High‐Pressure Stability and Electronic Properties of Sodium‐Rich Nitrides: Insights from First‐Principles Calculations

TL;DR

High-pressure calculations reveal new sodium-rich nitrides with unique electronic properties, including superconductivity and metal-to-semiconductor transitions.

Contribution

Prediction of three new Na-rich nitride stoichiometries and their pressure-induced structural and electronic transitions.

Findings

Na5N undergoes a structural transition from P6/mmm to P63/mmc with pressure-induced electron redistribution.

P63/mmc Na5N transitions from metallic to semiconducting behavior under pressure.

C2/m Na8N is predicted to exhibit superconductivity with triangular- and ship-like interstitial anionic electrons.

Abstract

Using first‐principles structure search calculations, we investigated the phase stability of sodium‐nitrogen (Na−N) compounds under high pressure. Our study reveals that increasing pressure promotes the formation of Na‐rich nitrides, leading to the prediction of three previously unreported stoichiometries: Na2N, Na5N, and Na8N. Notably, the electride Na5N undergoes a pressure‐induced structural transition from a P6/mmm to a P63/mmc phase. This transformation is characterized by spatial reorientation and redistribution of interstitial anionic electrons (IAEs). In the P63/mmc phase, IAEs adopt a zero‐dimensional, triangular‐like configuration, whereas in the low‐pressure P6/mmm phase, they form an interconnected, graphene‐like network. With increasing pressure, P63/mmc phase undergoes a transition from metallic to semiconducting behavior due to the increased interaction between sodium and IAEs. Additionally, C2/m Na8N, featuring triangular‐ and ship‐like IAEs, is predicted to exhibit superconductivity. Our findings provide new insights into the behavior and stability of Na‐rich nitrides under high‐pressure conditions.

This work highlights how pressure‐induced IAEs rearrangements influence the thermodynamic stability and electronic behavior of these compounds, including metal‐to‐semiconductor transitions in P63/mmc Na5N and superconductivity in C2/m Na8N.

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