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Molecular dynamics study of pressure induced structural changes in B_2O_3

机译:压力引起的B_2O_3结构变化的分子动力学研究

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The structural model of vitreous B_2O_3 which has a boroxol ring(highly planar 3-membered ring)fraction of 80%,is employed to investigate the structural changes in B_2O_3 glass upon pressure induced densification.The iso tropic load on the model structure was increased up to 30 GPa and subsequently released down to 0 GPa.The density increased by 8-8% and the boroxol ring fraction decreased from 80 to 20%.The calculated results showed two features peculiar to B_2O_3 glass.First,the number of fourfold coordinated boron and threefold coordinated oxygen atoms increased at the pressure of over 6 GPa and involved the rearrangement of B-O rings and irreversible structural change.Secondly,the destruction of boroxol rings led to the formation of medium size rings from 4- to 7-membered,during compaction.This transformation from the two-dimensional structural units into those more three-dimensional is the microscopic mechanism of the densification observed in this study.Though these rings were reduced in number after pressure release,some still remained.It suggests the possibility that a further relaxation occurs.
机译:采用玻璃纤维化的B_2O_3结构模型,其硼环(高平面三元环)分数为80%,研究了压力致密化后B_2O_3玻璃的结构变化。模型结构的各向同性载荷增加降低至30 GPa,随后释放至0 GPa。密度增加8-8%,硼环素环分数从80%降低至20%。计算结果显示B_2O_3玻璃具有两个特征:首先是四重配位硼的数量并且三重配位的氧原子在超过6 GPa的压力下增加,并涉及BO环的重新排列和不可逆的结构变化。其次,在压缩过程中,硼氧四环的破坏导致形成4至7元的中等尺寸环。从二维结构单元到更三维的这种转变是本研究中观察到的致密化的微观机制。压力释放后产生的数量仍然有些残留。这表明可能进一步放松。

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