In-situ HEED structure analysis of AlNx films grown by the simultaneous use of a radical beam source and ICB technique

A reactive ionized cluster beam technique (RICB) which was composed of a conventional ICB source and a radical beam source has been used to deposit stable and metastable polycrystalline AlN_x (0≤x≤1) films. Using in-situ high energy electron diffraction (HEED) at grazing incidence geometry, crystallographic properties such as structure, preferred orientation and interplanar dspacing values were determined and the relation to deposition parameters investigated. It could be shown that the simultaneous use of the ICB technique and a radical beam source to separately control the kinetic energy of the Al ions and the dissociation rate of molecular nitrogen, allows AlN films to be deposited with variable composition and crystal structures. In-situ HEED used in the transmission mode is an effective tool to investigate the crystallography of growing compound films such as AlN_x.     

The antiferromagnetic and ferrimagnetic properties of iron selenides with NiAs-type structure

The magnetic properties of the NiAs-type iron selenides have been investigated by susceptibility measurements between 100 and 450 K. Hexagonal -Fe_1-x Se exhibits both antiferromagnetism and ferrimagnetism depending on composition. For antiferromagnetic alloys with 0.02x0.10 (50.5 to 52.5 at % Se) the transition to the paramagnetic state is assumed to occur in the unstable range between room temperatur and about 573K. Ferrimagnetism is observed at compositions near Fe₇Se₈ (0.10x0.16; 52.5 to 54.3 at % Se) withCurie temperatures varying only slightly with composition. In Fe₇Se₈ the ferriparamagnetic transition is observable at 453 K. The characteristic discontinuities in the magnetization curves of Fe₇Se₈ in both superstructures (3c, 4c) are related to the rotation of the magnetic moments from a direction close to [001] into (001).The antiferromagnetism of Fe_0.89Se (52.8 at % Se) changes abruptly into ferrimagnetism when the temperature is raised above 160 K. The similar abrupt changes of the magnetic susceptibilities in the antiferromagnetic region are possibly associated with a crystallographic transformation. In the range of monoclinic -Fe_1-x Se with 0.24x0.36 (56.8 to 61.0 at % Se) only Fe₃Se₄ is ferrimagnetic above room temperature; alloys containing more selenium are ferrimagnetic far below room temperature. In Fe_0.69Se (59.1 at % Se) the transition from ferrimagnetism to paramagnetism was observed at 145 K. The saturation magnetization and the magnetic moments obtained from neutron diffraction are compared with values calculated from a simple ionic model.

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Die antiferromagnetischen und ferrimagnetischen Eigenschaften von Eisenseleniden mitNiAs-Struktur

Zusammenfassung Die magnetischen Eigenschaften von Eisenseleniden mit NiAs-Struktur wurden mittels Suszeptibilitätsmessungen zwischen 100 und 450 K untersucht. Hexagonales -Fe_1-xSe zeigt abhängig von der Konzentration sowohl Antiferromagnetismus als auch Ferrimagnetismus. In antiferromagnetischen Legierungen mit 0,02x0,10 (50,5 bis 52,5 At % Se) verläuft die Umwandlung in den paramagnetischen Zustand im nichfstabilen Bereich zwischen Raumtemperatur und 573 K. Ferrimagnetismus wurde in der Nähe von Fe₇Se₈ (0,10x0,16; 52,5 bis 54,3 At % Se) beobachtet mitCurietemperaturen, die sich nur wenig mit der Konzentration ändern. Fe₇Se₈ zeigt die ferri-paramagnetische Umwandlung bei 453 K. Die charakteristischen Diskontinuitäten der Magnetisierungskurven von Fe₇Se₈ in beiden Überstrukturen (3fache und 4fachec-Achse) hängen mit der Drehung der magnetischen Momente aus einer [001]-nahen Richtung in die (001)-Ebene zusammen. Der Antiferromagnetismus von Fe_0,89Se (52,8 At % Se) geht bei 160 K sprunghaft in Ferrimagnetismus über. Ähnliche sprunghafte Änderungen der magnetischen Suszeptibilitäten im antiferromagnetischen Bereich sind möglicherweise mit einer kristallographischen Umwandlung verbunden. Im Phasenbereich von monoklinem -Fe_1-x Se mit 0,24x0,36 (56,8 bis 61,0 At % Se) ist einzig Fe₃Se₄ oberhalb Raumtemperatur ferrimagnetisch; Legierungen mit mehr Selen sind weit unterhalb Raumtemperatur ferrimagnetisch. In Fe_0,69Se (59,1 At % Se) wurde der Übergang von Ferri- zu Paramagnetismus bei 145 K beobachtet. Die Sättigungsmagnetisierung und die magnetischen Momente aus Neutronenbeugungsexperimenten wurden mit Werten verglichen, die mit einem einfachen ionischen Modell berechnet wurden.

