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B Atoms (b + atom)

Distribution by Scientific Domains
Chemistry66%
Physics and Astronomy22%

Selected Abstracts

How do electronic properties of conventional III,V semiconductors hold for the III,V boron bismuth BBi compound?

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2005
D. Madouri
Abstract We have performed ab-initio self-consistent calculations using the full potential linear augmented plane wave method to investigate the structural and the electronic properties of the boron bismuth III,V compound BBi. Our calculations provide the first available information about the structural and electronic ground-state properties of BBi. Total energy calculations of the cubic zinc-blende, wurtzite, rock-salt, cesium chloride and orthorhombic Cmcm phases are made. The zinc-blende structure is found to be the ground-state phase of BBi; within the generalized gradient approximation (local density approximation), we found a lattice constant of 5.529 Å (5.416 Å) and a bulk modulus of 72.20 GPa (86.27 GPa). We found that, contrary to other boron compounds, the band gap of BBi is direct at the , point. The relativistic contraction of the 6s orbital of Bi has a strong influence on the bands and bonds of BBi. Consequently, the electronic properties of BBi are shown to differ considerably from those of common group III,V semiconductors (e.g. GaAs); in particular, we found an unusually strong p,p mixing of the valence-band maximum relative to most of the other III,V compounds. Furthermore, the calculated valence charge density shows an anomalous behavior, characterized by a charge transfer towards the ,cation' B atom, further illustrating the rich behavior of boron bismuth compounds. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The iso­thio­cyanate complex of tri­phenyl­borane forms an unusual coordination polymer with [K(18-crown-6)]+, both in the solid state and in solution

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2003
Orde Q. Munro
The title salt, (1,4,7,10,13,16-hexa­oxa­cyclo­octa­decane-,6O)[(iso­thio­cyanato)­tri­phenyl­borato-,S]­potassium(I), [K(C19H15BNS)(C12H24O6)] or [K(SCNBPh3)(18-crown-6)], where 18-crown-6 is 1,4,7,10,13,16-hexaoxa­cyclo­octa­decane and [SCNBPh3], is the (iso­thio­cyanato)­tri­phenyl­borate anion, exhibits a supramol­ecular structure that is best described as a helical coordination polymer or molecular screw. This unusual supramolecular structure is based on a framework in which the SCN, ion bridges the chelated K+ ion and the B atom of BPh3 in a ,2 fashion. The X-ray crystal structure of the title salt has been determined at 100,(1) and 293,(2),K. The K+ ion exhibits axial ligation by the S atom of the [SCNBPh3], anion, with a K,S distance of 3.2617,(17),Å (100,K). The trans -axial ligand is an unexpected ,2 -bound C=C bond of a phenyl group (meta - and para -C atoms) that belongs to the BPh3 moiety of a neighboring mol­ecule. The K,C bond distances span the range 3.099,(3),3.310,(3),Å (100,K) and are apparently retained in CDCl3 solution (as evidenced by 13C NMR spectroscopy). By virtue of the latter interaction, the supramolecular structure is a helical coordination polymer, with the helix axis parallel to the b axis of the unit cell. IR spectroscopy and semi-empirical molecular orbital (AM1) calculations have been used to investigate further the electronic structure of the [SCNBPh3], ion. [source]

Sol-Gel-Derived Silicon-Boron Oxycarbide Glasses Containing Mixed Silicon Oxycarbide (SiCxO4,x) and Boron Oxycarbide (BCyO3,y) Units

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2001
Christel Gervais
The introduction of B atoms in SiOC glass networks has been achieved through the pyrolysis of sol-gel-derived polyborosiloxanes under an inert atmosphere. The starting gels were obtained from hydrolysis-condensation reactions of triethylborate (B(OEt)3) and an organically modified trialkoxysilane (EtSi(OEt)3). The resulting hybrid EtSiO1.5 -B2O3 gels showed a homogeneous dispersion of the B atoms in the siloxane network via ,Si,O,B, bonds. The presence of such borosiloxane bridges prevents the formation of cyclic or cage siloxane entities and leads to relatively high ceramic yields (,80%). The transformation of the polyborosiloxanes into amorphous SiBOC glasses was followed using Fourier transform infrared spectroscopy and multinuclear magic-angle spinning-nuclear magnetic resonance (MAS-NMR) (11B, 13C, and 29Si). An important change in the carbon, silicon, and boron environments occurs during pyrolysis. Interestingly, the 11B MAS-NMR spectra suggest a progressive replacement of the B,O bonds by B,C bonds, which leads to a distribution of trigonal BCxO3,x sites in the glass that was pyrolyzed at 1000°C, with a residual amount of B(OSi)3 sites. The resulting glasses can thus be described as silicon-boron oxycarbide networks that are based on SiCxO4,x and BCyO3,y mixed environments. [source]

Theory of electronic structure of BGaAs and related alloys

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2008
A. Lindsay
Abstract Previous experiments on BxGa1,xAs containing a few percent boron show a dramatic increase in electron effective mass, m*e, similar to that observed in many GaNxAs1,x samples. By contrast, there is a near-linear blue-shift of the energy gap, which can be conventionally described using the virtual crystal approximation. We use a tight-binding model to show that isolated B atoms have little effect either on the band gap or lowest conduction band dispersion in BxGa1,xAs. By contrast, B pairs and clusters introduce defect levels close to the conduction band edge (CBE) which, through a weak band-anticrossing (BAC) interaction, significantly reduce the band dispersion in and around the , -point, thus accounting for the strong increase in m*e and reduction in mobility observed in these alloys. Calculations show that replacing gallium by aluminium shifts the CBE upwards, leading to a large density of B-related states in the energy gap. By contrast, indium shifts the band edge downwards, leading eventually to a band edge m*e close to that predicted by the virtual crystal approximation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Bond analyses of borates from the Inorganic Crystal Structure Database

