No abstract

No abstract

Abstract. We synthesized a cubic BC 3 (c-BC 3 ) phase, by direct transformation from graphitic phases at a pressure of 39 GPa and temperature of 2200 K in a laser-heated diamond anvil cell (DAC). A combination of x-ray diffraction (XRD), electron diffraction (ED), transmission electron microscopy (TEM) imaging, and electron energy loss spectroscopy (EELS) measurements lead us to conclude that the obtained phase is hetero-nano-diamond, c-BC 3 . Highresolution TEM (HRTEM) imaging of the c-BC 3 specimen recovered at ambient conditions demonstrates that the c-BC 3 is a single, uniform, nanocrystalline phase with a grain size of about 3-5 nm. The EELS measurements show that the atoms inside the cubic structure are bonded by sp 3 bonds. The zero-pressure lattice parameter of the c-BC 3 calculated from diffraction peaks was found to be a = 3.589 ± 0.007 Å. The composition of the c-BC 3 is determined from EELS measurements. The ratio of carbon to boron, C/B, is approximately 3 (2.8 ± 0.7).2

Samples held at pressures up to 260 kilobar in a diamond anvil pressure cell have been heated to very high temperatures by means of a laser beam introduced through one of the transparent diamond anvils. A 7 J pulsed ruby laser is able to produce temperatures as high as 3000°C in a high pressure sample. A 60 W cw YAG laser is able to produce sustained temperatures up to 2000°C. An optical pyrometer has been used in the latter case to measure the brightness temperature with an accuracy of ±50°C. The ruby laser has been successful in directly converting graphite to diamond; the YAG laser has made it possible to show that (Fe,Mg)2SiO4 disproportionates to (Fe,Mg)O plus SiO2 (stishovite) at pressures in excess of 200 kilobars and temperatures above 1000°C.

No abstract