Elastic moduli and refractive index of γ-Ge₃N₄

Area of Science:

• Materials Science
• Solid State Physics
• Crystallography

Background:

• Germanium nitride (γ-Ge3N4) is a wide band-gap semiconductor with promising thermal and mechanical properties.
• Existing experimental data on its elastic moduli (bulk B0 and shear G0) are limited and inconsistent.
• Previous theoretical calculations showed discrepancies with experimental G0 values.

Purpose of the Study:

• To experimentally determine the elastic properties (bulk and shear moduli) of polycrystalline γ-Ge3N4.
• To verify and refine existing theoretical predictions for G0.
• To measure the refractive index of γ-Ge3N4 and compare it with theoretical calculations.

Main Methods:

• High-pressure and high-temperature densification of polycrystalline γ-Ge3N4.
• Laser ultrasonics (LU) to measure sound velocities and derive elastic moduli.
• Brillouin light scattering (BLS) to investigate elastic anisotropy and refractive index.
• Extended first-principles density functional calculations for comparison.

Main Results:

• Experimental values for bulk modulus B0 = 322(44) GPa and shear modulus G0 = 188(7) GPa were determined for dense polycrystalline γ-Ge3N4.
• Theoretical calculations underestimated B0 by ~17% but showed good agreement with the experimental G0.
• The refractive index was measured as n = 2.4, consistent with theoretical predictions and comparable to diamond and GaN.

Conclusions:

• This study provides reliable experimental data for the elastic moduli of γ-Ge3N4, resolving previous inconsistencies.
• The findings validate theoretical predictions for shear modulus and offer insights into the material's mechanical behavior.
• The determined refractive index highlights γ-Ge3N4 as a material with significant optical potential.