Thermoelectric and Optoelectronic Properties of Rb₂LiMoX₆ (X = Br, I) Ferromagnets Using Density Functional Theory

The present study employs DFT to simulate the geometrical, magnetic, optoelectronic, and thermoelectric characteristics of Rb₂LiMoX₆ (X = Br, I) in the WIEN2K program implementing FP-LAPW method. The tolerance factor (τ) and formation enthalpy (ΔH_f) are estimated to verify the thermodynamic and structural stability of the Rb₂LiMoX₆ (X = Br, I) compounds. The values of τ are 0.91 and 0.89 for Rb₂LiMoBr₆ and Rb₂LiMoI₆, respectively. The anticipated spin-dependent band structure (BS) and density of states (DOS) exhibit p-type semiconductor behavior with a direct band gap at the X-X symmetry sites in both spin configurations. For Rb₂LiMoBr₆, the values are 2.37 eV in the spin-up and 3.54 eV in the spin-down. Similarly, for Rb₂LiMoI₆, the direct E_g is 1.30 eV in the spin-up and 1.72 eV in the spin-down. The ferromagnetic (FM) nature of Rb₂LiMoBr₆ and K₂LiMoI₆ was confirmed based on their respective total magnetic moment (µ_B) of 3.00 µ_B for both halides. The materials exhibited light absorbance within the visible to ultraviolet (UV) range, increasing their importance for photocell and optoelectronic devices. Furthermore, the ZT spectrum reveals that Rb₂LiMoI₆ reaches a peak value of 0.72 at 700 K, while Rb₂LiMoBr₆ achieves a slightly higher peak of 0.74 at 800 K. making them highly intriguing contenders for efficient heat energy conversion systems. The results of the examined compounds offer a novel avenue for researchers to explore the potential uses of spintronic and optical devices.