Thermoelectric Modification Of Bi₂Sr₂Co₂O_y By Doping And Composting

The development and application of new green and environment-friend energy is exceedingly necessary.Thermoelectric materials,converting heat into electrical power directly and inversely,with amounts of merits such as simple structure,small in size,noiselessness,none-discharging and long service life,is a very hopeful energy materials in future.Misfit layered Bi₂Sr₂Co₂O_y is considered to be good thermoelectric materials suitable for intermediate and high temperature due to its lower thermal conductivity,oxidation-resistance and non-toxic.However,the industrial application of Bi₂Sr₂Co₂O_y is limited because of its poorer electric conductivity.According to the recent research,doping and compositing are effective ways to improve the thermoelectric performance of Bi₂Sr₂Co₂O_y.By doping,this paper investigates the effect of layer misfitness on thermoelectric properties of Bi₂Sr₂Co₂O_y in order to lay the experimental basis for optimizing the thermoelectric performance of these materials.and in further,this paper explores the composites of Bi₂Sr₂Co₂O_y and Ca₃Co₄O₉,it is considered that compositing is an effective method for optimizing the thermoelectric performance of Bi₂Sr₂Co₂O_y.Sereral methods such as milling,solid-phase reaction,flux method and hot pressing have been employed for preparing samples.The optimized ball milling time and sintering process was adopted based on the measurement of thermoelectric properties and microstructure of sample.Thermoelectric properties of Bi₂Sr₂Co₂O_y was enhanced efficiently by doping and compositing.Co was replaced with Fe and Cu in the thesis,and then the carrier concentration was optimized to enhance electric conductivity,and at last the thermoelectric properties were enhanced.At the same time,Ba and Ca was chosen as doped element to induced different misfitness between layers.The results show that electrical conductivity was improved and thermal conductivity was decreased by Sr replaced,and thermoelectric performance was enhanced.It is known that Ca₃Co₄O₉ has good electric conductivity,but its higher thermal conductivity leaded to bad performance.This shortcoming has been overcome by compositing Bi₂Sr₂Co₂O_y and Ca₃Co₄O₉,when the compositing radio was 50%,its thermoelectric performance of composite was elevated a lot due to increased electric conductivity and decreased thermal conductivity.