## 3 Results and Discussion
This electrical conductivity could be due to point defects in the compound. Aluminum vacancies may be responsible for the increased carrier movement. The transport properties of the sample S1\({}_{2}\) from Table 1 are shown in Figure 3a-d. The highest Seebeck coefficient of the S1\({}_{2}\) sample was found to be 370 uV/K at 855 K. This high Seebeck coefficient might have been caused by a very low carrier concentration, which could also explain the low electrical conductivity. The highest electrical conductivity was 6.6 S/cm at 660 K. The electrical conductivity of the sample increased with increasing temperature as shown in Figure 3b, but after 660 K, the conductivity decreased with temperature. The conductivity initially increased because, with higher temperature, more electrons gained the energy to jump from the valence to conduction band. However, after 660 K, interactions of the carriers with vibrating atoms and phonons caused scattering of the electrons, thus reducing the overall conductivity, as is the case for metals [16]. In addition, the slight decrease in electrical conductivity could also be a result of the minority carriers across the band gap. At a high temperature, the carrier concentration of the minority carriers would also rise, thus increasing the overall electrical resistivity of the semiconductor. The thermal conductivity of the AlSb was found to be decreasing with increasing temperature. The lowest thermal conductivity was measured to be 4.7 W/mK at 873 K, as shown in Figure 3c. This thermal conductivity is rather high for applications in thermoelectric  
Figure 3: Variation of (**a**) Seebeck coefficient, (**b**) electrical conductivity, (**c**) thermal conductivity and (**d**) ZT with temperature for two at % Al excess (S1\({}_{2}\)) sample. reduction. The dimensionless figure of merit, ZT, was found to be the highest at 873 K and the value was 0.015. The ZT value was significantly low and might be largely due to very low electrical conductivity and high thermal conductivity. However, this was the first time that such properties of bulk aluminum antimonide were elucidated. With further engineering, the thermoelectric properties of this cheap and environmentally friendly semiconductor can be improved further. The thermoelectric properties of InSb and GaSb have been extensively studied. Pristine InSb is known to exhibit a ZT of 0.25, while improvements have resulted in ZT value as large as 1.28 at 773 K [17]. On the other hand, the thermoelectric properties of GaSb have been improved up to 0.23 at 873 K [18]. In comparison to the other antimony compounds of group III, the thermoelectric properties of AlSb are very low. It can be assumed that doping and nanostructuring in the AlSb system matrix might improve such properties of AlSb. As a continuation of this study, doping and subsequent improvement of thermoelectric properties are being planned. The as-casted AlSb was found to be very fragile. In fact, no electrical or thermal properties could be measured from it. The VHPed samples were also very brittle, but their superior microstructure, particularly after HEVM, made them strong enough for measurement of such properties. The mechanical properties were measured in terms of Vickers pyramid number (H\({}_{\text{V}}\)). The mechanical properties of the highly dense sample S3\({}_{3}\) from Table 1 were measured in terms of Vickers pyramid number (H\({}_{\text{V}}\)). Figure 4 shows a scanning electron microscopy image of the dent made by microhardness test. An H\({}_{\text{V}}\) value of 350 \(\pm\) 3.7 was found for the VHPed sample, showing moderately brittle behavior.