Improved thermoelectric performance of ternary Cu/Ni/Bi₂Te_2.7Se_0.3 nanocomposite prepared by pulsed laser deposition

This work reports the preparation of ternary Cu/Ni/Bi₂Te_2.7Se_0.3 nanocomposite thin films using pulsed laser deposition. For comparison, pure Bi₂Te_2.7Se_0.3 (BTS) sample as well as Cu/Bi₂Te_2.7Se_0.3 and Ni/Bi₂Te_2.7Se_0.3 nanocomposites were also fabricated. Morphological characterizations of all the samples revealed smooth films typical of BTS. Energy dispersive spectroscopy demonstrated that the metals existed in the film at a trace amount. X-ray photoelectron spectroscopy showed that both Cu and Ni existed in the nanocomposites as metallic atoms i.e. free from oxidation and telluride formation. Structural characterizations using X-ray diffraction and Raman spectroscopy for all the films showed peaks corresponding to pure BTS structure suggesting that the dopants are embedded in the BTS matrix only at the grain boundaries. The ternary nanocomposites were prepared using a special configuration at three different concentrations of the Cu/Ni elements. The highest room temperature thermoelectric figure of merit (ZT) of 0.97 was observed for the optimum doping concentration (BTS-2Cu/Ni) due to a simultaneous increase in the power factor (2988 μW/mK²) and decrease in the thermal conductivity (0.93 W/mK). The increase in the thermoelectric power factor for the optimum metals doping is because of the filtering of less energetic charge carriers which enhanced the Seebeck coefficient of the material.