Investigation of Structural, Optoelectronic, Thermoelectric, and Elastic Properties for Sr2NaXO6 (X = Cl, Br, and I) Advanced Double Perovskite Semiconductors: Ab Initio Study

An in-depth theoretical analysis for structural, optoelectronic, thermoelectric, and elastic characteristics of Sr2NaXO6 (X = Cl, Br, and I) double perovskites for the first time has been conducted; these analyses are undertaken using the WIEN2k package and accomplished within the density functional theory. Both of the structural and elastic characteristics have been executed using the PBEsol scheme; on the other hand, the improved modified Becke-Johnson (mBJ) scheme proposed by Koller et al. (KTB-mBJ), for electronic, optical, and thermoelectric features, in addition to TB-mBJ for electronic properties has been adopted. The results of structural parameters, energy formation, tolerance factor, and octahedral factor reveal the possibility of experimental synthesis and stable ideal cubic structure of the studied oxide double perovskites. The simulated results for the electronic band structure of the studied compounds Sr2NaXO6 (X = Cl, Br, and I) represent that the compounds are direct bandgap semiconductors, with increasing energy gap (Eg) from Sr2NaClO6 to Sr2NaIO6. Electronic results show that the double perovskites exhibit a direct bandgap of 1.3538, 1.8073, and 3.5202 eV for Sr2NaClO6, Sr2NaBrO6, and Sr2NaIO6, respectively, by using KTB-mBJ potential scheme. The thermoelectric quantities have been determined. Positive values of the Seebeck coefficient characterize the p-type nature of the compounds. At a temperature of 336.8 K, the Seebeck effect strength is the same for Sr2NaXO6 (X = Cl, Br, and I) oxide double perovskites, with a value of 253.18 mu V K-1. The ZT values are 0.747, 0.734, and 0.738 at 1000 K for Sr2NaClO6, Sr2NaBrO6, and Sr2NaIO6, respectively. The analysis of optical properties such as the dielectric function epsilon(omega), absorption coefficient alpha, and the parts of complex refractive index n(omega)$\overset{sim}{n} \left(\right. \omega \left.\right)$ exhibits a high performance of the titled compounds in the UV range. The calculated elastic constant and related parameters show that the compounds are mechanically stable and have brittle behavior. The results of optical and thermoelectric properties reveal the possible use of the double perovskites for thermoelectric and optoelectronic applications. Moreover, it has been found that compounds exhibit a notable absorption in the visible range for Sr2NaClO6 and Sr2NaBrO6 and in the UV light range for the compound Sr2NaIO6. No studies have been published yet on the significant double perovskite. Consequently, current research bridges the gap in both theoretical and experimental results for these double perovskites. A detailed investigation into elastic constants, mechanical properties, and anisotropic behavior has also been carried out.