Research On Preparation And Properties Of Functionally Graded Thermoelectric Materials Of P-type La_0.4FeCo₃Sb₁₂/Bi₂Te₃

Functionally graded thermoelectric materials(FGTM), with optimized design and consolidation of different monolithic thermoelectric materials which have different working temperature range, could work over a wide temperature range and make full use of figure of merit of every component material, therefore its thermoelectric properties and thermoelectric conversion efficiency could be improved remarkably.In this thesis, LaxNi0.2Co3.8Sb12 filled skutterudites with different La filling content (x=0.1,0.3,0.5,0.7) were prepared by mechanical alloying and hot pressing, effect of La content on thermoelectric properties of LaxNi0.2Co3.8Sb12 was studied and discussed. P-type La0.4FeCo3Sb12/Bi2Te3 FGTM were prepared with different junction layers by hot press sintering and their interface characteristics and thermoelectric properties were studied subsequently, and a computer simulation and calculation for FGTM were also performed. The main results are shown as follows:With increasing the La content, the Seebeck coefficent, electrical resistivity and thermal conductivity of LaxNi0.2Co3.8Sb12 filled skutterudites decreased more or less, and the thermoelectric properties improved remarkably. At 390℃, the ZT value of La0.3Ni0.2Co3.8Sb12 was 0.22, while the ZT values of La0.5Ni0.2Co3.8Sb12 and La0.7Ni0.2Co3.8Sb12 were 0.31 and 0.29, respectively.The interface morphologies and element diffusion of p-type La0.4FeCo3Sb12/Bi2Te3 with different joint materials were characterized by FESEM and EDAX. Power factor was calculated and used to evaluate thermoelectric properties of the FGTM. As a result, p-type La0.4FeCo3Sb12/Bi2Te3 with Fe junction layer, which had good bond with both segments at interface and prevented elements from diffusing to opposite side, got a better power factor, 1.796mW·m-1·K-2, and had a relative good and steady performance.A computer software was written and a simulation was performed to the FGTM with consideration of two different interface situations: with diffusion and without diffusion. The results of simulation are in good accordance with that of experiments.