The crystallographic texture of graphite-like and diamond-like boron nitride bulk materials (original) (raw)
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Features of a cBN-to-graphite-like BN phase transformation under pressure
Diamond and Related Materials, 2000
Phase transformations of cubic boron nitride to graphite-like forms cBNª gBN have been studied within the 1670᎐2970 K temperature range and at high pressures, which suppresses the dissociation decomposition of the compound, by using a recessed-type high pressure apparatus with a toroid-type lock. To clarify the degree of structure imperfection effect on the type and mechanism of transformation, various types of bulk cBN initial materials were used. A partial or complete cBNª gBN transformation has been observed in the studied temperature range. It has been found that in a pure recrystallized material with a low level of the structural imperfection, a two-stage transformation occurs to form an intermediate metastable rhombohedral Ž. Ž. phase rBN. Transformation into the hexagonal modification of graphite-like boron nitride hBN is realized only in material with a highly imperfect structure. From the analysis of the crystallographic correspondence between cBN, rBN and hBN lattices, and the differences in structure between the initial and forming materials, the possible structural mechanisms of the cBNª gBN transformation were proposed.
Chemistry of Materials, 1993
Graphitic BCzN has been compressed with Co metal at a pressure of 5.5 GPa and temperatures of 1400-1600 OC. The principal resulting products were crystals (average dimension 3 pm) with cubiclike facets. The powder X-ray diffraction pattern revealed two kinds of cubic phase, in approximately equal amounts, which were identified as diamond and cBN on the basis of their lattice parameters. Microelemental analyses on individual crystal fragments by K-edge electron energy-loss spectroscopy confirmed this disproportionating crystallization scheme: half of the grains were composed of carbon-only signals of which gave fine-structure characteristic of sp3 bonding and the other half gave spectra characteristic of sp3 boron and nitrogen. The crystallization of cBN as well as diamond in the catalytic solvent of pure Co metal is observed here for the first time and is of relevance to the mechanism of the accepted catalytic action of cobalt on the hexagonal/cubic transformation.
Transformation of fine-grained graphite-like boron nitride induced by concentrated light energy
Materials Chemistry and Physics, 2008
Results on investigations of structure and phase transformations of fine-grained h-BN graphite-like powders induced by heating to concentrated light beam of different energies in nitrogen flow in optical furnace are given. It is presented structures obtained on the surface of heated samples of moulding h-BN powders and on titanium substrate. Surface of titanium substrate has been studied by scanning electron microscopy to reveal the new structures and new morphologies produced after exposure to different light energies. Complicated structure of whiskers formed on the surface of heated samples of pressed h-BN powders has been investigated by transmission electron microscopy. A pronounced evolution in structure on the surface of heated samples of moulding h-BN powders is demonstrated.
Influence of Molecular Precursor Structure on the Crystallinity of Boron Nitride
Journal of Solid State Chemistry, 2000
Processible polymers have been prepared from borazinic derivatives. They were thermolyzed into boron nitride using an appropriate chemical and thermal treatment in order to obtain a carbon-free ceramic. Despite similar pyrolysis conditions, the crystallinity of the resulting BN was found to be di4erent for each polymer. These di4erences should be related to the structure of the molecular precursors and of the polymers derived therefrom. Polymers prepared from the borazine, (HNBH) 3 , always gave the more-crystallized materials.
Optical Properties of BN in the cubic and in the layered hexagonal phases
2001
Linear optical functions of cubic and hexagonal BN have been studied within first principles DFT-LDA theory. Calculated energy-loss functions compare well with experiments and previous theoretical results both for h-BN and for c-BN. Discrepancies arise between theoretical results and experiments in the imaginary part of the dielectric function for c-BN. Possible explanation to this mismatch are proposed and evaluated; lattice constant variations, h-BN contamination in c-BN samples and self-energy effects. Pacs numbers: 78.20 -e, 78.20.Ci, 78.20.Dj, 71.45.Gm Typeset using REVT E X The properties of boron nitride (BN) have motivated detailed theoretical and experimental studies since a long time [1,2,3]. Many advanced technologies rely on Boron Nitride and on materials based on it, due the wide spectrum of properties offered by its polymorphic modifications, two graphite-like and two dense ones. Boron nitride shares many of its properties, structures, processings and applications with carbon. Cubic boron nitride (also known as sphalerite boron nitride and abbreviated as Z-BN, c-BN or β-BN),with sp 3 -hybridized B-N bonds, has the diamond crystal structures and a similar lattice constants. Its physical properties, such as extreme hardness, wide energy bandgap, low dielectric constant and high thermal conductivity, are also very near to those of diamond. These amazing properties of c-BN have many appealing applications in modern microeletronic devices, and make it useful also as a protective coating material or in high-duty tools [4]. Hexagonal BN (h-BN or α-BN), an sp 2 -bounded layered compound and graphite also resemble each other in term of crystal structures, lattice constants, and physical properties such as strong anisotropy.
