Tetrahedral Ga Research Articles

Spectroscopic and catalytic evidence for the incorporation of gallium in the AEL framework

71Ga MAS n.m.r. analysis and the catalytic behavior during the transformation of 1-butene and n-butane strongly suggest the incorporation of Ga into the AlPO4-11 (AEL) framework during the synthesis of GaAPSO-11. A unique clear signal at around +120 ppm is proposed to be associated with the presence of tetrahedral Ga in the AEL framework of the unmodified GaAPSO-11. Migration of structural Ga atoms to the silicon domain of the AEL framework seems to occur as a result of a mild hydrothermal treatment, giving rise to an additional signal at +156 ppm, previously associated with tetrahedral gallium in gallosilicates with the MFI topology. The fact that GaAPO-11 and GaAPSO-11 behaved in a way similar to their counterparts AlPO4-11 and SAPO-11 during the skeletal isomerization of n-butenes reinforces the idea of an isomorphous substitution of Al(III) by Ga(III) in the AEL framework. The transformation of n-butane was shown to be a valuable test for detecting the presence of small amounts of hydro-dehydrogenating extraframework gallium species (EFGS) in Ga-supported SAPO-11 (Ga/SAPO-11). The fact that the sample of GaAPSO-11 was completely inactive for this transformation leads us to believe that the incorporation of gallium into the tetrahedral positions of the AEL framework was almost complete.

Structure and formation energy of steps on the GaAs(001)-2 × 4 surface

The energies of various steps on the As-terminated GaAs(001)-2 × 4 surface are evaluated using a novel, approximate method of “linear combination of structural motifs”. It is based on the observation that previous total energy minimizations of semiconductor surfaces produced invariably equilibrium structures made of the same recurring local structural motifs, e.g. tetrahedral fourfold Ga, pyramidal threefold As, etc. Furthermore, such surface structures were found to obey consistently the octet rules as applied to the local motifs. We thus express the total energy of a given semiconductor surface as a sum of (i) the energies ε M of the local structural motifs appearing in the surface under consideration and (ii) an electrostatic term representing the Madelung energy of point charges resulting from application of the octet rule. The motif energies are derived from a set of pseudopotential total energy calculations for flat GaAs(001) surfaces and for point defects in bulk GaAs. This set of parameters suffices to reproduce the energies of other (001) surfaces, calculated using the same pseudopotential total energy approach. Application to GaAs(001)-2 × 4 surfaces with steps reveals the following. (i) “Primitive steps”, defined solely according to their geometries (i.e. step heights, widths and orientations) are often unstable. (ii) Additional, non-geometric factors beyond step geometries such as addition of surface adatoms, creation of vacancies and atomic rebonding at step edges are important to lower step energies. So is step-step interaction. (iii) The formation of steps is generally endothermic. (iv) The formation of steps with edges parallel to the direction of surface As dimers (A steps) is energetically favored over the formation of steps whose edges are perpendicular to the As dimers (B steps).

Evidence of zeolite-solution equilibrium for isomorphous substitution using aqueous metal fluoride complexes

The reversibility of isomorphous substitution of tetrahedral framework metal ions using aqueous A1F 3 and (NH 4) 2SiF 6 treatments on zeolite ZSM-5 is reported. 19F NMR studies of A1F 3 and SiF 6 2− D 2O solutions after reaction at 85 °C which NH 4ZSM-5 showed formation of corresponding Si and A1 flouride species. Flouride material balances were reasonable within experimental error. These experiments qualitatively suggest an equilibrium condition exists between Al 3+ and Si 4+ using mild aqueous metal fluoride treatment and imply a general synthetic pathway to isomorphously substituted zeolites. As a further example, [Ga]ZSM-5 containing framework Ga 3+ was prepared by substitution of framework Al 3+ using aqueous GaF 3 treatment. The framework Ga 3+ was characterized by solid-state static and magic-angle spinning (MAS) NMR and the observed Ga chemical shift (155 ± 5 ppm) was consistent with tetrahedral framework Ga 3+ reported previously. Quantitation by Ga and Si NMR and temperature-programmed NH 3 desorption (TPAD) showed excellent agreement.

A neutron powder diffraction study of (Nd1.5Ce0.5)(Sr2-yNdy)Cu2MOx (M=Ga,Ta)

The (Nd,Ce)2Sr2Cu2MOx (M=Ga,Ta) are structurally related to YBCO with yttrium replaced by a fluorite-type block of composition (Nd,Ce)2O2 , and barium by strontium. Neutron powder diffraction studies on these materials have been performed to compare structural order within the layers containing the M atoms. For M=Ga, long-range ordering of the corner-linked GaO4 tetrahedra along the (110) direction of the simple perovskite cell results in an orthorhombic supercell. These zigzag chains of tetrahedra are of two types which are distinguished by the direction of atomic displacements in the chains; equal quantities of both types occur in (Nd,Ce)2Sr2Cu2GaOx. When the tetrahedral Ga ions are replaced by octahedral Ta, the oxygen positions in the basal plane are fully occupied, and the tetrahedral chains are converted into octahedral layers to give a smaller tetragonal unit cell. Cooperative rotation of the TaO6 octahedra within these layers has been confirmed.

