科研之友
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摘要
Recently, a new boron allotrope B-52 with orthorhombic structure was theoretically predicted to be more stable than alpha-tetragonal boron B-50. In experiments however, only tetragonal boron phases have been obtained so far. Here, we report for the first time on the preparation of orthorhombic boron phase of B-52-type, space group Pnnn, a = 8.894 angstrom, b = 8.784 angstrom, c = 5.019 angstrom, by normal-pressure annealing of alpha-tetragonal boron, synthesized at high pressures by pyrolysis of decaborane, B10H14. We have investigated temperature-induced structure evolution and thermal desorption of boron samples, which allowed us to regard the structure of mother "alpha-tetragonal boron" as a boron-rich hydride with composition close to B51.5H7.7. In accordance with density-functional theory calculations, the most preferable sites of hydrogen placement in tetragonal unit cell are 8j and 4g; the tetragonal-to-orthorhombic transition takes place spontaneously upon complete dehydrogenation.
- 出版日期2016-9
