Two metalloid Ga22 clusters containing a novel Ga22 core with an icosahedral Ga12 center

In addition to the two so far known types of metalloid Ga(22) clusters a new type is presented in two compounds containing the anions [Ga(22)Br[N(SiMe(3))(2)](10)Br(10)](3-) (1) and [Ga(22)Br(2)[N(SiMe(3))(2)](10)Br(10)](2-) (2). In both anions 10 Ga atoms of the icosahedral Ga(12) core are directly connected to further Ga atoms. The two remaining Ga atoms (top and bottom) of the Ga(12) icosahedron are bonded to one (1) and two Br atoms (2), respectively. The formation and structure of both compounds containing a slightly different average oxidation number of the Ga atoms is discussed and compared especially with regard to the Ga(84) cluster compound and similar metalloid Al(n) clusters. Finally, the consequences arising from the presence of two very similar but not identical Ga(22) cluster compounds are discussed and special consideration is given to the so far not understood physical properties (metallic conductivity and superconductivity) of the Ga(84) cluster compound.     

Simultaneous determination of Cr,Ga, In and V in soil and water samples by tungsten coil atomic emission spectrometry

Tungsten coil atomic emission spectrometry is employed for the simultaneous determination of Cr, Ga, In, and V. Both V and In are detected by this technique for the first time. The atomizer is a simple, inexpensive tungsten filament extracted from a mass-produced, commercially-available 150 W, 15 V microscope bulb. A 25 µl sample aliquot is placed directly on the coil and a small constant-current power source is used to carefully dry, ash and atomize the sample. Analytical signals are detected with a Czerny-Turner spectrograph and a charge coupled device detector. Multiple emission lines from all 4 elements are monitored simultaneously in a 54 nm spectral window. Concentration limits of detection are in the µg l^− 1 range for all elements, and the absolute limits of detection are 0.2, 2, 0.5, and 10 ng for Cr, Ga, In, and V, respectively. Even lower values may be obtained by combining the signals for the multiple emission lines of a single element. The method precision is typically better than 5.0% relative standard deviation, and sometimes as good as 0.95% (Ga). Standard reference materials of soil and water are used to check the method accuracy. After a simple acid extraction, the values determined by the method presented no significant difference from the reported values at the 95% confidence level.     

Analysis of radioactive metals by spark source mass spectrometry

A spark source mass spectrograph with photographic plate recording has been adapted for the analysis of plutonium and americium metals. Over seventy elements can be determined simultaneously in these metals. A comparison has been made between results obtained by mass spectrography and by conventional methods for impurity elements. The operations involved in handling radioactive materials in the mass spectrograph are also discussed.     

Ionic and Phase Compositions of Y2.5Ce0.5Fe2.5Ga2.5O12 Ferrogarnet Powder Produced by Gel Combustion

Doklady Physical Chemistry - The ionic and phase compositions of Y2.5Ce0.5Fe2.5Ga2.5O12 ferrogarnet samples obtained by gel combustion with subsequent vacuum annealing were studied for the first...     

Solid-state NMR characterization of 69Ga and 71Ga in crystalline solids

Gallium model systems containing four- and six-coordinate gallium sites have been investigated using solid-state NMR. Measurement of the isotropic chemical shift and electric field gradient (EFG) have been performed at 9.4 T on alpha-Ga2O3, beta-Ga2O3, LiGaO2, NaGaO2, KGaO2, Ga2(SO4)3, and LaGaO3 using a variety of techniques on both NMR active nuclei (69Ga and 71Ga) including static, high speed magic-angle spinning (MAS), satellite transition (ST) spectroscopy, and rotor-assisted population transfer (RAPT). The chemical shift is found to correlate well with the coordination number, with four-coordinate gallium having values of approximately 50 ppm and six-coordinate gallium having values near 225 ppm (referenced to 1 M gallium nitrate solution). The magnitude of the EFG is found to be correlated to the distortion of the gallium polyhedra, with the strained systems having EFGs of 3 x 10(21) Vm(-2) or more, while the less strained systems have values of 1.5 x 10(21) Vm(-2) or less. A plot of chemical shift versus EFG suggests that solid-state NMR of gallium oxyanions can be more discriminating than liquid state NMR chemical shifts alone.     

