Bulk and Monolayer ZrS<sub>3</sub> as Promising Anisotropic Thermoelectric Materials: A Comparative Study
Cong Wang, Changbo Zheng, Guoying Gao
Abstract
Different from two-dimensional (2D) transition-metal dichalcogenides, 2D transition-metal trichalcogenides with a quasi-one-dimensional chain offer additional advantages in electronics and optoelectronics. Based on the recent experimental synthesis of few layers of ZrS3, we present a comparative study on the electron and phonon transport properties of bulk and monolayer ZrS3 by using the first-principles calculations combined with the Boltzmann transport theory. The anisotropic electrical conductivity is obtained because of the different carrier effective masses along different directions, and consequently, a larger power factor along the y direction is achieved for both p-type and n-type. The multivalley degeneracy valence band contributes to the large Seebeck coefficient and the high power factor for holes. The carriers of electrons with higher mobility along the Γ–Y direction are responsible for the better transport properties of electrons than holes. In addition, the dimensionality reduction in the crystal structure enhances the phonon scattering and decreases the phonon group velocity and thus reduces the phonon thermal conductivity in monolayer ZrS3. The calculated total Grüneisen parameter of 1.8 at 300 K for monolayer ZrS3 is about 120% higher than that of bulk ZrS3 (0.8). The optimized n-type thermoelectric figure of merit at 800 K for monolayer ZrS3 reaches 2.44 along the y direction, while it is 1.75 for the n-type doping of bulk ZrS3. These results indicate that ZrS3 especially in the monolayer form is a promising anisotropic thermoelectric material.