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<p>The structural versatility and tunability of Alkaline metal hydrochloride alloys lead to the search for efficient thermoelectric and optoelectronic materials. In this study, we investigated MHCl (M = Mg, Ca, Sr) in tetragonal (P4/nmm) crystal structures using density functional theory implemented in quantum ESPRESSO with the GGA-PBE functional for electronic and optical properties. BoltzTraP2 was used to calculate thermoelectric properties. At the same time, phonopy was used for dynamic stability. Our investigation stated that CaHCl and SrHCl have energy band gaps of 3.89 and 4.02&#xa0;eV in the range of wide band materials, respectively. However, MgHCl has an indirect band gap of 2.01&#xa0;eV. Absorption coefficients derived from dielectric constants indicate that tetragonal geometry predominantly produces peaks in the ultraviolet band (~ 5–8&#xa0;eV), rendering them excellent candidates for optical devices. The properties related to the hydrogen storage capability of these alloys revealed that MgHCl has emerged as a promising candidate with 1.659% gravimetric capacity (<i>C</i><sub>Wt%</sub>) and 38.918&#xa0;g/L of volumetric capacity (<i>C</i><sub>vol</sub>). The <i>C</i><sub>vol</sub> of MgHCl comes well near the baseline set by the U.S. for hydrogen storage in 2025. The thermodynamic screening against competing phases (MH<sub>2</sub>, MCl<sub>2</sub>) yields decomposition energies of + 0.38, − 0.06, and − 0.12&#xa0;eV/fu for MgHCl, CaHCl, and SrHCl, respectively. In thermoelectric parameters, MgHCl, CaHCl, and SrHCl showed p-type behaviour represented by a positive Seebeck coefficient. At 1200&#xa0;K, the figures of merit for CaHCl, MgHCl, and SrHCl are 1.20, 0.97, and 0.74, respectively. Formation energies for MgHCl, CaHCl, and SrHCl are − 0.96, − 1.30, and − 1.36, respectively, which favour the formability of these alloys. Mechanical stability of these alloys is verified by the Born-Huang criteria collectively. All these properties make them promising candidates for optical and thermoelectric devices.</p>

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Exploring matlockite-type metal hydrides MHCl (M = Mg, Ca, Sr) for optoelectronic, thermoelectric and hydrogen storage applications: a DFT study

  • 期刊论文

  • 发表日期：

    2026年7月30日

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  • Muhammad Farhan Waris,
  • Yasir Altaf,
  • Fahim Ahmed

摘要

The structural versatility and tunability of Alkaline metal hydrochloride alloys lead to the search for efficient thermoelectric and optoelectronic materials. In this study, we investigated MHCl (M = Mg, Ca, Sr) in tetragonal (P4/nmm) crystal structures using density functional theory implemented in quantum ESPRESSO with the GGA-PBE functional for electronic and optical properties. BoltzTraP2 was used to calculate thermoelectric properties. At the same time, phonopy was used for dynamic stability. Our investigation stated that CaHCl and SrHCl have energy band gaps of 3.89 and 4.02 eV in the range of wide band materials, respectively. However, MgHCl has an indirect band gap of 2.01 eV. Absorption coefficients derived from dielectric constants indicate that tetragonal geometry predominantly produces peaks in the ultraviolet band (~ 5–8 eV), rendering them excellent candidates for optical devices. The properties related to the hydrogen storage capability of these alloys revealed that MgHCl has emerged as a promising candidate with 1.659% gravimetric capacity (CWt%) and 38.918 g/L of volumetric capacity (Cvol). The Cvol of MgHCl comes well near the baseline set by the U.S. for hydrogen storage in 2025. The thermodynamic screening against competing phases (MH2, MCl2) yields decomposition energies of + 0.38, − 0.06, and − 0.12 eV/fu for MgHCl, CaHCl, and SrHCl, respectively. In thermoelectric parameters, MgHCl, CaHCl, and SrHCl showed p-type behaviour represented by a positive Seebeck coefficient. At 1200 K, the figures of merit for CaHCl, MgHCl, and SrHCl are 1.20, 0.97, and 0.74, respectively. Formation energies for MgHCl, CaHCl, and SrHCl are − 0.96, − 1.30, and − 1.36, respectively, which favour the formability of these alloys. Mechanical stability of these alloys is verified by the Born-Huang criteria collectively. All these properties make them promising candidates for optical and thermoelectric devices.