Microstructure andtransport properties of nanosized powders of CoSb3 obtained withspray pyrolysis method
K. T. Wojciechowski1, J. Morgiel2
Nanostructured materials differ from conventionalpolycrystalline materials by the size of the structural units, that composethem, and they exhibit drastically different properties in relation to bulk,polycrystalline materials. It has been theoretically demonstrated that in thecase of thermoelectric materials, the measurable effect of the thermoelectricproperties improvement can be obtained for 1D or 2D structures in which atleast one of the dimensions is less than 10 nm. However, on the other hand,application requirements for thermoelectric materials impose the condition thatthe materials need to have a 3D thick-layered form. One of possible ways toreconcile those opposing requirements could be a production of thermoelectricmaterials in a form of hollow spherical particles, of which the surfaces willconstitute the approximation of the 2D structure. Then, thick-layeredthermoelectric elements could be formed from such powders.
The aim of this work was to modify the ultrasonicspray pyrolysis (USP) method and adjust the conditions for the method in orderto receive selected materials in a form of thin-walled hollow spheres. Usingthis method both nanostructured metallic (CoSb3) and composite (CoSb3-Al2O3) materials were prepared. From transmissionelectron microscope studies we found that obtained powders consist of finehollow spheres with diameter ranging from 100 nm to 3 mm. Sphere thickness ofvarious materials ranged from 8 to 50 nm. The average size of nanocrystalsforming the sphere walls was around 10 nm, but as small as 2 nm crystalliteswere also observed.
The materials were characterized using Seebeckcoefficient, thermal and electrical conductivity measurements. Obtained powdersof CoSb3 show Seebeck coefficient values close to values for bulkmaterials of CoSb3 and very low thermal conductivity.Microstructured parameters, as well as very low thermal conductivity, of theproduced precursors seems to be promising in terms of satisfying therequirements for further production of nanostructured thermoelectric materialsusing e.g. dynamic compaction techniques.