A study of anisotropic thermoelectric properties of bulk Germanium Sulfide in its Pnma phase: a combined first-principles and machine-learning approach

Abstract

This work reports a detailed and systematic theoretical study of the anisotropic thermoelectric properties of bulk Germanium Sulfide (GeS) in its orthorhombic Pnma phase. Density functional theory (DFT), employing the generalized gradient approximation (GGA), has been used to examine the structural and electronic band structure properties of bulk GeS. Electronic transport properties have been studied by solving semiclassical Boltzmann transport equations. A machine-learning approach has estimated the temperature-dependent lattice part of thermal conductivity. The study reveals that GeS has a direct band gap of 1.20 eV. Lattice thermal conductivity is lowest along crystallographic a-direction, with a minimum of ∼0.98 Wm-1K-1 at 700 K. We have obtained the maximum figure of merit (ZT) ∼ 0.73 at 700 K and the efficiency ∼7.86% in a working temperature range of 300 K - 700 K for pristine GeS along crystallographic a-direction.

Thermoelectric properties of Pnma and R3m GeS and GeSe

“…On the other hand, the predicted κ latt = 0.98 W m −1 K −1 along the b direction of Pnma GeS at T = 700 K predicted in ref. 45 is much larger than our predicted 0.56 W m −1 K −1 , which we attribute to the use of PBE and a smaller 64-atom supercell to compute the force constants.…”

“…44,45,99,112 For example, the study on Pnma GeS in ref. 45 predicted a ∼2.5× larger κ latt and 50% smaller ZT at 700 K than the present calculations, while the calculations in ref. 44 predicted a 5× larger σ , smaller κ el , and 2–4× larger ZT .…”

“…A small number of computational studies have predicted the orthorhombic Pnma phase of GeSe to have a large ZT max = 2.5 at 800 K, competitive with SnSe, and Pnma GeS to attain ZT max = 0.73 at 700 K, close to the industry-standard ZT = 1. 44,45 More recently, the R 3 m phase of GeSe was also reported to show a ZT > 1. 46…”

Importance of Four-Phonon Interactions in Lattice Thermal Conductivity and Thermoelectrics: A Case Study

“…The GeS material has gained great attention due to its similar electronic properties as that of phosphorene as well as analogous crystal structures. − Some previous reports investigated the TE parameters for Pnma GeS bulk with a combined first-principles and ML approach . This study considers the constant relaxation time approximation (CRTA) with a three-phonon scattering effect.…”

“…24−26 Some previous reports investigated the TE parameters for Pnma GeS bulk with a combined first-principles and ML approach. 27 This study considers the constant relaxation time approximation (CRTA) with a three-phonon scattering effect. Shafique and Shin studied the 2D (monolayer) class of SnSe, SnS, GeSe, and GeS systems for TE applications considering the three-phonon scattering channels.…”