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<p>Lead free double perovskite materials are gaining potential attention as sustainable substitutes for multifunctional energy and optoelectronic applications. In the present study, we have systematically investigated the structural, mechanical, electronic, optical and thermoelectric properties of cubic Rb<sub>2</sub>LiSbX<sub>6</sub> (X = F, Cl, Br, I) double perovskites using DFT simulations together with GGA and PBE. The thermodynamic and dynamical stability is confirmed by the computed negative formation enthalpy (∆H<sub>f</sub>) and positive phonon dispersion curve, which also supports the existence of their cubic phase. Mechanical stability of these materials was insured by calculated elastic constants (<i>C</i><sub>ij</sub>). Analysis of elastic properties reveals enlightened lattice relaxing from F to I substitution with the bulk and the Young moduli decreasing from 26.90 to 10.68 GPa. Increasing nature of machinability index as well as the Pugh ratio ensure a transition toward higher ductility especially for Rb<sub>2</sub>LiSbBr<sub>6</sub> and Rb<sub>2</sub>LiSbI<sub>6</sub> confirming their superior easy formability and suitability for flexible device fabrication. According to the elastic anisotropy factors, all of these materials are elastically anisotropic. Tunable semiconducting manner of Rb<sub>2</sub>LiSbX<sub>6</sub> (X = F, Cl, Br, I) is observed from electronic band structure analysis whereas band gaps are decreasing systematically from 4.224&#xa0;eV (F) to 1.678&#xa0;eV (I) enabling tunable UV-to- visible absorption. A noticeable decline in Debye temperature (272.84 → 91. 27&#xa0;K) as well as decrease in thermal conductivity (1.25 → 0. 32 Wm⁻<sup>1</sup>&#xa0;K⁻<sup>1</sup>) from F to I together with an increase in the Grüneisen parameter (1.37 → 2. 00) are confirming the higher lattice anharmonicity and phonon scattering in heavier halides. The superior lattice anharmonicity and low lattice thermal conductivity of Rb<sub>2</sub>LiSbI<sub>6</sub> and Rb<sub>2</sub>LiSbBr<sub>6</sub> highlight their probable use for thermoelectric energy harvesting and waste-heat recovery applications. Their optical spectra reveal strong absorption in the UV region, making them appropriate for high-frequency applications. The overall analysis provides that Br- and I-containing materials emerge as promising candidates for thermoelectric and photoelectric applications whereas F-based material is more appropriate for ultraviolet and high-temperature optoelectronic systems.</p>

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Ab-initio exploration to investigate the structural, mechanical, electronic, thermal and optical properties of new lead-free perovskites Rb2LiSbX6 (X = F, Cl, Br, I) for industrial applications

  • 期刊论文

  • 发表日期：

    2026年6月22日

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  • Md. Shoriful Islam,
  • Ahmad Irfan,
  • Md. Atikur Rahman,
  • Antor Saha,
  • Mst. Asma Khatun,
  • M. S. Ali

摘要

Lead free double perovskite materials are gaining potential attention as sustainable substitutes for multifunctional energy and optoelectronic applications. In the present study, we have systematically investigated the structural, mechanical, electronic, optical and thermoelectric properties of cubic Rb2LiSbX6 (X = F, Cl, Br, I) double perovskites using DFT simulations together with GGA and PBE. The thermodynamic and dynamical stability is confirmed by the computed negative formation enthalpy (∆Hf) and positive phonon dispersion curve, which also supports the existence of their cubic phase. Mechanical stability of these materials was insured by calculated elastic constants (Cij). Analysis of elastic properties reveals enlightened lattice relaxing from F to I substitution with the bulk and the Young moduli decreasing from 26.90 to 10.68 GPa. Increasing nature of machinability index as well as the Pugh ratio ensure a transition toward higher ductility especially for Rb2LiSbBr6 and Rb2LiSbI6 confirming their superior easy formability and suitability for flexible device fabrication. According to the elastic anisotropy factors, all of these materials are elastically anisotropic. Tunable semiconducting manner of Rb2LiSbX6 (X = F, Cl, Br, I) is observed from electronic band structure analysis whereas band gaps are decreasing systematically from 4.224 eV (F) to 1.678 eV (I) enabling tunable UV-to- visible absorption. A noticeable decline in Debye temperature (272.84 → 91. 27 K) as well as decrease in thermal conductivity (1.25 → 0. 32 Wm⁻1 K⁻1) from F to I together with an increase in the Grüneisen parameter (1.37 → 2. 00) are confirming the higher lattice anharmonicity and phonon scattering in heavier halides. The superior lattice anharmonicity and low lattice thermal conductivity of Rb2LiSbI6 and Rb2LiSbBr6 highlight their probable use for thermoelectric energy harvesting and waste-heat recovery applications. Their optical spectra reveal strong absorption in the UV region, making them appropriate for high-frequency applications. The overall analysis provides that Br- and I-containing materials emerge as promising candidates for thermoelectric and photoelectric applications whereas F-based material is more appropriate for ultraviolet and high-temperature optoelectronic systems.