IR laser‐induced synthesis of nanostructured gemanium telluride in the gas phase

The gas‐phase synthesis and chemical vapour deposition of nanostructured germanium telluride has been achieved for the first time. The pulsed IR laser irradiation of gaseous CH₃)₄Ge? (CH₃)₂Te? SF₆ mixtures results in homogeneous decomposition of both organometallics and formation of GeTe_x (x = 1, 2). The amorphous GeTe₂ and crystalline GeTe were identified by Raman and X‐ray photoelectron spectroscopy and by electron diffraction. Their formation is explained by an intermediacy of germanium and tellurium clusters and by reaction between these clusters in a hot laser‐induced zone. Copyright © 2005 John Wiley & Sons, Ltd.     

Unusual Solid Solutions in the System Ge‐Sb‐Te: The Crystal Structure of 33R‐Ge4−xSb2−yTe7 (x,y ≈ 0.1) is Isostructural to that of Ge3Sb2Te6

Whereas for a series of layered compounds with the general formula (GeTe)_n(Sb₂Te₃)_m the stoichiometry allows to predict the structure type and the average thickness of the hexagonal atom layers, these rules are not generally applicable for GeTe‐rich compounds like Ge₄Sb₂Te₇. A 39R layer stacking is expected, however, single crystal diffraction studies reveal a 33R layered structure ( , a = 4.1891(5) Å, c = 62.169(15), R = 0.047) closely related to that of Ge₃Sb₂Te₆. This is also corroborated by the average layer thickness that can be determined from the strong reflections of powder patterns and exhibits a direct relation to the structure type. Mixed occupancy of cation positions with Ge and Sb and possibly defects allow this unusual range of homogeneity. Bulk material of the kinetically stable compound can be synthesized by quenching stoichiometric melts of the pure elements and subsequent annealing.     

Bonding Nature of Local Structural Motifs in Amorphous GeTe

Despite its simple chemical constitution and unparalleled technological importance, the phase‐change material germanium telluride (GeTe) still poses fundamental questions. In particular, the bonding mechanisms in amorphous GeTe have remained elusive to date, owing to the lack of suitable bond‐analysis tools. Herein, we introduce a bonding indicator for amorphous structures, dubbed “bond‐weighted distribution function” (BWDF), and we apply this method to amorphous GeTe. The results underline a peculiar role of homopolar Ge? Ge bonds, which locally stabilize tetrahedral fragments but not the global network. This atom‐resolved (i.e., chemical) perspective has implications for the stability of amorphous “zero bits” and thus for the technologically relevant resistance‐drift phenomenon.     

The rotational spectra, potential function, Born-Oppenheimer breakdown, and hyperfine structure of GeSe and GeTe

The pure rotational spectra of 18 and 21 isotopic species of GeSe and GeTe have been measured in the frequency range 5-24 GHz using a Fabry-Pe?rot-type resonator pulsed-jet Fourier-transform microwave spectrometer. Gaseous samples of both chalcogenides were prepared by a combined dc discharge/laser ablation technique and stabilized in supersonic jets of Ne. Global multi-isotopologue analyses of the derived rotational data, together with literature high-resolution infrared data, produced very precise Dunham parameters, as well as rotational constant Born-Oppenheimer breakdown (BOB) coefficients (δ(01)) for Ge, Se, and Te. A direct fit of the same datasets to an appropriate radial Hamiltonian yielded analytic potential-energy functions and BOB radial functions for the X(1)Σ(+) electronic state of both GeSe and GeTe. Additionally, the electric quadrupole and magnetic hyperfine interactions produced by the nuclei (73)Ge, (77)Se, and (125)Te were observed, yielding much improved quadrupole coupling constants and first determinations of the spin-rotation parameters.     

Système AsGeTe: II. Diagramme de phase du système ternaire AsGeTe

The AsGeTe system is formed by three independent triangles, corresponding to the two quasibinary systems GeAsGeTe and As₂Te₃GeTe. The presence of four phases As₂Ge_nTe_3+n (n = 1 to 4) having peritectic decomposition introduces eight ternary peritectic invariants, whose temperatures and compositions are described. The three ternary eutectics have the following characters: E₁, As₁₉Ge₅₂Te₂₉ (662°C); E₂, As₄₂Ge₅Te₅₃ (368°C); E₃, As₂₂Ge₅Te₇₃ (350°C).     

