The Preparation And The Thermoelectric Properties' Study Of Bi-Substituted Ag Compoposite Ca₃Co₄O₉-Based Oxides

High-efficiency thermoelectric (TE) materials are important for power- generation devices that are designed to convert waste heat into electrical energy,which may play an important role in our current challenge to develop alternative energy technologies to reduce our dependence on fossil fuels and reduce green house gas emissions. Ca₃Co₄O_9+δ-based oxide is one of the most promising thermoelectric materials to be applied to the high-temperature industries, it has high temprature-resistance, anti-oxidation, thermal stability, and pollution-free, long service time, easy-preparation and low cost. But there is still a long distance from the performance targets of practical applications. Therefore, People constantly strive to find ways to enhance its thermoelectric properties.The homogeneous and superfine powers of CBCO,CCOA and CBCOA series were synthesized by the polyacrylamide gel method, and their powders were sintered by Spark Plasma Sintering(SPS). The microstructures of materials were characterized by XRD, SEM and EDS. The electrical conductivityσ, Seebeck coefficient S, power factor P of the three series ceramics were tested from 300⁹73K.The SEM photos of the cross-section of the three series ceramics illustrated that the particles formed a platelet shape,the grain sizes were around 1⁴μm,there was no observed pore in the Ca₃Co₄O_9+δ matrix,and its relative density was large. Otherwise, the XRD, SEM and EDS results of CCOA and CBCOA series indicated that Ag particles dispersed in the Ca₃Co₄O_9+δ matrix and no other second phase exist. The size of Ag particle is around 0.1¹μm, and Ag dispersed more even and smaller with the doping of Bi.The study of thermoelectric properties indicated that Bi-substituted improved the electrical conductivityσand the Seebeck coefficient S synchronously. The power factor P of the sample CBCO-0.5 was the largest, reached 4.8×10^-4 W·m^-1·K^-2 at 973K, which was 26.3% larger than that of Ca₃Co₄O_9+δ samples.The power factor P of CCOA and CBCOA series were larger than that of CBCO-0.5 and Ca₃Co₄O_9+δ samples. The power factor of CCOA-20 and CBCOA-10 reached 5.7×10^-4 W·m^-1·K^-2, 5.5×10^-4 W·m^-1·K^-2 respectively, which was the highest in respective system. It indicates that the addition of Ag is an effective method to enhance the thermoelectric properties of Ca₃Co₄O(9+δ)-based oxide thermoelectric materials.