X-ray photoelectron spectroscopic studies on oxidation behavior of nickel and iron aluminides under oxygen atmosphere at low pressures

Oxidation behaviors of NiAl, Ni₃Al, and FeAl under oxygen atmosphere at low pressures were studied by X-ray photoelectron spectroscopy (XPS). Clean surfaces of these aluminides were prepared by fracturing in an ultra high vacuum, and then the fractured surfaces were oxidized by exposing to high-purity oxygen at pressures up to 1.3 Pa without exposing to air. The oxides formed on NiAl and FeAl surfaces were Al₂O₃, whereas the oxide on Ni₃Al was NiAl₂O₄. Aluminum, nickel, and iron on clean surfaces were oxidized even at a pressure of 1.3 × 10⁻⁶ Pa. The oxidation evolves with an increase in the pressure of oxygen, and further oxidation of aluminum occurs prior to that of nickel or iron. The oxidation behaviors under such oxygen atmosphere were similar to those of the aluminides oxidized in air, and these behaviors could be predicted from thermodynamic consideration.     

An X-ray photoelectron spectroscopic study of some nickel (II) amine complexes

The X-ray photoelectron (XPS) spectra of several Ni(II) diamine complexes, a Ni(II) triamine complex and several Ni(II) diimine complexes are reported in terms of the Ni 2p, Cl 2p and N 1s core level binding energies. Theoretical models are presented to account for the quadratic relationship observed between XPS Ni 2p_{$\text{3}\text{2}$}binding energy shifts and the N-H infrared rocking frequency as related to these complexes. On the basis of this correlation, it is possible to discriminate between free counter-ions coordinated to the metal or involved in cluster-ion formation. Individual XPS data for these complexes are interpreted in terms of the intrinsic nature of the metal environment and an attempt is made to calculate the metal and donor nitrogen atomic charges for selected complexes.     

Crystal structure of simple metals at high pressures

The effects of pressure on the crystal structure of simple (or sp-) elements are analysed in terms of changes in coordination number, packing density, and interatomic distances, and general rules are established. In the polyvalent elements from groups 14–17, the covalently bonded structures tend to transform to metallic phases with a gradual increase in coordination number and packing density, a behaviour normally expected under pressure. Group 1 and 2 metallic elements, however, show a reverse trend towards structures with low packing density due to intricate changes in their electronic structure. Complex crystal structures such as host–guest and incommensurately modulated structures found in these elements are given special attention in this review in an attempt to determine their role in the observed phase-transition sequences.     

Elastic phase transitions in metals at high pressures

The elastic phase transitions of cubic metals at high pressures are investigated within the framework of Landau theory. It is shown that at pressures comparable with the magnitude of the bulk modulus the phase transition is connected with the loss of stability relative to uniform deformation of the crystalline lattice. Discontinuity of the order parameter at the transition point and its equilibrium value are expressed through the second-?to fourth-order elastic constants. The second-,third-?and fourth-order elastic constants and phonon dispersion curves of vanadium under hydrostatic pressure are obtained by first-principles calculations. Structural transformation in vanadium under pressure is studied using the obtained results. It is shown that the experimentally observed at P?≈?69?GPa phase transition in vanadium is the first-order phase transition close to a second-order phase transition.     

Formation of transition metal hydrides at high pressures

Silane (SiH₄) is found to (partially) decompose at pressures above 50 GPa at room temperature into pure Si and H₂. The released hydrogen reacts with surrounding metals in the diamond anvil cell to form metal hydrides. A formation of rhenium hydride is observed after the decomposition of silane and reaction of hydrogen with Re gasket. From the data of a previous experimental report [M.I. Eremets, I.A. Trojan, S.A. Medvedev, J.S. Tse, Y. Yao, Science 319 (2008) 1506], the claimed high-pressure metallic and superconducting phase of silane is identified as platinum hydride, that forms after the decomposition of silane. These observations show the importance of taking into account possible chemical reactions that are often neglected in high-pressure experiments.     

