Effect of Gd-doping on thermoelectric properties of Ca3Co4O9+δ ceramics
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A series of Ca3−x Gd x Co4O9+δ precursor powders were synthesized by the polyacrylamide gel method, and their ceramics were obtained by the Spark Plasma Sintering (SPS). There were lots of defects in the sheet-like grains from SEM and TEM observations. The electrical and the thermal transport properties were obviously affected by the material microstructure. The small polaron hopping conduction mechanism was determined above 600 K, and the hopping activation energy increased with the increase of doping contents. It was found that the Seebeck coefficient and the resistivity of doped samples were markly enhanced due to the impurity compensation effect, and their thermal conductivities were decreased due to the defects scattering. The maximum figure of merit of ZT = 0.24 at 973 K was obtained for Ca2.7Gd0.3Co4O9+δ.
KeywordsSpark Plasma Sinter Thermoelectric Property Seebeck Coefficient Dope Sample Negative Temperature Coefficient
The authors would like to thank the financial supports from National Basic Research Program of China (973 program) under Grant No. 2007CB607502, the National Natural Science Foundation of China (NSFC) of No. 50801054 and 50772026, and Natural Science Key Fund of Heilongjiang Province in China (grant No. ZJG0605-01).