Investigation of a new group of low band-gap semiconducting double perovskite K₂MgSnZ₆ (Z = Cl, Br, & I) materials and their structural, electronic, mechanical, and optical behaviors via DFT study

Abstract This study focuses on potassium based double perovskite materials, specifically a series of K 2 MgSnZ 6 (Z = Cl, Br, & I) halide materials. For the investigated materials, all primary calculations were performed using the Full-Potential Linearized Augmented Plane-Wave (FP-LAPW) method, supported by density functional theory (DFT), and implemented in the WIEN2k code. The Gold-Schmidt tolerance factor values confirm the structural stability of the compounds, while the negative values of formation energy indicate the feasibility of experimental synthesis of the studied materials. The lattice constants were observed to increase as the halide element at the ‘Z’ position was replaced by one with a larger ionic radius. The recorded band-gap values were 2.60 eV, 2.00 eV, and 1.37 eV for K 2 MgSnCl 6 , K 2 MgSnBr 6 , and K 2 MgSnI 6 , respectively. After calculating the elastic constants for all K 2 MgSnZ 6 (Z = Cl, Br, & I) materials, it was found that they satisfy the primary conditions for Born stability required for cubic-phase materials: (1) C 11 > B > C 12 , (2) C 11 + 2C 12 > 0, (3) C 11 > 0, (4) C 44 > 0, and (5) C 11 –C 12 > 0. The optical parameters of the K 2 MgSnZ 6 (Z = Cl, Br, & I) double perovskite materials suggest that these materials could play a significant role in practical applications such as solar cells, UV detectors, and various optoelectronic devices.