Study On Preparation And Properties Of Para Double Doped Cobaltite Calcium-Based Thermoelectric Materials

Ca₃Co₄O₉-based oxide has became one of the most attention oxide thermoelectric?TE?materials in recent years,which has the advantage of woring in high oxidation temperature for a long time,pollution-free,easy-preparation and low cost.However,conversion efficiency of the TE materials is low,and the doping method is usually adopted to improve the TE properties.In this paper,we use the rare earth element Sm and the transition element Cu to carry on the para doping to the Ca₃Co₄O₉ material,and try to improve its thermoelectric properties.The samples of Ca₃Co₄O₉,Ca_3-x Sm_xCo₄O₉,Ca3Co_4-yCu_yO₉ and Ca_3-x Sm_xCo_4-yCu_yO₉ TE materials have been prepared by the citrate sol-gel.The phase,morphology and TE properties of the oxides were characterized by XRD,SEM and EDS.And changes of the electrical resistivity???,Seebeck coefficient?S?and power factor?PF?with doping elements and doping ratio were studied.The conclusions are as follows:TG-DSC and XRD analysis determine the calcination temperature is 800?,and sintering temperature is 900?.The phase of the no-doping sample is Ca₃Co₄O₉+? phase,and with high doping ratio doped sample will appear the impurity phase.SEM analysis show that grain size of the doping Sm0.3 sample is smaller,in 1² ?m;the layered structure of doping Cu0.3 sample is obviously,and the grain size is larger,in 3⁵ ?m;the layered structure of doping Cu0.15 in Sm0.3 sample becomes obvious,and the grain size increase,in 2³ ?m.There are many tiny pores in the sample,which make the density low,resulting in the high resistivity.Study on TE properties shows that the power factor increases with temperature.900 K,the maximum power factor of not-doped sample is 0.155 m W·K-2·m-1.Sm doping lead to increase of resistivity and Seebeck coefficient at the same time,maximum power factor of doping sample at x=0.3,is 0.153 m W·K-2·m-1.Cu doping lead to decrease of resistivity and Seebeck coefficient at the same time,maximum power factor of doping sample at y=0.3,is 0.166 m W·K-2·m-1.The maximum power factor of para position double doping sample at x=0.15 and y=0.15,is 0.164 m W·K-2·m-1.The results show that the amount of Cu doping and the para position double doping has a certain improving effect on the TE properties of Ca₃Co₄O₉+?,while the effect of Sm doping is not obvious.