Vapor-liquid-solid and vapor-solid growth of phase-change Sb2Te3 nanowires and Sb2Te3/GeTe nanowire heterostructures

We report the synthesis and characterization of radial heterostructures composed of an antimony telluride (Sb2Te3) core and a germanium telluride (GeTe) shell, as well as an improved synthesis of Sb2Te3 nanowires. The synthesis of the heterostructures employs Au-catalyst-assisted vapor-liquid-solid (VLS) and vapor-solid (VS) mechanisms. Energy-dispersive X-ray spectrometry indicates that Sb and Ge are localized in the Sb2Te3 and GeTe portions, respectively, confirming the alloy-free composition in the core/shell heterostructures. Transmission electron microscopy and diffraction studies show that Sb2Te3 and GeTe regions exhibit rhombohedral crystal structure. Both Sb2Te3 and GeTe grow along the [110] direction with an epitaxial interface between them. Electrical characterization of individual nanowires and nanowire heterostructures demonstrates that these nanostructures exhibit memory-switching behavior.     

Synthesis and characterization of Ge2Sb2Te5 nanowires with memory switching effect

Ge2Sb2Te5 nanowires (NWs) were synthesized by vaporizing GeTe, Sb, and Te precursors assisted by metal catalysts. Current-voltage measurement of the Ge2Sb2Te5 NW device displays fast and reversible switching between two distinct resistive states, which is due to the crystalline-amorphous phase transition nature of these materials     

Stereoelectronic structure of 1-methyl-3-(trichlorogermyl)propionic acid as found by <Emphasis Type="Italic">Ab initio</Emphasis> calculations

Calculations of three structures of the 1-methyl-3-(trichlorogermyl)propionic acid molecule and its dimers were performed at the RHF/6-31G(d) level with the full geometry optimization. According to the calculations, in this molecule in a gaseous state the Ge atom is most likely pentacoordinated due to the Ge←O coordination interaction. The dimerization does not diminish, but slightly increases the strength of Ge←O coordination bond. At the formation of the Ge←O bond the electron density on the oxygen atom increases and on the Ge atom decreases. The comparison of the results of calculations with X-ray diffraction data and with the ³⁵Cl NQR spectrum shows that stereoelectronic structure of this compound in the crystalline and gaseous states are quite different.     

Notizen zum chemischen Transport von Ge mit Gacl3 und zum Nachweis von GeGaCl5,g

Remarks on the Chemical Transport of Ge with GaCl₃ and on the Detection of GeGaCl_5,g Ga has been chemically transported by means of GaCl₃. The gaseous complex GeGaCl₅ has been observed by mass spectroscopy.     

Germanium-Iodine System,Thermodynamic Study assessment and complementary experiments

Literature thermodynamic data (enthalpies, entropies, and heat capacities) of the condensed species GeI₄(s)(I) and GeI₂(s) are revised. Entropies and heat capacities of the gaseous species GeI₄(g), GeI₂(g), and GeI(g) are calculated by the R.R.H.O. method. Published experimental investigations of the equilibria: GeI₄(l) ? GeI₄(g), GeI₄(s) ? GeI₄(g), 2 GeI₂ ? Ge(s) + GeI₄(g), GeI₄ ? GeI₂(g) + I₂(g), GeI₂(s) ? GeI₂(g) and Ge(s) + GeI₄(g) ? 2 GeI₂(g) are discussed. In addition, new measurements of the total pressure above the saturation ranges of the GeI₄(l) and for the reaction: Ge(s) + GeI₄(l) ? 2 GeI₂(g) are performed. Enthalpies of formation of GeI₄(g) and GeI(g) are deduced. Enthalpy of formation of GeI(g) is estimated from the evolution of the dissociation energy D°(Ge? X) (X = Cl, Br, I) against the Z atomic number and from the spectroscopic constants of this molecule. In conclusion a self consistent set of thermodynamic data concerning the germanium-iodine system is proposed.     

Bulk Gas‐Phase Acidity

The capability of a gaseous Brønsted acid HB to deliver protons to a base is usually described by the gas‐phase acidity (GA) value of the acid. However, GA values are standard Gibbs energy differences and refer to individual gas pressures of 1 bar for acid HB, base B^?, and proton H⁺. We show that the GA value is not suited to describe the bulk acidity of a gaseous acid. Here the pressure dependence of the activities of HB, H(HB)_n⁺, and B(HB)_m^? that result from gaseous autoprotolysis have to be considered. In this work, the pressure‐dependent absolute chemical potential of the proton in the representative gaseous proton acids CH₄, NH₃, H₂O, HF, and HCl was worked out and the general theory to describe bulk gas phase acidity—that can directly be compared with solution acidity—was developed.     

