Synergistic effect of energy filtering, modulation doping and boundary scattering of multiphase Cu-Sb-Bi-S system for enhanced thermoelectric performance

Abstract

In this a multiphase cubic system has been successfully synthesised by solvothermal method. The profile fitting using Rietveld refinement confirms the phase fraction of monoclinic-Cu4Bi5S10, orthorhombic-Cu3BiS3, orthorhombic-Sb2S3 and tetragonal- Cu3SbS4 as 54.56%, 40.33%, 2.96%, 2.15%, respectively. Further, the presence of multiphase was additionally confirmed using HR-TEM analysis from observing the various patterns of atomic arrangement in the lattice plane. Moreover, a narrow band gap of 0.64 eV was confirmed using UV-DRS analysis. Electrical transport properties such as the Seebeck coefficient and electrical conductivity has been determined using ZEM-3 measurement which depicts the negative value of the Seebeck coefficient that conforms to the negative charge carrier transport. Interestingly the very low thermal conductivity of 0.37 Wm−1K−1 at 303 K is observed for the S2 sample. Overall, with enhanced electrical conductivity of 59.7 S.cm−1 at 473 K, and Seebeck coefficient of 60.3 μVK−1 at 353 K leads to a maximum ZT of 0.0068 at 473 K, which is due to the synergistic effects of boundary phonon scattering, energy filtering and modulation doping effect in the multiphase Cu-Bi-Sb-S system.