Enhancing the Thermoelectric Properties of Misfit Layered Sulfides (MS)1.2+ q (NbS2) n (M = Gd and Dy) through Structural Evolution and Compositional Tuning

Aleksandr V Sotnikov; Priyanka Jood; Michihiro Ohta

doi:10.1021/acsomega.0c00908

Enhancing the Thermoelectric Properties of Misfit Layered Sulfides (MS)_{1.2+ q} (NbS₂) _n (M = Gd and Dy) through Structural Evolution and Compositional Tuning

ACS Omega. 2020 May 26;5(22):13006-13013. doi: 10.1021/acsomega.0c00908. eCollection 2020 Jun 9.

Authors

Aleksandr V Sotnikov¹, Priyanka Jood^{2

3}, Michihiro Ohta^{2

3}

Affiliations

¹ Nikolaev Institute of Inorganic Chemistry, Siberian Branch of RAS, Akademika Lavrent'eva Avenue 3, Novosibirsk, 630090, Russian Federation.
² Global Zero Emission Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.
³ Research Institute for Energy Conservation, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan.

Abstract

The misfit monolayered sulfides, (GdS)_1.20NbS₂, (DyS)_1.22NbS₂, (Gd_0.1Dy_0.9S)_1.21NbS₂, (Gd_0.2Dy_0.8S)_1.21NbS₂, and (Gd_0.5Dy_0.5S)_1.21NbS₂ and the misfit bilayered sulfide (GdS)_0.60NbS₂ were synthesized via sulfurization under flowing CS₂/H₂S gas and consolidated by pressure-assisted sintering. The thermoelectric properties of the monolayered and bilayered sulfides perpendicular (in-plane) and parallel (out-of-plane) to the pressing direction were investigated over a temperature range of 300-873 K. The crystal grains in all the sintered samples were preferentially oriented perpendicular to the pressing direction, which resulted in highly anisotropic electrical and thermal transport properties. All the sintered samples exhibited degenerate n-type semiconductor-like behavior, leading to a large thermoelectric power factor. The misfit layered structure yielded low lattice thermal conductivity. The evolution of the monolayered structures into bilayered structures affected their thermoelectric properties. The thermoelectric figure of merit (ZT) of monolayered (GdS)_1.20NbS₂ was higher than that of bilayered (GdS)_0.60NbS₂ due to the larger power factor and lower lattice thermal conductivity of (GdS)_1.20NbS₂. The lattice thermal conductivity of the monolayered sulfide was lower in (Gd _x Dy_1-x S)_1.2+q NbS₂ solid solutions. The large power factor and low lattice thermal conductivity allowed a ZT value of 0.13 at 873 K in (Gd_0.5Dy_0.5S)_1.21NbS₂ perpendicular to the pressing direction.