Determination of distinct Cr doping sites and their effects on tribological properties

Molybdenum disulfide (MoS 2 ), a graphite-like layered two-dimensional material with excellent inherent lubricating properties, is commonly employed in dry vacuum environments. However, its lubrication performance deteriorates significantly under non-vacuum and humid conditions, limiting its broader practical applications. Cr doping has been shown to enhance the intrinsic anti-wetting properties of MoS 2 , enabling it to maintain favorable lubrication performance even in humid environments. Nevertheless, existing explanations for the anti-wetting mechanism of Cr-doped MoS 2 remain inconsistent with computational findings, and a clear molecular-level understanding is still lacking. This study supplementary developed high-precision all-atom force field parameters for the Cr-doped MoS 2 , with deviations of less than 1% from experimental test results and DFT-derived reference values, ensuring high reliability of subsequent simulations. The research found that neither single substitutional nor interstitial doping can match the crystallographic characteristics of materials prepared by the hydrothermal method, thus a mixed doping mode was proposed. Results suggest that when the ratio of substitutional to interstitial chromium atoms is 1:3, the simulated crystal characteristics achieve optimal consistency with experimental results; under this mode, the significant increase in shear modulus leads to a decrease in lubrication performance, which is consistent with experimental results. This manuscript investigates the intrinsic causes of friction performance variations in MoS 2 -based lubricating materials at the molecular level. It develops an empirical model correlating simulated mechanical properties and experimental average coefficient of friction (COF), laying a solid theoretical foundation for the subsequent molecular-level design of lubricants.