高取向纳米结构Na1-xAgxCo2O4的可控制备及其热电性能

Oxide thermoelectric materials such as NaCo2O4 have special advantages and potential applications. Although NaCo2O4 single crystal possesses good thermoelectric property, its application is restricted by small size and preparation technology. Moreover, the NaCo2O4 polycrystalline bulk material shows low thermoelectric property, which is normally improved by element doping and microstructure controlling respectively. We propose a method to improve its thermoelectric property by combining element doping and microstructure controlling simultaneously. Firstly, Ag element, which can significantly improve the thermoelectric property of NaCo2O4, is selected to be doped in NaCo2O4 and the size and morphology of Na1-xAgxCo2O4 is controlled by macromolecular. The nano plate Na1-xAgxCo2O4 crystals with high ratio of diameter to thichness are obtained as raw powders. Furthermore, using optimized forming method and SPS sintering technology for holding nano mature and morphology of powders, the highly orientecd Na1-xAgxCo2O4 nanostructured polycrystalline bulk materials with improved thermoelectric property are fabricated. Based on this, the relationship between thermoelectric property and microstructure is studied and the mechanism improving thermoelectric property is discussed. This project will provide a easy technology for preparing high performance NaCo2O4 thermoelectric material.

氧化物热电材料NaCo2O4具有独特的优点和潜在的应用前景，虽然其单晶具有良好的热电性能，但单晶尺寸和制备工艺限制了它的应用；而其多晶块体性能普遍偏低，目前的研究分别通过掺杂、微结构控制来改善其热电性能。本项目拟结合元素掺杂和微结构控制来建立一种改善其热电性能的方法，选取对NaCo2O4热电性能影响显著的Ag元素，首先通过大分子物质控制Na1-xAgxCo2O4晶体的尺寸和形态，获得高径厚比的Na1-xAgxCo2O4纳米片状晶体作为原料粉末；再结合优化的成型方法和SPS烧结技术，保持原料粉末的纳米特性和分布形态，制备高结晶取向的Na1-xAgxCo2O4纳米多晶块体材料，来提高其热电性能；在此基础上，进一步研究高结晶取向Na1-xAgxCo2O4纳米多晶块体材料的热电性能与微结构的关系，弄清改善其热电性能的机制，为制备高性能NaCo2O4热电材料提供一种简便易行的制备技术。

氧化物热电材料NaCo2O4具有独特的优点和潜在的应用前景，虽然其单晶具有良好的热电性能，但单晶尺寸和制备工艺限制了它的应用，而其多晶块体性能普遍偏低。因此，研究可提高NaCo2O4多晶块体陶瓷热电性能的方法具有重要的意义。本项目分别通过掺杂、微结构控制来改善其热电性能，开展了NaxCo2O4原料粉末合成工艺的研究，探讨了反应温度、高分子添加剂、原料反应浓度、对粉末晶体的尺寸、径厚比和分布形态的影响；开展了NaxCo2O4陶瓷烧结工艺的研究，优化了烧结工艺参数，包括升温速率、烧结气氛、烧结压力和烧结时间等；探讨了陶瓷微结构对热电性能的影响规律，以及元素掺杂对提高陶瓷热电性能的作用。通过本项目的研究，发展了三种制备γ­NaxCo2O4粉体的合成工艺：聚乙二醇（PEG）改进柠檬酸盐溶胶凝胶法，聚丙烯酸钠（PAAS）凝胶法和超声喷雾制备法，实现了γ­NaxCo2O4粉体的可控合成；建立并优化了NaxCoO2陶瓷等离子活化烧结(PAS)工艺参数，ZT值在800 K时可达到0.22；通过提高Na含量，以及Ca、Cu、Ag和Ni元素掺杂，实现了NaxCoO2陶瓷热电性能的提高：900 K时Na1.1CoO2样品ZT值（0.39）是Na0.8CoO2样品ZT值（0.12）的三倍；Na0.5Ca0.3CoO2样品在900 K时ZT值为0.25，提高了108%； Na0.8Co0.95Cu0.05O2样品在900 K时ZT值0.32，提高了167%；当Ag含量为2.5%时，样品在800 K时ZT值达到0.29；Ni作为受主杂质，提高了样品的空穴浓度，提升电导率，ZT值在800 K时达到0.31，提高了41%。