Effects of Processing Techniques on Thermoelectric Transport properties of Hypoeutectic and Eutectic alloy of Cu- Bi-Te systems

Abstract

The effect of different processing techniques on thermoelectric transport properties of Cu3Bi38.2Te58.8 (hypoeutectic compositions) and Cu32Bi20.8Te47.2 (eutectic compositions) systems were investigated. The samples of each system prepared through three different approaches. Those were Flame-melting, ball-milling, and Twin-roll casting (TRC) processing techniques, followed by spark plasma sintering (SPS). Among the prepared samples, four samples grounded into powder through mortar and pestle and high-energy ball milling and one sample was characterized as melted. The spark plasma sintering instrument were used to consolidate the powder samples at a temperature of 400oC and 50MPa pressure for 5 minutes. Phases identification techniques were done by using an X-ray diffractometer (XRD), and microstructural characterization were carried out by using a scanning electron microscope (SEM), Backscattered secondary electron (BSE), and Optical Microscope (OM). Identification of elemental compositions of a synthesized materials is also carried out by energy dispersive X-ray analysis (EDAX). Seebeck coefficient, and electrical resistivity measurement were done by using ZEM-3, and flash laser analyzer (FLA) were used for determination of thermal diffusivity. The maximum value of Seebeck coefficient 43.2µV/K at 375K, and 38.4µV/K at 541K was obtained from ball-milled hypoeutectic composition alloy and flame-melted (as-melted) eutectic composition alloy, respectively. For both hypoeutectic and eutectic compositions, low thermal conductivity of 2.5227W/mK at 297 and 0.9259W/mK at 297K was obtained from twin roll casting (TRC) processed samples respectively. This, is due to low lattice thermal conductivity contribution as a result of phonon scattering caused by grain refinement achieved by the twin-roll casting processing technique. 0.12 thermoelectric figure of merit (ZT) at 375K for ball-milled hypoeutectic alloy and 0.5 thermoelectric figure of merit (ZT) for as-melted eutectic alloy was obtained from hypoeutectic and eutectic compositions, respectively