Electronic structure and optical properties of complex hydrides LiBH4 and NaAlH4 compounds

Abstract

Summary The properties of the complex hydrides LiBH4 and NaAlH4 such as structural, electronic, and optical properties were calculated using the augmented plane wave plus local orbitals (APW + lo) method. The three phases α, β, and γ of LiBH4 and NaAlH4 hydrides are studied, the β‐phase is transformed at the high‐pressure to γ phase for the compound LiBH4 with the generalized gradient approximation (GGA) with a 16% volume decrease. However, NaAlH4 compound did not show any phase transition. The interaction between the boron (aluminum) atoms and the hydrogen atoms in the [AlH4]− ([BH4]−) complexes is strongly covalent, and between the complexes [AlH4]− and the lithium Li+ cations for the LiBH4 compound and between the complexes [AlH4]− and the sodium Na+ cations for the NaAlH4 compound, the bond is ionic. For the most stable phases of the two complex hydrides, different optical parameters have been calculated as a function of the photon energy. The plasma frequency ωp is calculated from the mean peak of the energy loss function. Therefore, by way of example, the plasma energy ħωp of its peak position is 13.23 (12.93) eV for α‐NaAlH4 (α‐LiBH4).

Structural, vibrational, mechanical, and optoelectronic properties of LiBH4 for hydrogen storage and optoelectronic devices: First‐principles study

“…Comparatively, it is concluded that our theoretically estimated value of band gap energy, that is, 6.81 eV, using the PBE functional is ~4.1% smaller than the experimental value of 7.1 eV reported for LiBH 4, [ 32 ] which lies in an acceptable precision range. This value of band gap energy is found to be very close to the previously reported values of 6.80 eV by Miwa et al [ 8 ] and 6.95 eV by Ghellab et al [ 13 ] using diverse calculation codes.…”

“…Khalil et al [ 12 ] recently studied the spectroscopic and thermodynamic properties of a similar hydride, MgH 2 , in the presence of catalysts and found that hydrogen release temperature is reduced due to the reaction of metal hydrides with catalysts. Ghellab et al [ 13 ] reported the phase transition in LiBH 4 system at high values of pressures based on density functional theory (DFT) calculations using the WIEN2K code. As far as the “mechanical properties” are concerned, a generic term used to demonstrate the endurance/strength and ductility of the materials has been given the least attention.…”

First Principles Insight of Structural, Vibrational, Mechanical and Optoelectronic Properties of LiBH4 for Hydrogen Storage and Optoelectronic Devices

“…[27], which is an acceptable precision range. The value of band gap was found to be very close to the previously reported values of 6.80 eV and 6.95 eV by Miwa et aland Ghellab et al [31][32] respectively using diverse calculation codes.…”

“…Particularly, its real part describes polarization of the materials, since dielectric function can be split into two parts; the real and imaginary parts which are drawn as a function of frequency and shown in figure 9. The complex dielectric function can be expressed through well-recognized Kramer-Kronig [32][33][34][35][36][37][38][39][40][41] relation as given below:…”

“…Khalil et al [12] recently studied the spectroscopic and thermodynamical properties of a similar hydride, MgH 2 in the presence of catalysts and found that hydrogen release temperature is reduced due to reaction of metal hydride with catalysts. Ghellab et al [13] reported the phase transition in LiBH 4 system at high values of pressure based on density functional theory calculations using the WIEN2K code.…”