Raman effect in icosahedral boron-rich solids

Abstract

We present Raman spectra of numerous icosahedral boron-rich solids having the structure of α-rhombohedral, β-rhombohedral, α-tetragonal, β-tetragonal, YB 66 , orthorhombic or amorphous boron. The spectra were newly measured and, in some cases, compared with reported data and discussed. We emphasize the importance of a high signal-to-noise ratio in the Raman spectra for detecting weak effects evoked by the modification of compounds, accommodation of interstitial atoms and other structural defects. Vibrations of the icosahedra, occurring in all the spectra, are interpreted using the description of modes in α-rhombohedral boron by Beckel et al. The Raman spectrum of boron carbide is largely clarified. Relative intra-and inter-icosahedral bonding forces are estimated for the different structural groups and for vanadium-doped β-rhombohedral boron. The validity of Badger's rule is demonstrated for the force constants of inter-icosahedral B-B bonds, whereas the agreement is less satisfactory for the intra-icosahedral B-B bonds.

Fracture Strength ofAlLiB14

“…Experimental results indicate that the inter-icosahedra B-B bonds spanning between the layers are stronger than the intra-icosahedra bonds. [12] Here we find that regardless the strength of the inter-icosahedra bonds the fracture is significantly more likely to proceed between the icosahedron rather than through, due to the density of bonds at the cleavage plane. In fact the {010}-M planes are the weakest of those examined in this study, which suggests that the hardness of the material may be closely tied to the B-B bonding that connects the icosahedra layers.…”

“…Recent spectroscopy evidence indicates that the B-B bonds that span between the B layers, directly connecting icosahedron, are very strong. [12] Unlike many metal-boride compounds the metal atoms are not covalently bonded to the B, but instead the metal atoms ionize and donate their valence electrons to the covalently bonded B network. [13][14][15][16] As a near-superhard material, this crystal family is unique, which has led us to investigate the bonding in the crystal as it affects the crystal's mechanical strength.…”

“…12, the B-B bonds that span between the B layers and connect the icosahedron are expected to have a greater binding strength than the bonds inside the icosahedron. This can be examined qualitatively by plotting the bonding charge density, as shown in Fig.…”

Electronic structures and mechanical properties of boron and boron-rich crystals (Part I)

“…On the other hand, in the history of the boron study, phonon properties have sometimes decisive roles in our understanding of bonding nature of boron solids. For experimental data, the most updated reference is a review by Werheit [143].…”

Study of multi-carbide B4C-SiC/(Al, Si) reaction infiltrated composites by SEM with EBSD

“…Boron carbide has an atomic structure that can be described as composed of two atom arrangements: a primary structure formed by 12-atom icosahedra with B as the corners, linked by 3-atom C-B-C linear chains along the (111) rhombohedral axis, corresponding to the model stoichiometry of (B 13 C 2 ), the icosahedra sitting on the vertices of a lattice with trigonal symmetryspace group R3 m; or in terms of an hexagonal lattice in which the [0001] direction axis matches the [111] rhombohedral direction [2]. B 4 C structure has been extensively described in the literature [3][4][5][6][7] and although the crystal symmetry is obtained by diffraction methods, the resemblance in terms of nuclear scattering of boron and carbon atoms [8][9] makes almost indistinguishable the two atoms. Zoning of the B 4 C solid solution displaying fluctuations of B/C ratio often yields B 13 C 2 -domains formed between B 4 C zones of composition close to the B 12 C 3 stoichiometry, the average size of the B 13 C 2 -domains being smaller than those of B 4 C [10].…”