Stabilities and defect-mediated lithium-ion conduction in a ground state cubic Li3N structure

Area of Science:

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

Background:

• Lithium nitride (Li3N) is a material of interest for solid-state ionics.
• Understanding different phases and their properties is crucial for material design.
• The ionic conduction mechanism in Li3N influences its application potential.

Purpose of the Study:

• To identify a stable ground state structure for lithium nitride.
• To characterize the physical and electronic properties of the newly found phase.
• To investigate native point defects and their role in ionic conduction.

Main Methods:

• Ab initio crystal structure prediction using a symmetric random-generated approach.
• Quasi-harmonic approximation for Gibbs free energy calculations.
• Hybrid density functional theory for electronic band structure and defect energetics.

Main Results:

• Discovery of a stable cubic lithium nitride (c-Li3N) ground state structure.
• c-Li3N exhibits negative thermal expansion below room temperature and is a semiconductor with a 1.90 eV indirect band gap.
• Lithium interstitials are identified as the dominant charge carriers with low migration barriers and formation energies.

Conclusions:

• The cubic phase of Li3N is thermodynamically stable over a wide temperature range.
• The unique properties of c-Li3N, including negative thermal expansion and semiconducting behavior, are elucidated.
• Ionic conduction in c-Li3N is predicted to proceed via an interstitial mechanism, distinct from the vacancy mechanism in α-Li3N.