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Context <p>The present work illustrates the first systematic assessment of the structural, electronic and optical characteristics of the cubic halide double perovskite compounds Na<sub>2</sub>AgInX<sub>6</sub> (X = F, Cl, Br and I). All four compounds were observed to stabilize in a crystalline face-centered-cubic (FCC) structure (Fm-3m) with lattice parameter values ranging from 8.891 Å (Na<sub>2</sub>AgInF<sub>6</sub>) to 11.942 Å (Na<sub>2</sub>AgInI<sub>6</sub>) and decreasing values of lattice stiffness as the halide size increased. These compounds exhibit direct bandgaps in the range from 3.126 eV (Na<sub>2</sub>AgInF<sub>6</sub>) to 0.818 eV (Na<sub>2</sub>AgInI<sub>6</sub>). The analysis of optical behaviours indicates a systematic increase in both dielectric constant and the refractive index as the size of the halogen is increased. The extensive absorption and optical conductivity observed in the visible–UV region, particularly for the Br- and I-components, indicate that they have potential for optoelectronic and photonic applications. Thermoelectric calculations predict high ZT values approaching unity (≈0.99) over 300–900 K, particularly for F- and Cl-based systems. Elastic and thermodynamic analyses confirm ductile behavior of these compounds.</p> Methods <p>We have performed DFT calculations using FP-LAPW method employed in WIEN2k with a GGA exchange correlation function. Firstly, we performed the structural optimization to get the optimal structure of the lowest energy configuration. Afterwards, Electronic properties such as band structures and DOS were computed. To get the more accurate bandgap we used the TB-mBJ approach with the PBE-GGA functional. The optical properties such as dielectric function, reflectivity, refractive index, etc. were calculated using the enhanced bandgap values for detailed representation of the spectra. The transport coefficients of thermoelectric materials were calculated using a Boltzmann approach under the constant relaxation time approximation employed in BoltzTraP code. The method for determining the elastic constants is based upon the finite strain theory, while the thermodynamic properties are determined using the quasi-harmonic Debye model in Gibbs2 code.</p>

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Investigation of structural, electronic, optical, thermoelectric, and stability properties of Na2AgInX6 (X = F, Cl, Br and I) halide double perovskites

  • 期刊论文

  • 发表日期：

    2026年5月25日

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  • Anita Kumari,
  • Deo Prakash,
  • Keshav Deo Verma,
  • Priyanka Dhariwal,
  • Peeyush Kumar Kamlesh,
  • Ajay Singh Verma

摘要

Context

The present work illustrates the first systematic assessment of the structural, electronic and optical characteristics of the cubic halide double perovskite compounds Na2AgInX6 (X = F, Cl, Br and I). All four compounds were observed to stabilize in a crystalline face-centered-cubic (FCC) structure (Fm-3m) with lattice parameter values ranging from 8.891 Å (Na2AgInF6) to 11.942 Å (Na2AgInI6) and decreasing values of lattice stiffness as the halide size increased. These compounds exhibit direct bandgaps in the range from 3.126 eV (Na2AgInF6) to 0.818 eV (Na2AgInI6). The analysis of optical behaviours indicates a systematic increase in both dielectric constant and the refractive index as the size of the halogen is increased. The extensive absorption and optical conductivity observed in the visible–UV region, particularly for the Br- and I-components, indicate that they have potential for optoelectronic and photonic applications. Thermoelectric calculations predict high ZT values approaching unity (≈0.99) over 300–900 K, particularly for F- and Cl-based systems. Elastic and thermodynamic analyses confirm ductile behavior of these compounds.

Methods

We have performed DFT calculations using FP-LAPW method employed in WIEN2k with a GGA exchange correlation function. Firstly, we performed the structural optimization to get the optimal structure of the lowest energy configuration. Afterwards, Electronic properties such as band structures and DOS were computed. To get the more accurate bandgap we used the TB-mBJ approach with the PBE-GGA functional. The optical properties such as dielectric function, reflectivity, refractive index, etc. were calculated using the enhanced bandgap values for detailed representation of the spectra. The transport coefficients of thermoelectric materials were calculated using a Boltzmann approach under the constant relaxation time approximation employed in BoltzTraP code. The method for determining the elastic constants is based upon the finite strain theory, while the thermodynamic properties are determined using the quasi-harmonic Debye model in Gibbs2 code.