     

Phase Equilibria in the System CuO-Fe2O3-Sb2O4-O2

Results of X-ray phase analysis were used to construct the phase diagram of the system CuO-Fe₂O₃-Sb₂O₄-O₂ at 1000°C in air. Two Cu_2x Fe_4-3x Sb _x O₆ solid solutions (0 x 0.154 and 0.923 x 1) of, respectively, hematite and bixbyite structure were identified.     

Hydrophile-lipophile balance of alkyl ethoxylated surfactants as a function of intermolecular energies

Summary The semiempirical MNDO method has been used in order to examine the variation of the molecular properties of hydrocarbons C_nH_2n+2 (with 1n19) and ethylene oxide chains CH₃(CH₂CH₂O)_mCH₃ (with 1m19) as a function of their molecular length. Least-square fits of those properties have been calculated, along with two mathematical relations between the hydrophile-lipophile balance of alkyl-phenol ethoxylated surfactants and (1) the ratio of molecular lengths between their lipophilic and hydrophilic branches; (2) the intermolecular energies between the molecules of surfactant, water and hexane.     

Metallreiche Phasen im ternären System Ni-Se-Te

Zusammenfassung Die metallreichen Phasen im System Ni-Se-Te wurden durch Röntgenaufnahmen bei Zimmertemp. und bei höheren Temperaturen sowie durchDTA untersucht. Bei Zimmertemp. wurden im pseudo-binären Schnitt Ni₃(Se_1-x , Te _x )₂ Phasen mit den folgenden Strukturen gefunden: rhomboedrischer Ni₃S₂-Typ fürx=0; tetragonaler (Ni,Fe)₁₁Se₈-Typ für 0,15x0,35; tetragonaler Rickardit-Typ für 0,50x0,80; Überstrukturen des Rickardit-Typs für 0,95x1. Bei höheren Temperaturen verbreitert sich das Homogenitätsgebiet der Phase mit der tetragonalen Rickardit-Struktur. Über 600–770°C tritt im ganzen Gebiet 0x1 eine kubisch.

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Metal-rich phases in the ternary system Ni-Se-Te

The metal-rich phases in the system Ni-Se-Te have been studied by X-ray diffraction at room temperature and elevated temperatures, and byDTA. At room temperature phases with the following structures were found in the pseudo-binary section Ni₃(Se_1-x , Te _x )₂: rhombohedral Ni₃S₂ type forx=0; tetragonal (Ni,Fe)₁₁Se₈ type for 0,15x0,35; tetragonal rickardite type for 0,50x0,80; superstructures of the rickardite type for 0,95x1. At higher temperatures the homogeneity range of the phase with the tetragonal rickardite structure broadens. Above 600–770°C a face-centered cubic phase exists in the whole range 0x1; a model for the structure of this phase is proposed. The compound Ni_2,6Te₂ is orthorhombic at room temperature; it becomes hexagonal at 720°C and disproportionates at 820°C; by partial substitution of Te by Se the hexagonal form is stabilized at room temperature. Similarly, the compound Ni₆Se₅ which is stable above 440°C only, is stabilized at room temperature by partial substitution of Se by Te. The phase Ni₆(Se_1-x , Te _x )₅ decomposes by a peritectoid reaction at 650° (x=0) to 590°C (x=0,3).

