Elastic and structural instability of cubic Sn3N4 and C3N4 under pressure

TL;DR

This study investigates the high-pressure behavior of cubic Sn3N4 and C3N4, revealing their elastic properties, stability limits, and predicting a phase transition at high pressure through experimental and computational methods.

Contribution

It provides the first in-situ high-pressure measurements of cubic Sn3N4's equation of state and combines this with first-principles analysis to refine understanding of its structural stability and elastic properties.

Findings

Sn3N4 has a bulk modulus of 145 GPa, lower than previous estimates.

No structural phase transition observed up to 26 GPa for Sn3N4.

C3N4 has the highest bulk modulus (379 GPa) but is structurally unstable at ambient conditions.

Abstract

We use in-situ high pressure angle dispersive x-ray diffraction measurements to determine the equation of state of cubic tin nitride Sn3N4 under pressure up to about 26 GPa. While we find no evidence for any structural phase transition, our estimate of the bulk modulus (B) is 145 GPa, much lower than the earlier theoretical estimates and that of other group IV-nitrides. We corroborate and understand these results with complementary first-principles analysis of structural, elastic and vibrational properties of group IV-nitrides, and predict a structural transition of Sn3N4 at a higher pressure of 88 GPa compared to earlier predictions of 40 GPa. Our comparative analysis of cubic nitrides shows that bulk modulus of cubic C3N4 is the highest (379 GPa) while it is structurally unstable and should not exist at ambient conditions.