An experimental and theoretical approach for temperature-dependent Raman-active optical phonons driven thermal conductivity of layered PbBi₂Se₄ nano-flowers

Abstract

Topologically active, crystalline layered PbBi₂Se₄ has been probed for significantly low thermal conductivity and excellent thermal properties. The present work focuses on the investigation of thermal properties of the PbBi₂Se₄ composite, such as diffusivity, effusivity, specific heat, Debye temperature, thermal conductivity, lattice thermal conductivity using temperature, and incident laser power-dependent Raman scattering. The thermal properties are very important for thermal energy harvesting applications. The obtained results have been substantiated with first-principles calculations. It is observed that the septuple interface Se atoms govern high-frequency Raman Active modes, and their role is crucial for thermal properties. High phonon density of states at low-frequency, strong phonon coupling drove scattering, and low phonon lifetime of optically active ${\mathrm{E}}_{\mathrm{g}}^{2}$ and ${\mathrm{A}}_{1\mathrm{g}}^{2}$ modes govern the low thermal conductivity (55 Wm⁻¹ K⁻¹). The thermal conductivity of PbBi₂Se₄ is an order of magnitude lower than the other ternary compounds from the Pb_xBi_2ySe_3x+y family but is comparable to that of transition metal chalcogenide materials (e. g. MoS₂). The present work provides an efficient method to investigate the thermal conductivity of layered material. Further, it can be used to tune the thermal properties of the topological insulators by exploring the phonon dynamics.