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Herrn Prof. Dr.H. Nowotny gewidmet.     

Trapping of Transformation Products of a Palladium Catalyst for Ammonia Oxidation by a Calcium Oxide Absorbent

The chemical regularities of trapping palladium and its compounds lost in the process of high-temperature ammonia oxidation by a calcium oxide absorbent are studied. In the interaction with the absorbent, the products of palladium catalyst transformation form CaPd₃O₄, which is a derivative of the nonstoichiometric intercalation compound Ca _x Pd₃O₄, where 0 x 1. Physicochemical properties of this compound and the conditions of its formation are considered.     

1A1⇔5T2 Spin Transition in Heterometallic Solid Phases FexNi1-x(Htrz)3(NO3)2 · H2O (Htrz = 1,2,4‐Triazole)

Solid phases Fe_xNi_1-x(Htrz)₃(NO₃)₂ · H₂O (0.4 x 0.8$) and Ni(Htrz)₃(NO₃)₂ · H₂O were synthesized and studied. The phases were studied by means of magnetochemistry, powder Xray difraction analysis, and electronic and IR spectroscopy. The heterometallic phases are described by the stoichiographic method of differentiating dissolution (DD). The values of x were determined by two methods — atomic absorption and DD. Magnetochemical data showed that the solid phases exhibit a hightemperature ¹A₁ ⁵T₂ 0.5 x 0.8 and disappears at x = 0.4. The spin transition is accompanied by thermochromism (color changed from pink to white at 0.6 x 1 and from pink to light lilac at x = 0.5). A decrease in x leads to a decrease in the temperature of the forward (under heating T_c ) and reverse (under cooling T_c ) transitions, a decrease in hysteresis value ( T_c), and a smearing of the spin transition.     

Thermal Expansion of Mixed Zirconium Phosphates

A series of framework phosphates with varied ratio of cations Na_5-2x B _x ^IIZr(PO₄)₃, B^II = Mg, Ca, Sr, Ba (0 x 2) and Na_5-3x Fe _x Zr(PO₄)₃ (0 x 1.33) were synthesized and studied under heating. The coefficients of thermal expansion along crystal axes _a and _c were calculated, and their dependences on the cationic composition (nature and concentration) and on the occupancy of out-of-framework structural positions were established.     

Sol-Gel Preparation of Silica Films with Controlled Surface Morphology and Their Application to a Low Reflective Glass

Silica coating films with various surface morphologies, such as flat, porous (with deep pores), concave-convex (with hills and valleys), and convex (with hills on flat plane) structure were prepared from a mixture of two kinds of sols derived from polymerized tetraethoxy-silane (TEOS) and methyltriethoxysilane (MTES). Different surface morphologies were obtained by varying the molar ratio r = MTES/TEOS of the coating solution. The surface was flat for r less than 2.5, porous for 2.5 r < 5, concave-convex for 5 r < 7.5, convex for 7.5 r < 13, and again flat for r larger than 13. For 2.5 r < 5, the apparent refractive index of the silica film with porous morphology was decreased to 1.23 by selecting the solvent and by controlling the relative humidity of the coating atmosphere and the heat treatment temperature. Coating of glass with silica films of low refractive index of 1.23 led to the low reflective glasses with visible light reflectance Rvis of less than 0.2%.     

