Strong phonon anharmonicity and low thermal conductivity of monolayer tin oxides driven by lone-pair electrons

Motivated by the excellent electronic and optoelectronic properties of two-dimensional (2D) tin oxides, we systematically investigated the thermal conductivity (κ) of monolayers SnO and SnO2 by the first-principles calculations. The room-temperature κ of monolayers SnO and SnO2 reaches 9.6 W/(m K) and 98.8 W/(m K), respectively. The size effect is much weaker for monolayer SnO than for monolayer SnO2, due to the coexistence of size dependent and independent components in the κ value of monolayer SnO. The large difference between the κ values of 2D tin oxides can be attributed to the small phonon group velocity and strong anharmonicity strength of monolayer SnO. Further electronic structure analysis reveals that the existence of sterically active lone-pair electrons is the key factor for the small κ value of monolayer SnO. These results provide a guide for the manipulation of thermal transport in electronic or thermoelectric devices based on 2D tin oxides.