Structural and thermoelectric properties of doped Bi 2 Te 3 crystalline alloys

Bulk alloys of Bi 2 Te 3 doped with various amounts of Se, Sb and Na were synthesized by simple melting. Structural and morphological properties have been checked using x-ray diffraction (XRD) and scanning electron microscope (SEM) observations. XRD and SEM investigations revealed that the obtained samples are of high crystallinity with the structural characteristics of the Bi 2 Te 3 phase. Electrical and thermoelectric properties of the prepared samples were investigated over the temperature range 283 - 473 K. Seebeck coefficient and electrical and thermal conductivities were measured and studied as functions of temperature between 283 K and 473 K. The power factor (PF) was calculated and examined against the temperature increasing, as well. The thermoelectric figure of merit (ZT) was estimated from the materials power factor and thermal conductivity. The Sbdoped alloy exhibited the largest power factor, recorded at 285.23 mu W/m.K 2 at 430 K. On the other side, the Sb-doped and the Na-doped Bi 2 Te 3 showed increased ZT than that of the pristine alloy. The maximum ZT was recorded at 1.97 for the highest Sb-doped Bi 1.94 Sb 0.06 Te 3 sample, observed at 430 K. It is believed that the increased number of grain boundaries besides the decreased grain size are main reasons behind the high observed ZT in this work, especially because the phonon scattering on grain boundaries results in reducing the lattice part of the thermal conductivity.