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High pressure modifications in amorphous boron suboxide: An ab initio study
Affiliation:1. School of Material Science and Engineering, Beihang University, Beijing, 100191, PR China;2. Research Center of Light-alloy Materials, Frontier Institute of Science and Technology Innovation, Beihang University, Beijing, PR China;3. Ningbo Institute of Technology (NIT), Beihang University, Ningbo, PR China;4. Beijing Hangda MICRO/NANO Science and Technology Co. Ltd., Beijing, 100191, PR China
Abstract:Using constant pressure ab initio calculations, we probe the high-pressure modifications in amorphous boron suboxide (B6O) consisting of glassy boron trioxide (B2O3) and boron (B) domains up to a theoretical pressure of 100 GPa. At this pressure, the structure remains amorphous. We find a steady increase in the average coordination of both B and oxygen (O) atoms. O atoms mostly attain threefold coordination as in B2O3 glass at high pressures. On the other hand, the mean coordination number of B-atoms reaches six at high pressures and the structural changes in B-rich regions are perceived to be quite analogous to those of amorphous B. B12 clusters are found to persevere during the pressurizing process and the high-pressure modifications occur predominantly around O-atoms and the regions that connect the pentagonal pyramid-like motifs to each other. Upon pressure release, some high-pressure configurations persist in the model and another noncrystalline structure being about 10% denser than the original state is recovered, suggesting a permanent densification and a possible irreversible amorphous-to-amorphous phase transformation in B6O. The recovered network shows slightly better mechanical properties than the uncompressed model. During the compression and decompression processes, amorphous B6O remains semiconducting. The delocalization of some band tail states is seen at high pressures.
Keywords:Amorphous  Boron suboxide  Hardness  Phase transformation  Densification
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