Ultralow Interlayer Friction of Layered Electride Ca2N: A Potential Two-Dimensional Solid Lubricant Material

Jianjun Wang,Lin Li,Ziting Shen,Linfeng Yang,Peng Guo,Meng Li,Bin Zhao,Lili Fang

doi:10.3390/ma11122462

Abstract

Dispersion-corrected density functional theory (DFT) calculations reveal that the layered electride of dicalcium nitride (Ca2N) exhibits stronger interlayer binding interactions but lower interlayer friction behavior than that of traditional layered lubricants weakly bonded by van der Waals (vdW) interactions, such as graphite, h-BN, and MoS2. These results are attributed to the two-dimensional (2D) homogeneous conduction electrons distribution in the middle of the interlayer space of Ca2N, which yields a smooth sliding barrier and hence ultralow friction behavior. The interesting results obtained in this study have not only broadened the scope of 2D solid lubricants but also enriched the physical understanding of ultralow friction mechanism for 2D systems.

Highlights

The understanding of friction origins and the search for new effective lubricants have been the focus of tribology studies [1]
These values are very close to the experimental values of the corresponding bulk structure (3.66 and 2.51 Å) and the other calculation results of the monolayer Ca2 N
Based on the optimized structure, two sheets of Ca2 N monolayer were placed to slide against each other along two high symmetrical paths to model the friction process, as shown in the top, hollow, and bridge stackings appeared on path II periodically

Summary

Introduction

The understanding of friction origins and the search for new effective lubricants have been the focus of tribology studies [1] Layered bulk materials, such as graphite, hexagonal boron nitride (h-BN), and molybdenum disulfide (MoS2 ), exhibit excellent lubricating properties and have been used to reduce friction and wear in mechanical systems for a long time [2]. The two-dimensional (2D) strong covalent bonding in plane and the weak van der Waals (vdW) interaction between adjacent layers can effectively explain the lubricating properties of these traditional solid lubricants [2,3] These multilayer or even single-layer bulk materials possess excellent frictional characteristics due to their high load carrying capacity and passivating effect, which can serve as protective coating films or nanolubricants and are used in several systems [4,5,6,7,8]. All above discussions support that layered materials are excellent lubricants from the macroscale to the microscale, and ideal models for investigations of the mechanism of friction

Methods

Results

Conclusion