Improved Thermoelectric Performance for β-Zn4Sb3 by Na/Zn Co-doping
In this study, β -Zn 4 Sb 3 was prepared using the Zn-NaCl mixed-flux method based on the stoichiometric ratio of Zn/Sb/NaCl = (4− x ):3:(7+ x ) ( x = 0, 0.1, 0.2, 0.3). X-ray diffraction results showed that all samples were hexagonal rhombic crystal structures with the space group \(R\overline{3}c\) . A second phase of ZnSb was detected in the samples with x = 0.2 and x = 0.3. In addition, the crystal-cell volume and lattice parameter of all samples increased for the larger ion radius of Na + than Zn 2+ . The transmission electron microscopy image and corresponding area electron diffraction pattern demonstrated that the prepared samples had a complete crystal structure. All samples had hole conduction and exhibited p-type conduction behavior. The carrier concentration of the material increased with increased Na content and decreased Zn, ranging from 8.89 × 10 19 cm −3 to 17.82 × 10 19 cm −3 . Moreover, the thermal conductivity ( κ ) of x = 0–0.2 samples decreased with increased Na content; however, the sample with x = 0.3 had a higher κ owing to the appearance of a ZnSb phase. Thermogravimetric differential thermal analysis showed that no weight loss occurred below the melting point. Eventually, the sample with the nominal composition of β- Zn 3.8 Sb 3 NaCl 7.2 achieved a ZT value of 1.43 at 690 K.
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