Structure of Cubic Boron Nitride

The structure of cubic boron nitride is of the zincblende (or sphalerite) type which is similar to that of diamond and p-SiC and is characterized by extremehardness and excellent chemical resistance. It is shown in Fig. 12.3. Note the similarity with Fig. 7.1 of Ch. 7. This structure is relatively simple in the sense that it is essentially isotropic, in contrast with the pronounced anisotropy of hexagonal boron nitride. It can be visualized as a stacking of puckered infinite 111 layers or as two face-centered interpenetrating cubic sublattices, one consisting entirely of boron atoms and the other entirely of nitrogen atoms.I l 

Density of Cubic Boron Nitride. The c-BN structure, with its tetrahedral bonding, is isotropic and, except on the (111) plane, is more compact than that of h-BN (with its sjp anisotropic structure and wide interlayer spacing). Consequently c BN has higher theoretical density than h-BN (3.43 g/cm vs. 2.34 g/cm ). It should be pointed out that the diamond-like structure of cubic boron nitride is similar to those of the other two refiactory covalent nitrides, i.e., aluminum nitride and silicon nitride, as weU as silicon carbide (see Ch. 7, Sec. 3.0). 

---

The spatial arrangement of atoms around each N atom is the same as that around each B atom. Structurally there are many similarities between h-BN and graphite and both can be converted under high temperature and pressure into a cubic form. The crystal structures of cubic boron nitride (c-BN) and diamond are similar. However, unlike graphite, h-BN is an electrical insulator. The reason for this difference is that the pz orbitals in h-BN, which lie perpendicular to the plane of the network, are either empty in the case of B or filled in the case of N. Because the energies of the p orbitals on B and N are quite different, there is little interaction, with no delocalization as was the case in graphite. 

The layer sequence of the 111 plane is ABCABCABC which means that every third layer is identical (Fig. 7.3).1 1 This gives a Ramsdell notation of 3C SiC where the numeral 3 refers to the number of layers of carbon atoms and silicon atoms necessary to produce a unit cell and C indicates cubic symmetry. It is analogous to the diamond structure and is also the structure of cubic boron nitride (see Ch. 12). 

Figure 12.3 Schematic representation of the crystal structure of cubic boron nitride (c-BN).

The structure of aluminum nitride is normally hexagonal close-packed (hep) of the wurtzite (2H) type (hP4) and is shown in Fig. 12.4. The difference between this structure and the zincblende structure of cubic boron nitride shown in Fig. 12.3 should be noted (the so-called chair form vs the boat form). 

Cubic Phase of Boron Nitride c-BN. The cubic phase of boron nitride (c-BN) is one of the hardest materials, second only to diamond and with similar crystal structure. It is the first example of a new material theoretically predicted and then synthesized in laboratory. From automated synthesis a microcrystalline phase of cubic boron nitride is recovered at ambient conditions in a metastable state, providing the basic material for a wide range of cutting and grinding applications. Synthetic polycrystalline diamonds and nitrides are principally used as abrasives but in spite of the greater hardness of diamond, its employment as a superabrasive is limited by a relatively low chemical and thermal stability. Cubic boron nitride, on the contrary, has only half the hardness of diamond but an extremely high thermal stability and inertness. 

Moon, W.H., M.S. Son, and H.J. Hwang 2003, Molecular-dynamics simulation of structural properties of cubic boron nitride. Physica B, 336(3 ) pp. 329-334. 

Cubic boron nitride (c-BN) is a different material altogether from h-BN, with a structure similar to that of diamond, which is characterized by extremely high hardness (second to diamond) and high thermal conductivity.As such, it is a material of great interest and a potential competitor to diamond, particularly for cutting and grinding applications. Its characteristics and properties are shown in Table 10.3... 

Cubed compound, in PVC siding manufacture, 25 685 Cube lattice, 8 114t Cubic boron nitride, 1 8 4 654 grinding wheels, 1 21 hardness in various scales, l 3t physical properties of, 4 653t Cubic close-packed (CCP) structure, of spinel ferrites, 11 60 Cubic ferrites, 11 55-57 Cubic geometry, for metal coordination numbers, 7 574, 575t. See also Cubic structure Cubic symmetry Cubic silsesquioxanes (CSS), 13 539 Cubic structure, of ferroelectric crystals, 11 94-95, 96 Cubic symmetry, 8 114t Cubitron sol-gel abrasives, 1 7 Cucurbituril inclusion compounds,... 

