Abstract
Several off-stoichiometric compositions Bi0.5Sb1.5Te3+x (x = 0, 0.01, 0.015, 0.02) with varying Te concentrations were synthesized via melting the elemental components of stoichiometric compositions in a furnace operating at temperature 800 °C to study the role of excess Te on enhancing the thermoelectric properties. The structural characterization performed by XRD and TEM reveals the formation of a matrix phase of Bi0.5Sb1.5Te3and a minor phase of Te. A systematic investigation of electronic and thermal transport behaviour of Bi0.5Sb1.5Te3+x (x = 0, 0.01, 0.015, 0.02) were performed in wide temperature range. Interestingly, enhanced power factor (~22.6 μW/cm K2 at 486K) was optimized for composition Bi0.5Sb1.5Te3.010which is18% enhanced power factor(PF) than that of pristine Bi0.5Sb1.5Te3 material (PF~19.1 μW/cm K2 at 486K). In addition to this, a drastic reduction in thermal conductivity (1.01 W/m K at 486K) was also observed which is 11% reduction when compared to that of bare state-of-art Bi0.5Sb1.5Te3 material. This reduction in thermal conductivity is explained in terms of the scattering of phonons due to mass fluctuation, strain field domains, grain boundaries, and multiple interfaces. An enhanced ZT~1.08 at 486 K for the composition Bi0.5Sb1.5Te3.010 was optimized which is primarily due to enhanced power factor and reduced thermal conductivity.
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