| Compared with alloy thermoelectric materials,althoudi the series of Ca-Co-O oxide thermoelectric materials have a lower thermoelectrnc properties,they have advantages in high temperature stability,environmental protection,and have been widely studied.As one of the most promising materials in Ca-Co-0 series,Ca3CO4O9 has high seebeck coefficient and low thermal conductivity,but high resistivity limits its thermoelectric properties.So this thesis tries to reduce its resistivity by compositing and doping.Firstly,we had studied the thermoelectric performance of Bi2Ca2CO2Oy-Ca3CO4O9 composites.Large Ca3CO4O9 particles were synthesized by flux method,and then mixed with Bi2Ca2CO2Oy which were synthesized by solid reaction method,after that we used hot pressing to prepare samples.The results showed that the density of samples were increased with the adding of Bi2Ca2CO2Oy,and composite particles were generated with the size of 50-60 ?m.At 973 K,the resistivity of 0.3Bi2Ca2Co2Oy-0.7Ca3Co4O9 is 15.2 m?·cm and the power factor is 0.23 mW·m-1K-2.According to the appropriate composite ratio,we optimized the preparation process by adding Bi2Ca2Co2Oy powders into Ca3Co4O9 for three times accompanied with ball milling and hot pressing,The results showed that some of the particles were refined,and the Bi2Ca2Co2Oy powers Were filled uniformly in the gap of Ca3Co4O9 pieces.At 973 K,the resistivity of 0.3Bi2Ca2Co2Oy-0.7Ca3Co4O9 is 9.2 m?·cm and the power factor is 0.4 mW·m-1K-2The thermoelectric properties of composite had been futher optimized by Cu doping in Ca3Co4O9 and Bi2Ca2Co2Oy respectively.The results showed that Cu doped in Ca3Co4O9 leaded the increasing of carrier concentration.At 973 K,the resistivity of 0.3Bi2Ca2Co2Oy-0.7Ca3Co3.85Cu0.15O9 is 9.7 m?·cm.Cu doped in Bi2Ca2Co2Oy leaded the increasing of seebeck coefficient.At 973 K,the power factor of 0.3Bi2Ca2Co1.9Cu0.1Oy-0.7Ca3CO3.95Cu0.05O9 reaches 0.39 mW·m-1K-2. |
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