Yanshan University has made important progress in the research of graphite/diamond phase transition

Recently, Zhao Zhisheng and others from the State Key Laboratory of Metastable Materials Preparation Technology and Science of Yanshan University, academician Tian Yongjun, and others cooperated with domestic and foreign scholars to clarify the problem of direct phase transition from graphite to diamond under static high pressure, which has plagued the scientific community for more than half a century. , and discovered a new class of hybrid carbon materials with an excellent combination of properties. The research results, titled "Coherent interfaces govern direct transformation from graphite to diamond", were published online in Nature on July 6, 2022.

 

Paper link: https://www.nature.com/articles/s41586-022-04863-2.

 

Graphite and diamond are the most common carbon materials in nature. The direct transformation from graphite to diamond is usually carried out in a "black box" at high temperature and high pressure, and the mechanism of phase transformation has been greatly debated. The Yanshan University research team observed and determined the coherent interface structure between graphite and diamond for the first time in a graphite sample that undergoes partial phase transition under static high pressure, and then clarified the graphite/diamond phase transition mechanism under static high pressure: the graphite layer passes through two kinds of diamond The structural element and the two rectangular structural elements are locally bonded to form a coherent interface, and the transition from graphite to diamond is realized through the advancement of the coherent interface to the graphite region. Different combinations of structural elements form a variety of coherent interface structures, leading to the formation of abundant substructures (stacking faults, twins, diamond polymorphs, etc.) in the diamond phase transition region. This new solid/solid phase transition mechanism is different from the classical nucleation growth and cooperative shear mechanism, and may be applicable to solid-solid phase transition processes of other covalent materials, such as IVA simple substances, IIIA-VA compounds, etc. .

 

The research team named this type of hybrid carbon material with a graphite/diamond coherent interface Gradia. Gradia has an excellent combination of mechanical properties and electrical properties: Knoop hardness is adjustable between 51-115GPa; room temperature resistivity is adjustable between 8´10-4-4.9´105Ω m; fracture toughness is very high, and cannot Measurements were made using the conventional indentation method. Gradia combines the performance advantages of graphite and diamond, and its performance can be further adjusted by changing the ratio of graphite and diamond. It is a new generation of high-performance carbon material that realizes the combination of electrical conductivity/superhardness, extreme toughness/ultrahardness and other superior properties.

 

The graphite/diamond direct phase transition mechanism revealed by the research enriches the solid/solid phase transition types, and the discovered new hybrid carbon materials provide inspiration for the development of high-performance new materials. The research results have applied for invention patents in China, the United States, Japan, and Europe. The previous theoretical work predicting that this type of hybrid structure can exist stably was published in Chin. Phys. Lett. 38, 028102 (2021); Chin. Phys. Lett. 39, 036301 (2022); Mater. Today Phys. 23, 100630 (2022).

 

This work was supported by the National Natural Science Foundation of China (52090020, 91963203, 51772260, U20A20238, etc.), the National Key Research and Development Program (2018YFA0703400, 2018YFA0305900), and the Hebei Provincial Science Foundation for Outstanding Youth (E2018203349). The co-first authors of the paper are Luo Kun, Liu Bing, Hu Wentao and Dong Xiao, and the corresponding author is Professor Zhao Zhisheng.