Investigation of Temperature-Dependent Phonon Anharmonicity and Thermal Transport in SnS Single Crystals

Abstract

Tin sulfide has outstanding thermoelectric properties in the b-axis direction of crystallography as a IV−VI group layered compound, which arouses great attention. In this study, temperature-dependent Raman spectroscopy (TDRS) is used to quantify the phonon anharmonicity in SnS crystals from 77 to 475 K, where the three-phonon process dominates in this temperature region. Moreover, integration of the four-phonon process and lattice thermal expansion will better describe the temperature-dependent Raman experimental phenomenon. The good agreement between the calculated and experimental lattice thermal conductivity confirms the three-phonon scattering process is the dominant scattering mechanism at this temperature range. Further, combining the atomic thermal displacement and charge density through density functional theory calculation, the inherently low thermal conductivity of SnS is because of strong lattice anharmonicity, which is brought by the presence of asymmetric chemical bonding resulting from the Sn 5s 2 lone pair electrons. These results provide key insights for studying thermal properties of other lowdimensional materials.

Composition‐tunable SnSe(1−x)Sx (0 ≤ x ≤ 1) single crystals toward efficient bandgap engineering and optical/thermal properties

“…Five typically Raman modes, namely, 𝐵 1 3𝑔 (50 cm −1 ), 𝐴 1 𝑔 (96 cm −1 ), 𝐵 2 3𝑔 (166 cm −1 ), 𝐴 2 𝑔 (194 cm −1 ), and 𝐴 3 𝑔 (220 cm −1 ) are observed for SnS; four Raman modes, 𝐴 1 𝑔 (70 cm −1 ), 𝐵 3𝑔 (118 cm −1 ), 𝐴 2 𝑔 (141 cm −1 ), and 𝐴 3 𝑔 (154 cm −1 ) are obtained for SnSe, respectively. 41,42 The corresponding Raman modes for other stoichiometric ratio crystals are consequently located between these two extremes. On the one hand, the 𝐵 3𝑔 and 𝐴 2 𝑔 are associated with the in-plane vibration modes, while 𝐴 1 𝑔 and 𝐴 3 𝑔 belong to the out-of-plane vibration modes.…”

“…Figure 4A elucidates the normalized Raman spectra of synthetic SnSe (1− x ) S x (0 ≤ x ≤ 1) SCs in the range from 40 cm −1 to 300 cm −1 . Five typically Raman modes, namely, $$B_{3g}^1$$ (50 cm −1 ), $$A_g^1$$ (96 cm −1 ), $$B_{3g}^2$$ (166 cm −1 ), $$A_g^2$$ (194 cm −1 ), and $$A_g^3$$ (220 cm −1 ) are observed for SnS; four Raman modes, $$A_g^1$$ (70 cm −1 ), $${B_{3g}}$$ (118 cm −1 ), $$A_g^2$$ (141 cm −1 ), and $$A_g^3$$ (154 cm −1 ) are obtained for SnSe, respectively 41,42 . The corresponding Raman modes for other stoichiometric ratio crystals are consequently located between these two extremes.…”