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Crystal Structure Of Boron-rich Metal Borides (data Page)
This article contains crystal structure data used in the article crystal structure of boron-rich metal borides Metals, and specifically rare-earth elements, form numerous chemical complexes with boron. Their crystal structure and chemical bonding depend strongly on the metal element M and on its atomic ratio to boron. When B/M ratio exceeds 12, boron atom .... Table I *Chemical composition can be calculated as Y0.62Al0.71B14. Table II Table III a The number ''n'' in the atom designation B''n,n'' refers to the B12-''n''th icosahedron to which the B''n,n'' belongs. Si6.''n'' and B6.''n'' belong to the B12Si3 unit. b,c,d The Si and B sites are in the same interstice, which is assumed to be fully occupied by both Si and B atoms with occupancies of Occ.(Si) and Occ.(B), respectively, where Occ.(Si)+Occ.(B) = 1. Position of the boron atom was adjusted independently by fixing the thermal parameters at the same value as for the Si atom in the same interstice. e The temperature ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crystal Structure Of Boron-rich Metal Borides
Metals, and specifically rare-earth elements, form numerous chemical complexes with boron. Their crystal structure and chemical bonding depend strongly on the metal element M and on its atomic ratio to boron. When B/M ratio exceeds 12, boron atoms form B12 icosahedra which are linked into a three-dimensional boron framework, and the metal atoms reside in the voids of this framework. Those icosahedra are basic structural units of most allotropes of boron and boron-rich rare-earth borides. In such borides, metal atoms donate electrons to the boron polyhedra, and thus these compounds are regarded as electron-deficient solids. The crystal structures of many boron-rich borides can be attributed to certain types including MgAlB14, YB66, REB41Si1.2, B4C and other, more complex types such as RExB12C0.33Si3.0. Some of these formulas, for example B4C, YB66 and MgAlB14, historically reflect the idealistic structures, whereas the experimentally determined composition is nonstoichiometric ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Borides
A boride is a compound between boron and a less electronegative element, for example silicon boride (SiB3 and SiB6). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. Some borides exhibit very useful physical properties. The term boride is also loosely applied to compounds such as B12As2 (N.B. Arsenic has an electronegativity higher than boron) that is often referred to as icosahedral boride. Ranges of compounds The borides can be classified loosely as boron rich or metal rich, for example the compound YB66 at one extreme through to Nd2Fe14B at the other. The generally accepted definition is that if the ratio of boron atoms to metal atoms is 4:1 or more, the compound is boron rich; if it is less, then it is metal rich. Boron rich borides (B:M 4:1 or more) The main group metals, lanthanides and actinides form a wide variety of boron-rich borides, with metal:boron ratios up to YB66. The properties of this g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
