The Hydrothermal Synthesis Of Several Thermoelectric Nanomaterials

Since 1950s, thermoelectric materials attract much attention because of its potential application for refrigerators or power generators. If the thermoelectric figure of merit ZT could be improved to about 3, quiet and environmental-friendly solid-state devices could be widely used in high-performance electronic and laser products. Further, conventional compressor-based cooling systems could be eventually replaced, most heat distribution could be efficiently utilized and much less fossil fuel would be consumed. Among all kinds of thermoelectric materials, filled-skutterudite is one of the most promising. PbTe, PbSe and their related alloys are traditional thermoelectric materials for middle-range temperature applications (500-700K) due to their narrow band gaps and face-centered cubic structure. In recent years, thermoelectric low dimensional structures such as quantum wells, quantum wires and quantum dots have been proven to have much higher thermoelectric coefficients than conventional bulk materials, according to both theoretical and experimental investigations. After reviewing the basic thermoelectric theories and recent progresses, we investigated filled-skutterudite Li_xFe₄P₁₂, chalcogenide compounds PbTe and PbSe in this thesis.Hydrothermal method is a relative simple, cheap and clean approach for the preparations of a great number of different materials. In this paper, filled-skutterudite Li_xFe₄P₁₂ nanobelts, cubic PbTe, PbSe nanocrystals and assembly were synthesized under different reaction conditions by a hydrothermal synthesis method. The composition, morphology and some properties of the synthesized products were investigated. Formation mechanism and growth models of the nanostructures were proposed. Some original results were obtained in hydrothermal synthesis of low dimensional thermoelectric materials.Li_xFe₄P₁₂ nanobelts were synthesized by a hydrothermal-reduction-alloying method at 180 °C for 16-32 hours. XRD results and ED patterns indicate that the nanobelts have the skutterudite crystal structure. The nanobelts are 1000-6000nm in length and 50-150nm in width. The crystal structure of the product can be easily destroyed by TEM electron beams due to its low thermal conductivity. The Li_xFe₄P₁₂ cathode...