Microwave Synthesis And Properties Optimization Of Ca-Co-O Thermoelectric Materials

In this present study,the oxide thermoelectric material Ca₉Co₁₂O₂₈ were analysised by microwave sintering,doping,and metal recombination with the changed of carrier concentration,crystal boundary intensity and phonon scattering center.Thereby the properties of thermomaterials were optimized.the results are as follows:Firstly,Ca₉Co₁₂O₂₈ was prepared by microwave heating method.Through the grain refinement effect of microwave sintering process to introduce a large number of grain boundaries,making the phonon grain boundary scattering probability increases,reducing the thermal conductivity,and ultimately improving the thermoelectric value.The experimental results showed that the structure of the sample which under the microwave sintering was more compact and the smaller of grain size,the average grain size of 1um below,the highest figure of merit of 0.042 at 500.Secondly,(Ca_3-xLa_x)3Co₁₂O₂₈?x=0,0.05,0.1,0.15,0.2,0.3?thermoelectric materials were prepared by sol-gel method.the carrier concentration were changed by doping La with the properties will be improved.The results showed that?Ca2.9La0.1?3Co12O28 had the highest figure of merit of 0.068 at 500,Compared with pure Ca₉Co₁₂O₂₈ phase,increased by about 61.9%.Confirming the fact that doping rare earth elements can effectively improve the thermoelectric properties of materials.Thirdly,(Ca₉Co₁₂O₂₈)_1-xAg_x?x=0,0.005,0.01,0.015,0.02?thermoelectric composite was prepared by the chemical solution infiltration method,Ag was uniformly dispersed between the Ca-Co-O oxide grains to formate effective phonon scattering center,reducing the thermal conductivity of materials,improving its thermoelectric value.The resulted found that the highest ZT value of x=0.015 sample achieved 0.07 at 500,which was about 66.7% higher than that of pure phase.In summary,The method of doped La can change the material carrier concentration and improve the thermoelectric properties of the material;Microwave technology can improve the grain boundary density and reduce the thermal conductivity of the material;the thermoelectric properties were also effectively improved by Ag recombination which will produce a great deal of phonon scattering center with the coefficient of thermal conductivity will be depressed remarkably.the research in this study will be the foundation of further preparation and optimization of high-properties thermoelectric materials.