Extolling thermoelectric properties of incommensurate (IC) TlBiSe2 polycrystals prepared by melt temperature oscillation method

Abstract

The high-ordered crystal structure of a thermoelectric material does not delimit the phonon conductivity but shows improved electrical properties. Disordered crystal structures act as scattering centers for phonon, but at the expense of the electrical properties of the material. Hence, a diminished thermal (phonon) conductivity and improved electronic conductivity can be obtained from an incommensurate (IC) phase structure. This paper reports that TlBiSe2 polycrystal material exhibits incommensurate (IC) phase (disordered structure). The ‘Tl+’ connecting chains and the disordered structure inherent in the IC phase enhance the TE properties in TlBiSe2. The crystalline phase was confirmed for TlBiSe2 by X-ray diffraction (XRD). These polycrystals have shown their characteristic Raman modes and micro flake-like morphology, as observed by Raman spectroscopy and field emission scanning electron microscopy (FESEM). X-ray photoelectron spectroscopy confirmed the IC phase formation by observing the characteristic binding energy shift of ‘Tl’ and ‘Se’ states. The parallel plane symmetry break in the IC phase has resulted in a hall carrier concentration (n) of 3.49 × 1020 cm−3 and mobility (μ) of 8.27 m2V−1s−1. Further, Seebeck coefficient showed 80 μV/K; the Wiedemann Franz law calculation reserved a lower electronic thermal conductivity of 0.003381 Wm−1K−1 and a power factor of 2.956 μW/m K2 has been attained.