On the Role of Interlayer Electrons on the Frictional Behavior of Two-Dimensional Electrides

TL;DR

This paper investigates the frictional properties of 2D electrides, revealing their potential for superlubricity through electron redistribution, twist engineering, and doping, with Ba2N serving as a key example.

Contribution

It uncovers the unique friction mechanisms of 2D electrides and demonstrates how electron redistribution and structural manipulation enable superlubricity.

Findings

Ba2N exhibits lower interlayer friction than graphene despite stronger adhesion.

Twist angles between 2° and 58° induce structural superlubricity in Ba2N.

A critical load of 2.3 GPa enables barrier-free sliding in Ba2N.

Abstract

Friction accounts for up to 30% of global energy consumption, underscoring the urgent need for superlubricity in advanced materials. Two-dimensional (2D) electrides are layered materials with cationic layers separated by 2D confined electrons that act as anions. This study reveals the unique frictional properties of these compounds and the underlying mechanisms. We establish that interlayer friction correlates with the cationic charges and sliding-induced charge redistribution. Remarkably, the 2D electride Ba2N stands out for its lower interlayer friction than graphene, despite its stronger interlayer adhesion, defying conventional tribological understanding. This anomalous behavior arises from electron redistribution as the dominant energy dissipation pathway. Combining ab initio calculations and deep potential molecular dynamics (DPMD) simulations, we show that incommensurate twisted interfaces (2{\deg} < {\theta} < 58{\deg}) in Ba2N achieve structural superlubricity by suppressing out-of-plane buckling and energy corrugation. Notably, a critical normal load of 2.3 GPa enables barrier-free sliding in commensurate Ba2N ({\theta} = 0{\deg}), with an ultralow shear-to-load ratio of 0.001, suggesting the potential for superlubricity. Moreover, electron doping effectively reduces interlayer friction by controllably modulating stacking energies in 2D electrides. These findings establish 2D electrides as a transformative platform for energy-efficient tribology, enabling scalable superlubricity through twist engineering, load adaptation, or electrostatic gating. Our work advances the fundamental understanding of electron-mediated friction, with Ba2N serving a model system for cost-effective, high-performance material design.