Meeting room "Glova", 4 floor, Integrated Research Building
Abstract
In recent years, many researchers take notice of C3N4 what is harder than diamond. Teter and Hemley(1996) suggested that C3N4 has five polymorphs, graphitic-C3N4, α-C3N4, β-C3N4, pseudocubic-C3N4 and cubic-C3N4. Graphitic-C3N4 and cubic-C3N4 are most stable in ambient and HPHT condition, respectively. Ming et al.(2006) reported that graphitic-C3N4(with NaCl PTM) changed to an unknown phase at 23 GPa, 1600 K and the recovered sample changed to meta-stable cubic phase. They also showed that this cubic phase has a different lattice constant(a=3.878 Å) and ?space group(P-type) from Teter's. Recently, Sougawa et al.(2010) conducted the HPHT experiments with no PTM using C3N4 synthesied by thermal plasma method. The orthorhombic phase with a lattice constant: a=7.635 Å, b=4.487 Å, c=4.040 Å, was appeared at about 40 GPa, 2000 K, was quenchable. This was a good consistent with C2N3H reported by Bordon et al.(2007). So, they pointed out that the absorbed water affects the composition of the product. Thus, we don't have a unified view of HPHT experiments of C3N4. In this study, first, I decide the phase diagram of C3N4 with nonhydrostatic conditions. For example, I found that at 30 GPa, ~1800 K, graphitic-C3N4 changed to orthorhombic phase (a=7.4042 Å, b= 4.3350 Å, c=3.9542 Å) which is good consistent with C2N3H phase. This phase is stable at ~80 GPa, but decomposes to diamond and nitrogen at 30 GPa, >2000 K. It suggests orthorhombic phase is stable at high pressure but unstable at low pressure. Second, I conducted the HPHT experiment with pressure medium, NaCl. I reappear meta-stable cubic phase by Ming et al.(2006), but HPHT phase isn't consistent. I will investigate the component analysis and micro-textures.
For inquiry：Taku Tsuchiya TEL:（089）927-8198
E-mail takut@sci.ehime-u.ac.jp
