TY - JOUR
T1 - Ionic high-pressure form of elemental boron
AU - Oganov, Artem R.
AU - Chen, Jiuhua
AU - Gatti, Carlo
AU - Ma, Yanzhang
AU - Ma, Yanming
AU - Glass, Colin W.
AU - Liu, Zhenxian
AU - Yu, Tony
AU - Kurakevych, Oleksandr O.
AU - Solozhenko, Vladimir L.
N1 - Funding Information:
Acknowledgements A.R.O. acknowledges the Swiss National Science Foundation (grant 200021-111847/1) and the ETH Research Equipment Programme for support of this work. J.C. and T.Y. were supported by the NSF (grant EAR0711321) and the DOE (contract DE-FG02-07ER46461), Yanzhang Ma was funded by the DOE (agreement DE-FC03-03NA00144) and the NSF (grant DMR-0619215), and O.O.K. and V.L.S. were supported by the Agence Nationale de la Recherche (grant ANR-05-BLAN-0141). The use of the NSLS at Brookhaven National Laboratory was supported by the US Department of Energy under contract DE-AC02-98CH10886, and high pressure beamlines at the NSLS were supported by COMPRES under NSF cooperative agreement EAR 06-49658. Calculations were performed at CSCS (Manno), ETH Zurich, and the Joint Supercomputer Centre of the Russian Academy of Sciences.
PY - 2009/2/12
Y1 - 2009/2/12
N2 - Boron is an element of fascinating chemical complexity. Controversies have shrouded this element since its discovery was announced in 1808: the new 'element' turned out to be a compound containing less than 60-70% of boron, and it was not until 1909 that 99% pure boron was obtained. And although we now know of at least 16 polymorphs, the stable phase of boron is not yet experimentally established even at ambient conditions. Boron's complexities arise from frustration: situated between metals and insulators in the periodic table, boron has only three valence electrons, which would favour metallicity, but they are sufficiently localized that insulating states emerge. However, this subtle balance between metallic and insulating states is easily shifted by pressure, temperature and impurities. Here we report the results of high-pressure experiments and ab initio evolutionary crystal structure predictions that explore the structural stability of boron under pressure and, strikingly, reveal a partially ionic high-pressure boron phase. This new phase is stable between 19 and 89 GPa, can be quenched to ambient conditions, and has a hitherto unknown structure (space group Pnnm, 28 atoms in the unit cell) consisting of icosahedral B12 clusters and B2 pairs in a NaCl-type arrangement. We find that the ionicity of the phase affects its electronic bandgap, infrared adsorption and dielectric constants, and that it arises from the different electronic properties of the B2 pairs and B 12 clusters and the resultant charge transfer between them.
AB - Boron is an element of fascinating chemical complexity. Controversies have shrouded this element since its discovery was announced in 1808: the new 'element' turned out to be a compound containing less than 60-70% of boron, and it was not until 1909 that 99% pure boron was obtained. And although we now know of at least 16 polymorphs, the stable phase of boron is not yet experimentally established even at ambient conditions. Boron's complexities arise from frustration: situated between metals and insulators in the periodic table, boron has only three valence electrons, which would favour metallicity, but they are sufficiently localized that insulating states emerge. However, this subtle balance between metallic and insulating states is easily shifted by pressure, temperature and impurities. Here we report the results of high-pressure experiments and ab initio evolutionary crystal structure predictions that explore the structural stability of boron under pressure and, strikingly, reveal a partially ionic high-pressure boron phase. This new phase is stable between 19 and 89 GPa, can be quenched to ambient conditions, and has a hitherto unknown structure (space group Pnnm, 28 atoms in the unit cell) consisting of icosahedral B12 clusters and B2 pairs in a NaCl-type arrangement. We find that the ionicity of the phase affects its electronic bandgap, infrared adsorption and dielectric constants, and that it arises from the different electronic properties of the B2 pairs and B 12 clusters and the resultant charge transfer between them.
UR - http://www.scopus.com/inward/record.url?scp=60149096355&partnerID=8YFLogxK
U2 - 10.1038/nature07736
DO - 10.1038/nature07736
M3 - Article
C2 - 19182772
AN - SCOPUS:60149096355
SN - 0028-0836
VL - 457
SP - 863
EP - 867
JO - Nature
JF - Nature
IS - 7231
ER -