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<p>We performed a comprehensive first-principles investigation of the cubic double perovskites Rb<sub>2</sub>NaIrBr<sub>6</sub> and Rb<sub>2</sub>NaIrI<sub>6</sub> using density functional theory. Structural optimization confirms that both compounds crystallize in the stable Fm-3m phase with corner-sharing [IrX<sub>6</sub>] octahedra, while Br → I substitution expands the lattice and reduces the bulk modulus, indicating higher compressibility for the iodide. Electronic calculations within WC-GGA and TB-mBJ show that both materials are direct band gap semiconductors at the Γ point, with tunable band gaps ranging from ~ 0.87 to 1.09&#xa0;eV (WC-GGA) and from ~ 1.64 to 2.11&#xa0;eV (TB-mBJ). Optical spectra reveal high dielectric constants and strong visible–UV absorption, with enhanced optical response for Rb<sub>2</sub>NaIrI<sub>6</sub>. Elastic constants satisfy the Born–Huang stability criteria, and both compounds are predicted to be brittle and elastically anisotropic. Thermoelectric transport calculations based on Boltzmann theory indicate <i>p</i>-type behavior with large Seebeck coefficients and increasing ZT at elevated temperature, reaching ~ 0.78 for Rb<sub>2</sub>NaIrBr<sub>6</sub> and ~ 0.85 for Rb<sub>2</sub>NaIrI<sub>6</sub> at 900&#xa0;K. These results highlight Ir-based halide double perovskites as mechanically stable, optically active, and thermoelectrically promising lead-free materials for multifunctional energy and optoelectronic applications.</p>

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Halogen-tunable Rb2NaIrX6 double perovskites: a computational study of optoelectronic, photocatalytic, and thermoelectric performance

  • 期刊论文

  • 发表日期：

    2026年5月24日

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  • Si Mohammed Djamel Eddine,
  • Debidatta Behera,
  • Mohammed Batouche,
  • Mohamed El Amine El Goutni,
  • Tabeti Abdelkader,
  • Taieb Seddik,
  • Dalila Hammoutène

摘要

We performed a comprehensive first-principles investigation of the cubic double perovskites Rb2NaIrBr6 and Rb2NaIrI6 using density functional theory. Structural optimization confirms that both compounds crystallize in the stable Fm-3m phase with corner-sharing [IrX6] octahedra, while Br → I substitution expands the lattice and reduces the bulk modulus, indicating higher compressibility for the iodide. Electronic calculations within WC-GGA and TB-mBJ show that both materials are direct band gap semiconductors at the Γ point, with tunable band gaps ranging from ~ 0.87 to 1.09 eV (WC-GGA) and from ~ 1.64 to 2.11 eV (TB-mBJ). Optical spectra reveal high dielectric constants and strong visible–UV absorption, with enhanced optical response for Rb2NaIrI6. Elastic constants satisfy the Born–Huang stability criteria, and both compounds are predicted to be brittle and elastically anisotropic. Thermoelectric transport calculations based on Boltzmann theory indicate p-type behavior with large Seebeck coefficients and increasing ZT at elevated temperature, reaching ~ 0.78 for Rb2NaIrBr6 and ~ 0.85 for Rb2NaIrI6 at 900 K. These results highlight Ir-based halide double perovskites as mechanically stable, optically active, and thermoelectrically promising lead-free materials for multifunctional energy and optoelectronic applications.