Thermoelectric Preferred Orientation of (GeTe)_0.962(Bi₂Te₃)_0.038

In an attempt to reduce our reliance on fossil fuels, associated with severe environmental effects, the current research is focused on the identification of the thermoelectric potential of p-type (GeTe)_1-x(Bi₂Te₃)_x alloys. The doping potential of GeTe was extended by the Bi₂Te₃ donor dopant for an effective compensation of the high inherent hole concentration of GeTe toward thermoelectrically optimal values. In the current research, the effect of the preferred orientation of the (GeTe)_0.962(Bi₂Te₃)_0.038 alloy is studied. For this purpose, a (GeTe)_0.962(Bi₂Te₃)_0.038 ingot was synthesized by a rocking furnace melt, pulverized to a powder, and sieved to powder particle sizes of either smaller than 1 μm or smaller than 25 μm. It was found from X-ray diffraction after hot pressing that a rhombohedral structure was observed. Variations in the crystallographic structure were obtained depending on the pressing direction and the sizes of powder particles. Moreover, the percentage of preferred orientation decreases with reducing the powder particle size. Parallel to the pressing direction, a plate-like pattern in the ⟨HK0⟩ orientation was observed, compared to the vertical direction, exhibiting a preferred orientation toward ⟨00L⟩. The thermoelectric properties transverse to the hot-pressing direction showed lower electrical resistivity values and higher thermal conductivity values, compared to the hot-pressing direction. This is due to the nature of van der Waals, VDW, bonds which exist along the c-axis, while introducing bismuth telluride to GeTe. At the particle size range of <1 μm, a maximal thermoelectric figure of merit, ZT, of ∼2 was obtained at ∼440 °C, which is one of the highest ever reported for any p-type thermoelectric alloy.