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2006
Daqiu Yu
Various fundamental building blocks (FBBs) are observed in the crystallographic structures of oxoborates available in the Inorganic Crystal Structure Database, Version 1.3.3 (2004); the occurrence of borate groups with low complexity is dominant. Bond-valence parameters d0 of B,O bonds in 758 oxoborates with various FBBs have been calculated using the bond-valence sum model. Some discrepancies in the d0 values obviously occur if the detailed configurations of FBBs in borate crystals are considered; d0 is sensitive to the chemical bonding structure of B atoms in the crystallographic framework. Moreover, d0 values are affected by the existence of interstitial atoms and the substitution of other anionic groups. In addition, the d0 parameters for B,N, B,S, B,P and B,F bonds are also calculated statistically. Some suitable d0 data for various borate FBBs are recommended according to their particular configurations, especially for those with low complexity. On the basis of the proposed linear relationship between calculated nonlinear optical (NLO) coefficients of borates and the current d0 values for various FBBs, it is found that the d0 values may be regarded as a useful parameter for pre-investigating the NLO properties of borates, leading to an efficient structural evaluation and design of novel borates. [source]

Features of the electron density in magnesium diboride: reconstruction from X-ray diffraction data and comparison with TB-LMTO and FPLO calculations

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2003
S. Lee
Features of the electron density in MgB2 reconstructed from room-temperature single-crystal X-ray diffraction intensities using a multipole model are considered. Topological analysis of the total electron density has been applied to characterize the atomic interactions in magnesium diboride. The shared-type B,B interaction in the B-atom layer reveals that both , and , components of the bonding are strong. A closed-shell-type weak B,B , interaction along the c axis of the unit cell has also been found. The Mg,B closed-shell interaction exhibits a bond path that is significantly curved towards the vertical Mg-atom chain ([110] direction). The latter two facts reflect two sorts of bonding interactions along the [001] direction. Integration of the electron density over the zero-flux atomic basins reveals a charge transfer of ,1.4,(1) electrons from the Mg atoms to the B-atom network. The calculated electric-field gradients at nuclear positions are in good agreement with experimental NMR values. The anharmonic displacement of the B atoms is also discussed. Calculations of the electron density by tight-binding linear muffin-tin orbital (TB-LMTO) and full-potential non-orthogonal local orbital (FPLO) methods confirm the results of the reconstruction from X-ray diffraction; for example, a charge transfer of 1.5 and 1.6 electrons, respectively, was found. [source]

The centrosymmetric metal metaborate KCdB3O6

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009
Shifeng Jin
The title compound, potassium cadmium metaborate, crystallizes in a monoclinic cell, featuring infinite one-dimensional CdO5 chains and trigonal planar B atoms in hexagonal B3O6 metaborate ions. The trigonal bipyramidal CdO5 chains and metaborate ions are interlinked to form a three-dimensional framework, creating channels running parallel to the [10] direction in which the potassium ions reside. [source]

Synthesis and crystal structure of three nido 11-vertex platinaborane clusters

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 11 2005
Jianmin Dou
Abstract The reaction of [PtCl2(PPh3)2] with closo -B10H102, in ethanol under reflux conditions gave two nido 11-vertex platinaundecaborane clusters: [(PPh3)2PtB10H10 -8,10-(OEt)2]·CH2Cl2(1) and [(PPh3)2PtB10H11 -11-OEt]·CH2Cl2(2). A novel B10H102, deboronated nido 11-vertex diplatinaundecaborane [(µ-PPh2)(PPh3)2Pt2B9H6 -3,9,11-(OEt)3]·CH2Cl2(3) was obtained when the same reaction was carried out under solvothermal conditions. All of these compounds were characterized by infrared spectroscopy, NMR spectroscopy, elemental analysis and single-crystal X-ray diffraction. Both clusters 1 and 2 have a nido 11-vertex {PtB10} polyhedral skeleton in which the Pt atom lies in the open PtB4 face. Each Pt atom connects with four B atoms and two P atoms of the PPh3 ligands. Cluster 3 has a nido 11-vertex {Pt2B9} polyhedral skeleton in which two Pt atoms sit in neighbouring positions of the open Pt2B3 face, bridged by a PPh2 group. Each Pt atom connects three B atoms and a P atom of the PPh3 ligand. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Preparation and Charactrization of Fibrous Crystals of Boron-containing MTW-type Zeolite

CHINESE JOURNAL OF CHEMISTRY, Issue 2 2004
Mao-Ying Song
Abstract Fibrous crystals of boron-containing MTW-type zeolite have been hydrothermally synthesized in B2O3 -SiO2 -HF-H2O gel system at 170 °C in 20 to 28 d by using 1, 4-diazabicyclo[2.2, 2]octane (DABCO) and methylamine as the co-template, and characterized with XRD, SEM, TEM, HRTEM and SAED. The results of characterizations show that B atoms are incorporated into the zeolite framework as tetrahedron of B(OSi)4. The fibrous single crystals of 5,50 ,m in length and 100,500 nm in width inter-grow along the c -axis of the zeolite, and the one dimension 12 oxygen ring channels are perpendicular to the fibber axis. [source]