Scholars Discover a New Mechanism for Graphite Phase Transition Through Electronic Cloud Regulation.
The University of Science and Technology of China reported that Professor Zhu Yanwu’s team, through in-situ X-ray studies and first-principles calculations, has proposed a layer-sliding pathway from 3R graphite to 2H graphite. By examining the changes in Raman signals of thin-layer graphite before and after its contact with lithium nitride in the same region, they confirmed the associated changes in charge states. The relevant findings have been published in the well-known domestic academic journal, Nano Letters.
As an important raw material in the fields of lithium-ion battery cathode materials and graphene synthesis, graphite typically contains two crystal structures: the hexagonal phase (2H phase) and the rhombohedral phase (3R phase). Among these, the 2H phase has lower energy and thus constitutes a higher proportion in the powder; conversely, the 3R phase has higher energy and generally accounts for a lower proportion in the powder. However, as graphite particles are broken down and the flake diameter decreases, the proportion of the 3R phase gradually increases, eventually reaching 50%.
Recent studies have shown that the band structure of 3R graphite features a three-dimensional Dirac cone, with a band gap in the electronic states; at low temperatures, electron transport is predominantly governed by surface states. The flat band on the surface of three-layer graphene stacked in the 3R configuration facilitates the emergence of strongly correlated phenomena, leading to spontaneous symmetry breaking—such as ferromagnetic ordering and surface superconductivity. In existing research on graphite phase transitions, converting all 3R phases into the 2H-phase graphite powder typically requires high-temperature and high-pressure graphitization or the use of laser heating, resistive heating, and other methods. These approaches demand harsh experimental conditions and consume significant amounts of energy.
After extensive research, researchers have found that adding a small amount of lithium nitride crystal powder to graphite powder can enable the complete transformation of macroscopic graphite powder with large particle sizes—from the 3R phase to the 2H phase—even at low temperatures. Further investigation revealed that under the conditions of graphite phase transformation, differences in work functions lead to the transfer of certain electrons, which in turn cause the conjugated π-electron cloud of graphite to interact with the lithium nitride crystals in the graphite powder. This interaction results in an unusual increase in the interlayer spacing of graphite and significantly reduces the energy barrier for sliding between graphite layers, thereby facilitating the transformation of the 3R phase into the 2H phase under milder conditions.
This research achievement holds promise for achieving precise control over the stacking morphology and properties of graphite by regulating the shape of its electronic cloud. It also offers new insights into the structural modulation of other carbon-based materials and the preparation of novel carbon materials.
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