Ge[N(SiMe2iPr)2]2: Ein neues Germylen und dessen Koordinationschemie führt zu der kürzesten Ge–Co‐Bindung

Ge[N(SiMe₂iPr)₂]₂: A New Germylene and its Coordination Chemistry leads to the Shortest Ge–Co Bond The high temperature reaction of Germanium with HBr, which is used for the synthesis of GeBr leads at a higher reaction pressure to a mixture of GeBr and GeBr₂. GeBr₂ reacts with the lithiumsalt LiN(SiMe₂iPr)₂ in good yield to the germylene Ge[N(SiMe₂iPr)₂]₂. Subsequent reaction of this germylene with Co₂(CO)₈ leads to the germanium cobalt cluster compound {Co(CO)₃Ge[N(SiMe₂iPr)₂]₂}₂ featuring the shortest Ge–Co bond giving hints to a possibly multiple bonded system.     

The Sections GeSnSb<Subscript>4</Subscript>Te<Subscript>8</Subscript>–GeTe and GeSnSb<Subscript>4</Subscript>Te<Subscript>8</Subscript>–SnTe of the Quasi-Ternary System GeTe–Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>–SnTe

By differential thermal, X-ray powder diffraction, and microstructural analyses and microhardness and density measurements, phase equilibria in the sections GeSnSb₄Te₈–GeTe and GeSnSb₄Te₈–SnTe were studied and their state diagrams were constructed. It was determined that these sections are quasi-binary sections of the eutectic type of the GeTe–Sb₂Te₃–SnTe system. The coordinates of the eutectic points in the sections GeSnSb₄Te₈–GeTe and GeSnSb₄Te₈–SnTe are (40 mol % GeTe, 700 K) and (30 mol % SnTe, 750 K), respectively. Regions of solid solutions based on the initial components in the sections were identified. Alloys in the regions of solid solutions are p-type semiconductors.     

A new high‐pressure strontium germanate,SrGe2O5

The Sr–Ge–O system has an earth‐scientific importance as a potentially good low‐pressure analog of the Ca–Si–O system, one of the major components in the constituent minerals of the Earth's crust and mantle. However, it is one of the germanate systems that has not yet been fully examined in the phase relations and structural properties. The recent findings that the SrGeO₃ high‐pressure perovskite phase is the first Ge‐based transparent electronic conductor make the Sr–Ge–O system interesting in the field of materials science. In the present study, we have revealed the existence of a new high‐pressure strontium germanate, SrGe₂O₅. Single crystals of this compound crystallized as a co‐existent phase with SrGeO₃ perovskite single crystals in the sample recovered in the compression experiment of SrGeO₃ pseudowollastonite conducted at 6 GPa and 1223 K. The crystal structure consists of germanium–oxygen framework layers stacked along [001], with Sr atoms located at the 12‐coordinated cuboctahedral site; the layers are formed by the corner linkages between GeO₆ octahedra and between GeO₆ octahedra and GeO₄ tetrahedra. The present SrGe₂O₅ is thus isostructural with the high‐pressure phases of SrSi₂O₅ and BaGe₂O₅. Comparison of these three compounds leads to the conclusion that the structural responses of the GeO₆ and GeO₄ polyhedra to cation substitution at the Sr site are much less than that of the SrO₁₂ cuboctahedron to cation substitution at the Ge sites. Such a difference in the structural response is closely related to the bonding nature.     

Construction of a novel electrochemical sensor for the determination of tellurium in soil and water samples by Co nanoparticles-modified electrode

ABSTRACT

The spherical Co nanoparticles (Co-NPs) were successfully fabricated through a facile one-step reduction approach. Due to the large specific surface area and excellent electronic conductivity, Co-NPs displayed excellent electrochemical performance and exhibited high sensitivity towards the detection of Tellurium (IV). The electroanalysis of Tellurium (IV) on the modified electrode was investigated by differential pulse anodic stripping voltammetry. The peak currents of Tellurium (IV) increased proportionally within the range of 0.02–1.8 and 1.8–400 mg L^?1 in the 0.1 M H₂SO₄ solution, under the optimal conditions. The detection limit was 0.2 μg L^?1 (S/N = 3). Moreover, the proposed method was successfully applied to determine Tellurium (IV) in real samples with satisfactory results. The Co-NPs/GCE not only showed good reproducibility, stability and anti-interference but also supplied a viable way for designing low toxic, environment-friendly and low-cost sensors to detect Tellurium (IV).     

