Collaboration Between Theoreticians and Experimentalists Made Discovery of Single Element Compound at High Pressure
Experimental teams led my Jiuhua Chen and Vladimir Solozhenko successfully synthesized a new phase of boron at pressures and temperatures above 12 GPa and 1800K. The sample was characterized at the NSLS using x-ray diffraction and infrared spectroscopy indicating many complex and unique features that the new phase holds. Theoretician Artem Oganov and his team employed a computational technique that they have developed for predicting crystal structures, and were able to determine the structure, which matched all experimental observations. The crystalline phase consists of two substructures. One is an icosahedron made of 12 boron atoms. The other is a simple pair of boron atoms. These two sub-substructures stack together in the same way that ions of chlorine and sodium in table salt (sodium chloride) do. Electronegativities of the B12 icosahedra and B2 pairs are so different that it causes charge redistribution and the emergence of partial ionicity in this elemental structure.
Figure: The newly discovered phase of boron consists of two substructures ─ one is a 12-atom cage, purple, the other is a two-atom dumbbell, orange. Ionic bonds form between the two substructures. This is the first time that ionic bonds have been seen in crystal structures consisting of a single element.
This research was partially supported by COMPRES, EAR 10-43050
Oganov A.R., Chen J., Gatti C., Ma Y.-Z., Ma Y.-M., Glass C.W., Liu Z., Yu T., Kurakevych O.O., Solozhenko V.L. (2009). Ionic high-pressure form of elemental boron. Nature 457, 863-867