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The Preparation and Thermoelectric Properties of Rare Earth Subsituted Ag Composite Ca3Co4O9-Based Oxides

Author: LuYan
Tutor: SongYing
School: Harbin Institute of Technology
Course: Chemical Engineering and Technology
Keywords: Thermoelectric properties Ca3Co4O9 Ag composite doped rare earth
CLC: TQ174.1
Type: Master's thesis
Year: 2008
Downloads: 90
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Abstract


Energy is very important for the development of economy and society. It plays a key role to improve the living standard of people. Therefore, people pay gradually attention to develop alternative energy technologies. Ca3Co4O9-based oxide is one of the most promising thermoelectric（TE） materials to be applied as the high-temperature TE generator, which has high temperature-resistance, anti-oxidation, thermal stability, and pollution-free, long service time, easy-preparation and low cost. However, there is still a long distance from the performance targets of practical applications. Therefore, hard work must be done to enhance its TE properties.The homogeneous powers of Ca3Co4O9/Ag, (Ca0.9Sm0.1)3Co4O9/Ag and (Ca0.9Yb0.1)3Co4O9/Ag series were synthesized by the polyacrylamide gel method, and their powders were sintered by Spark Plasma Sintering （SPS）. The microstructures and compositions were characterized by XRD and SEM. The electrical conductivityσ, Seebeck coefficient S and power factor P of the three series ceramics were changed with increasing Ag content.The XRD and SEM results of Ca3Co4O9/Ag, (Ca0.9Sm0.1)3Co4O9/Ag and (Ca0.9Yb0.1)3Co4O9/Ag series indicate that Ag particles disperse in the Ca3Co4O9 matrix as the second phase. The size of Ag particle is around 0.11μm. The SEM photos of the cross-section of the three series ceramics illustrate that the particles formed a platelet shape. The grain sizes are around 12μm. There were no observed pores in the Ca3Co4O9 matrix. The relative densities of the SPS samples are all over 98%, which illustrates that Ag disperses more even and smaller by the polyacrylamide gel method and Spark Plasma Sintering process.The electrical measurement shows that the electrical conductivity increases while the Seebeck coefficient decreases with increasing Ag contents in the Ca3Co4O9/Ag, (Ca0.9Sm0.1)3Co4O9/Ag and (Ca0.9Yb0.1)3Co4O9/Ag series. The power factor P of the three series Ag composites is improved due to the obvious increase in electrical conductivity. The power factor of Ca3Co4O9/0.3Ag, (Ca0.9Sm0.1)3Co4O9/0.2Ag and (Ca0.9Yb0.1)3Co4O9/0.3Ag reaches 3.72×10-4W·m-1·K-2, 2.56×10-4W·m-1·K-2 and 2.73×10-4W·m-1·K-2 respectively, which is the highest in respective system. It indicates that the addition of Ag is an effective method to enhance the TE properties of Ca3Co4O9-based oxide thermoelectric materials.

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