Experimental estimation of the Lorenz number and scattering parameter for p-type bismuth antimony telluride via multiple doping under constant temperature conditions

The effects of the addition of lead as one of the multiple dopants in p-type Bi0.3−xSb1.7Te3.0+0.01Pbx (x = 0, 0.001, 0.002, 0.003) fabricated by mechanical alloying followed by hot pressing were investigated. Measurements by X-ray diffraction (XRD), differential thermal analysis (DTA), and scanning electron microscopy (SEM) showed the same matrix morphology. The second phase by doped elements was not confirmed by transmission electron microscopy (TEM). By using the lead addition results and previously studied tellurium doping effects, the Lorenz number L was evaluated to be 0.73–1.18 × 10−8 W S−1 K−2. The scattering parameter γ and reduced Fermi energy η were estimated by using expressions on the basis of a one-electron approximation, measured Seebeck coefficients, and the estimated L at room temperature. The γ ranged approximately from −1.06 to −0.60 and showed a mutual effect of acoustic and optical phonon scattering. The relationship between a dimensionless figure of merit ZT and η was clarified. The optimum η was determined as −1.25 at ZT = 1.26. From these results, multi-doped Bi0.3Sb1.7Te3.0 could be applied to evaluate L, γ, and η at a constant temperature.

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