Synthesis And Thermoelectric Properties Of In And Ce Double Doping N-Type Skutterudite Compounds

Thermoelectric materials, environmentally friendly materials in the 21st century, are considered to be very competitive in the energy alternative media. Skutterudite (such as binary CoSb3 compound) compounds have become one of the most promising TE materials because of their higher carrier mobility and high Seebeck coefficient. However, the figure-of-merit ZT using to evaluate the performance of TE materials and conversion of thermo-electricity of binary skutterudites are not famous owing to its relatively large thermal conductivity, severely limiting its commercial application.In this research, we focus on the n-type filled CoSb3 compound, expecting to regulate and control the electrical properties while lowering the lattice thermal conductivity and thereby enhancing the figure-of-merit ZT by in situ formation method. In and Ce are used as the doping elements and the forms of existence and the effects on the microstructure and TE properties of the n-type filled CoSb3 compound of these doping elements are discussed. The main contents and findings of the research work above are as follows:We used In as the doping element and discussed the forms of existence of In, the stability of the nano phase InSb and the effects of In doping on the microstructure and thermoelectric properties in the CoSb3-based skutterudite. The results show that:In can fill the void in the structure of skutterudites but the filling-form is metastable and In can separate out from the void to form the nano second phase InSb compound. But In with filling-form are better able to optimize the thermoelectric properties of compounds. We find that the existence of nanostructured secondary phase InSb can increase the power factor, decrease the lattice thermal conductivity and therefore improve the thermoelectric properties of the compounds when the content of In with filling-form are close to each other. Wih regard to the InxCo4Sb12 compound, the highest thermoelectric figure of merit ZT=1.16 is achieved at 800 K in the In0.35Co4Sb12 compound, In addition, In0.35Co4Sb12 compounds were annealed respectively at 400℃for 7 days and 14 days. The grain size of annealed samples are more uniform and the content of secondary phase InSb of the sample annealed 14 days are more than the annealed-7 days sample because of the metastable state of filling-form In.Based on the in situ secondary phase InSb dispersed on the boundary in the n-type skutterudites compounds, we use In and Ce as the filling element to form the double-filled skutterudits, hoping to achieve more optimized thermoelectric properties. The results show that, the filling fraction limit of Ce in CexCo4Sb12 compounds is about 0.11 and CeSb is formed and dispersed in the grain boundaries when the content of Ce exceed its filling fraction limit. As the filling element, Ce can improve the electric properties, lower the lattice conductivity and therefor enhance the igure of merit ZT. Wih regard to the CexCo4Sb12 compound, the highest thermoelectric figure of merit ZT=0.97 is achieved at 800 K in the Ce0.15Co4Sb12 compound. Using the same method, InxCe0.1Co4Sb12 compounds were synthesized. We find that when the content of doping-In was more than 0.2 there was nano secondary phase InSb compound distributed on the boundaries with the islandstructure. Compared with the the InxCo4Sb12 compound, InxCe0.1Co4Sb12 compound have higher Power factor and lower lattice conductivity and more optimize thermoelectric properties. The highest thermoelectric figure of merit ZT=1.25 is achieved at 800 K in the In0.25Ce0.1oCo4Sb12 compound.