMZNT弛豫铁电陶瓷介电性能的影响，总结了弛豫铁电陶瓷在不同外电场下介电特性的变化规律。直流偏压场的增大可使介电常数最大值出现的温度Tmax增大，同时介电常数下降，频率色散受到抑制；交流测试场的增大可使Tmax降低，同时介电常数上升，频率色散度、弥散相变度均加大。研究了PNN-PT弛豫铁电陶瓷体系中，单相钙钛矿结构的形成机理及PT含量对该体系介电性能的影响。结果表明，通过添加过量Ni(Ac)2可以获得单相钙钛矿结构。并对0.75PNN-0.25PT弛豫铁电陶瓷直流电场诱导下的压电性能进行了探索性研究。研究了PMW-PT-PNN三元体系中介电性能随各单元组分的变化规律。在一定组成范围内，随之PMW含量的增高，除了介电常数降低、Tmax移向低温外，弥散相变度也呈现了增大的趋势。另外，PMW含量的增大有助于改善低温端的容温系数；PT含量的增大有助于改善高温端的介电性能；PNN含量的增大有助于提高介电常数。通过大量的实验研究，得出了获得X7R特性的最佳材料组成，研究了各种掺杂剂、工艺因素对该三元体系温度特性的影响。利用SEM、TEM、HREM分析手段并结合实验结果，证实了材料内部的化学不均匀结构的存在是获得X7R特性的重要因素。并就有关化学不均匀结构的形成机理提出了独到的见解。TEM透射电镜分析、SEM背散射分析均表明晶粒内不同部位组成的差异，导致了介温特性的不同，因而叠和的效果形成了平坦的介温关系曲线。通过掺入适量MnO2方法有效地降低了材料的介电损耗。并采用缺陷化学理论及畴壁钉扎模型分析了掺杂MnO2降低材料介电损耗的机制。

Multilayer ceramic capacitors (MLCC)with high volumetric capacitance are one of the most important electronic components. The widely applications of lead based relaxed ferroelectrics as dielectrics of MLCC have contributed to high performance and low cost. To meet the ever-increasing demands for high reliability under dc and ac fields and stable response over a wide temperature range of MLCC, this paper aims at the dielectric response under various external field and temperature-stable characteristic of relaxed ferroelectrics.The dc field dependence of the dielectric constant at various temperatures has been measured for PMN-PZN-PT(PMZNT) relaxed ferroelectric ceramics. The bias characteristic ceramics are concluded. It is compared with the results calculated with the theoretical model by using Monte Carlo method. These results were interpreted with dipole glass model and multinomial model. In terms of theoretical analysis and experimental results, the method about how to improve the bias characteristic of relaxed ceramics is given.Complex dielectric permittivity of PMZNT ceramics and PNN-PT ceramics has been investigated as a function of ac driving field. The ac field dependence of dielectric constant and dissipation factor of relaxed ceramics is summed up. Domain walll kinetic and dipole glass model were used to explain the similar effect of increasing ac drive and decreasing frequency.The influences of the bias and ac drive on the dielectric properties of PMZNT relaxed ceramics were compared. The external field dependence of dielectric response was studied in depth. It is found that the influence of increasing dc bias and ac drive are in opposition：increasing bias results in a decrease in the temperature of dielectric maximum Tmax and the dielectric constant and a reduce in the degree of frequency dispersion, whereas increasing drive results in an increase and a broaden.The effects of phase formation and lead titanate content on PNN-PT system has been investigated. The results showed the addition of excess Ni(Ac)2 could obtain pure perovskite phase, while the addition of stabilizer lead titanate could not. The piezoelectric effect induced by a dc bias field of 0.75PNN-0.25PT relaxed ceramics was studied preliminarily.Dielectric properties were investigated in ternary system PMW-PT-PNN as a function of relative content of three components. The experimental results indicated that in a certain range of composition, the degree of diffuse phase transition enhanced and the dielectric constant and Tmax decreased with the increase of PMW content. In addition, the increase of PMW content help to improve the temperature coefficient at low temperature. The PT content determined the dielectric properties at high temperature. PNN increases the dielectric constant over a wide temperature range.The optimal composition, which meets EIA X7R specification was obtained through extensive experimental studies. The influences of various dopants and processing methods on the temperature dependence could be attributed to the inhomogeneous compositional distribution, confirmed by SEM, TEM and HREM results. The formation mechanism of this inhomogeneous structure was also proposed. TEM experiments and backward electron image by SEM both revealed typical core-shell structured within one grain. The different parts in a grain have different temperature dependence of dielectric constant due to compositional variation. Therefore, the overlapped dielectric curves show flat temperature dependence. It was also found that Mn doping decreases the dissipation factor effectively. The mechanism was interpreted in terms of defect chemistry theory and domain wall pinning model.