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N-type (Bi x Pb 1− x Te) 0.88 (PbS) 0.12 composites with x = 0, 0.001, 0.003 and 0.005 have been prepared by melting the elements in sealed quartz tubes followed by ball milling and spark plasma sintering. The XRD results indicate that all samples are composites containing both major NaCl-type structure PbTe and minor NaCl-type structure PbS. The Hall measurements show that the electron carrier concentrations increase, from 4.5 × 10 18 cm −3 for x = 0 to 2.8 × 10 19 cm −3 for x = 0.003 at 298 K, and electrical resistivity reduces with the increase of doped Bi. The absolute Seebeck coefficients decrease, from 1.96 × 10 −4 V/K for x = 0 to 4.31 × 10 −5 V/K for x = 0.005 at 298 K, and the thermal conductivity increases, from 0.65 W/m K for x = 0.001 to 1.63 W/m K for x = 0.005 with Bi doping. However, both the power factor and the dimensionless thermoelectric figure of merit ZT can be enhanced by proper Bi doping. The maximum ZT value of 1.20 has been obtained in the sample (Bi 0.001 Pb 0.999 Te) 0.88 (PbS) 0.12 at 573 K. |
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