The elastic, mechanical, and thermodynamic properties of NaXH4 (X = B, Al) intended for the storage of hydrogen: An ab-initio study

• Published in: Physica. B, Condensed matter Vol. 638; p. 1
• Main Authors: Ghellab, T., Charifi, Z., Baaziz, H., Latteli, H., Güler, M., Uğur, Ş., Güler, E., Uğur, G.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-08-2022; Elsevier BV
• Subjects: Anisotropy; Bulk modulus; Compressibility; Covalent bonds; Debye temperature; Decomposition; Elastic properties; First principles; Fuel cells; Gamma phase; Heat conductivity; Hydrides; Hydrogen; Hydrogen storage; Mechanical properties; Melting; Melting points; Modulus of elasticity; Simulation; Single crystals; Strain; Stress-strain relationships; Temperature; Thermal expansion; Thermodynamic properties; Thermodynamics; Hydrogen storage; Hydrides; Elastic properties; Anisotropy
• ISSN: 0921-4526; 1873-2135
• DOI: 10.1016/j.physb.2022.413851

Analyses based on first-principles simulations have revealed new details about the mechanical and thermodynamic characteristics of NaBH4 and NaAlH4 complex hydrides in α, β and γ phases. Using the quasi-harmonic Debye model, thermal parameters like the Debye temperature, the heat capacity, and the thermal expansion coefficient of NaXH4 (X = B, Al) complex hydrides are calculated in α, β and γ phases at different pressures and temperatures for the first time. Single-crystal elastic constants may be derived from the stress-strain relationship calculations. Although NaBH4 has a stronger compressibility modulus than NaAlH4, the distance dB-H is shorter than dAl-H, which may be explained by the presence of the covalent bond in BH4 and AlH4 in NaXH4 (X = B, Al). The melting points of NaXH4 (X = B, Al) may be used to estimate the decomposition temperatures of hydrogen. β-NaBH4 has a higher melting point than α-NaAlH4. Thus, the decomposition temperature of NaAlH4 at which hydrogen is released from a fuel cell is expected to be lower than that of NaBH4. β-NaBH4 has a more directed bonding tendency than α-NaAlH4 does. Except for the phase γ-NaAlH4, the NaXH4 (X = B, Al) compounds are ductile. NaBH4 deforms more than NaAlH4 in uniaxial deformation, yet both are centrally strong solids. Our PBE calculations result in the linear compressibility and orientation-dependent Young's modulus. Tetragonal β-NaBH4 and α-NaAlH4 structures have an isotropic bulk modulus but an anisotropic Young's modulus.
•Although NaBH4 has a stronger compressibility modulus than NaAlH4.•The mechanical stability demonstrate that investigated compounds are mechanically stable.•Tetragonal β-NaBH4 and α-NaAlH4 structures have an isotropic bulk modulus but an anisotropic Young's modulus.•These materials could be useful for storage of hydrogen application.