Functionally Graded and Segmented Thermoelectric Materials for Power Generation Based on (Bi₂Te₃)_1-x-y(Sb₂Te₃)_x(Sb₂Se₃)_y Solid Solutions and Ternary Layered Tetradymite-like Chalcogenides

Kurzfassung

New functionally graded (FGTM) and functionally segmented (FSTM) thermoelectric (TE) materials of n- and p-type conductivity were fabricated by means of crystal growth applying a Czochralski technique. FGTM based on pseudo-ternary (Bi2Te3)1-x-y(Sb2Te3)x(Sb2Se3)y solid solutions were prepared by introducing variable concentrations of doped impurities into the seed and the melt charge. FSTM were grown by pulling the crystals from the melt corresponding to the composition of ternary layer compounds in the PbTe–Bi2Te3 and PbTe–Sb2Te3 quasi-binary systems using (Bi2Te3)1-x-y(Sb2Te3)x(Sb2Se3)y single crystals as a seed. This way, monolithic two-stage materials were prepared. The spatial distribution of the Seebeck coefficient (recording 2D Seebeck scans) has been studied on the crystals´ surfaces near the interface between the seed and the grown crystal by the Seebeck scanning micro-thermoprobe (SMP). A steep gradient of the Seebeck coefficient was discovered over a short interval near the seed–crystal interface. A quantitative analysis of the abundance distribution of the Seebeck coefficient from the SMP measurement by Gaussian fitting resulted in separate peaks corresponding to the segments in the grown FSTM. The peak width as a measure of the homogeneity may certify on the high uniformity within the corresponding segments of the Czochralski FSTMs.