Ab Initio Computational Studies of Mg Vacancy Diffusion in Doped MgB₂ Aimed at Hydriding Kinetics Enhancement of the LiBH₄ + MgH₂ System

Abstract

We report an ab initio density functional theory (DFT) study that investigates the effect of transition metal dopants on diffusion of Mg vacancies in MgB 2 . This study has implications for the diffusion-controlled hydriding kinetics of the technologically important LiBH 4 + MgH 2 hydrogen storage system. The first-principles calculation reveals that the solubility of M (M ) Ni, Mn, V, Ti, Sc, and Y) in MgB 2 and the migration barriers of Mg vacancies are dictated by the dopant's atomic radius, whereas the formation energies of Mg vacancies are strongly affected by both the dopant's atomic radius and charge distribution. Mn, Sc, and Y are found to have the potential to enhance the diffusion rate of Mg, whereas V and Ti are poor dopants in enhancing the diffusion rate of Mg in MgB 2 . The findings in this study are consistent with existing experimental results.

Microstructures and superconducting properties of high performance MgB2 thin films deposited from a high-purity, dense Mg–B target

“…Moreover, the B c2 (0 K) of MgB 2 single crystals can be improved by introducing a moderate level of defects via C doping or proton irradiation [24–26]. This appears different from our observations in MgB 2 thin films, but both relationships are valid due to difference in the defect density in samples.…”

Hydrogen storage: beyond conventional methods

“…Shaw et al focused on the vacancy diffusion of doped magnesium borides, concluding that manganese, scandium and yttrium offer enhanced migration rates due to their compatibility with the atomic size of magnesium. 80 Ozolins et al modeled group 1 and 2 mixed metal hydride, boride and borohydride structures, along with their intermediate phases and hydrogen storage capacities, 81 while ammonia borane was investigated by Miranda and Ceder, who calculated structures, vibrational spectra, and entropy, enthalpy and free energy changes during dehydrogenation. 82 Further computational studies will be pivotal in realizing novel hydrogen storage materials that are viable in laboratory and commercial settings.…”

Fundamental Material Properties of the 2LiBH4-MgH2 Reactive Hydride Composite for Hydrogen Storage: (I) Thermodynamic and Heat Transfer Properties

“…However, the reasons behind the single-step absorption and two-steps desorption reactions may not be inferred by thermodynamically considerations alone. In several works, the reaction mechanism of the Li-RHC has been investigated in dynamic conditions [23,[26][27][28][29]. In particular, the existence of a ternary specie such as (Mg 1−x Li 2x )B 2 , which has been confirmed using nuclear magnetic resonance (NMR) [27][28][29], is an interesting evidence concerning the diffusion processes that are suspected to play a fundamental role in the Li-Mg ion exchange that needs to take place for the reaction to occur at all.…”