Discovery of γ-B 28, a novel boron allotrope with partially ionic bonding

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Abstract

γ-B 28 is a recently discovered high-pressure phase of boron, with the structure consisting of icosahedral B 12 clusters and B 2 pairs in a NaCl-type arrangement: (B 2) δ+(B 12) δ-, and displaying a significant charge transfer δ∼0.48. Boron is the only light element, for which the phase diagram has become clear only a few years ago, with the discovery of γ-B 28, and this phase diagram is discussed here among other recent findings. γ-B 28 was first experimentally obtained as a pure boron allotrope in early 2004 by J.H. Chen and V.L. Solozhenko (although a similar diffraction pattern was published in a 1965 by R.H. Wentorf, in a paper that until recently was believed to be wrong) and its unique structure was discovered by A.R. Oganov in 2006 with the use of the ab initio evolutionary algorithm USPEX (Oganov & Glass, 2006) and later confirmed by other studies. This allotrope, thermodynamically stable at high pressures, is shown to be also quenchable and dynamically stable upon decompression to 1 atm, and we show its phonon dispersion curves. Present discussion includes also the relative stability of other boron allotropes as a function of pressure. We also discuss more recent publications on the putative isosymmetric phase transition in γ-B 28 and the nature of chemical bonding in it. We demonstrate that a qualitative difference in the evolution of the band gap of γ-B 28 and the related α-B 12 structure, which is due to the partial tonicity of γ-B 28.

Original languageEnglish
Title of host publicationBoron and Boron Compounds - From Fundamentals to Applications
Pages1-14
Number of pages14
DOIs
Publication statusPublished - 2011
Externally publishedYes
Event2010 MRS Fall Meeting - Boston, MA, United States
Duration: 29 Nov 20103 Dec 2010

Publication series

NameMaterials Research Society Symposium Proceedings
Volume1307
ISSN (Print)0272-9172

Conference

Conference2010 MRS Fall Meeting
Country/TerritoryUnited States
CityBoston, MA
Period29/11/103/12/10

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