# First-principles high pressure studies on group-14 element pernitrides

## TL;DR

This study uses first-principles calculations to explore the structural, electronic, and vibrational properties of group-14 element pernitrides under high pressure, revealing their potential as ultra-hard materials and providing new insights into their behavior.

## Contribution

It presents the first detailed theoretical investigation of SiN2, GeN2, and SnN2 pernitrides under high pressure, including their physical and vibrational properties.

## Key findings

- SiN2 has the highest bulk modulus among MN2 compounds.
- Elastic moduli increase with pressure due to shorter M-N bonds.
- Bandgap widens as pressure increases.

## Abstract

The search for ultra hard materials is inevitable in high pressure device applications. Nitrides of group-14 elements have been foreseen as potential candidates in replacing existing hard materials. In a recent experiment, pyrite structures of SiN2, GeN2 and SnN2 have been synthesized at high pressure and were shown to have high bulk modulus. Though their existence and bulk modulus are known, limited studies have been devoted to SiN2, GeN2 and SnN2. In the present work, we perform first-principles calculations to investigate structural, electronic, mechanical and vibrational properties at ambient as well as high pressure condition. The physical properties of SnN2 and high pressure lattice dynamical properties of SiN2 and GeN2 are explored for the first time. SiN2 has higher bulk modulus among all MN2 (where M = Si, Sn and Ge), and increases further with increase in pressure. The increase in elastic moduli of MN2 have been related to the shortening of M-N bond length at high pressures. Electronic properties of these pyrite structures suggest that the bandgap increases with applying pressure. We further characterize these MN2 compounds at high pressures using theoretically calculated Raman spectroscopy. Frequency of N-N stretching Ag and Tg modes confirms the single bond character of nitrogen dimer in all MN2.