Modeling and simulation of multifaceted properties of X2NaIO6 (X = Ca and Sr) double perovskite oxides for advanced technological applications

<bold>Context: </bold>In this study, the authors have investigated the structural, optoelectronic, thermoelectric, and thermodynamic properties of Ca2NaIO6 and Sr2NaIO6 double perovskite oxides. Both materials exhibit semiconductor behavior with direct band gaps (E-g) of 0.353 eV and 0.263 eV, respectively. Optical parameters like absorption coefficient alpha(omega), reflectivity R(omega), dielectric constants, and refractive index have been calculated. The most notable absorption peaks are identified at 5.52 eV (equal to 108.33 x 10(4) cm(-1)) in the case of Ca2NaIO6 and at 11.16 eV (equivalent to 118.17 x 10(4) cm(-1)) for Sr2NaIO6. These findings suggest a promising outlook for applications in optoelectronics. Moreover, their commendably low thermal conductivity and a high figure of merit, particularly at low temperatures (100 K), indicate their effectiveness as thermoelectric materials. This analysis underscores that these materials hold potential as suitable candidates for n-type doping, making them well-suited for use in thermoelectric devices. Studying thermal properties, including thermal expansion, bulk modulus, acoustic Debye temperature, entropy, and heat capacity, contributes to understanding the materials' thermodynamic stability. The titled materials are dynamically stable. The analysis of these double perovskite materials highlights their potential across various technological applications due to their advantageous structural, electronic, optical, and transport properties, offering new possibilities in material science and technology development.<bold>Methods: </bold>The study utilized the full potential linearized augmented plane wave (FP-LAPW) method in conjunction with density functional theory within the WIEN2k simulation code. This approach is widely recognized as one of the most dependable methods for evaluating the photovoltaic characteristics of semiconducting perovskites. The thermoelectric properties were ascertained using the rigid band approach and the constant scattering time approximation, both implemented in the BoltzTraP computational code.