A new member of the carbon family! Scholars discover subcrystalline diamond
Recently, Huiyang Gou, a researcher at the Beijing High Pressure Science Research Center, and other scholars synthesized a new form of diamond, hypocrystalline diamond (Paracrystalline diamond), under high temperature and high pressure, which fills in the missing link on the scale of atomic arrangement between amorphous and crystalline structures, and provides a key to deep understanding of the This provides a key to the deep understanding of the complex structure of amorphous materials. The results were published online on November 25 in the journal Nature.
In general, solids are classified into crystalline and amorphous states based on the presence or absence of long-range periodicity. However, when the degree of long-range ordering in crystals is significantly reduced, distinguishing between the two states becomes exceptionally difficult, especially for strongly covalent and covalent-like solids.
In order to explore this structural enigma, theoretical scientists have proposed a structural model for the subcrystalline state, which essentially involves the introduction of nanometer-sized medium-range ordered (MRO) structures in an amorphous matrix, i.e., consisting entirely of medium-range ordered subcrystals with no long-range ordering. Previously, it has not been possible to find such a state of matter in nature or experiment.
Through the latest extreme high-pressure technology developed by Hui-Yang Gou and his collaborators in a large-cavity press, the high-temperature and high-pressure treatment of fullerene (C60) precursors at a temperature and pressure of 30 GPa and 1500-1600 K revealed that the compressed fullerene polymerization transformed into a high-density disordered sp3-bonded carbon. High-resolution transmission electron microscopy revealed the presence of high-density and uniformly distributed crystal-like clusters (0.5-1.0 nm in size) in the samples with atomic configurations close to those of cubic and hexagonal diamonds and high lattice distortion, i.e., hypocrystalline diamond.
In order to explore the formation process of hypocrystalline diamond, the researchers conducted large-scale molecular dynamics simulations of the structural evolution of C60 under high temperature and high pressure conditions, and established a hypocrystalline diamond model that is highly compatible with the experimental results. The simulation results show that the synthesis is mainly attributed to two factors: first, due to the fact that diamond has the largest tetrahedral order parameter. Compared with amorphous silicon, amorphous diamond has superb diamond-like short-range ordering within the two-atom coordination shell layer, a feature that facilitates the formation of medium-range ordered structures; and secondly, it relies on the structural characteristics of C60, which undergoes three major stages in its transformation to hypocrystalline diamond.
“The simulation results show that hypocrystalline diamond and amorphous diamond have significant structural differences. Both do not have long-range ordering and, at the first ligand atomic level, both hypocrystalline and amorphous diamond have similar ordering at the same time. However, in the mid-range scale range (2-5 atomic layers), hypocrystalline diamond is much more ordered than amorphous diamond, although the ordering decreases progressively.” Hongwei Sheng, co-corresponding author of the paper and professor at George Mason University, said.
“The discovery of this hypocrystalline state, which links the amorphous and crystalline states in terms of structural topology, has far-reaching significance in revealing the complex structural nature of amorphous materials,” Tang Hu, first author of the paper and a PhD at the Beijing High Pressure Science Research Center, told China Science Daily, ”The discovery of hypocrystalline diamond adds a new structure to the carbon The discovery of hypocrystalline diamond adds a new structural form to the carbon family of materials, which combines excellent mechanical properties, thermal stability, and unique optical properties, and has important application prospects in high-end technology fields and extreme environments. It is conducive to the further development of new diamond-like materials.”
