First-Principles Investigations of Mechanical, Electronic and Optical Properties of Heavy Thallium Perovskites TlSnX<sub>3</sub> (X = F, Cl, Br and I)

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In this paper, the mechanical, elastic, electronic and optical properties of thallium based-perovskites TlSnX3 (X = F, Cl, Br and I) were investigated using the first-principles calculations. The elastic parameters calculations show that the perovskites are ductile, anisotropic, and mechanically stables. The cohesive energy calculations indicate that the evaluated perovskites are thermodynamically stable. Moreover, the band calculations with HSE06 method reveal that all perovskites TlSnX3 (X = F, Cl, Br and I) present a semiconductor feature. Further, the optical properties such as reflectivity, refractive index, extinction and absorption coefficients have been calculated and compared for all perovskites compounds. Interestingly, the found results show that the absorption coefficient α(ω) in the visible and infrared regions reaches high values of 1.02, 1.19, 1.14 and 1.03 × 106 cm-1 for TlSnI3, TlSnBr3, TlSnCl3 and TlSnF3 , respectively. These results suggest that the heavy thallium perovskites TlSnX3 (X = F, Cl, Br and I) have potential for optoelectronic applications.