Preparation, Thermoelectric Properties And Service Behavior Of Barium And Indium Double-filled Skutterudite Based Thermoelectric Materials

Skutterudite is one of the promising thermoelectric materials in the moderate and high temperature range.But many study of skutterudite is focusing on the methods to enhance its thermoelectric properties by filling atoms and lowering its dimensions at present.There is a short of deep and systemic study of its service behavior when the material is used in the moderate and high temperature range.In the present work,a series of n-type Ba_0.3In_0.2Ni_xCo_4-xSb₁₂(x=0.0～0.1,Δx=0.02) filled skutterudite thermoelectric material and SiO₂/Ba_0.3In_0.2Ni_0.05Co_3.95Sb₁₂(ΔR=1,5,10,20å'Œ40 nm) nanocomposite were prepared with a combination methods of vacuum high-temperature melting and spark plasma sintering(SPS) technique and a combination methods of chemical coating method and SPS process respectively.The service behavior of them was investigated based on the systemic study of those microstructure and thermoelectric properties.The thermoelectric properties of Ba_0.3In_0.2Ni_xCo_4-xSb₁₂ were studied,the results indicate that the electrical conductivity decreases and the absolute value of Seebeck coefficient increases while the thermal conductivity first decreases then increases with the increased content of Ni.The ZT_max of 1.14 is obtained for single-phase material of Ba_0.3In_0.2Ni_0.05Co_3.95Sb₁₂ at 800 K.The thermoelectric properties of SiO₂/ Ba_0.3In_0.2Ni_0.05Co_3.95Sb₁₂ were studied,the results indicate that the electric conductivity and thermal conductivity decreases but the absolute value of Seebeck coefficient increases as the thickness of SiO₂ coating layers increased.The ZT value of the nanocomposite with 1 nm thickness of nano SiO₂ varies hardly.But the ZT value of 0.67 which is obtained for the nanocomposite with the nano SiO₂ coating layer of 40 nm is 46.7 percent lower than the ZT value of 1.25 which is is obtained for Ba_0.3In_0.2Ni_0.05Co_3.95Sb₁₂ at 800 K。The service behavior of Ba_0.3In_0.2Ni_0.05Co_3.95Sb₁₂ indicates that Sb volatilizes slightly and Ba separates from the structure partly and enriches on the boundary of gains,more and more second phase ouccurs and enriches on the boundary of grains then it falls off or volatilizes from the boundary as increasing times of quenching and days of annealing.The electrical conductivity first decreases then increases and the absolute value of Seebeck coefficient increases while the thermal conductivity first decreases then increases as increasing times of quenching.The ZT value of 1.10 which is obtained for the material after 2000 quenching times is 0.09 lower than the ZT value of 1.19 which is is obtained before quenching at 800 K.The electrical conductivity first decreases then increases and decreases again and the absolute value of Seebeck coefficient increases while the thermal conductivity has to be investigated more as the increasing days of annealing.The ZT value of 1.11 which is obtained for the material after 40 annealing days is only 0.11 lower than the ZT value of 1.22 which is is obtained before annealing at 800 K.The service behavior of SiO₂/Ba_0.3In_0.2Ni_0.05Co_3.95Sb₁₂ nanocomposite with 3 nm thickness of nano SiO₂ indicates that the coating of nano SiO₂ can enthance the stability of Ba_0.3In_0.2Ni_0.05Co_3.95Sb₁₂,there is no evident alteration of its microstructure and distribution of every element afer quenching and annealing。As increasing times of quenching and days of annealing,the electrical conductivity decreases and the absolute value of Seebeck coefficient increases.The thermal conductivity first increases then decreases and increases again after quenching.But it has to be investigated more as the increasing days of annealing.The ZT value of 1.01 which is obtained for the material after 2000 quenching times is only 0.07 lower than the ZT value of 1.08 which is obtained before quenching at 800 K.But the ZT value of 0.87 which is obtained for the material after 40 annealing days is 0.25 lower than the ZT value of 1.12 which is is obtained before annealing at 800 K.