Gas-phase reactions of free phenylium cations with C3H6 hydrocarbons

Free, unsolvated phenylium ions formed by the spontaneous β decay of a constituent atom of multitritiated benzene have been allowed to react with gaseous propene and cyclopropane in the pressure range from 10 to 700 torr. Phenylium ions attack efficiently both the C-H and the C-C bonds of cyclopropane, yielding respectively tritiated cyclopropylbenzene and indane as the major products. Selective attack of phenylium ions on the π bond of propene is suggested by the composition of tritiated products, isomeric phenylpropenes and isopropylbenzene. The different behavior of propene and cyclopropane toward gaseous phenylium ions is consistent with the results of related radiolytic investigations concerning gaseous systems at nearly atmospheric pressure. The reactivity pattern of the isomeric C₃H₆ hydrocarbons toward gaseous phenylium ions is discussed and compared with pertinent mass spectrometric data.     

Laser‐induced dielectric breakdown in tetramethylgermane/tetramethyltin mixtures: deposition of nanostructured Sn/Ge/C and Ge?Sn/C films

Transversely Excited Atmospheric (TEA) CO₂ laser‐irradiation of gaseous tetramethylgermane (TMG)–tetramethyltin (TMT) mixtures in Ar results in decomposition of both organometallic compounds and in chemical vapour deposition of nanostructured films analyzed by FTIR and Raman spectroscopy, X‐ray diffraction and electron microscopy. They were shown to have similar morphology and elemental composition and constituents dependent on the TMG–TMT ratio. The analyses confirm the presence of nanosized carbon‐rich (graphitic) structures that incorporate C? M and M? M (M ?Ge, Sn) bonds containing an amorphous phase together with crystalline, either β‐Sn or metastable Sn‐rich Ge? Sn alloy. The unique latter constituent is favored at high concentrations of TMG precursor. Copyright © 2010 John Wiley & Sons, Ltd.     

Heteronuclear Complexes of Germanium(IV) and of Some Other 3<Emphasis Type="Italic">d</Emphasis> Metals with Diethylenetriaminepentaacetic Acid

Heteronuclear Ge(IV) complexonates with Co(II), Ni(II), and Zn(II) based on diethylenetri-aminepentaacetic acid (H₅Dtpa) are synthesized for the first time. The composition of the complexes is found from the chemical analysis and thermogravimetry data. The coordination polyhedra of cobalt and nickel are determined by the analysis of the diffuse reflection spectra and effective magnetic moments. Information on the coordination of the polydentate ligand is obtained by the comparative analysis of the IR spectra of the synthesized complexes and previously structurally characterized compounds [Ge(OH)(H₂Dtpa)] · H₂O and [Cu{Ge(OH)(µ-HDtpa)}₂] { 12H₂O.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 8, 2005, pp. 572–575.Original Russian Text Copyright © 2005 by Martsinko, Seifullina, Verbetskaya.     

Chemischer Transport von Eisensulfid. III. Der Transport von Bodenkörpern der Zusammensetzung FeS1,00

Chemical Transport of Iron Sulphide. III. The Transport of Solids of the Composition FeS_1,00 It is possible to transport FeS_1,0 using such transport systems, in which S₂ and other sulphur-consisting gaseous species exist, for instance H₂S or some metal sulphides. The systems Fe/S/H/halogene and Fe/S/Ge (Sn)/halogene are studied experimentally and theoretically. The role of the influence of the solid composition upon the gas phase equilibria and the transport behaviour is discussed concerning a solid of the type AB_x.     

Galvanic solid electrolyte cells for the measurement of CO<Subscript>2</Subscript> concentrations

The first commercially offered CO₂ sensors with galvanic solid electrolyte cells have very different properties. A review of the numerous carbonate cells described in the literature shows that it is easy to obtain CO₂-sensitive systems with Au, Na₂CO₃ measuring electrodes. The problems of obtaining reproducible CO₂ sensors with long-term stability mainly concern the reference electrode. Only electrodes composed of pure solid substances, stable under the operational conditions, promise the desired properties. Reference electrodes with the oxides of Mo, W, Sn, Ti, Si and Ge have been tested, with different degrees of success. With silica and sodium silicate on β-alumina, a CO₂ sensor results that can be used also in reducing gas phases and without calibration because the evaluation of the signals is possible by a thermodynamically precalculated equation. The volatility of Na₂CO₃ is presumably caused by the vapor pressure of thin layers of the creeping substance and by the formation of gaseous Na₂(OH)₂. The properties of Na₂CO₃ are particularly unfavorable for planar sensors. The sensor signals are independent of the partial pressure of O₂ and H₂O, but the participation of O₂ in the electrode reactions causes cross sensitivities not only for carbon-containing gases but also, for example, for NH₃ and H₂. The cross sensitivities against halogens and SO₂ are irreversible. At sudden changes of the CO₂ concentration the sensor signal follows within less than a few seconds, but questions remain concerning the observable differences in the response times of differently arranged sensors. The response times are highly important for a sensor arrangement that is aimed at simultaneous measurements of CO₂ and O₂ in real time for each breath.