A,B位双掺杂及LaAlO3复合钙钛矿LnFeO3的载流子输运特性与介电损耗机理研究

The high dielectric constant materials is the basic requirement for the miniaturization of the electronic device. Searching for the novel high dielectric constant materials and controlling the dielectric loss are very important. In this project, perovskite-typed oxides LnFeO3 (Ln=La,Pr,Nd,Sm) were selected as basis to tune phase component,crystal structure, band gap，electronic characteristic and dielectric properties via combination and double-doping. Firstly, the combination with the wide band-gap LaAlO3 is to change the gap of system and then the concentration of carriers. Secondly, via A-site doping with alkaline-earth metals ions (acceptor) and B-site with transition metal ions (Ti4+,Zr4+,Nb5+)(donor) the concentration of carriers was further controlled but also the concentration of defects increased. The possibility of association of defects also increased, which result the reduction of the mobility of carriers. Finally, the temperature dependence of impedance spectroscopy was investigated to obtain the conduction of bulk and interface. The dielectric relaxation was analyzed to obtain the effects of combination and doping on the dielectric loss and to reveal the intrinsic relationship between the electronic characteristic and loss. Then the key factor that determined the loss of material was confirmed and to optimize the dielectric properties of the material. This study will establish the theory foundation for the practical application.

高介电常数材料是电子元器件能够满足小型化的基本要求，寻求新的高介电材料以及控制其介电损耗至关重要。本项目以钙钛矿型LnFeO3 (Ln=La,Pr,Nd,Sm)为基础，通过复合以及双掺杂对其相组分、晶体结构、能带结构、电子特性以及介电性能进行调控。首先通过复合宽带隙的LaAlO3调节其能隙以及载流子浓度；其次分别在A,B位进行碱土金属离子（受主）与过渡金属离子（Ti4+，Zr4+，Nb5+）（施主）双掺杂，一方面进一步调控载流子浓度，另一方面增加缺陷浓度，或引起缺陷的缔合来增强载流子的局域性，以降低其迁移率；最后，利用变温阻抗谱分析样品的体相与界面的电传导，并研究其介电弛豫，重点分析复合与掺杂对材料介电损耗的影响，揭示载流子输运特性与损耗之间的内在物理机制，确定影响此类材料介电损耗的关键因素，以优化材料的介电性能，为材料的实际应用奠定理论基础。

本项目主要研究过渡金属氧化物材料中的介电弛豫来源以及介电损耗的机理，以获得高介电低损耗的材料。主要通过A、B位对PrCoO3进行双掺杂来调控材料的晶体结构、载流子输运特性，进而找出此类材料中介电弛豫以及损耗与载流子输运之间的关系。.采用Sol-Gel法合成了单相的A位Bi3+与Y3+掺杂的PrCoO3，发现Bi3+掺杂能够增强载流子的局域性，降低材料的电导率，同样降低其介电常数与介电损耗。相反，掺杂离子半径更小的Y3+则能够同时提高材料的电导率与介电常数，明显地改善材料的介电性能。.采用熔盐法合成了一系列A位取代的LnCoO3，发现随着镧系收缩，其正交扭曲先减小再增加，而Co-O-Co夹角则单调减小，八面体的倾斜度增加，Co3+的带宽减小，导致载流子的迁移率下降，局域性增强，相应的介电常数减小，介电损耗得到了一定的控制。.采用Sol-Gel法合成了单相的B位Mn3+与Ni3+掺杂的PrCo1-xMnxO3，发现随着Mn3+浓度的增加晶格膨胀，但是其正交性下降，对称性增加；FT-IR光谱显示CoO6八面体中ab面上的Co-O键收缩，而c轴方向的Co-O键增加，Co3+逐渐从低自旋态向高自旋态转变，同时Co3+的带宽减小，对应载流子迁移率的减小，但是同样导致介电常数下降。.采用球磨加高温退火的方法合成了不同卤素离子掺杂的argyrodite型Li6PS5X离子导体，发现卤素离子的极化率以及S/X的无序性对该类材料的电导率有着重要的影响，随着极化率与无序性的增加电导率增加，交流阻抗谱与固态NMR均证实了这一点，固态电池Li2S/Li6PS5X/In表现出优异的充放电性能，可逆容量达到750 mAh/g.