First-Principles evaluation of Lead-Free X2NaIO6 (X=Sr, Ba) Double-Perovskite: For optoelectronic and solar cell applications

[Display omitted] •DFT study of lead-free X2NaIO6 double-Perovskite.•X2NaIO6 are narrow bandgap semiconductor materials.•They absorb light more strongly in the visible region.•Both of these compounds are mechanically stable, anisotropic, and brittle.•X2NaIO6 are potential candidate for optoelectronic and solar cell applications. The standard lead-free double perovskite X2NaIO6 has become a viable alternative for lead-based perovskites due to its remarkable optoelectronic capabilities, high stability, non-toxicity, and multifunctionality. This study is presented to evaluate the structural, electronic, optical, and mechanical properties of X2NaIO6 (X=Sr, Ba) by applying a first-principles method based on density functional theory (DFT). These investigations were carried out at the level of the generalized gradient approximation (GGA) for the exchange–correlation functional, parameterized by Perdew Burke and Erenzerhof (PBE) within the CASTEP code. The tolerance factors (τ) for Sr2NaIO6 and Ba2NaIO6 are 0.98 and 1.0, confirming the cubic nature of both compounds. Both compounds Sr2NaIO6 and Ba2NaIO6 have direct narrow bandgap values of 1.57 eV and 1.42 eV, respectively. We also presented a comprehensive study of their optical properties. Shear modulus (G), Poisson’s ratio (v), elastic coefficient (Cij), anisotropy (A), bulk moduli (B), Young’s modulus (Y), and Pugh’s ratio (B/G) are computed. The combined electronic, optical, and mechanical investigations show that both materials are suitable for optoelectronic, photovoltaic, and solar cell applications.