Preparation And Thermoelectric Properties Of Nonequilibrium-structure Filled Skutterudite Based Thermoelectric Materials

Skutterudite is one of the most promising thermoelectric materials in the moderate and high temperature range. But many studies of skutterudites are focusing on the methods to enhance its thermoelectric properties by filling atoms and lowering its dimensions at present, few researchs on batch preparation are studied although general preparation is time-consuming and energy-wasting. Now a high-efficiency rapid preparation by SPS reaction sintering is adopted to fabricate CoSb3-based thermoelectrical materials. And the effect of sintering pressure is studied as one of the most important parameter to the composition, structure and properties, as well as two-step-sintering process.Results show that a high-efficiency rapid preparation method of melting-quenching combined with Spark Plasma reaction Sintering(SPS) process was developed to fabricate single-phase Ba0.3In0.2Co4Sb12. Non-equilibrium structure such as crystal-whisker and helix structure were found in all SPS samples at different temperature by rapid preparation for nominal composition Ba0.3In0.2Co4Sb12. With SPS temperature increasing, electrical conductivity lowered, Seebeck coefficient increased and ZT improved subsequently. A ZT of 0.72 has been achieved for Ba0.3In0.2Co4Sb12 SPS samples by reaction sintering at 675 K when sintering at 823K.Study on samples prepared by rapid preparation with different sintering pressure indicates that all of the samples are single-phase filled skutterudites from 5 MPa to 50 MPa, with a crystal-whisker and helix non-equilibrium structure. Electrical conductivity, Seebeck coefficient, and thermal conductivity of all samples are no significant differences. A ZT of 0.71 has been achieved for Ba0.3In0.2Co4Sb12 SPS samples by reaction sintering at 675 K when sintering at 5 MPa. This demonstrates pressure is not such a important parameter to the rapid prepared samples.Two-step low-temperature-reaction-high-temperature-sintering rapid preparation process based on previous reaction sintering rapid preparation is studied too. Results show that single-phase filled skutterudites can obtained by two step process. With increasing second-step-sintering temperature, helix whisker non-equilibrium structure grows to be helix grain non-equilibrium structure, and thermoelectrical properties are improved. This indicates that rapid preparation is optimized by a two step process. A ZT of 0.77 has been achieved for Ba0.3In0.2Co4Sb12 SPS samples by two step process at 800 K when reacting at 798 K and consolidating at 898 K.