Reproducibility Of Structure And Thermoelectric Properties And Amplification Preparation Of Barium And Indium Double-filled Thermoelectric Skutterudite Materials

Skutterudite is one of the promising thermoelectric materials in the moderate temperature range. However, there are rare study of its reproducibility of structure and thermoelectric properties and its preparation techniques in large magnitude production.In this thesis, a series of Ba and In double-filled skutterudite thermoelectric materials with nominal composition Ba0.4InmCo4Sb12 (0-0.4, Am=0.1) was prepared by melt-quenching, annealing, and spark plasma sintering method. The occurrence of In impurity and its effect on the thermoelectric properties of the filled skutterudite materials was investigated. Based on these investigation, the reproducibility of the structure and thermoelectric properties of four batches 10-gram scale samples, and the phase composition and thermoelectric properties of different magnitude samples with nominal composition Ba0.4In0.4Co4Sb12 were investigated. The preparation technique of 100-gram scale samples was explored and their phase composition and chemical composition were characterized.The properties of Bao.4InmCo4Sb12 (0-0.4,Δm=0.1) thermoelectric materials were studied, the results indicate that all the samples were composed of skutterudite and a few BaO while InSb was detected in those samples with m>0.3. The electrical conductivity and thermal conductivity increased and the absolute value of Seebeck coefficient decreased with increasing m in the range of 0-0.2, however, the counter evolvements for the electrical conductivity, thermal conductivity, and Seebeck coefficient were observed in those samples with m≥0.3. The evolvements of thermoelectric properties are attributed to the carrier concentration degeneration and strong lattice scattering induced by In filler in the m range of 0-0.2, and affected by InSb when m>0.3. The power factor of all Ba and In double-filled skutterudite materials significantly increased and the lattice thermal conductivity dramatically decreased. As a result, the largest ZT values for the samples when m=0.2 and 0.4 reached 1.19 and 1.25 at 800 K, which are increased by 52% and 60%, respectively.The four batches 10-gram of thermoelectric materials with nominal composition Ba0.4In0.4Co4Sb12 were studied, the results indicate that four batches of samples were composed of CoSb3 phase with a few second phases BaO and InSb and the grain size was about 3-5μm. The difference values between maximum and minimum of the electrical conductivity and Seebeck coefficient of four batches decreased with temperature. The statistical average values of the electrical conductivity, Seebeck coefficient, thermal conductivity and ZT of four batches of samples were very close to the average values of their maximum and minimum. The ZT value of four batches of samples were more than 1.0 at 800 K. Those results imply that the structure and thermoelectric properties of four batches of barium and indium double-filled thermoelectric materials with nominal composition Bao.4In0.4Co4Sb12 have good reproducibility.The study of Ba0.4In0.4Co4Sb12 thermoelectric materials with different magnitude samples indicated that all the samples with 10-gram,20-gram,50-gram and 100-gram scales were mainly composed of CoSb3 phase, while trace InSb was detected in samples with 20-gram,50-gram and 100-gram scales, and CoSb2 was detected in samples with 50-gram and 100-gram scales. The electrical conductivity, Seebeck coefficient and thermal conductivity of the samples with 10-gram and 20-gram scales were very close. The ZT values of 10-gram and 20-gram scales samples increased with temperature and exceeded 1.0 at 800 K. Compared with the thermoelectric properties of 10-gram and 20-gram scales samples, the electical conductivity of the 50-gram scale samples was much lower and the thermal conductivity of the 50-gram scale samples was much higher, which was due to the second phase CoSb2. The largest ZT value of 50-gram scale samples was just 0.6.