Search and Characterization of Novel Superhard Phases in the B-C-N System Under Extreme Conditions L. C. Ming, P. V. Zinin, and M. H. Manghnani, U niversity of Hawaii, DMR Fig. 1. Possible structure of the new phase: black sphere represent N atoms, and blue spheres represent C atoms. A new phase of C 3 N 4 was recovered for the first time at ambient conditions from the graphite-like C 3 N 4 (g-C 3 N 4 ) phase subjected at pressures between 23 and 43 GPa in a diamond anvil cell and laser-heated to temperatures between 1600 and 3000 K. X-ray diffraction data of the new phase could be best explained by a cubic unit cell, which is related to and yet different from the defect-zincblende phase previously proposed by Liu and Wentzcovitch (1994) on the basis of theoretical calculations. A new phase has not been predicted theoretically, and represents a new type structure of C 3 N 4. Based on the intensity data of the x- ray pattern, a possible structure of the new phase is proposed as shown in Fig. 1. Reference L. C. Ming, P. Zinin, Y. Meng, X. Liu, S.M. Hong, Y. Xie. “A new cubic phase of C 3 N 4 synthesized in diamond-anvil cell”, Nature Materials submitted (2005).

Search and Characterization of Novel Superhard Phases in the B-C-N System Under Extreme Conditions L. M. Ming, P. Zinin, and M. H. Manghnani University of Hawaii, DMR Fig. 2. An optical image showing the laser heating of a B-C sample under high pressure in a diamond anvil cell. A direct transformation from the g-BC1.6 phase to a new diamond-like BC1.6 phase was obtained in a diamond anvil cell (DAC) at high temperature, 2230 ± 140 K and high pressure, 45 GPa. This is the first observation of such a transition in the B-C system. The recovered samples were examined using both synchrotron-based X- ray diffraction and confocal micro-Raman spectroscopy at ambient conditions. The lattice parameter of the new phase is close to that of diamond. It is also found that the orthorhombic/hexagonal phase was formed under high pressure in the areas where heating was not enough to make transformation in the cubic phase possible. References P. V. Zinin, I. Kudryashov, N. Konishi, L. C. Ming, V. L. Solozhenko, S. K. Sharma. Spectrochim. Acta Part A: Mol. Biol. Spectrosc., (2005). P.V. Zinin, L. C. Ming, Kudryashov, N. Konishi, M.H. Manghnani, S. K. Sharma. Phys. Rev. B, submitted (2005).

Search and Characterization of Novel Superhard Phases in the B-C-N System Under Extreme Conditions L.C. Ming, P. V. Zinin, M.H. Manghnani, University of Hawaii, DMR Fig. 4. Nanostructure of cubic BC 2 N nano-phase obtained by AFM image (tapping mode, scale 2 x 2 mm). Fig. 3. Raman intensity mapping of peak 1332 cm -1, field of view was 16 x 16  m The X-Y Raman mapping was used to investigate the spatial distribution of the diamond-like phase in B-C- N compounds recovered from high pressure and temperature and thus, was demonstrated to be a powerful tool in study the sp 2 -to-sp 3 phase transformation in these compounds. In Fig. 3 the bright area corresponds to the area where graphite was converted into diamond under laser heating; the dark area shows unconverted sample. References P. V. Zinin, I. Kudryashov, N. Konishi, et al. Spectrochim. Acta Part A: Mol. Biol. Spectrosc., (2005). The surface morphology of the cubic BC2N nano-phase was studied by AFM. The AFM (Nanoscope III) was used in contact imaging mode to obtain constant force topographic images. Both silicon and silicon nitrate cantilevers were used, with approximately 10-nm and 20-nm tip curvation radius, respectively (Digital Instruments, USA). The average grain size was measured to be 225 ± 87 nm in the AFM image (Fig. 4). It was found it was nearly ten times higher than the value of the grain size obtained from TEM measurements. P.V. Zinin, V.L. Solozhenko, A. Malkin, L.C. Ming. J. Mater. Sci. Lett., (2005).