In general, (GeTe)n(Bi2Te3)m compounds in GeTe-Bi2Te3 pseudo-binary system possess a relatively low thermal conductivity, however, the thermoelectric properties of these compounds have not been evaluated systematically. In this study, a series of single-phase (GeTe)nBi2Te3 (n=10, 11, 12, 13, 14) compounds were prepared by a melting-quenching-annealing process combined with spark plasma sintering. The phase compositions and thermoelectrical properties of these samples were characterized. It is found that doping with Bi2Te3 intensifies the phonon scattering and significantly reduces the lattice thermal conductivities of these samples, producing a low total thermal conductivity of 1.63 W?m -1?K -1 at 723 K for (GeTe)13Bi2Te3 compound. Moreover, the effective mass of these compounds is enhanced through adjustment of the relative amount of Bi2Te3 and GeTe. Therefore, the Seebeck coefficient and power factor of these samples remain superior even at high carrier concentration. At 723 K, the maximum power factor of (GeTe)13Bi2Te3 compound is 2.88×10 -3 W?m -1?K -2 and the maximum ZT of (GeTe)13Bi2Te3 is 1.27, which is 16% higher than that of pristine GeTe.
(a, e) Back-scattering electron (BSE) images and (b, f)Ge, (c, g)Te and (d, h) Bi elemental distributions of the polished surfaces for (GeTe)nBi2Te3 samples ((a-d) n=10, (e-h) n=14)Fig. 2
Temperature dependence of (a) electrical conductivity, (b) Seebeck coefficient, (c) Pisarenko plots, (d) room temperature carrier mobility as a function of the carrier concentration for (GeTe)nBi2Te3Fig. 3
Temperature dependence of the power factor for (GeTe)nBi2Te3 compounds with inset showing the corresponding relationship between carrier concentration and power factor at 723 KFig. 4
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