Abstract
Tight-binding molecular-dynamics (TBMDs) simulations are performed to study atomic and electronic structures during high-temperature consolidation processes of nanocrystalline silicon carbide under external pressure. We employ a linear-scaling method (the Fermi-operator expansion method) with a scalable parallel algorithm for efficient calculations of the long time-scale phenomena. The results show that microscopic processes of the consolidation depend strongly on initial orientations of the nanocrystals. It is observed that an orientational rearrangement of the nanocrystals initially misaligned is induced by an instantaneous shearing force between nanocrystals, whereas the aligned system undergoes densification without shearing. Analysis on an effective-charge distribution and an average bond-order distribution reveals electronic-structure evolutions during these processes.
Highlights
Nanocrystalline ceramics have been one of the most fascinating research subjects because of their promising properties for industrial applications, such as larger fracture toughness, higher sinterability than conventional ceramics, and superplastic behavior at elevated temperatures [1, 2]
Four copies of the nanocrystal were placed at the positions of face-centered cubic (FCC) cell with a periodicity 42 Afor three {100} directions, respectively
Using a linear-scaling parallel algorithm, we have performed large-scale/long time-scale Tight-binding molecular-dynamics (TBMDs) simulations with NPT ensembles for analyses of the initial stage of consolidation of nanocrystalline SiC with a diameter of 2.4 nm
Summary
Nanocrystalline ceramics have been one of the most fascinating research subjects because of their promising properties for industrial applications, such as larger fracture toughness, higher sinterability than conventional ceramics, and superplastic behavior at elevated temperatures [1, 2]. Ohyanagi et al have reported [6] that nanocrystalline SiC (nc-SiC) without additives has an onset temperature of sintering, which is significantly lower than that of coarse-grained powders Such a high sinterability of pure nc-SiC and the better radiation resistance possessed by highly densified nc-SiC have been indicated by classical molecular-dynamics simulations [7, 8]. Further understanding of consolidation processes of nc-SiC from an electronic-structure level leads to an essential improvement in designing and optimizing materials performance especially in optoelectronic applications. The density-functional-theory (DFT-) based electronic-structure calculation is known to have an advantage in its accuracy and transferability compared with other semiempirical methods including the tight-binding approach and, has been widely adopted for various types of materials simulation. Semi-empirical tight-binding molecular dynamics method [9] with highly optimized parallel algorithms is a key to approaching alternatively to this demand
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