Research Of Segmented Thermoelectric Materials Of Filled-skutterudite/Bi₂Te₃-Based Compounds

Thermoelectric effect is a coupling effect between the transport of thermal and electricity , the conversion between thermal energy and electricity may be realized by the thermoelectric devices based on this point. The thermal energy can be converted into electricity by means of Seebeck effect, on the contrary, the thermoelectric refrigeration can be realized by Peltier effect. Therefore, thermoelectric materials can be used for thermoelectric generator, refrigerator, temperature measurement and control and etc.The figure of merit Z of thermoelectric materials varies with carrier concentration and temperature ,.A single monolithic thermoelectric material usually works only at a specific narrow temperature range due to its structure and thermal stability, however , the temperature range of the segmented thermoelectric materials can be extended, and the thermoelectric conversion efficiency could also be kept at high level in more extensive temperature range.The work of this thesis is focused on preparing segmented thermoelectric materials combination of the filled-skutterudite compounds with good thermoelectric property at high temperature and the Bi2Te3-based compounds with good thermoelectric property around room temperature.The main works are as follows:The filled-skutterudite compounds LayFexCo4-xSb12 (y=0～1.0,x=0～2.0) and the Bi2Te3-based compounds (Bi2Te3)0.25(Sb2Te3)0.75 were prepared via the route of mechanical alloying plus hot (cold) pressed. The powder sizes were measured by a granularity analysis instrument. An X-ray diffractometer was used to measure and analyse the structure of the as-milled powers and as-sintered samples respectively. The scanning electronic microscope (SEM) was used to analysis the fractograph of sintered samples. The electrical properties were measured by the Physical Properties Measurement System(PPMS). The granularity of the LayFexCo4-xSb12 powders milled for 10h was about 2.05μm. Filled-skutterudite compounds were synthesized by both sintering the as cold pressed billet at 700℃ for 48h and hot pressing at 650℃ for 2h. The density and thermoelectric properties of the hot pressed samples are greater than that of the cold pressed samples. And the La0.6FeCo3Sb12 compounds were found to be excelled in thermoelectric properties. (Bi2Te3)0.25(Sb2Te3)0.75 compound was synthesized after milled for 10h. The density of the sintered samples increased with increasing the hot press temperature, however the Seebeck coefficiect and electrical resistivity decreased with that.The filled-skutterudite compound of La0.6FeCo3Sb12 and (Bi2Te3)0.25(Sb2Te3)0.75 compounds which have good thermoelectric properties were used to compose segmented thermoelectric material by hot press. The interface property was researched which there was no diffuse barrier and there was Sn as the diffuse barrier. The results showed that the interface intensity was good which has no diffuse barrier than the interface which there was Sn as the diffuse barrier.