Title  3d element replacement for cobalt oxide thermoelectric material impact study spin entropy

  Abstract With the increasing shortage of energy and the environment pollution problem is becoming more and more serious, thermoelectric materials as new functional materials for energy conversion, no pollution to the environment; no effluent; work without noise; and the core components of thermoelectric materials, thermoelectric device service state stability, long service life, is friendly to environment type of functional material with wide application prospect. The use of angle to determine, hot potential must be one of the necessary conditions for high performance thermoelectric materials. At present, the hot research potential has become one of the hot talk. Some research shows that, the spin entropy plays an important role in improving the thermoelectric potential of Co-based oxide thermoelectric material, theory of spin entropy is also verified by experiments. Spin entropy is the enhanced potential source materials. Spin degeneracy spin entropy cobalt oxides on thermal potential contribution and concentration of Co4+ ions and Co ions and the degree of. Doping transition metal elements is an effective way to change the Co4+ ion concentration, which can change the spin entropy material or provide another jump model spin entropy transport. Therefore, can affect the study of transition metals doping on spin entropy to study how to improve the thermoelectric potential provides important guidance role. In this paper, closely follow the international front, the Co-based oxide as the research object, the metal elements doping effect on the spin entropy Co-based oxide materials and studied by combining magnetic analysis and magnetic potential measurement. The experimental study on the effect of Ni doping on NaCoxO4 spin entropy. It is found that the magnetic field has strong inhibitory effect on the thermal potential, that spin entropy effect exists in the material. Magnetic potential increases with the increase of Ni content, indicating that Ni doping can significantly improve the spin entropy NaCoxO4. We found a new spin entropy transport mechanism, and puts forward a theoretical model of a spin entropy competition. Research on the magnetocaloric potential doped samples. Inhibitory effect of magnetic field on potential found strong power, which shows that the spin entropy effect exists in the material. Compared to the undoped Ca3Co4O4, thermal magnetic potential doped samples are increased to a certain extent. This provides experimental evidence for spin entropy increase as the doping lead. Analysis showed that 3D doping Co4+ ion concentration decrease in magnetic materials. Research shows that reducing Co4+ ion concentration resulted in increased spin entropy. 67155

Keywords：cobalt oxide, thermoelectric materials, thermoelectric, spin entropy, mixed, thermoelectric properties.

目录 Ⅰ

摘要 Ⅱ

英文摘要 Ⅲ

一、绪论 Ⅳ

1、 3d元素置换原理概述

2、 热电材料基本理论

3、 钴基氧化物热电材料自旋熵特性和研究意义

二、实验方法 Ⅴ

1、 实验装置及原料

2、 材料的制备方法

3、 自旋熵的研究

4、 X射线光电子能级光谱分析

5、 X射线吸收谱分析

三、Ni参杂对3d元素置换钴基氧化物热电材料熵的影响Ⅵ

四、全文总结 Ⅶ

五、致谢 Ⅷ

第一章  绪论

1.1  3d 元素置换原理概述

本项目的主要研究NaCo2NiO4自旋熵的变化及输运机制，通过NaCo2NiO4中人为引入均匀分布的3d过渡金属元素研究Ca3Co4O9+d中自旋熵的变化，及可能引起的输运机制的改变。通过对材料的磁性、热输运及电输运性质测量分析，及不同磁场和温度下的磁热电势测量分析。得出这类材料的热电性能随温度、置换量的变化关系和磁热电势随温度、磁场、置换量的变化关系。在钴基氧化物中自旋熵对热电势的贡献与Co4+离子浓度及Co离子的自旋简并度有关。认为过渡金属元素位掺杂是改变 Co4+离子浓度的一种很有效的方式，可以通过 Co 位掺杂改变材料的自旋熵或者掺杂离子可能提供其它的自旋熵输运方式。因此，研究过渡金属元素掺杂对NaxCo2O4 自旋熵的影响可以为探寻提高材料的自旋熵及热电势提供指导作用。我们从实验和理论上研究了 Ni 元素掺杂对NaxCo2O4 材料自旋熵的影响。通过研究NaxCo2−yNiyO4 体系的磁热电势发现了热电势对磁场强的依赖关系，磁热电势随着 Ni 掺杂量增加。这些结果说明了 Ni 掺。通过实验测量定量地研究元素置换对材料自旋熵的影响，从而得到自旋熵变化的机制和输运规律。有人研究了过渡金属元素掺杂对 NaCo2O4 热电性能的影响。但还没有人研究过渡金属元素掺杂对其自旋熵的影响。在钴基氧化物中，自旋熵对热电势的贡献与 Co4+ 离子浓度及 Co 离子的自旋简并度有关。过渡金属元素 Co 位置换是改变 Co4+ 离子浓度的一种有效方式。由于 Co4+ 离子浓度在自旋熵的变化中起着关键作用，Co 位置换能改变材料的自旋熵。研究过渡金属元素掺杂对自旋熵的影响可以为研究如何提高材料的热电势指明方向。Fe 元素掺杂对 NaCo2O4材料自旋熵的影响。通过详细的研究掺杂 Fe 后材料的磁热电势，穆斯堡尔谱和磁特性，发现了高自旋 Fe3+离子掺杂能抑制 NaCo2O4的自旋熵通过对这些样品的磁性和热输运及电输运性质测量，如材料的磁化率、热导率、电导率、热电势、比热、霍尔系数等，及不同磁场和温度下的磁热电势测量，获得测试样品中与电子自旋相关方面的信息，给出这类材料的热电性能，热电势随温度、置换量的变化关系和磁热电势随温度、磁场、置换量的变化关系。从磁热电势随温度、磁场、置换量的变化关系，分析出自旋熵的大小和掺杂量对自旋熵的影响。