Binding of 67 Ga and 59 Fe to ferritin or transferrin

The bindings of 67Ga and 59Fe to ferritin or transferrin in vitro has been investigated. Affinity constants have been measured using the equilibrium dialysis, and the results have been obtained as follows: 1 Apo-ferritin could not bind to 67Ga until it was transformed into ferritin in presence of Fe-citrate. On the contrary, the affinity of 67Ga to ferritin was reduced when Fe was released from ferritin; thus indicating that Fe-core has been required for the binding of 67Ga to ferritin. 2 Binding of 67Ga to ferritin was inhibited with apo-transferrin, and this was also shown in the case of 59Fe. In the presence of NaHCO3 or citrate, more remarkable inhibitions were observed. NaHCO3 or citrate was found to give a synergistic effect on the binding of 67Ga to transferrin, as well as Fe-transferrin. Therefore, both 67Ga and 59Fe could not bind to ferritin in the state of 67Ga- or 59Fe-transferrin. 3 The release of 59Fe from 59Fe-transferrin was enhanced with adenosine triphosphate (ATP), citrate, or ascorbic acid, while any of these reagents did not affect the release of 67Ga from 67Ga-transferrin. The comparison of 59Fe and 67Ga through their bindings to ferritin or transferrin has suggested one of points to distinguish 67Ga from 59Fe in the cell.     

Structural, energetic, electronic, bonding, and vibrational properties of Ga3O, Ga3O2, Ga3O3, Ga2O3, and GaO3 clusters

The results of density functional theory based calculations on Ga3O, Ga3O2, Ga3O3, Ga2O3, and GaO3 clusters are reported here. A preference for planar arrangement of the constituent atoms maximizing the ionic interactions is found in the ground state of the clusters considered. The sequential oxidation of the metal-excess clusters increases the binding energy, but the sequential removal of a metal atom from the oxygen-excess clusters decreases the binding energy. The increase in the oxygen to metal ratio in these clusters is accompanied by increase in both electron affinity and ionization potential. The ionization induced structural distortions in the neutral clusters are relatively small, except those for Ga3O2. In anionic (cationic) clusters, the added (ionized) electron is shared by the Ga atoms, except in the case of GaO3. The vibrational frequencies and charge density analysis reveal the importance of the ionic Ga-O bond in stabilizing the gallium oxide clusters considered in this study.     

Thermodynamic properties of Ga27Si3 cluster using density functional molecular dynamics

Density functional molecular dynamical calculations have been carried out to explore the effect of silicon impurities on thermodynamic properties of Ga(30). We have obtained 500 distinct low energy equilibrium geometries of Ga(27)Si(3) in order to obtain reliable ground state geometry. The specific heat has been calculated using multiple histogram techniques and compared with that of Ga(30). We demonstrate that silicon impurities have a dramatic effect on the thermodynamic properties of the host cluster. In contrast to Ga(30), the specific heat of Ga(27)Si(3) shows a clear melting peak at ≈500 K, changing the character of Ga(30) from a nonmelter to a melter.     

Preparation and electrical properties of ultrafine Ga2O3 nanowires

Uniform and well-crystallized beta-Ga2O3 nanowires are prepared by reacting metal Ga with water vapor based on the vapor-liquid-solid (VLS) mechanism. Electron microscopy studies show that the nanowires have diameters ranging from 10 to 40 nm and lengths up to tens of micrometers. The contact properties of individual Ga2O3 nanowires with Pt or Au/Ti electrodes are studied, respectively, finding that Pt can form Schottky-barrier junctions and Au/Ti is advantageous to fabricate ohmic contacts with individual Ga2O3 nanowires. In ambient air, the conductivity of the Ga2O3 nanowires is about 1 (Omega.m)-1, while with adsorption of NH3 (or NO2) molecules, the conductivity can increase (or decrease) dramatically at room temperature. The as-grown Ga2O3 nanowires have the properties of an n-type semiconductor.     

