Ab initio calculation of the lattice dynamics of the Boron group-V compounds under high pressure (original) (raw)
Related papers
Journal of Alloys and Compounds, 2011
The structural, electronic, mechanical properties and hardness of orthorhombic B 28 and tetragonal B 48 boron phases have been studied by first-principles of pseudopotential calculations. The results indicated that both boron phases are energetically and also mechanically stable. In addition to electronic properties of highly directional covalent bonds, mechanical properties, and also the Debye temperatures of structures support that both are superhard materials. Calculated electronic band structures and density of states revealed that orthorhombic B 28 crystal is a semiconductor, and the tetragonal B 48 is metallic. The pressure-dependent behaviors of both structures are different, and both are ultra-incompressible and anisotropic materials. The physical parameters of the structures such as lattice parameters, bond lengths, and also energy gaps between valance and conduction bands are closely sensitive to applied external pressures. By means of pressure-volume graphs, obtained EOSs for ␣-rhombohedral B 12 , orthorhombic B 28 and tetragonal B 48 boron phases are compared with available data. However, energetically possible pressure-induced phase transitions among the purposed structures are predicted on the pressure range of 0-460 GPa. Furthermore, our calculations showed that for the pressures from 0 GPa to 24 GPa energetically the more stable elemental boron phase is ␣-rhombohedral B 12 , and from 24 GPa to 106 GPa is orthorhombic B 28 , and from 106 GPa to 460 GPa is ␣-Ga-type boron.
Electronic and optical properties of BAs under pressure
Physica B: Condensed Matter, 2011
The electronic and optical properties of boron arsenide (BAs) in the zinc-blende (ZB) and rock-salt (RS) phases have been studied by the density functional theory (DFT) method based on the generalized gradient approximation (GGA). Using the enthalpy-pressure data, the structural phase transition from ZB to RS is observed at 141 GPa. Our calculated electronic properties show that ZB-BAs is a semiconductor, whereas RS-BAs is a semi-metal. Calculations of the dielectric function and absorption coefficient have been performed for the energy range 0-30 eV. The dependence of pressure on band structure and optical spectra is also investigated. The results are compared with available theoretical and experimental data.
Boron under Pressure: Phase Diagram and Novel High-Pressure Phase
NATO Science for Peace and Security Series B: Physics and Biophysics, 2010
Boron has a unique chemistry, responsible for remarkable complexities even in the pure element. I review some of the history of the discovery of this element, and recent surprises found in boron under pressure. I discuss the recent discovery of a new high-pressure phase, γ-B 28 , consisting of icosahedral B 12 clusters and B 2 pairs in a NaCl-type arrangement: (B 2 ) δ+ (B 12 ) δ− , and displaying a significant charge transfer δ ~ 0.48. Boron is the only light element, for which the phase diagram has become clear only in the last couple of years, and this phase diagram is discussed here among other recent findings. diagram 1 One parameter quantifying localization of valence electrons is their orbital radius; the outermost valence orbital radius for the boron atom is 0.78 Å, only slightly larger than that of carbon (0.62 Å), and much smaller than that of metals aluminum (1.31 Å) or gallium (1.25 Å).
