1. STEF-NANO-ACC
Stimulating, Encouraging and Facilitating the Participation of
ACC Nanotechnology and Nanoscience Research Organisations To FP6
Topic:
Three dimensional nano-structures based on elements other than carbon
Manufacturing of nano-sized spherical particles for thermoelectric applications
Krzysztof Wojciechowski
AGH University of Science and Technology
Faculty of Materials Science and Ceramics
Department of Inorganic Chemistry
Al Mickiewicza 30
Kraków, Poland
phone: (+48)

2. Introduction
The ability of the thermoelectric materials for applications in the energy conversion systems is usually described by the dimensionless figure of merit ZT:
where: a - is the Seebeck coefficient, s - electrical conductivity, l - thermal conductivity, and T - the average temperature of a sample.
Although there are no physical laws limiting thermoelectric figure of merit, the value of ZT for the best materials is about unity. In general it is difficult to improve ZT of the materials due to following reasons:
increase in Seebeck coefficient a leads to simultaneous decrease in the electrical conductivity s
increase in the electrical conductivitys leads to comparable increase in the electronic contribution of thermal conductivity l due to Widemann-Franz law.
The solution: low dimensional structures of thermoelectric materials

3. Preparation procedure of nanostructured thermoelectric materials
Solutions of soluble
salts of metals
1 mm
USP spray pyrolysis
technique
Amorphous particles
of precursor material
Chemical reduction
Powders of nanocrystaline
thermoelectric materials
TEM image of hollow particles of the precursor material (2CoO · 3Sb2O4)
Densification

4. Structural and chemical properties of powders after reduction process
100 nm
Reduction process in H2; 400°; 2 h
Distribution of elements on the particle
110
[001]
110
Reduction process in H2; 500°; 5 h
Analysis of the electron diffraction pattern
(* data calculated for the CoSb3 structure with lattice parameter a= nm)
Results of analysis of the TEM diffraction pattern of
reduced particles (* data calculated for the CoSb3
structure with lattice parameter a= nm)
Results of analysis of the TEM diffraction pattern of
reduced particles (* data calculated for the CoSb3
structure with lattice parameter a= nm)

5. Thermoelectric properties – electrical conductivity
Electrical conductivity of densified powders and
coarse-grained CoSb3 as a function of temperature

6. Thermoelectric properties – Seebeck coefficient
Seebeck coefficient of densified powders and
coarse -grained CoSb3 as a function of temperature

7. Thermoelectric properties – thermal conductivity
Thermal conductivity of densified powders and
coarse-grained CoSb3 as a function of temperature

8. Summary
A novel technique involving the pyrolysis of an ultrasonically atomized solution has been used to prepare nanograined powders of CoSb3 semiconductor.
The microstructure observations performed using transmission electron microscopy (TEM) technique shown that spheres were built either from nanocrystalline or amorphous material. The energy dispersive spectrometry EDS microanalysis and SADP analysis proved the proper chemical and phase composition of obtained powders.
Preliminary examinations of powders densified with conventional static methods indicates that the obtained materials possess particular electronic parameters (such as energy gap value Eg and Seebeck coefficient a) comparable to parameters of CoSb3 bulk material.