MgAuGa and MgAu2Ga: first representatives of the Mg–Au–Ga system

MgAuGa (magnesium gold gallium), the first ternary representative of the Mg–Au–Ga system, crystallizes in the space group P2m and adopts the Fe₂P structure type (Pearson symbol hP9). Various phases with the general composition AB₂ have been reported in the surrounding binary systems, viz. Mg₂Ga (hP18), MgGa₂ (hP6; CaIn₂ type), AuGa₂ (cF12; CaF₂ type), Au₂Ga (oS24; Pd₂As type) and Mg₂Au (oP12; Co₂Si type). In principle, MgAuGa can be obtained from each of them by partial replacement of the major element with the missing element. In fact, the structure of MgAuGa closely resembles hexagonal Mg₂Ga through a direct group–subgroup relationship. MgAu₂Ga (magnesium digold gallium) also crystallizes hexagonally in the space group P6₃/mmc and is isotypic with Na₃As. It adopts the structure of another binary compound, viz. Mg₃Au (hP8), but shows an unexpected distribution of Mg, Au, and Ga among the atomic positions of the asymmetric unit. Both MgAuGa and MgAu₂Ga can be described as formally anionic Au/Ga frameworks, with pseudo‐hexagonal tunnels around Mg in MgAuGa or cages in MgAu₂Ga.     

Spectroscopic properties of gallium arsenide tetramers: Ga2As2, Ga2As2+ and Ga2As2-

Spectroscopic properties of the low-lying electronic states of Ga2As2 and its ions are studied using the complete active-space self-consistent field (CASSCF) and density function theory (DFT) followed by the coupled-cluster single and double substitutions (including triple excitations) (CCSD(T)) calculations. The stability of low-lying electronic states is examined by computing vibrational frequency. The energies of the ground states and a number of excited electronic states have been computed to predict the spectra of Ga2As2 and its ions. The ionization energy, electronic affinity, and atomization energy are estimated at the CCSD(T)/6-311+G(d) level and compared with the available experimental results.     

Untersuchungen zur Bildung von Molekülionen in Funken- und Laserplasmen

Zusammenfassung Mit Hilfe eines massenspektrographischen Systems, bestehend aus einer Nd: YAG-Laser- oder einer Funken-Ionenquelle und einem doppeltfokussierenden Massenspektrographen vom Mattauch-Her-zog-Typ, wurde die Bildung von Molekülionen in Laser- und Funkenplasmen untersucht. Die Häufigkeitsverteilung der nachgewiesenen Cluster- und Molekülionen im untersuchten Graphit und Uranylnitrat wurde in Laser- und Funken-Massenspektren verglichen.

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Investigation of the formation of molecular ions in spark and laser plasmas

Summary A mass spectrometer system consisting of a Nd: YAG laser or a spark ion source and a double focusing mass spectrograph of the Mattauch-Herzog type was used to investigate the formation of molecular ions in laser and spark plasmas. The abundance of the cluster and molecular ions in the investigated graphit and uranylnitrate detected was compared in laser and spark mass spectrum.

     

Radio-paperchromatographic determination of different chemical forms of Ga

Model experiments for Ga/Zn separation were carried out using Dowex 1 anion exchanger. Some chemical forms of Ga were identified by radio-paperchromatography and the R_f values have been determined.     

Characterization of isolated Ga2 molecules by resonance Raman spectroscopy and variations of Ga-Ga bonding

Isolated Ga2 dimers were characterized in an argon matrix with the aid of resonance Raman and UV/Vis spectroscopy. The resonance Raman spectra gave evidence of not only the nu(Ga-Ga) fundamental, but also four overtones. Each of the signals exhibits 69Ga/71Ga isotopic splitting leading to the triplet pattern characteristic of two equivalent Ga atoms. On the basis of the experimental data, a harmonic frequency and anharmonicity constant have been determined for Ga2. An estimate of the dissociation energy on the assumption of a Morse-type potential energy curve results in a De value (upper limit) of about 145 kJ mol(-1). The force constant (64.8+/-0.3 N m(-1)) and dissociation energy of Ga2 are compared with those of other diatomics and those of molecules featuring Ga-Ga bonds.     

Ga(22)

A metal-rich intermediate was captured prior to metal formation by means of a substitution reaction during the disproportionation of a metastable Ga(I) bromide solution. In the thus obtained Ga(22) cluster (see structure), the central gallium atom displays the unusual coordination number of 13.     