Ionic high-pressure form of elemental boron
Nature, 2009
Boron is an element of fascinating chemical complexity. Controversies have shrouded this element since its discovery was announced in 1808: the new 'element' turned out to be a compound containing less than 60-70% of boron, and it was not until 1909 that 99% pure boron was obtained 1 . And although we now know of at least 16 polymorphs 2 , the stable phase of boron is not yet experimentally established even at ambient conditions 3 . Boron's complexities arise from frustration: situated between metals and insulators in the Periodic electrons, which would favour metallicity, but they are sufficiently localized that insulating states emerge. However, this subtle balance between metallic and insulating states is easily shifted by pressure, temperature and impurities. Here we report the results of high-pressure experiments and ab initio evolutionary crystal structure predictions 4,5 that explore the structural stability of boron under pressure and, strikingly, reveal a partially ionic high-pressure boron phase. This new phase is stable between 19 and 89 GPa, can be quenched to ambient conditions, and has a hitherto unknown structure (space group Pnnm, 28 atoms in the unit cell) consisting of icosahedral B 12 clusters and B 2 pairs in a NaCl-type arrangement. We find that the ionicity of the phase affects its electronic bandgap, infrared adsorption and All known structures of boron contain icosahedral B 12 clusters, with metallic-like three-centre bonds within the icosahedra and covalent two-and three-centre bonds between the icosahedra. Such bonding satisfies the octet rule and produces an insulating state, but impurity-doped boron phases are often metallic. The sensitivity of boron to impurities is evidenced by the existence of unique icosahedral boron-rich compounds such as YB 65.9 , NaB 15 , MgAlB 14 , AlC 4 B 40 , NiB 50 and PuB 100 (refs 2, 6). In fact, probably only three of the reported boron phases correspond to the pure element 2,7,8 : rhombohedral α-B 12 and β-B 106 (with 12 and 106 atoms in the unit cell, respectively) and tetragonal T-192 (with 190-192 atoms per unit cell) 8 . At ambient conditions, α-B 12 and β-B 106 have similar static energies 9,10 , but disordered β-B 106 becomes marginally more stable (in what could seem a violation of the third law of thermodynamics) when zero-point vibrational energy is taken into account 10 . At pressures above several gigapascals, the much denser α-B 12 phase should be more stable at all temperatures. At high pressures, opposing effects come into play: although pressure favours metallic states and might stabilize metallic-like icosahedral clusters 11 , the very low packing efficiency of atoms in icosahedral structures (34% for α-B 12 ) necessitates the destruction of the icosahedra and formation of denser phases (for example, the α-Ga-type phase 12 ). In experiments, the room-temperature compression of β-B 106 showed metastable amorphization 11 at 100 GPa and the onset of superconductivity 13 at 160 GPa. When using laser heating to overcome kinetic barriers, it was found that β-B 106 transforms into the T-192 phase above 10 GPa at 2,280 K (ref. 14).
Metallicity of boron carbides at high pressure
Journal of Physics: Conference Series, 2010
Electronic structure of semiconducting boron carbide at high pressure has been theoretically investigated, because of interests in the positive pressure dependence of resistivity, in the gap closure, and in the phase transition. The most simplest form B12(CCC) is assumed. Under assumptions of hydrostatic pressure and neglecting finite-temperature effects, boron carbide is quite stable at high pressure. The crystal of boron carbide is stable at least until a pressure higher than previous experiments showed. The gap closure occurs only after p=600 GPa on the assumption of the original crystal symmetry. In the low pressure regime, the pressure dependence of the energy gap almost diminishes, which is an exceptional case for semiconductors, which could be one of reasons for the positive pressure dependence of resistivity. A monotonous increase in the apex angle of rhombohedron suggests that the covalent bond continues to increase. The C chain inserted in the main diagonal of rhombohedral structure is the chief reason of this stability.
Pramana, 2012
In this paper we present the results obtained from first-principles calculations of the effect of hydrostatic pressure on the structural, elastic and electronic properties of (B3) boron phosphide, using the pseudopotential plane-wave method (PP-PW) based on density functional theory within the Teter and Pade exchange-correlation functional form of the local density approximation (LDA). The lattice parameter, molecular and crystal densities, near-neighbour distances, independent elastic constants, bulk modulus, shear modulus, anisotropy factor and energy bandgaps of (B3) BP under high pressure are presented. The results showed a phase transition pressure from the zinc blende to rock-salt phase at around 1.56 Mbar, which is in good agreement with the theoretical data reported in the literature.
Phonon study of rhombohedral BS under high pressure
Raman spectra of rhombohedral boron monosulfide (r-BS) were measured under pressures up to 34 GPa at room temperature. No pressure-induced structural phase transition was observed, while strong pressure shift of Raman bands towards higher wavenumbers has been revealed. IR spectroscopy as a complementary technique has been used in order to completely describe the phonon modes of r-BS. All experimentally observed bands have been compared with theoretically calculated ones and modes assignment has been performed. r-BS enriched by 10B isotope was synthesized, and the effect of boron isotopic substitution on Raman spectra was observed and analyzed.
Lattice dynamics of boron nitride
Materials Science and Engineering B, 1999
Using the density-functional theory within the full potential linear augmented plane-wave (FP-LAPW) method, we have calculated ab initio the equation of state and the principal phonon modes in cubic boron nitride (c-BN), including their pressure dependence and the amplitude of the eigendisplacements. A good agreement with the experiments is obtained, whenever a comparison is possible: in fact, most of the results are predictions. A ten-parameter valence overlap shell model (VOSM) was constructed and we obtained the phonon dispersion curves, elastic constants and effective charges. Our results were compared with calculated theoretical data for c-BN and for other III–V materials and we found that the lattice dynamics properties for cubic boron nitride is very close to those of diamond.