Effect of Cation Nonstoichiometry on the Properties of Solid Electrolyte Ba x Ce0.97Nd0.03O3 - δ (0.90 ≤ x ≤ 1.10)

The effect of the cation nonstoichiometry on the electroconduction, electrotransfer, and stability in humid air of solid proton-conducting electrolyte Ba _x Ce_0.97Nd_0.03O_{3 -} (0.90 x 1.10) is studied. The electroconduction is found to decrease with decreasing content of BaO (x 1.0) and weakly depend on the BaO excess (x> 1.0). Ceramics of a stoichiometric composition (x = 1) and with lack of barium is stable when stored in humid air at room temperature, as opposed to the ceramics with barium excess, which rapidly decomposes in these conditions. The conduction of materials under study in oxidizing environment is ion-hole and in reducing media, ionic (proton + oxygen). The cation nonstoichiometry barely affects the nature of the ion transfer. An analysis of possible models for the formation of defects shows oxygen vacancies to be always present in Ba _x Ce_0.97Nd_0.03O_{3 -} , even at the CeO₂ excess exceeding the content of neodymium.     

Hydrolysis of Protactinium(V). III. Determination of Standard Thermodynamic Data

Hydrolysis constants of protactinium(V) at tracer scale were deduced from the variations of partition coefficient of Pa(V) in the system: TTA/toluene/Pa(V)/H₂O/H⁺/Na⁺/ClO^– ₄, as a function of TTA and proton concentrations, ionic strength (0.1 3 M), and temperature (10 60°C). Extrapolations of theses constants to zero ionic strength were performed using the SIT model. Standard thermodynamic data (under atmospheric pressure) related to the two hydrolysis equilibria involved, were derived from the temperature dependence of the hydrolysis constants at infinite dilution.     

Physikalisch-chemische Eigenschaften der Halbleiter im System GeS x Se1−x

Specimens of the system GeS _x Se_1–x were examined by means of X-ray and differential thermal analysis for 0x1. The activation energy of the specimens was calculated according to a semi-empirical method on the basis of the known thermodynamic parameters of the components.

     

Optimizing Instrumental Neutron Activation Analysis of Extraterrestrial Materials: Fragments of Lunar Rocks, Meteorites, Chondrules, and Ultrarefractory Inclusions

A previously developed approach to the optimization of instrumental neutron activation analysis based on the simulation of gamma spectra of samples of the specified composition was extended to the analysis of samples of cosmic origin differing in chemical composition, including samples of small mass (0.01 mg) and dimensions (100 m). The approach was justified by comparing the results obtained with the published data.     

18O-isotope exchange behavior and oxidation activity of La1-xSrxMnO3+δ

Different preparation routes derived both from the usual high-temperature solid state synthesis and the sol-gel process were applied for the synthesis of crystalline La_1-xSr_xMnO₃₊ phases with 0x 0.2. They were investigated by means of temperature programmed isotope exchange (TPIE) under various conditions. The ¹⁸O isotope exchange experiments yielded information on the dependence of the oxygen mobility on temperature and the Mn⁴⁺/Mn³⁺ratio. Both are related to the defect structure of the solid. TPIE was applied for studying the interaction between ¹⁸O₂ and CH₄ under static conditions and was compared with results obtained from catalytic investigations, i.e. the behavior of La_1-xSr_xMnO₃₊ (0x0.2) in both CO and CH₄ oxidation with normal oxygen ¹⁶O₂ under steady flow conditions.This revised version was published online in November 2005 with corrections to the Cover Date.     

Some remarks on the solubility of gases in liquid long-chainn-alkanes andn-alkan-1-ols

The Ostwald coefficients L_2,1 of He, Ne, Ar, Kr, Xe, N₂, O₂, CH₄ CF₄ and SF₆ dissolved in several homologous_n-alkanes,_n-C₁H₂₁₊₂, 6l16, andn-alkan-1-ols,n-C₁H₂₁₊₁OH, 1l11, were recently measured at 298.15 K and atmospheric pressure with a modified Ben-Naim/Baer apparatus. Altogether, 201 gas/liquid systems were investigated. For about half of these systems, both pressure control and measurement of the volume of gas dissolved in a given volume of solvent were achieved with a microprocessor. This improved medium-precision instrument (0.5% in most cases) combines easy handling with fully automated data retrieval, and is totallymercury-free. In this communication, the salient points of data reduction are presented, with the focus on the estimation of several important auxiliary quantities such as second virial coefficients and partial molar volumes at infinite dilution. The effect of the chain lengthl of then-alkane or then-alkan-1-ol upon solubility is demonstrated, and some correlations betweenL _2,1, or the derived Henry fugacitiesH _2,1, and appropriate molecular and/or bulk properties of the gases and the solvents are discussed.     