The cubic y-modification has been recently observed under a pressure of 15 GPa and temperatures above 2000 K by the laser heating technique in a diamond cell [23] and in shock-wave compression experiments with pressures >33 GPa at 1800 K and >50 GPa at 2400 K [29]. This modification is often designated as the c-modification in the literature in analogy to the cubic boron nitride (c-BN). It has a spinel-type structure in which two silicon atoms are octahedrally coordinated by six nitrogen atoms, one silicon atom is coordinated tetrahedrally by four nitrogen atoms (Fig. 3c). The atomic coordinates for the cubic modification are given in Table 2. From calculations it is shown that this structure should have a high hardness similar to that of diamond and c-BN [23]. 

Kawai et al. (2006) extended the design of a high-pressure cell to accommodate operating conditions of 50 bar and 723 K. The cell had low volume, with flat windows that were chemically, structurally, and thermally stable, fabricated from a novel material, cubic boron nitride, which was synthesized by the authors by sintering hexagonal boron... 

Boron phosphide occurs in two forms, one of which, cubic BP, has a diamondlike structure analogous to cubic boron nitride (see above). The other variety, Bi2PL8, has a partially disordered crystal structure that contains icosahedral Bi2 units, as found in many metal borides (Section 5-3). Cubic BP is extremely inert, resisting attack by boiling concentrated acids or bases, is not oxidized in air below... 

The effects of substrate temperature (Ts b) on cubic boron nitride (c-BN) films synthesized using magnetron sputtering were studied. Fourier transform infrared (FTIR) spectroscopy. X-ray photoelectron spectroscopy (XPS) were employed to characterize the structure and composition of the films. It is found that Ts , plays a crucial role on the formation of cubic phase, and an appropriate T, , can lead to a high content. A tentative explanation on the mechanism of such Ts b effects is reported with the most details. 

Cubic boron nitride (cBN) has a zinc blende-type crystal structure with a lattice constant of 3.615 A, which is very close to that of diamond (3.567 A). The difference is only about 1.3%. According to RHEED measurements with the electron beam parallel to the 111 layer of cBN, a growth of diamond by DC plasma CVD on cBN(lll) [150] using c = 0.5%CH4/H2, T = 900°C, and F=180Torr led to a result that a smooth (111) layer of diamond was epitaxially deposited in such a way that the [110] direction of diamond was parallel to that of cBN. Namely, D 111 //cBN(lll and D[110]//cBN[110]. In the RHEED pattern, however, extra spots were observed, which were presumably due to the twinnings of (111 diamond layers. In the Raman spectra, there were two lines due to cBN at 1054.5 and... 

Two boron phosphides have been isolated, BP and Bi2P2-Heating elemental boron and red phosphorus at 900-1100 °C yields BP as refractory brown crystals having a cubic zinc blende structure similar to cubic boron nitride. This material can also be prepared by a number of other methods including the pyrolysis of CHP-BCH, reaction of boron or boron trichloride with zinc phosphide or phosphine, and hydrogen reduction of CRP-BCls. 

Fig. 1 4.48 Optical micrographs of unetched sections normal to surfaces with cubic boron nitride friction stir processed (FSP) fine-° grained globular structures, and adjacent as-cast structures dealloyed for 24 h at-200 mV (versus saturated calomel...

Boron compounds with nonmetals, i.e., boron hydrides, carbides, nitrides, oxides, silicides, and arsenides, show simple atomic structures. For example, boron nitride (BN) can be found in layered hexagonal, rhombohedral, and turbostratic or denser cubic and wurtzite-like structures, as well as in the form of nanotubes and fullerenes. Boron compounds with metalloids also differ from borides by electronic properties being semiconductors or wide-gap insulators. 

At room temperature the hardness of B4C is only inferior to diamond and cubic boron nitride, which tend to weaken above 500-600°C due to the beginning of the transformation from the diamond structure into the graphite structure. Above... 

---