Structural evolution of boron nitride films grown on diamond buffer-layers
Thin Solid Films, 2006
Boron nitride films on diamond buffer layers of varying grain size, surface roughness and crystallinity are deposited by the reaction of B 2 H 6 and NH 3 in a mixture of H 2 and Ar via microwave plasma-assisted chemical vapor deposition. Various forms of boron nitride, including amorphous α-BN, hexagonal h-BN, turbostratic t-BN, rhombohedral r-BN, explosion E-BN, wurzitic w-BN and cubic c-BN, are detected in the BN films grown on different diamond buffer layers at varying distances from the interface of diamond and BN layers. The c-BN content in the BN films is inversely proportional to the surface roughness of the diamond buffer layers. Cubic boron nitride can directly grow on smooth nanocrystalline diamond films, while precursor layers consisting of various sp 2-bonded BN phases are formed prior to the growth of c-BN film on rough microcrystalline diamond films.
Optical properties of BN in cubic and layered hexagonal phases
Physical Review B, 2001
Linear optical functions of cubic and hexagonal BN have been studied within first principles DFT-LDA theory. Calculated energy-loss functions compare well with experiments and previous theoretical results both for h-BN and for c-BN. Discrepancies arise between theoretical results and experiments in the imaginary part of the dielectric function for c-BN. Possible explanation to this mismatch are proposed and evaluated; lattice constant variations, h-BN contamination in c-BN samples and self-energy effects. Pacs numbers: 78.20 -e, 78.20.Ci, 78.20.Dj, 71.45.Gm Typeset using REVT E X The properties of boron nitride (BN) have motivated detailed theoretical and experimental studies since a long time [1,2,3]. Many advanced technologies rely on Boron Nitride and on materials based on it, due the wide spectrum of properties offered by its polymorphic modifications, two graphite-like and two dense ones. Boron nitride shares many of its properties, structures, processings and applications with carbon. Cubic boron nitride (also known as sphalerite boron nitride and abbreviated as Z-BN, c-BN or β-BN),with sp 3 -hybridized B-N bonds, has the diamond crystal structures and a similar lattice constants. Its physical properties, such as extreme hardness, wide energy bandgap, low dielectric constant and high thermal conductivity, are also very near to those of diamond. These amazing properties of c-BN have many appealing applications in modern microeletronic devices, and make it useful also as a protective coating material or in high-duty tools [4]. Hexagonal BN (h-BN or α-BN), an sp 2 -bounded layered compound and graphite also resemble each other in term of crystal structures, lattice constants, and physical properties such as strong anisotropy.
Epitaxy of cubic boron nitride on (001)-oriented diamond
Nature Materials, 2003
C ubic boron nitride (c-BN),although offering a number of highly attractive properties comparable to diamond, like hardness, chemical inertness and a large electronic bandgap, up to now has not found the attention it deserves. This mostly has to do with preparational problems, with easy chemical routes not available and, instead, the necessity to apply ion-bombardment-assisted methods. Hence, most of the c-BN samples prepared as thin films have been nanocrystalline, making the prospect of using this material for high-temperature electronic applications an illusion. Although heteroepitaxial nucleation of c-BN on diamond substrates has been demonstrated using the high-pressure-hightemperature technique 1,2 , none of the low-pressure methods ever succeeded in the epitaxial growth of c-BN on any substrate.Here,we demonstrate that heteroepitaxial c-BN films can be prepared at 900°C on highly (001)-oriented diamond films, formed by chemical vapour deposition, using ion-beam-assisted deposition as a low-pressure technique. The orientation relationship was found to be c-BN(001)[100]||diamond(001)[100]. High-resolution transmission electron microscopy additionally proved that epitaxy can be achieved without an intermediate hexagonal BN layer that is commonly observed 3 on various substrates. Beside their potential use as protective coatings for cutting tools and optical instruments, cubic boron nitride (c-BN) films have been considered as an ideal material for electronic devices applicable at high temperatures, because it is a wide-bandgap semiconductor and, unlike diamond, it can be doped both n-and p-type. During the past few years, thin c-BN films have been deposited by a variety of experimental approaches 4-9 .However,most of these films were composed of very small grains (some nanometres in size) resulting in a high density of defects and grain boundaries. A significant improvement in film quality could be
New Experimental Results on the Phase Diagram of Boron Nitride
Journal of Solid State Chemistry, 2000
In order to clarify the discrepancy of the phase diagram on boron nitride as it is found in the literature we have made numerous in situ di4raction experiments using synchrotron radiation. The conditions were temperatures in the range of 16003C and pressures up to 6.5 GPa. For the experiments diamond anvil squeezers and the MAX80 high-pressure/high-temperature device installed at the DESY synchrotron facility in Hamburg/ Germany were used. We studied the transformation from hBN to cBN at 6.5 GPa/12003C and the backtransformation from cBN to hBN around 0.9 to 2 GPa. The experiments included kinetics measurements. The experiments veri5ed the theoretical results by V. L. Solozhenko (1991, High Pressure Res. 7, 201) and J. Maki et al. (1991, 99Proceedings II: International Conference on New Diamonds Research and Technology::). Further on the calculations for the equilibrium boundary between cBN and hBN were repeated including uncertainties of the thermodynamic data. The cubic phase, cBN, is de5nitely the stable phase, in contrast to metastable diamond.