| Thermoelectric Oxides are promising for high-temperature thermoelectric application due to their excellent stability at high-temperature,low toxicity,no pollution and abundant reserve.The ZnO thermoelectric material is one of the reported n-type oxide thermoelectric materials with high thermoelectric performance.However,the intrinsic ZnO has low eletrical conductivity and large thermal conductivity.In this paper,the thermoelectric properties of ZnO were improved by co-doping Al and W.AlxZn1-x-xO?x=0,0.01,0.02,0.04?powders were synthesized by a sol-gel method,and then were sintered at 1200?,1300? and 1400? in three sintering atmosphere?Air,nitrogen and 10%H2/Ar?,respectively.The effects of sintering atmosphere and Al doping on the composition,morphology and thermoelectric properties of ZnO were investigated.The experiment results showed that the AlxZn1-x-xO ceramics could not be sintered directly in 10%H2/Ar atmosphere.The high density ceramics could be obtained by being sintered at 1400? in Air,nitrogen or pre-calcined the powder first in 10%H2/Ar and then sintered in nitrogen?marked as H2+N2 sintering atmosphere?.For the samples sintered in the three sintering atmospheres,the doping of Al improved the thermoelectric properties of ZnO,and at 773 K,the power factors of the samples with x=0.02 reached maximum.The power factor of AlxZn1-x-xO ceramics sintered in N2 or H2+N2 atmosphere was much higher than that of samples sintered in Air atmosphere.Among them,the samples sintered in H2+N2 atmosphere had optimal thermoelectric performance,and the power factor of Al0.02Zn0.98O reached a maximum of 5.86×10-4W·m-1·K-2,which was 2.3 times higher than that of ZnO.Zn0.98-y.98-y Al0.02Wy O?y=0,0.005,0.01,0.02?ceramics were sintered in N2atmosphere at 1200?,1300? and 1400?,respectively.The effects of Al and W co-doping on the composition,microstructure and thermoelectric properties of ZnO were investigated by XRD,SEM and thermoelectric parameters test.For the samples sintered at 1200?,the doping of W could promote the growth of grain and acted as a sintering aid.But compared to sintered samples at 1300? and1400?,the thermoelectric properties of the samples sintered at 1200? were low.For the samples sintered at 1300?and 1400?,the electrical conductivity and power factor were significantly increased,and thermal conductivity was decreased,as the doping amount of W was y=0.005,which resulted in a significant increase in ZT value.However,the porosity increased and density reduced with increasing the doping of W,which decreased the thermoelectric properties.TheZn0.975Al0.02W0.005O sample sintered at 1400? had a maxium power factor of5.69×10-4W·m-1·K-2at 773 K,which was 50%higher than that of Al0.02Zn0.98O prepared at the same condition.Finally,the ZT value of Al0.02W0.005Zn0.975O sample sintered at 1400? reached a maximum value of 0.047 at 773 K,which was 66%higher than that of Al0.02Zn0.98O. |
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