Study On The Effect Of Element Substitution Combined With SiC Dispersion On The Thermoelectric Properties Of B_i2Ba₂Co₂O_y And Ca₃Co₄O_9+?

The massive consumption of fossil fuel energy will produce many harmful gases(such as carbon dioxide and carbon monoxide),leading to serious deterioration of the Earth's ecosystem.Thermoelectric materials can directly convert heat and electric energy in a static process,and therefore are a new type of environmentally friendly materials with high expectations.Due to the advantages of non-toxicity,wide element distribution and stable operation at high temperatures,in recent years,there have been more and more studies on layered Co-based oxide thermoelectric materials such as Bi₂Ba₂Co₂O_y and Ca₃Co₄O_9+?.Compared with traditional thermoelectric materials,the thermoelectric performance of layered Co-based oxide thermoelectric materials has been significantly improved.However,compared with alloy-based thermoelectric materials,its(5value is still low.Element doping,material recombination and improving preparation process are effective ways to further improve the thermoelectric properties of layered Co-based oxides.In this paper,the thermoelectric properties of layered Co-based oxide thermoelectric materials are optimized by the method of combining element doping and dispersing Si C nanoparticles.In this paper,the samples were prepared with solid-phase sintering method and their electrical and thermal transport properties were characterized.The Bi₂Ba₂Co₂O_yand Ca₃Co₄O_9+?materials were dispersed with different contents of Si C nanoparticles,and the effect of the content of Si C nanoparticles on their thermoelectric properties was studied.Bi site in Bi₂Ba₂Co₂O_y was partially replaced with Na element,Ca site in Ca₃Co₄O_9+?was partially replaced with Sr and Ba elements,and then Si C nanoparticles were dispersed with different contents.The influence of element doping and Si C composite on the thermoelectric properties was studied.The experimental results show that with the increasing contents of Si C nanoparticles,the resistivity of the samples decreases first and then increases.This may be attributing to the change of carrier concentration and mobility in the samples caused by the emerging of Si C nanoparticles.The Seebeck coefficients of the samples have little to do with the mixing amount of Si C nanoparticles.The reason may be that the mixing of Si C nanoparticles has positive and negative influence on the Seebeck coefficients respectively,and combined action of the two effects keeps the Seebeck coefficient basically unchanged.Adding Si C nanoparticles will introduce a large number of grain boundaries and crystal planes which will greatly increase the internal phonon scattering and decrease the mean free path of phonons.As a result,the total thermal conductivity will be reduced due to the decrease of lattice thermal conductivity of phonons.On the whole,the introduction of an appropriate amount of Si C nanoparticles into the samples will decrease their resistivity and thermal conductivity and keep Seebeck coefficient basically unchanged,so the thermoelectric properties of the samples can be effectively improved.For Bi₂Ba₂Co₂O_y system,the Bi₂Ba₂Co₂O_y+0.05 wt%Si C sample has the largest(5value 0.17 at 923 K,which is 65.8%higher than Bi₂Ba₂Co₂O_y sample.After Bi element was partially replaced with Na element,the mixing of Si C nanoparticles has more obvious effect.The(5value of the Bi_1.975Na_0.025Ba₂Co₂O_y+0.1 wt%Si C sample reaches the maximum 0.21 at 923 K,which is 26.6%higher than Bi_1.975Na_0.025Ba₂Co₂O_y and 93%higher than Bi₂Ba₂Co₂O_y.For Ca₃Co₄O_9+?system,the Ca₃Co₄O_9+?+0.05 wt%Si C sample has the highest(5value 0.218 at 923 K,which is 40.9%higher than Ca₃Co₄O_9+?sample.The(5value of Ca_2.93Sr_0.07Co₄O_9+?+0.10wt%Si C sample reaches 0.246 at 923 K,which is34.2%higher than Ca_2.93Sr_0.07Co₄O_9+?sample and 58.7%higher than Ca₃Co₄O_9+?sample.The(5value of Ca_2.9Ba_0.1Co₄O_9+?+0.025wt%Si C can reach 0.248 at 923K,which is 19.3%higher than Ca_2.9Ba_0.1Co₄O_9+?sample and 60.04%higher than Ca₃Co₄O_9+?sample.In summary,dispersing an appropriate amount of Si C nanoparticles into Bi₂Ba₂Co₂O_y and Ca₃Co₄O_9+?samples can significantly increase their(5value;on the basis of element doping,redispersing Si C nanoparticles can further improve their thermoelectric properties.