Physical Properties of Oxide Thermoelectric Materials Prepared by the Polymerized Complex Method

本研究采用聚合络合法制备了微观结构可控的氧化物热电材料，并对其物理性能进行了测试。通常认为，聚合络合法制备各种氧化物材料是一种简便的方法。我们研究了Zn_&lt；1-x&Gt；Al_xO和层状Na_xCO_2O_4系统。化学计量的金属硝酸盐水合物和柠檬酸溶解在乙二醇中。对溶液进行浓缩，形成粘性聚合络合物。这些聚合物在空气中分解成细小而均匀的粉末。对于Zn_&lt；1-x&Gt；Al_xO系，粉末用放电等离子烧结装置在1100℃，压力10~30 Mpa下烧结10min；对于Na_xCO_2O_4系，粉末经900℃，25 Mpa，热压1~2小时烧结。用X射线衍射仪和m-…对样品进行了物相鉴定用扫描电子显微镜观察了样品的微观结构。测试了样品的塞贝克系数、电阻率和热导率等物理性能。聚合络合物法制备的Zn_(1-x)&Gt；Al_xO的晶粒度约为1~2μm，远小于传统固相反应法制备的10μm，其塞贝克系数和电阻率的绝对值一般随Al含量x的增加而减小，在Al含量一定的情况下，与固相反应法制备的样品相比，聚合络合物法制备的样品具有较小的塞贝克系数和电阻率。尽管前者的晶体尺寸要小得多，但它们的导热系数几乎没有差别。结果表明，聚合络合物法制备的样品更均匀，更容易实现载流子的掺杂。另一方面，与固相反应法制备的NaxCo2O4陶瓷相比，聚合络合法制备的NaxCo2O4陶瓷具有更高的结晶各向异性，并且具有更低的电阻率，保持了中等的Seebeck系数。结果表明，用聚合络合法制备的样品具有较大的优值因子。较少

In this Study we have prepared the oxide thermoelectric materials with controlled microscopic structure by the polymerized complex method, and measured their physical properties. It is generally considered that the polymerized complex method is a convenient method for preparing various oxide materials. We have investigated the Zn_<1-x>Al_xO and Layered-Na_xCo_2O_4 systems. Stoichiometric amounts of metal nitrate hydrate and citric acid were dissolved in ethylene glycol. The solution was concentrated and the viscous polymerized complexes were formed. These polymeric products were decomposed to a fine and uniform powder in air. In the case of Zn_<1-x>Al_xO system the obtained powder was sintered by SPS (Spark Plasma Sintering) apparatus at 1100℃ for 10min at a pressure of 10〜30MPa, while in the case of Na_xCo_2O_4 system the obtained powder was sintered by Hot-Pressing at 900℃ for 1〜2h at a pressure of 25MPa. The phase identification of the samples was made by X-ray diffraction and the m … More icroscopic structure of the samples was examined using SEM. The physical properties such as Seebeck coefficient, the electrical resistivity and thermal conductivity of the samples were measured. The crystal grain size of Zn_<1-x>Al_xO prepared by the polymerized complex method is about 1〜2μm, which is much smaller than that by the conventional solid state reaction method, 10μm. The absolute value of the Seebeck coefficient and the electrical resistivity for Zn1-xAlxO generally decreases with increasing Al content of x. Comparing theses values at fixed Al content between the samples prepared by the polymerized complex and solid state reaction methods, the samples by the polymerized complex method have smaller values. There is almost no difference in the thermal conductivity between these samples, although the crystal grain size of the former is much smaller. These results indicate that the more homogeneous samples were obtained by the polymerized complex method and the doping of the carrier into the material can be more easily realized in the samples prepared by the polymerized complex method. On the other hand, NaxCo2O4 ceramics prepared by the polymerized complex method show higher crystallographic anisotropy than that by the solid state reaction method, and have lower electrical resistivity maintaining moderate Seebeck coefficient. As a result, lager figure of merit was obtained on the samples prepared by the polymerized complex method. Less