We report on rapid solidification of an Ag16.7Sb30.0Te53.3 compound using planar flow casting to stabilize the δ-AgSbTe2 single phase and avoid precipitation of the interconnected Sb2Te3 phase, which leads to deterioration of thermoelectric properties. Rapidly solidified samples are in form of flakes with different thickness (60-400 μm). Precipitation of Sb2Te3 phase is fully inhibited in thin flakes (thickness below 100 μm), which consist of an homogeneous δ-AgSbTe2 matrix, whereas isolated Sb2Te3 precipitates, dispersed throughout the δ-AgSbTe2 matrix, were found in thick flakes (thickness above 100 μm). The lattice parameter of the δ-AgSbTe2 phase progressively increases with the cooling rate, indicating progressive supersaturation of the matrix for high degree of supercooling. Bulk specimens were prepared by hot pressing of the rapidly solidified flakes to evaluate thermoelectric properties. After sintering of the rapidly solidified flakes, the differential scanning calorimetry (DSC) traces indicates partial decomposition of the non equilibrium δ-AgSbTe2 into the stable phases. Measurements of the thermoelectric transport properties indicate the positive effects of rapid solidification on thermal conductivity and Seebeck coefficient and its negative effect on electrical conductivity, suggesting an operative way to improve thermoelectric performance.
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- Metastable phases
- Rapid solidification
- Thermoelectric materials
- Thermoelectric transport properties