Crystal growth, structure, and physical properties of SmCu4Ga8

Single crystals of SmCu4Ga8 have been grown using Ga flux and characterized by single-crystal X-ray diffraction. SmCu4Ga8, isostructural to SmZn11, crystallizes in the hexagonal P6/mmm (No. 191) space group, with Z = 3 and lattice parameters a = 8.865(2) A and c = 8.607(2) A. Magnetic susceptibility data show antiferromagnetic ordering at 3.3 K. Metallic behavior is observed in the temperature range 2-300 K. A large positive magnetoresistance (MR % = (rho H - rho 0)/rho 0 x 100) up to 40% is also observed near T N. In this paper, we present the structure and physical properties of SmCu4Ga8.     

Mg35Cu24Ga53: a three-dimensional cubic network composed of interconnected Cu6Ga6 icosahedra, Mg-centered Ga16 icosioctahedra, and a magnesium lattice

Single-crystal X-ray structural determinations for the Mg(35.12(4))Cu24Ga(53.58(6)) and Mg(35.6(4))Cu24Ga(52.66(6)) refined compositions (Fdm, Z = 4) reveal empty (Cu,Ga)12 icosahedra and centered MgGa16 icosioctahedra that are interconnected at every vertex to a compact three-dimensional anion network. A small range of variable occupancy exists on one of three Ga and one of four Mg positions. The clusters are well-bonded and held in different sized cavities, in which they are also directly bonded to a Mg cation network. The two networks thus interpenetrate each other, and there are no spacers. The new phase is isostructural with K39In80, K17In41, and the electron-poorer Na35Cd24Ga56, all of which contain clathrate-II-type cation frameworks. Electron counting using the classic (MO-based) cluster assignments indicates that the refined structure is substantially ideal and closed-shell. The symmetry of the present structure does not suggest a ready conversion to an icosahedral quasicrystal or its approximants.     

Self-interaction effects in (Ga,Mn)As and (Ga,Mn)N

The electronic structures of Mn-doped zincblende GaAs and wurtzite GaN are calculated using both standard local-spin density functional theory (LSDA), and a novel pseudopotential self-interaction-corrected approach (pseudo-SIC), able to account for the effects of strong correlation. We find that, as expected, the self-interaction is not strong in (Ga,Mn)As, because the Fermi energy is crossed by weakly correlated As p–Mn d hybridized bands and the Mn 3d character is distributed through the whole valence band manifold. This result validates the extensive literature of LSDA studies on (Ga,Mn)As, including the conclusion that the ferromagnetism is hole-mediated. In contrast, the LSDA gives a qualitatively incorrect band structure for (Ga,Mn)N, which is characterized by localized Mn 3d bands with very strong self-interaction. Our pseudo-SIC calculations show a highly confined hole just above the Fermi energy in the majority band manifold. Such a band arrangement is consistent with (although by no means conclusive evidence for) a recent suggestion [Phys. Rev. B 033203 (2002)] that formation of Zhang–Rice magnetic polarons is responsible for hole-mediated ferromagnetism in (Ga,Mn)N.     

Ba5Ga4Se10: a new selenidogallate containing the novel [Ga4Se10](10-) anionic cluster with Ga in a mixed-valence state

The new compound Ba(5)Ga(4)Se(10) has been synthesized for the first time. It crystallizes in the tetragonal space group I4/mcm with a = 8.752(2) ?, c = 13.971(9) ?, and Z = 2. The structure contains discrete [Ga(4)Se(10)](10-) anions and charge-compensating Ba(2+) cations. The novel highly anionic [Ga(4)Se(10)](10-) cluster is composed of two Ga(Se)(4) tetrahedra and two Ga(Ga)(Se)(3) tetrahedra with Ga in the 2+/3+ valence states. It also exhibits an unusually long Ga-Se distance of 2.705(2) ?, which has only been observed under high pressure conditions before. A band gap of 2.20(2) eV was deduced from the UV/vis diffuse reflectance spectrum.     

Experimental observation of line hyperfine structure with a plane grating spectrograph

For observing the hyperfine structure (HFS) of spectral lines it is required that the spectral bandwidth is smaller than or equal to both the physical widths of the HFS components and the wavelength distances between these components. The paper discusses how these conditions can be fulfilled for a 2.1-m plane grating spectrograph equipped with a 1200 grooves/mm grating. Using such a spectrograph observations were made of the HFS of lines emitted by hollow cathode lamps or an arc. Typical results for lines of Bi, Cu and In are reported. Wavelengths and relative intensities of HFS components are given.