Preparation And Thermoelectric Properties Of Co-riched Nd_yFe_4-xCo_xSb₁₂-based Thermoelectric Materials

Skutterudites become one of the most likely material used in practice because of its’unique crystal structure. So far, the n-type skutterudites has a ZT about2, while thecorresponding p-type skutterudites’ ZT is only about1and all of them are rich in Co.However, the coefficient of thermal expansion of this p-type skutterudites raise with thecontent of Fe. Therefore, The study of the p-type skutterudites which are rich in Co iscrucial.RzFe2Co2Sb12-xQx(R stand for rare earth, Q stand for ⅣA、ⅤA and ⅥA elements onthe periodic table) are chosen as the research objects. The preparation method is traditionalmelting and quenching and combine with advanced spark plasma sintering (SPS).Thermoelectric properties are investigated by electric constants instrument and laserthermal conductivity; The phase, cross-sectional structure, actual sample compositions andcarrier concentrations are analyzed by X-ray diffraction, scanning electronic microscope(SEM), transmitting electronic microscope (TEM), physical property measurement system(PPMS) and Renishaw invia system etc.The results indicate that the RzFe2Co2Sb12-xQxsamples with different Ge contents arepure skutterudites phase. The effects of Ge contents on thermoelectric properties of thesamples were compared: thermoelectric properties increases with increasing Ge contentwhen Ge contents less than0.3; when Ge content greater than0.3, it has the oppositeeffect. The highest ZT value of1.1is achieved at700K with the sample ofNd0.6Fe2Co2Sb11.7Ge0.3. The conclusion is that with appropriate Ge doping level can formin situ nanostructure which can decrease thermal conductivity effectively and at the sametime has little influence on its electric properties, thus improve its ZT value drastically.We also prepared Nd0.6Fe2Co2Sb12-xSnxsamples with different Sn contents. Theresults indicate that doping with proper Sn contents can reduce thermal conductivityeffectively and no obvious effect on electrical properties.Compared with Nd0.6Fe2Co2Sb12,The highest ZT value of0.92is achieved at680K with the sample ofNd0.6Fe2Co2Sb11.6Sn0.4. The ZT value increased about35%. In order to match the n-type skutterudites better, NdyFe1.5Co2.5Sb12-xGexsamples wasprepared with the same method. Firstly, NdyFe1.5Co2.5Sb12samples was prepared and thehighest ZT value of0.66is achieved when y=0.55. Then a series ofNd0.55Fe1.5Co2.5Sb12-xGexsamples was prepared. Doping Ge in these samples also reducethermal conductivity effectively and maintain excellent electrical properties. the ZT valueobtain0.9with x=0.15, which increased about37%compared with the sample without Gedoping.