Triterpene Glycosides of Astragalus and Their Genins. LXI. Occurrence of Cycloartane 6-O-Monodesmosides

Cyclosiversigenin 6-O--L-rhamnopyranoside and 6-O--D-glucopyranoside were isolated fromAstragalus coluteocarpusBoiss. (Leguminosae) andAstragalus dissectusB. Fedtsch. et N. Ivanova, respectively. Cyclosiversigenin 5-O--L-rhamnopyranoside was shown to be an artifact forAstragalus coluteocarpus.Thus, the cyclosiversigenin 6-O--D-glucopyranoside that was isolated from certainAstragalusspecies is hypothesized also to be an artifact. Glycosylation of the 6 -hydroxyl group of cycloartanes by D-glucose and D-xylose, in contrast with other substituents, does not change the low-field position of the PMR signal of the 4-CH ₃ group (1.65 2.01 ppm) that is caused by the influence of deuteropyridine directly on the 6 -hydroxyl. Obviously one of the hydroxyls of the -D-glucopyranoside or -D-xylopyranoside residues has the same effect in this instance.     

Erbium-Activated Silica-Titania Planar Waveguides

(100 – x)SiO₂-(x)TiO₂-ErO_3/2 planar waveguides, with 7 x 20 have been prepared by sol-gel route using the dip-coating technique. The thickness of the films was optimized to support a single propagating mode at 1550 nm, with a confinement coefficient higher than 0.75. The process of densification of the gel and the devitrification with the growth of TiO₂ nanocrystals were studied by Raman scattering. Devitrification is important only for x 15, but it was not possible to obtain full densification of the samples, even at the lowest TiO₂ content, without the appearance of nanocrystals.Emission in the C telecom band was observed; the spectral width of the ⁴I_13/2 ⁴I_15/2 transition of Er³⁺ slightly increases with the titania content. For x 12 most of Er³⁺ ions (about 65%) decay exponentially with a lifetime of about 8 ms.     

Kinetics of acid and base catalysed hydrolysis ofcis-α- andcis-β2-[Co(trien)(aniline)Cl]2+ cations

Summary The rate of hydrolysis of the title cations obey the rate law:-d ln[Complex]/dt=k_obs=k₀+k₁[OH^–] in the range: 1pH3. The rate and activation parameters for acid and base hydrolysis (k₀ and k₁ paths respectively) are reported in the 40–60 °C range.     

Reactions of 1-Cyanoimidazoles with Phenols

Phenols with pK _a 7 react with 1-cyanoimidazole and 1-cyano-2-methylimidazole to give addition products at the cyano group; phenols with pK _a 1 give rise to the corresponding quaternary salts, 1-cyanoimidazolium phenolates; phenols with pK _a 4 do not react with 1-cyanoimidazoles.     

Positron annihilation studies in YBa2Cu3O x (6<x≤7)

Positron lifetime and Doppler broadening of the annihilation line measurements, as a function of temperature between 14 and 300 K, have been performed on four YBa₂Cu₃O _x (6<x7) samples with different oxygen deficiency. It was found that the positron lifetime and theS parameter values increase as the oxygen deficiency increases in the YBa₂Cu₃O _x (6<x7) samples. It was also observed that the positron annihilation parameers show different temperature dependence in the YBa₂Cu₃O _x (6<x7) samples associated with their different oxygen deficiency.