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<p>A comprehensive first-principles investigation of the structural, electronic, optical, thermodynamic, and thermoelectric properties of cubic double-perovskite halides M<sub>2</sub>NdCuCl<sub>6</sub> (M = Na, K, Rb) was carried out using density functional theory within the FP-LAPW method as implemented in the WIEN2k package. Structural optimization confirms that all compounds crystallize in the stable elpasolite-type cubic structure with space group Fm–3m (No. 225). The lattice parameter systematically increases from Na to Rb due to the larger ionic radius of the alkali metals, demonstrating compositional tunability while preserving cubic symmetry. Electronic band-structure calculations using the TB-mBJ potential reveal indirect semiconducting behavior with band gaps of approximately 2.55–2.65&#xa0;eV. The valence band is mainly dominated by hybridized Cl–3p and Cu–3d states, whereas the conduction band originates primarily from localized Nd–4f states. This exceptionally strong ultraviolet absorption response is physically driven by the dense manifold of localized Nd–4f states present in the conduction band, which provides a high density of available pathways for high-energy photon excitations originating from the deep Cl–3p/Cu–3d valence states. Optical properties indicate strong absorption in the ultraviolet region and a high dielectric response, suggesting potential for UV optoelectronic applications. Furthermore, thermodynamic and structural analyses reveal that antisite disorder and localized lattice distortions critically govern the magnetic ground state. Thermodynamic analysis shows mechanical softness typical of halide perovskites and confirms lattice stability through temperature- and pressure-dependent variations in bulk modulus, entropy, Debye temperature, and thermal expansion. Thermoelectric calculations reveal negative Seebeck coefficients, indicating n-type conductivity. Among the studied compounds, Rb<sub>2</sub>NdCuCl<sub>6</sub> exhibits enhanced thermopower and reduced thermal conductivity, resulting in comparatively improved thermoelectric performance. Overall, alkali-metal substitution effectively tunes structural and transport properties without altering the fundamental electronic framework, highlighting these rare-earth halide double perovskites as promising candidates for multifunctional optoelectronic and energy-conversion applications.</p>

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Computational study of lead-free double perovskites M2NdCuCl6 (M = K, Na, Rb) for photovoltaic applications

  • 期刊论文

  • 发表日期：

    2026年7月4日

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  • Anuj Kumar,
  • Vivek Kumar Nautiyal,
  • Amreeta Preetam,
  • R. S. Baghel,
  • Pravin Kumar,
  • Bhupendra Singh,
  • Aman Kumar

摘要

A comprehensive first-principles investigation of the structural, electronic, optical, thermodynamic, and thermoelectric properties of cubic double-perovskite halides M2NdCuCl6 (M = Na, K, Rb) was carried out using density functional theory within the FP-LAPW method as implemented in the WIEN2k package. Structural optimization confirms that all compounds crystallize in the stable elpasolite-type cubic structure with space group Fm–3m (No. 225). The lattice parameter systematically increases from Na to Rb due to the larger ionic radius of the alkali metals, demonstrating compositional tunability while preserving cubic symmetry. Electronic band-structure calculations using the TB-mBJ potential reveal indirect semiconducting behavior with band gaps of approximately 2.55–2.65 eV. The valence band is mainly dominated by hybridized Cl–3p and Cu–3d states, whereas the conduction band originates primarily from localized Nd–4f states. This exceptionally strong ultraviolet absorption response is physically driven by the dense manifold of localized Nd–4f states present in the conduction band, which provides a high density of available pathways for high-energy photon excitations originating from the deep Cl–3p/Cu–3d valence states. Optical properties indicate strong absorption in the ultraviolet region and a high dielectric response, suggesting potential for UV optoelectronic applications. Furthermore, thermodynamic and structural analyses reveal that antisite disorder and localized lattice distortions critically govern the magnetic ground state. Thermodynamic analysis shows mechanical softness typical of halide perovskites and confirms lattice stability through temperature- and pressure-dependent variations in bulk modulus, entropy, Debye temperature, and thermal expansion. Thermoelectric calculations reveal negative Seebeck coefficients, indicating n-type conductivity. Among the studied compounds, Rb2NdCuCl6 exhibits enhanced thermopower and reduced thermal conductivity, resulting in comparatively improved thermoelectric performance. Overall, alkali-metal substitution effectively tunes structural and transport properties without altering the fundamental electronic framework, highlighting these rare-earth halide double perovskites as promising candidates for multifunctional optoelectronic and energy-conversion applications.