Study On Preperation And Electrical Preperties Measurement Of Ca₃Co₄O₉Thermoelectric Materials

Thermoelectric material is one of the most important functional materials which can be used to convert thermal energy into electrical energy directly. Devices made of thermoelectric material have many special advantages, and have been successfully used in a few acmes of science and technology. Ca-Co-O thermoelectric oxides are widely applied due to its stability and performance under high temperature and oxidation resistance. But the application of this kind of material is limited because of its unsatisfying thermoelectric properties.Firstly, thermoelectric materials Ca3Co4O9doped with Y in the composition of Y0.2Ca2.8Co4O9were prepared by sol-gel method combined high-pressure compacting technique followed by pressureless sintering. The microstructures of the oxides were investigated and the electrical properties (including Seebeck coefficient and electrical conductivity) were measured from room temperature to1000K. It was found that high pressure compacting is helpful to improve the density and texture of Ca3Co4O9. The electrical resistivity decreases with an increase of temperature. While the Seebeck coefficient increases with an increase of temperature. The maximum power factor3.9μW/cmK2at1000K is obtained for the sample pressed by high pressure.Then, this article made a systematic research of typical thermoelectric materials, including Ca3Co4O9, CoSb3, Bi2Te3, PbTe, PbSe and Constantan. The impact of Seebeck effect of thermocouples, temperature settings, the way of curve fitting on the measurement of resistivity and surface oxide film of the sample on Seebeck coefficient measurement were investigated. The impact of contact resistance, additional Seebeck voltage, the measuring of thermocouples distance and surface oxide film of the sample on the measurement of resistivity were discussed. The standards of electrical properties measurement of thermoelectric materials were made based on this, and it can be used to measure Seebeck coefficient and resistivity of thermoelectric materials from room temperature to1100℃.Finally, the verification of precision and evaluation of measurement uncertainty for this standard was made based on GB/T6379-2004Accuracy (trueness and precision) of measurement methods and results and JJF1059-1999Evaluation and Expression of Uncertainty in Measurement.