Coherent interfaces with mixed hybridization govern direct transformation from graphite to diamond

Abstract

Understanding the direct transformation from graphite to diamond has been a long-standing challenge with great scientific and practical importance. Previously proposed transformation mechanisms1-3, based on traditional experimental observations that lacked atomistic resolution, cannot account for the complex nanostructures occurring at graphite-diamond interfaces during the transformation4,5. Here, we report the identification of coherent graphite-diamond interfaces constituted with four structural motifs in partially transformed graphite samples recovered from static compression, using high-angle annular dark-field scanning transmission electron microscope. These observations provide vital insight into possible pathways of the transformation. Theoretical calculations confirm that transformation through these coherent interfaces is energetically favored to those through other paths previously proposed1-3. The graphite-to-diamond transformation is governed by the formation of nanoscale coherent interfaces (diamond nucleation), which, under static compression, advance to consume the remaining graphite (diamond growth). These results also shed light on transformation mechanisms of other carbon materials and boron nitride under different synthetic conditions.

Shock-formed carbon materials with intergrown sp 3 - and sp 2 -bonded nanostructured units

“…The broadness of the peak is likely to be due to a slight variation in interlayer spacing for the graphene layers depending on the size of the graphene/diamond domains, a feature also observed in our computational models. Such interlayer spacings have been reported from the quenched material obtained following HP-HT treatment of graphite (21) and fullerenes (26).…”

“…In addition to shock-formed samples ( 9 , 10 , 18 ), diaphite has also been reported from meteoritic nanodiamonds and thosed produced by chemical vapor deposition ( 17 ). Recently, researchers proposed another graphene-diamond structure called gradia ( 21 – 24 ), which in contrast to diaphite lacks a definitive epitaxial relationship. Such gradia structures have been recognized from static high-pressure (HP) and high-temperature (HT) compression of graphite ( 21 ) as well as HP and HT treatment of multiwall carbon nanotubes ( 25 ) and fullerenes ( 26 ).…”

“…Recently, researchers proposed another graphene-diamond structure called gradia ( 21 – 24 ), which in contrast to diaphite lacks a definitive epitaxial relationship. Such gradia structures have been recognized from static high-pressure (HP) and high-temperature (HT) compression of graphite ( 21 ) as well as HP and HT treatment of multiwall carbon nanotubes ( 25 ) and fullerenes ( 26 ). The mixed hybridized bonding in diaphite and gradia structures contributes further to determining the mechanical and thermal relaxation properties as well as the structural transformation pathways encountered during compression and decompression events from initially graphitic to diamond-related phases, while resulting in unique low-dimensional electronic conductivity and superconductivity at the sp 3 /sp 2 interface within the otherwise insulating material ( 9 , 10 , 17 , 24 ).…”

Novel Boron Nitride Polymorphs with Graphite-Diamond Hybrid Structure

“…Furthermore, diamond could form by interlayer bonding in local areas with reduced interlayer spacing and an appropriate stacking order; however, other areas still maintained graphite structure. [33] As a result, the graphite domains were intimately connected with the diamond domains through a completely coherent interface in the hybrid structure. [33] The graphite component in the hybrid structure had an interlayer spacing of ∼3.1 Å, and this could explain the origin of compressed graphite observed in the experiments.…”

“…[31,32] Furthermore, four other types of graphite-diamond hybrid structures with completely coherent interface structures were confirmed through atomic-resolution HAADF images of partially transformed graphite samples recovered from static compression. [33] During the formation of these hybrid structures, [33,34] compression-induced bending of the graphite layers resulted in inconsistencies between the interlayer distances and stacking orders at different local areas of the structure. Furthermore, diamond could form by interlayer bonding in local areas with reduced interlayer spacing and an appropriate stacking order; however, other areas still maintained graphite structure.…”