Thermoelectric performance enhancement of (BiS)1.2(TiS2)2 misfit layer sulfide by chromium doping

Abstract

Abstract:A misfit layer sulfide (BiS) 1.2 (TiS 2 ) 2 with a natural superlattice structure has been shown to be a promising thermoelectric material, but its high carrier concentration should be reduced so as to further optimize the thermoelectric performance. However, ordinary acceptor doping has not succeeded because of the non-parabolic band structure. In this paper, we have successfully doped chromium ions into the Ti sites, which can maintain or even enhance the high effective mass of electrons so as to effectively improve ZT value. X-ray diffraction analysis, coupled with X-ray photoelectron spectroscopy, shows that chromium has been substituted into titanium sites in TiS 2 layers and confirms its ionic state. The chromium doping has successfully reduced the carrier concentration with the subsequent reduction of electrical conductivity. Unlike other acceptor dopants (alkaline earth metals), chromium also enhances Seebeck coefficient and the effective mass, which can possibly be attributed to the formation of additional resonant states near Fermi level. Though the power factor does not improve, the significant reduction in the electronic part of the thermal conductivity leads to a measurable improvement in ZT.

Promising Thermoelectric Bulk Materials with 2D Structures

“…New fabrication methods have been developed for other materials with 2D structures, such as transition metal dichalcogenides (TMDCs), to achieve low thermal conductivity by misfit layers. [67][68][69] These studies also offer a controllable way to further optimize existing thermoe lectric materials. For practical applications, thermoelectric bulk materials with 2D structures are easier to fabricate for use in film TE devices.…”

High-temperature thermoelectric properties and thermal stability in air of copper zinc tin sulfide for the p-type leg of thermoelectric devices

“…9,10) In particular, we considered p-type Cu 2 ZnSnS 4 -and n-type TiS 2 -based layered materials as strong candidates for p-n pairs of TE devices for the intermediate temperature range because both materials exhibit relatively high performance. [11][12][13][14] While the high-temperature thermal stability in air of the latter has already been confirmed, 13) that of the former has not yet been reported.…”

Enhancement of Thermoelectric Properties of Layered Chalcogenide Materials

“…The enhanced electrical conductivity is attributed to the high carrier concentration induced by Cu dopants, whereas the presence of Cu atoms plays an important role as scattering centers for the phonon. A significant reduction in the lattice thermal conductivity, which led to a measurable improvement in ZT, was reported by Putri et al [59], who used chromium as a dopant for n-type (BiS) 1.2 (TiS 2 ) 2 misfit layer compound. The calculated ZT values for doped samples with different doping amounts (x = 0.025, x = 0.05, x = 0.1) exhibit an increase in ZT to 0.24-0.3.…”

“…Heavily doped semiconductors are the best thermoelectric materials with a greater power factor than the undoped counterpart [3,76]. Dopant additions have been shown to have a significant impact on the electron density distribution in thermoelectric chalcogenides [59,77]. Moreover, doping can play an important role in reducing the lattice thermal conductivity by creating defects and scattering phonons.…”