Intrinsic defects and dopants in LiNH2: a first-principles study.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Materials Science

Background:

• The lithium amide (LiNH(2)) + lithium hydride (LiH) system is a key candidate for lightweight hydrogen storage materials.
• Dehydrogenation in this system relies on mass transport through lattice defects within the bulk amide crystal.

Purpose of the Study:

• To investigate native point defects and dopants in LiNH(2) using first-principles calculations.
• To understand the role of these defects in hydrogen storage properties.

Main Methods:

• Density Functional Theory (DFT) was employed for first-principles calculations.
• Analysis of native point defects (interstitials and vacancies) and dopant effects in LiNH(2).

Main Results:

• Both Li-related (Li(i)(+), V(Li)(-)) and H-related (H(i)(+), V(H)(-)) defects are charged and significantly influence hydrogen storage.
• Li-related defects are abundant with low diffusion barriers (0.3-0.5 eV), enabling rapid diffusion at moderate temperatures.
• The hydride vacancy (V(H)(-)), corresponding to the [NH](2-) ion, is the dominant species for proton transport with a barrier of ~0.7 eV.

Conclusions:

• Native defects, especially Li-related ones and the hydride vacancy, play critical roles in the hydrogen storage mechanism of LiNH(2).
• Dopants like Mg and Ca can moderately alter defect concentrations, potentially influencing material performance.
• Understanding these defects is crucial for optimizing LiNH(2) for hydrogen storage applications.