Investigation of Room Temperature Formation of the Ultra‐Hard Nanocarbons Diamond and Lonsdaleite

Abstract

Diamond is an attractive material due to its extreme hardness, high thermal conductivity, quantum optical, and biomedical applications. There is still much that is not understood about how diamonds form, particularly at room temperature and without catalysts. In this work, a new route for the formation of nanocrystalline diamond and the diamond‐like phase lonsdaleite is presented. Both diamond phases are found to form together within bands with a core‐shell structure following the high pressure treatment of a glassy carbon precursor at room temperature. The crystallographic arrangements of the diamond phases revealed that shear is the driving force for their formation and growth. This study gives new understanding of how shear can lead to crystallization in materials and helps elucidate how diamonds can form on Earth, in meteorite impacts and on other planets. Finally, the new shear induced formation mechanism works at room temperature, a key finding that may enable diamond and other technically important nanomaterials to be synthesized more readily.

Developments in Synthesis and Potential Electronic and Magnetic Applications of Pristine and Doped Graphynes

“…Nevertheless, this structural diversity and versatility of chemical bonding brings an enormous pool of physicochemical properties, reactivities, and so on; crystal structures of over 500 periodic allotropes, known and hypothesized, have been collected 2 of 39 in a unique Sacada database (https://www.sacada.info/) [19]. Despite the long-lasting research of carbon-based materials, some fundamental issues related to the shape of the phase diagram and mutual stability of polymorphs, or even their existence, remain unresolved to this day [20][21][22]; e.g., it has been recently claimed that lonsdaleite is not a genuine allotropic form but a twin of cubic crystals, which raised controversy [23,24]. One illustration of the intensity of the research field of carbon materials can be provided by an inspection of the Web of Science database; this resource lists approximately 114,000 papers using the keyword 'diamond', approximately 147,000 papers discussing 'graphite', and approximately 240,000 papers featuring 'graphene'.…”

Modifying Electronic and Elastic Properties of 2-Dimensional [110] Diamond by Nitrogen Substitution

“…Graphene can persist with a high load of an indentation without breaking bonds showing remarkably high tensile strength [1]; however, its hardness cannot be measured. Other sp 3 carbon allotrope, i.e., lonsdaleite, is predicted to be harder than diamond, but its existence is under discussion [2][3][4].…”

A comprehensive account of biomedical applications of CVD diamond coatings

“…Hexagonal diamond was first synthesized by Bundy et al [85] in the laboratory from graphite under HPHT conditions using static or shock compression techniques This was later followed by a series of studies focusing on the CVD synthesis of lonsdaleite (hexagonal diamond) under varying gaseous, pressure and temperature conditions [70,89,95,96]. In addition, lonsdaleite formation at atmospheric pressure [97,98] and room temperature [99] has also been reported. Structurally, lonsdaleite consists of hexagonal carbon planes, which are stacked in AB ′ sequence, buckling into boat-type links with adjacent planes (see figure 4(b)).…”