The nature of the chemical bonding in boron carbide, B13C2. III. Static deformation densities and pictorial representation

Kirfel, Α.; Gupta, A.; Will, G.

doi:10.1107/s0567740880005997

Cited by 20 publications

(9 citation statements)

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“…A standard view of the structural change from B 12 C 3 to B 13 C 2 is the successive replacement of an icosahedral C atom with a B atom, maintaining the CBC chain, until the stoichiometric compound B 12 (CBC) is obtained. The B 12 (CBC) structure has been used in many studies [11,[16][17][18][19]. However, there is a large discrepancy between theory and experiment.…”

Section: Introductionmentioning

confidence: 99%

Theoretical study of the structure of boron carbideB13C2

2014

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We have resolved long-standing discrepancies between the theoretical and experimental crystal structures of boron carbide B 13 C 2 . Theoretical studies predict that B 13 C 2 should be stoichiometric and have the highest symmetry of the boron carbides. Experimentally, B 13 C 2 is a semiconductor and many defect states have been reported, particularly in the CBC chain. Reconciling the disordered states of the chain, the chemical composition, and the lowest-energy state is problematic. We have solved this problem by constructing a structural model where approximately three-quarters of the unit cells contain (B 11 C)(CBC) and one-quarter of them contain (B 12 ) (B 4 ). This structural model explains many experimental results, such as the large thermal factors in x-ray diffraction and the broadening of the Raman spectra, without introducing unstable CBB chains. The model also solves the energy-gap problem. We show that there are many arrangements of these two types of unit cells, which are energetically almost degenerate. This demonstrates that boron carbides are well described by a geometrically frustrated system, similar to that proposed for β-rhombohedral boron.

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Section: Introductionmentioning

confidence: 99%

Theoretical study of the structure of boron carbideB13C2

2014

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“…% carbon, they have been the subject of various structural studies over the years in order to better understand the structural changes that accompany changes in stoichiometry. These studies included single-crystal X-ray diffraction for alloys near the B 4 C, ,− B 13 C 2 , , and B 10 C compositions. On the basis of these and other experimental results, various models have been proposed that describe changes in the boron/carbon distribution on the icosahedral and chain sites. ,,− This has culminated in a model proposed by Emin based principally on transport data …”

Section: Introductionmentioning

confidence: 99%

“…Such atomic thermal parameters were obtained in structure refinements with room temperature data on single crystals near B 4 C, , near 16 at. % C, , and B 13 C 2 …”

Section: Introductionmentioning

confidence: 99%

Structures of the Boron-Rich Boron Carbides from Neutron Powder Diffraction: Implications for the Nature of the Inter-Icosahedral Chains

1996

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Results from structure refinement using neutron powder diffraction data for boron carbide samples with 10, 13, 16, and 20 at. % carbon are reviewed. Those obtained for ceramic powder samples show an apparent large vacancy concentration (as high as 25%) at the central atom position of the linear three-membered chains. A model deduced from the previous X-ray structure of the boron-rich end member, B 9 C, suggests the shift of sufficient scattering density from the central chain position into adjacent voids to account for the observed vacancies. On the other hand, neutron powder diffraction from ground, Cu-melt-grown single crystals gives a structure which shows no such vacancies. This, together with results from sequential runs with the same ceramic sample, suggests that the vacancies in the ceramic materials are intrinsic to their synthesis and do not result from radiation damage, as has been suggested. Our results support the more recent interpretation of other experimental results concerning the nature of the three-membered C-B-C chains in the boron carbides, i.e., that the bonding to the central atom is very weak. Further, low-temperature structural studies of the ground single crystals suggest that even at the nominal B 4 C composition, there is site disorder at the chainend "C" site. It is most likely that this disorder arises from the presence of boron (or C-B-B) chains.

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“…In the beginning of electron density studies, the examination of the static deformation densities was the main basis of bonding type evaluation. [61][62][63][64][65] Their results provided the first confirmation, that bonding features were indeed accessible by accurate X-ray methods. However, it has been shown, that the static deformation density cannot serve as the only mean of analysis, [66] as the result obtained is biased by the modeldependence of the promolecule describing the spherical ED.…”

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confidence: 79%

“…The bonding characteristics of such compounds are always under debate. [63,[119][120][121][122][123][124][125][126] In the priority program 1178, several projects study the bonding situation of boron in different chemical environments. The bonding in borides is discussed, [103] as well as the bonding and coordination of boron in classical boranes, borates, and boranates.…”

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confidence: 99%

Experimental Electron Density Determination of Unconventionally Bonded Boron

Flierler¹

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The nature of the chemical bonding in boron carbide, B13C2. III. Static deformation densities and pictorial representation

Cited by 20 publications

References 3 publications

Theoretical study of the structure of boron carbideB13C2

Theoretical study of the structure of boron carbideB13C2

Structures of the Boron-Rich Boron Carbides from Neutron Powder Diffraction: Implications for the Nature of the Inter-Icosahedral Chains

Experimental Electron Density Determination of Unconventionally Bonded Boron

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