Annealing effect on the Frenkel-type defect of gallium in fast ion-conductor K x[Ga 8Ga 8+xTi 16−xO 56

Floating zone grown crystals of 1-D fast ion conductor K x [Ga 8Ga 8+ x Ti 16− x O 56] (=KGGTO) contain Frenkel-ty pe defects on 3% of the tetrahedral Ga sites. The effect of annealing on these defects was analyzed through structural properties. This KGGTO annealed at 1200°C had two alternative variation routes. Some changed from colorless transparent directly to brown, and others to brown by way of pale green. The pale green crystal showed significant variations of lattice constants but little compositional changes. Both direct and indirect brown crystals had mutually similar lattice constants and compositions, but they lost K ions as much as 50%. Defect ratios decrease slightly in the pale green crystal (2.9%) and increase considerably in the brown one (5.7%). The defect ratios of floating zone KGGTO are much larger than that of flux-grown KGGTO (0.6%). Tunnels in KGGTO are divided into segments by impurity oxygen atoms which stabilize interstitial Ga ions, or the Frenkel defects. The change of the unannealed to the pale green crystal can be regarded as the process to homogenize a distribution of impurity oxygen, or to uniform the lengths of segments, by annealing. The mean segment length is 26 and 125 Å for the pale green and flux grown crystals, respectively. Discussion is given on the behaviors of K ions and the defects.

Determination of gallium in H(Ga)ZSM5 zeolites by gallium-71 MAS NMR spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDetermination of gallium in H(Ga)ZSM5 zeolites by gallium-71 MAS NMR spectroscopyCees R. Bayense, Arno P. M. Kentgens, Jan W. De Haan, Leo J. M. Van de Ven, and Jan H. C. Van HooffCite this: J. Phys. Chem. 1992, 96, 2, 775–782Publication Date (Print):January 1, 1992Publication History Published online1 May 2002Published inissue 1 January 1992https://doi.org/10.1021/j100181a047RIGHTS & PERMISSIONSArticle Views431Altmetric-Citations66LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1020 KB) Get e-Alerts

Full profile analysis of the 29Si NMR spectra of LTL-framework zeolites

Full profile analyses of the digitized 29Si NMR spectra of a potassium zeolite L and a gallosilicate analog are described. Both spectra can be fitted reasonably based on the assumption that they comprise only a single set of Si nAl(Ga); n=0−4 peaks, reflecting that the mean T-O-T angles for the two T-sites (T=tetrahedral species, Si, Al or Ga) are similar.

Effect of diamagnetic substitution on growth-induced anisotropy in (YBi)3Fe5O12

Films of (Y3−x−yBixPby) (Fe5−zGaz)O12 (z=0–1.1) and (Y3−x−yBixPby) (Fe5−wInw)O12 (w=0–0.6) garnets were prepared by liquid-phase epitaxy. The effects of tetrahedral Ga and octahedral In substitution on the Bi-based growth-induced uniaxial anisotropy in (YBi)3Fe5O12 films were measured. Both Ga and In resulted in a linear decrease in the anisotropy with increasing substitution. The effect of octahedral In was twice that of tetrahedral Ga.

Structural characterization of dehydrated gallium zeolite L

The structure of the dehydrated gallium analog of zeolite L, K 9Ga 9Si 27O 72 has been determined by full profile analysis of powder neutron diffraction data. The gallium partitioning between the two T-sites (T = Tetrahedral species, Si, Al, or Ga) is random. The individual O-T-O angles show small but consistent deviations from the ideal tetrahedral value. The mean T4OT and T6OT angles are nearly identical in both the present and previously studied LTL-framework structures, enabling assignment of the 29Si nmr spectra. The observed cation configuration is similar to that described previously for the hydrated (Na,K) aluminum zeolite L which, therefore, suggests that little change in cation distribution accompanies dehydration.

X-ray crystal structure of the quaternary semiconductor compound: AgGaSn()Se 4

This is the first diffractometric X-ray structural study of a quaternary semiconductor compound. Crystals of AgGaSn()Se 4 are tetragonal with space group I 4 2d and cell dimensions: a = 5.853(2) A ̊ , c=10.820(4) A ̊ , V=370.7 A ̊ 3 , Z=2, Dx = 5.419 g/ cm 3. The structure was refined by full matrix anisotropic-isotropic least-squares technique using data taken at room temperature with MoK α radiation, λ = 0.71069 A ̊ ( μ = 281.1 cm -1, F(000) = 528). Final value of R = 0.0455, Rw = 0.0396 for 185 unique reflections with I #62; 3σ(I). The structure determination has shown that Se atom occupies the general position (0.2530 0.2749 0.1398) with an occupation factor of 0.5; Ag and () share the position (0 0 0) and Ga and Sn the (0 0 1 2 ). The crystalline structure of the studied quaternary compound presents disordered tetrahedral (Ag)(Ga)Se(Sn)() units with bond distances (Sn,Ga)-Se = 2.471 (2) A ̊ ; Ag-Se = 2.659 (2) A ̊ and ()-Se = 2.314(2) A ̊ . The fundamental difference between this structure and the chalcopyrite one is the anions position: e vs d (Wyckoff notation) respectively. The structure can also be described as I 4 2d coming from an I 4 structure comprised of distorted tetrahedral (Ag)(Ga)Se(Sn)() units disordered in such a way that a 2 ( z= 1 8 ) is generated.

