Thermoelectric Properties of Solution Grown (beta)-FeSi2 Single Crystals

We have measured the Seebeck coefficient of single crystalline (beta)-FeSi2 grown by a temperature gradient solution growth (TGSG) method using Ga solvent. Rectangular-like (beta)-FeSi2 plates with the size of (3-6)×(1-2)× 0.3 mm^3, where the longitudinal axis was [011], were prepared from the grown ingots. Typical resistivity and hole concentration of the crystals were 4× 10^-4 (omega)m and 2× 10^25 m^-3 at room temperature (RT), respectively. The Seebeck coefficient measured along the [011] direction was approximately 350 (mu)V/K at RT and showed the maximum value of 500 (mu)V/K between 20 and 25 K. We also found that the solution grown single crystals had large power factors below RT. The value was 3.4× 10^-4 Wm^-1 K^-2 at RT, which was about three times larger than that of sintered poly-crystals and CVT-grown single crystals. The maximum power factor was 4.5× 10^-4 Wm^-1 K^-2 around 150 K. The value was more than one order of magnitude larger than reported values.