A catalyst-free new polyol method synthesized hot-pressed Cu-doped Bi2S3 nanorods and their thermoelectric properties

This is the first report on the thermoelectric properties of a catalyst-free polyol method used to prepare stoichiometric Bi2-x Cu (x) S-3 samples, x = 0.1, 0.2, 0.3, 0.4, via hot pressing. Various systematic approaches to arrive at in their stoichiometric compositions are explored precisely with introduction of excess precursor of S. X-ray diffraction data analysis using Rietveld refinement confirms a polyhedral orthorhombic crystal structure with a space group Pnma, in contrast to Pbnm reported earlier. Raman data further substantiates this. X-ray photoelectron spectroscopy confirms the valence states of the constituent elements (Bi3+, Cu2+, and S2-) and energy dispersive X-ray analysis corroborates their compositions. The particle sizes of the pure Bi2S3 nanoparticles were 20, 35, and 82 nm as determined from the Scherrer formula, atomic force microscopy, and dynamic light scattering, respectively. Their transmission electron microscopy image shows rod-like nanostructures elongated in the aEuro010aEuroe direction with an average diameter of 23 nm and a length of several hundreds of nanometers. A 34% improvement in the thermoelectric figure of merit is observed for Bi1.6Cu0.4S3 as compared to pure Bi2S3 at 300 K.