High-pressure study of lithium azide from density-functional calculations

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Chemistry

Background:

• Lithium azide (LiN3) is a material with potential applications.
• Understanding its behavior under high pressure is crucial for predicting its properties and stability.

Purpose of the Study:

• To investigate the structural, electronic, optical, and vibrational properties of LiN3 under high pressure.
• To provide theoretical insights into the mechanical stability and high-pressure phase transitions of LiN3.

Main Methods:

• Density Functional Theory (DFT) calculations using plane-wave pseudopotentials.
• Generalized Gradient Approximation (GGA) for exchange-correlation functional.
• Analysis of structural, elastic, electronic, optical, and vibrational properties.

Main Results:

• Calculated lattice parameters and bulk modulus (23.23 GPa) show good agreement with experimental data.
• Anisotropic compressibility observed, with the b-axis being most compressible.
• Mechanical stability confirmed by elastic constants (C33 > C11 > C22), indicating stiffness along the c-axis.
• Electronic band gap decreases with pressure, suggesting a transition towards semiconductor behavior.
• Optical properties (refractive index, absorption, photoconductivity) exhibit anisotropy and shift to higher energies with pressure, implying light-assisted decomposition.
• Lattice modes show a higher pressure response than internal azide ion modes.

Conclusions:

• LiN3 is mechanically stable and exhibits anisotropic compressibility under high pressure.
• High pressure induces semiconductor-like electronic properties and influences optical and vibrational responses.
• Theoretical predictions on elastic constants and high-pressure behavior await experimental validation.