A new family of sheet structures: the oxyselenides formed by a rare earth and a second metal

Sheet structures are observed in oxyselenides formed by La and a second metal of the IIIA- VA groups of the periodical classification. ▪ (LaO) 4Ge 1.5Se 5: orthorhombic cell of the (NdO) 4 Ga 2S 5 type, with disordered arrangement of Ge atoms on the Ga sites. (LaO) 2SnSe 3: orthorhombic pseudo tetragonal cell of the (LaO) 2SnS 3 type. (LaO)SbSe 2: tetragonal cell of the (CeO)BiS 2 type. All this structures are formed by alternating (LaO) sheets and (M xSe y) sheets (M = second metal). The (LaO) sheets are formed by La 4O tetrahedra which share 4 of their 6 edges in a tetragonal or pseudo tetragonal arrangement. The (M xSe y) sheets are formed by 2,3 or 4 layers of Se atoms. The M atoms are only bonded to Se atoms, in octahedral (Sb) or tetrahedral (Ga, In, Ge, Sn) arrangements. Similar compounds are not obtained with the other rare earths. The structure of (LaO)GaSe 2, which is only observed with selenides, is described: the cell is orthorhombic space group P 2 1 ab; a = 5.951(3); b = 5.963(3); c = 12.256(7) Å; Z = 4; d x = 5.84 Mg m −3; M (MoKα) = 31.3 mm −1. The structure was established on single crystal data and refined by a least-squares procedure; the final R value is 0.07 on 523 independent reflections. The structure is formed by alternating (LaO) and (GaSe 2) layers, parallel to the (001) plane.

The interactions of gallium with various buffers and chelating agents in aqueous solution: Gallium-71 and hydrogen-1 NMR studies

The interactions of gallium (Ga) with the ligands, EDTA, NTA, phosphate, lactate, MOPS, TRIS and HEPES are investigated using both 71Ga and 1H nmr measurements. Both EDTA and NTA form strong complexes with gallium, which have a 1:1 stoichiometry. In alkaline solution the tetrahedral Ga(OD) 4 — competes strongly with EDTA in complex formation. In the lactate complex, there are probably three lactates per gallium present. The phosphate complexes of gallium are difficult to characterize on the basis of this investigation. The buffers, MOPS, TRIS, and HEPES, do not interact with gallium significantly. The ability of the ligands to bind gallium correlates well with their ability to inhibit gallium incorporation by L1210 leukemic cells.

Crystal Structure of β-Ga2O3

The crystal structure of β-Ga2O3 has been determined from single-crystal three-dimensional x-ray diffraction data. The monoclinic crystal has cell dimensions a=12.23±0.02, b=3.04±0.01, c=5.80±0.01 A and β=103.7±0.3° as originally reported by Kohn, Katz, and Broder [Am. Mineral. 42, 398 (1957)]. There are 4 Ga2O3 in the unit cell. The most probable space group to which the crystal belongs is C2h3—C2/m; the atoms are in five sets of special positions 4i: (000, ½½0)±(x0z). There are two kinds of coordination for Ga3+ ions in this structure, namely tetrahedral and octahedral. Average interionic distances are: tetrahedral Ga–O, 1.83 A; octahedral Ga–O, 2.00 A; tetrahedron edge O–O, 3.02 A; and octahedron edge O–O, 2.84 A. Because of the reduced coordination of half of the metal ions, the density of β-Ga2O3 is lower than that of α-Ga2O3 which has the α-corundum structure. Also the closest approach of two Ga3+ ions in β-Ga2O3 is 3.04 A which is considerably larger than the closest approach of metal ions in the sesquioxides with the α-corundum-type structure and, in agreement with the results of thermodynamic measurements, the β phase appears to be the structurally more stable one. The average Ga–O distances in the structure seem to account for the fact that although the Ga3+ ion is substantially larger than the Al3+ ion its quantitative preference for tetrahedrally coordinated sites when substituted for Fe3+ ion in the iron garnets is very nearly the same as that of the Al3+ ion. The structure accounts for a recent result obtained by Peter and Schawlow from paramagnetic-resonance measurements on Cr3+-ion-doped β-Ga2O3, namely that the Cr3+ ion substitutes for the Ga3+ ions in a single set of equivalent octahedral sites. The magnetic aspects of the β-Ga2O3 structure are discussed and it is shown that a possible Fe2O3 isomorph could be expected to be at least antiferromagnetic with a Néel temperature of about 700°K Furthermore, a knowledge of the β-Ga2O3 structure and of the nature of site preferences of the Ga3+ and Fe3+ ions in the garnets lead to a prediction regarding the structure of the ferrimagnetic crystals of formula Ga2—xFexO3 recently discovered by Remeika.