Ag-ZnO纳米复合热电材料的制备及其性能研究

ZnO是一类具有潜力的热电材料, 但其较大声子热导率影响了热电性能的进一步提高. 纳米复合是降低热导率的有效途径. 本文以醋酸盐为前驱体, 溶胶-凝胶法制备了Ag-ZnO纳米复合热电材料. 扫描电镜照片显示ZnO颗粒呈现多孔结构, Ag纳米颗粒分布于ZnO的晶粒之间. Ag-ZnO纳米复合材料的电导率比未复合ZnO材料高出100倍以上, 而热导率是未复合ZnO材料的1/2. 同时, 随着Ag添加量的增加, 赛贝克系数的绝对值逐渐减小. 综合以上原因, 添加7.5%mol Ag的Ag-ZnO纳米复合材料在700 K时的热电优值达到0.062, 是未复合ZnO材料的约25倍. 在ZnO基体中添加导电金属颗粒有利于产生导电逾渗通道, 提高材料体系的电导率, 但同时导致赛贝克系数的绝对值减小. 总热导率的差异来源于声子热导率的差异. 位于ZnO晶界的纳米Ag颗粒, 有利于降低声子热导率. 关键词： 热电材料 ZnO 纳米复合 热导率

Preparation and thermoelectric properties of Ag-ZnO nanocomposites synthesized by means of sol-gel

Zinc oxide (ZnO) has attracted increasing attention as one of the most promising n-type thermoelectric materials. Although ZnO has been screened for high power factor, the ZT results were discouraging for its high thermal conductivity. Preparing nanocomposite is an effective way to reduce the thermal conductivity. The Ag-ZnO nanocomposites were synthesized by means of sol-gel method and their thermoelectric properties were investigated. Their XRD pattern and SEM miro graphs show that Ag nanoparticles are mainly lecated at the grain boundary of ZnO. Increasing Ag content leads to a significant decrease in absolute value of Seebeck coefficient (|S|). The electrical conductivity increases with increasing Ag content, while the thermal conductivity of Ag-ZnO nanocomposites is much lower than the bulk ZnO sample. The highest ZT (0.062) is found for 7.5 mol% Ag@ZnO nanocomposite at 750 K, thirty-five times of that of bulk ZnO. Since the Ag-ZnO junction leads to charge redistribution, the deflexed energy band obtained for ZnO should facilitate the electron transfer across the interface and thus accelerates the mobility of charge carriers. Thus increasing mobility of charge carriers would lead to the increase in electrical conductivity and a decrease in Seebeck coefficient. The difference of thermal conductivity comes from the lattice thermal conductivity. Due to the high density of interfaces and grain boundaries present in the nanocomposites, the scattering of phonons across a broad wavelength spectrum is enhanced. This suppresses the lattice thermal conductivity of the nanocomposites significantly.
Keywords： thermolelectric materials ZnO nanocomposite thermal conductivity