Mechanical, optical, and thermoelectric properties of α-BaSnS₃ and β-BaSnS₃

This study explores the mechanical, optical, and thermoelectric properties of α-BaSnS₃ and β-BaSnS₃ through first-principles calculations. The mechanical analysis reveals that both structures exhibit ductile behaviour. Furthermore, phonon dispersion calculations at 0 K show no imaginary frequencies, confirming their dynamical stability. The electronic structure analysis identifies both compounds as indirect bandgap semiconductors, with a bandgap of 1.63 eV for α-BaSnS₃ and 1.12 eV for β-BaSnS₃. Optical property analysis indicates that both compounds exhibit high absorption coefficients, reaching up to ∼10⁶ cm^-1 in the ultraviolet region and approximately ∼10⁵ cm^-1 in the visible spectrum, demonstrating their potential for optoelectronic applications. To explore the thermal transport properties, we calculated the lattice thermal conductivity using particle-like and wave-like transport channels. At 300 K, α-BaSnS₃ exhibits an average <i>k</i> _p of 1.030 W m^-1 K^-1 and <i>k</i> _c of 0.112 W m^-1 K^-1, whereas β-BaSnS₃ exhibits average values of 0.128 W m^-1 K^-1 for <i>k</i> _p and 0.179 W m^-1 K^-1 for <i>k</i> _c. This reduction in β-BaSnS₃ is primarily attributed to its pronounced anharmonicity and extremely short phonon lifetimes, which predominantly range from 0.1 to 1 ps. In terms of thermoelectric performance, α-BaSnS₃ achieves a <i>ZT</i> value of 1.05 at 600 K, while β-BaSnS₃ achieves an even higher <i>ZT</i> value of 1.06 under specific doping conditions. These results highlight the potential of the two phases of BaSnS₃ for applications in thermoelectric and optoelectronic technologies.