Superhard semiconducting optically transparent high pressure phase of boron
Zarechnaya, L. Dubrovinsky, N. Dubrovinskaia, Y. Filinchuk, D. Chernyshov, V. Dmitriev, N. Miyajima, A. El Goresy, H. F. Braun, S. Van Smaalen, I. Kantor, A. Kantor, V. Prakapenka, M. Hanfland, A. S. Mikhaylushkin, I. A. Abrikosov, S. I. Simak
Combined efforts of an international group of scientists, due to synergy of experiment and theory, led to a synthesis of single crystals of high pressure boron that has a great potential for application in electronics and optics. The structure and physical properties of this material have been investigated by the members of the research team in scientific laboratories in Germany , France and the USA , while our group carried out advanced quantum mechanical calculations. It is worth mentioning an interesting history of the discovery of B28 that goes almost 45 years back. A synthesis of a “new boron form” was reported in Science 1965 by R.H. Wentorf, who also realised the first synthesis of such well-known materials as artificial diamonds and cubic boron nitride. However, he reported only a characteristic red colour and a powder x-ray diffraction pattern that was insufficient at that time to solve the material’s structure. In our work nice red single crystals of the high pressure boron phase B28 were synthesised for the first time. Due to collaborative interdisciplinary efforts, the unique optical , spectroscopic, mechanical and structural properties of the high-pressure boron phase were revealed: it was found to be an optically transparent and thermally stable wide band gap semiconductor. Theory showed very strong polar covalent bonding in the structure consisting of highly incompressible units, B12 icosahedra and B2 dumbbells (see figure), which is characteristic for superhard materials. Indeed, measured hardness (58 GPa) and low compressibility (bulk modulus of 227 GPa) make B28 the second hardest elemental material after diamond.
Calculated charge density distribution in B28
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Last updated: 03/08/10