Confinement of quasi-atomic structures in Ti$_2$N and Ti$_3$N$_2$ MXene Electrides

TL;DR

This study uses first-principles calculations to reveal that Ti$_2$N and Ti$_3$N$_2$ MXenes are electride materials with unique electronic and magnetic properties, including excess interstitial electrons and magnetic configurations.

Contribution

It is the first report of non-nuclear interstitial anionic electrons in titanium nitride MXenes, highlighting their potential as electrides with novel magnetic behaviors.

Findings

Ti$_2$N$ is nonmagnetic and contains excess interstitial electrons.

Ti$_3$N$_2$ exhibits antiferromagnetic and ferromagnetic configurations, with the monolayer being a ferromagnetic electride.

Bulk Ti$_3$N$_2$ favors antiferromagnetic order, while TiN is neither an electride nor magnetic.

Abstract

Metal carbides, nitrides, or carbonitrides of early transition metals, better known as MXenes, possess notable structural, electrical, and magnetic properties. Analyzing electronic structures by calculating structural stability, band structure, density of states, Bader charge transfer, and work functions utilizing first principle calculations, we revealed that titanium nitride Mxenes, namely Ti$_2$N and Ti$_3$N$_2$, have excess anionic electrons in their pseudo-atomic structure inside the crystal lattice, making them MXene electrides. Bulk Ti$_3$N$_2$ has competing antiferromagnetic (AFM) and ferromagnetic(FM) configurations with slightly more stable AFM configurations, while the Ti$_2$N MXene is nonmagnetic. Although Ti$_3$N$_2$ favors AFM configurations with hexagonal crystal systems having $6/mmm$ point group symmetry, Ti$_3$N$_2$ does not support altermagnetism. The monolayer of the Ti$_3$N$_2$ MXene is a ferromagnetic electride. These unique properties of having non-nuclear interstitial anionic electrons in the electronic structure of titanium nitride MXene have not yet been reported in the literature. Density functional theory calculations show TiN is neither an electride, MXene, or magnetic.