电荷有序Ln2-xSrxNiO4陶瓷的巨介电效应与小极化子跃迁

The giant dielectric responses in the charge-ordered Ln2-xSrxNiO4 (x=0.5,0.25) ceramics up to high frequency were observed, and this might provide the possible application of giant dielectric materials at high frequency. After analysising the link between charge ordering and giant dielectric response, a small polarnic hopping model was proposed. Based on aboved results, we focuse on the giant dielectric response and dielectric relaxation in the charge-ordered Ln2-xSrxNiO4 (Ln=La, Nd, Sm) ceramics in the present project. First, the size and concentration of small polaron can be tuned by changing the component and the post heat-treating, after comparing the experimental dielectric constant, response frequency and activation energy of dielectric relaxation with the predicted results from the small polaronic hopping model, the correlation between the giant dielectric respone and small polaronic hopping can be confirmed. Then, with the help of character of small polaron from the electric transport measurement, the detailed structural origin of the giant dielectric response in the present materials are given. Final, based on the above model, a new effective method, formation of the core-shell structure, to optimize and control the giant dielectric response of Ln2-xSrxNiO4 ceramics is proposed, and the method may lead to the practical application of the present materials.

电荷有序Ln2-xSrxNiO4(x=0.5,0.25)陶瓷中观测到高频巨介电效应，这为巨介电常数材料在高频应用打开了大门，在分析电荷有序与巨介电效应关联的基础上，我们提出了小极化子跃迁模型。本项目拟在以上工作基础上，着眼于电荷有序Ln2-xSrxNiO4 (Ln=La, Nd, Sm) 陶瓷中的介电弛豫及巨介电效应，首先通过改变材料的组成并结合烧结后的热处理来调控小极化子的尺度与浓度，分析材料介电常数、介电响应频率以及激活能的变化规律，并与小极化子跃迁模型的预测结果进行比对来确认两者的关联；随后，利用材料的电输运特性给出小极化子的特性，从而给出该材料体系巨介电效应的物理本质与结构根源；最后在该模型基础上，利用形成核-壳结构新方法，来探索优化与调控Ln2-xSrxNiO4陶瓷巨介电效应的有效途径，为该材料的实用化奠定基础。

在具有K2NiF4结构的镍酸盐中发现了温度稳定的高频巨介电效应，极大地拓宽了巨介电常数材料的应用范围。通过研究其介电响应与电荷有序等结构、性能的关联，建立了小极化子跃迁模型。按照该模型，材料的介电效应是与小极化子浓度及尺度密切相关，而小极化子则是由Ni3+离子中t2g轨道的空穴引起的。因此，控制材料中Ni3+离子的浓度成为调控材料的巨介电效应的关键。本项目通过研究氧空位对La5/3Sr1/3NiO4+δ和Sm1.5Sr0.5NiO4-δ陶瓷巨介电效应的影响规律，揭示了氧空位在该材料体系的特殊作用，给出了获得巨介电效应的有效途径；通过烧结后热处理的方法来控制Nd2NiO4+δ陶瓷中的过量氧含量，有效地调节了材料小极化子的浓度，达到了优化材料巨介电效应的目标；通过用不可变价Al离子来置换可变价的Ni离子，实现了对材料中的小极化子浓度和尺度的调控，进而强化了其巨介电效应，并最终揭示了镍酸盐陶瓷的巨介电效应的物理本质与微结构起源；在以上研究基础上，通过引入绝缘阻挡层来降低小极化子的长程迁移，在保持温度稳定的巨介电常数的前提下有效地降低了材料的介电损耗，为该材料的实用化指明了方向。同时，根据该领域发展的新趋势，适度增加了相关材料的非本征铁电性和巨磁介电效应的研究，取得的重要进展、并促进了具有K2NiF4结构的镍酸盐陶瓷本身的研究。