Suppressing adverse intrinsic conduction of Bi2Te3 thermoelectric bulks by Sb and Cu co-substitutions via HPHT synthesis

Abstract

Chemical substitution combined with high-pressure tuning (high pressure and high temperature, HPHT) was applied to synthesize Bi₂Te₃ polycrystalline bulks. The synthesis time was sharply shortened to about half an hour, which is a distinct advantage over conventional synthesis methods for mass production. Acceptor-like antisite and substitutional defects owing to Sb and Cu substituting Bi sites were responsible for the increase in carrier concentration. Pressure-induced multiple textures and microstructures contributed to phonon scattering, including grain boundaries, lattice distortions, and dislocations. A maximum ZT value of 1.20 was achieved for Cu_0.005Bi_0.5Sb_1.495Te₃ at 473 K. Moreover, an available ZT value of 1.17 was obtained in a wide temperature range of 423–523 K. The increases in carrier concentration and band gap effectively suppressed the adverse intrinsic conduction and delayed the onset of the bipolar effect. Cu-substituted samples exhibit new vibrational modes in Raman spectroscopy, which implies that the substitutions induced significant changes in lattice vibrations.