Trace impurities in synthetic diamonds are characterized by using a scanning x-ray microprobe with synchrotron radiation. The diamond crystals analyzed were grown under high pressure and high temperature with the various metalic solvents. Utilizing synchrotron radiation (SR) x-ray fluorescence (XRF) analysis, concentrations of trace impurities down to 0. 1 ppm can be evaluated. Moreover, the x-ray energy dependence of XRF yield around the absorption edge shows the near-edge x-ray absorption fine structure of the trace impurities, which provides chemical-state information on the trace impurities in the diamond crystal. The future expectation of analytical capability with the next generation synchrotron light source is also described.
Pure diamond has no absorption bands in a wide range of wave lengths from ultraviolet to infrared. However, diamond crystals show some colors usually, although most of them are nonattractive yellow or brown. Diamond crystals also give off a variety of luminescence with stimulation from an electron beam, UV light, etc. The colors are produced by the incorporation of impurities. In the case of diamond, the impurities which are incorporated are limited. They are nitrogen, boron, nickel, cobalt, silicon and phosphorus. The color features of high pressure synthetic diamonds are described in terms of the impurities.
Liquid carbon was formed by the melting of diamond and the metastable melting of graphite in the diamond stable regions at 15 and 18 GPa. The diamond crystallized by cooling the molten carbon was investigated by visible and ultraviolet absorption spectra, cathodoluminescence (CL) and transmission electron microscopy (TEM). The diamond contains nitrogen and is classified as Type I. The color centers of blue band A, green band A, H3, 575 nm and N3 were found and a vacancy-type dislocation loop and a cavity with a cuboctahedral shape were observed in the diamond. The solidification behaviors of a diamond from the molten C-BN and C-aluminosilicate are also discussed.
A single crystal of cubic boron nitride (cBN) was grown under the high-pressure and high-temperature conditions of 5. 5 GPa and 1500-1700 for 10min. -100 h. A temperature gradient method was employed for the crystal growth by using lithium boron nitride as a solvent. In order to characterize the growth features of cBN single crystal on seed surfaces, large seeds of diamond crystals were employed, and the heteroepitaxial growth of cBN on (100) and (111) diamond surfaces was studied. The initialgrowth feature of the cBN crystal was found on the diamond seed surface after a growing time of 10 min. On the (100) seed surface, typical anti-phase boundaries were exhibited in the grown crystals, while they were not seen in crystals grown on a (111) surface. Two types of growth features such as (111) and (113) facetted growth typically appeared in the grown crystal on the (111) surface. Considering the growth process under a constant P-T growing condition, the growth rate of cBN crystal was significantly small as compared to that of diamond.
This article reviews recent progress in the syntheses of B-C-N ternary materials. A number of B-C-N graphites of various stoichiometry have been synthesized via chemical vapor deposition and pyrolysis of precursors. One of the typical compositions, BC2N, has been relatively well-characterized, revealing that it is a genuine B-C-N compound with a semiconductive nature with a bandgap around 2 eV. Static and dynamic compressions on the B-C-N graphites have been conducted to explore the phase relationship and stability of B-C-N high-pressure phases. The results from these studies can systematically be understood by the fact that segregation into diamond and cBN is thermodynamically favored rather than formation of a B-C-N diamond-like compound.
A brief historical review of research concerning super-hard materials in the boron suboxide system is described with an emphasis on the synthesis and sintering of hexaboronoxide (B6O). Authors' investigations of the preparation of B6O-based super-hard materials are also described along with the formation behavior of B6O powder in a high temperature reaction between amorphous boron and B2O3. The structure and properties of the single phase B6O sintered compact obtained under high pressure are discussed in reference to the literature. The sintered composites in the B6O-B4C and B6O-cBN systems were prepared under high pressure and temperature conditions (3-6 GPa, 1500-1800Åé). The mechanical properties (hardness and toughness) and chemical stability are related to the phase relationship in the above quasi-two component systems and the microstructures of sintered composites.
The theory of outer-sphere electron tranfer processes has been developed by many scientists since the first publication by Libby in 1952 referring to the role of the solvent. After the establishment of Marcus Theory, the electron transfer reactions have been analysed on the basis of activation free energy, provided that the inner-sphere and outer-sphere changes are concerted. However, this approach was proved to be rather inaccurate because of the uncertainties in the estimation of the inner-sphere contribution to the activation free energy. A recent development of the analyses based on the volume profiles of reactions, however, proved that the more accurate interpretation of the outer-sphere electron transfer processes is possible as the uncertainty related to the inner-sphere contribution diminishes. Theoretical treatment and the application of the "volume analysis" to various outer-sphere reactions are summarized in this review, together with an application of the volume analysis to the "Gated" electron transfer processes.