Light Atomic Mass Induces Low Lattice Thermal Conductivity in Janus Transition-Metal Dichalcogenides MSSe (M═Mo, W)
J. R. Sun, Chen Ge, Shouhang Li, Xiangjun Liu
Abstract
Transition-metal dichalcogenides (TMDs) have great potential in the field of thermoelectric conversion due to their remarkable transport properties. However, the large lattice thermal conductivity of TMDs is a fundamental bottleneck in achieving high thermoelectric conversion efficiency. The Janus structures are formed by replacing one of the chalcogenide layers in the primitive cell of MX 2 (M═Mo and W, X═S and Se) with other chalcogen elements. In this work, we perform a comprehensive first-principles investigation on the phonon thermal transport in bulk Janus materials MSSe. It is found that both the in-plane and out-of-plane thermal conductivities of MoSSe and WSSe are considerably lower than that of MoS 2, which is mainly attributed to the larger phonon–phonon scattering in Janus materials. The relatively light Mo atom in MoSSe leads to its larger lattice thermal conductivity compared to WSSe with a heavier W atom, which violates the empirical rule. By analyzing the phonon linewidth, it is revealed that this anomalous tendency originates from the relatively light Mo atomic mass in MoSSe. Additionally, the chemical bonds of MoSSe and WSSe are metavalent bonding, which is ascribed to their pronounced phonon anharmonicity. Our results reveal the thermal transport mechanisms in Janus materials, which are helpful to design thermoelectrics and nanoelectronics based on TMDs.