Preparation of Fine-Grained Single Phase ZnSb Thermoelectric Materials Using a Mechanical Grinding Process

Fine grained ZnSb with an orthorhombic structure was prepared using fine grains ground mechanically below 150 pm (several tens micrometers in an average grain size). Source materials were the alloy of 50 atomic percent zinc and antimony (stoichiometric composition), which was quenched from melt at rates high enough to prevent the nucleation and growth of equilibrium phases. The alloy was ground using a mechanical grinding (MG) technique, and the grains were sintered by hot-pressing with 147 MPa at 673 K. The results of the X-ray diffraction (XRD) experiments and differential thermal analysis (DTA) showed that the ZnSb alloys were single phase and crack free. The thermal conductivity of the ZnSb alloy was 1.41 Wm(-1) K-1 at room temperature, that was about half in comparison with the data for ZnSb single crystal or polycrystals prepared by conventional metallurgy. This could be ascribed to the effect of the grain boundary scattering of phonons. As a result, the ZnSb sintered alloy with single phase was found to have a reasonably high ZT (dimensionless figure of merit) value of about 0.8 at 573 K.