掺杂二氧化锰纳米材料合成及热电效应研究

Based on the previous study of thermoelectric ZnSb nanomaterials, this project aims to further synthesize doped MnO2 nanostructured materials and study their thermoelectric transport. The composition, structure, morphology, size, surface area and other factors of doped nanomaterials and their thermoelectric properties will be researched; By improving the design, pre-processing, and preparation techniques of doped nano-structure, we shall fabricate a variety of different morphologies and structures of the doped MnO2 nanostructures. Little effect on the premise of the Seebeck coefficient, by chemical doping of the nanostructured, carrier concentration and the mobility will increase, while enhancing its selective scattering, thereby the corresponding thermoelectric figure of merit (ZT) will be improved. According to controlling and optimizing structures and doping in the materials, their thermoelectric properties will be advanced. Combined with the Hall coefficient, thermoelectric transport measurements, and theoretical calculations, we study the thermoelectric properties and explore counterpart mechanism in depth. The microscopic mechanism of constraints of the thermoelectric properties under chemical doping MnO2 system will be revealed to achieve the purpose of significantly improving the performance of thermoelectric, to develop doped oxide thermoelectric materials and sensors containing these advantages including non-toxic, non-polluting, low cost, simple preparation process, easy to be miniaturized, etc.

本项目拟在前期锑化锌纳米材料合成及热电性质研究的基础上进一步合成掺杂MnO2纳米材料并研究其热电输运性能。研究掺杂纳米材料的组成、结构、形貌、尺寸及比表面积等因素对其热电性能的影响。通过进一步完善掺杂纳米结构的设计、预处理及制备技术，制备出各种不同形貌的掺杂MnO2纳米结构。在对Seebeck系数影响不大的前提下，通过化学掺杂，使纳米结构中的载流子浓度和迁移率提高，同时增强其选择性散射，从而提高材料热电优值。优化调控结构及掺杂，达到改善其热电性能的目的。结合霍耳系数、热电输运等测量手段及理论计算，深入系统地研究其热电性能，探索其机理，揭示化学掺杂MnO2体系下制约其热电性能的微观机制，大幅度提高材料的热电性能，发展具有无毒害、零污染、低成本、制备过程简单、易于微小化等优点的掺杂氧化物热电材料及热电传感器。

通过简单的化学气相沉积法合成MnO2纳米线，并对其成分、结构和形貌进行表征。研究证明，制备的样品由许多形貌均匀且结晶性良好的MnO2纳米线构成，且其直径约为100 nm,长度可高达到几十个微米。随后对其热电性能进行测试。热电性能测试表明，与其块体材料相比，MnO2纳米线的热电性能有所增加，这主要归功于纳米化增强了晶界散射，从而降低了其热导率。但是与优异的热电材料相比，我们所合成的MnO2纳米线的ZT值仍然较低，不适合大规模的商业应用，这主要是由其电导率仍然较低所致。. 以银作为掺杂剂，通过化学气相沉积法合成不同银浓度掺杂的MnO2纳米线, 研究了银掺杂对MnO2纳米材料的形貌、晶体结构和热电性能的影响。结果表明银掺杂对MnO2纳米材料的形貌没有明显影响，产物仍由大量直径约为100 nm的纳米线组成；且当银掺杂浓度较低时，其晶体结构也没有显著变化，而较高时，产物中会出现Ag2O的杂质相。同未掺杂的MnO2进行比较，低浓度银掺杂后MnO2的热电性能明显提高；且当银的掺杂浓度为2% 时，MnO2纳米线的ZT值在580 K可达到最大值，约为2.18。这主要归因于银掺杂使得MnO2的功率因子显著增加，热导率明显降低。此外我们还能够观察到，低浓度的银掺杂导致MnO2纳米线由原来的n型半导体转变为p型半导体。