Interlaced nanotwinned diamond and its deformation mechanism under pure shear strain

Abstract

While there is a relatively clear understanding of the deformation mechanisms of parallel nanotwinned diamonds with a single-orientated twin plane under shear strain from both experimental and theoretical studies, significant discrepancies remain between single-orientated parallel twins and experimentally observed twinned structures. These discrepancies hinder a comprehensive explanation of the structural evolution and deformation mechanisms in real twinned diamonds. To address this gap, we constructed an interlaced nanotwinned diamond structure with coexisting twins of different orientations and investigated its deformation mechanisms under pure shear strain. The interlaced twins with different orientations inevitably lead to the coexistence of sp³ bonds and sp² line defects at the intersecting sites. Our findings reveal that under shear strain, the ideal twin interfaces in the interlaced nanotwinned diamond structure first undergo flip, transforming into a defective parallel nanotwinned diamond structure. As shear strain increases, this defective structure evolves into a unique diamond/graphite interface structure. Due to the strong local carbon bonds associated with sp² defects, graphitization lags behind that of sp³ carbon bonds, leading to the formation of pentagonal ring structures at the interface. This imparts edge dislocation characteristics to the interface structure, which is significantly different from the diamond/graphite interfaces observed in high-temperature and high-pressure experiments on graphite. Calculations further indicate that continued increase in shear strain may lead to a series of transformations among diamond/graphite interface structures, defective diamond structures, and back to diamond/graphite interface structures. This study provides important insights into the deformation mechanisms of interlaced nanotwinned diamonds under extreme conditions and reveals a new type of diamond/graphite interface structure.