Influence of impurities on the metallization of inert gases at high pressures

It is shown that the introduction of heavy inert gas impurities into the condensed phase of a lighter inert gas can significantly change the kinetic properties of the latter at high pressures. The electronic structure of the ordered Ar₁₅Xe solid solution is calculated. Doping of the condensed phase of a light inert gas with atoms of a heavier inert gas may become a new convenient tool in high-pressure experiments.     

High resolution X-ray diffraction studies at high pressures

Abstract

The principal sources of systematic error in high-pressure x-ray structure determination with a diamond anvil cell have been studied in detail. The results of these studies have been used to develop techniques to minimise or correct for these effects.     

Laboratory set-up for X-ray diffraction at high pressures

We describe here a simple set-up for X-ray diffraction under high pressure using a diamond anvil cell employing a sealed tube. The set-up works in angular dispersive geometry and is built using rather common components that are available in a research laboratory. We show that using this set-up one can routinely acquire good-quality data for the determination of structural properties under pressure and the equations of state. Technical details are presented along with examples of experimental results for sodium chloride and LiV₂O₄.     

Phase transition of ZnS at high pressures and temperatures

The high-pressure behaviour of zinc sulphide, ZnS, has been investigated, using an in situ X-ray powder diffraction technique in a diamond anvil cell, at pressures and temperatures up to 35 GPa and 1000 K, respectively. The pressure-induced phase transition from a zincblende (B3) to a rocksalt (B1) structure was observed. This transition occurred at 13.4 GPa and at room temperature, and a negative dependence on temperature for this transition was confirmed. The transition boundary was determined to be P (GPa) = 14.4 ? 0.0033 × T (K).     

On some hydrogen bond correlations at high pressures

Structural data from in situ high pressure neutron diffractions studies are analysed to show that the measured lengths of O?H and H---O pairs in hydrogen bonds follow the correlation between them established from 0.1 MPa data on different chemical compounds. In particular, the accepted view in literature that the high pressure data on ice VIII differ from it is not supported. For compounds in which the O?H stretching frequencies red shift under pressure, it is shown that wherever structural data is available, they follow the stretching frequency versus H---O (or O---O) distance correlation. For compounds displaying blue shifts with pressure, an analogy appears to exist with ‘improper’ hydrogen bonds. Another pressure effect expected is the symmetrization of a hydrogen bond with evolution of the double-welled, hydrogen bond potential into a single-well potential. Using the results from some recent ab initio electronic structure studies, we show that the bulk modulus shows a discontinuity at this point and this can be taken as signature for hydrogen bond symmetrization. This is supported by analysing a few available experimental data.     

Effect of spin crossovers on the Mott-Hubbard transition at high pressures

The effect of spin crossovers in d _n terms on the effective Hubbard parameter (U _eff) determining the gap between the lower and upper Hubbard bands is analyzed using a many-electron approach to describe the electron structure of Mott insulators. A new mechanism of the insulator-metal transition is established for d ⁵ ions, which is related to a decrease in U _eff caused by spin crossover. For other ions, the U _eff value is either independent of pressure (d ², d ⁴, d ⁷) or it exhibits nonmonotonic growth (d ³, d ⁶, d ⁸).     

Site occupation of CO adsorbed on Ni(100) at high CO pressures

The adsorption of CO on Ni(100) has been investigated by infrared reflection-absorption spectroscopy in the temperature range of 85 to 300 K. At 300 K we achieved CO coverages up to 0.8 ML by applying CO pressures up to 1 mbar. The fraction of CO molecules adsorbed at terminal and bridge sites on Ni(100) at a fixed temperature depends strongly on the total CO coverage. The variation of the adsorption site occupancy with coverage is well reproduced by a lattice-gas model which takes into account the lateral interaction of the adsorbed molecules.     

Magnetic study of some liquids and gases adsorbed on polymers

The paper reports on the measurements of magnetic susceptibility of methylalcohol and toluene adsorbed on polypropylenes of two different molecular masses PP 5056, PP 5078, polyethylene-terephtalate and cellulose. The measurements were carried out for the full range of covering, possible at room temperature, and comparison with the additivity law was made in the whole range of concentrations. With the exception of methylalcohol in PP 5078, all samples showed noticeable deviations from linearity in the dependence of susceptibility on the percentual share of the adsorbate, the deviations were towards decreasing diamagnetism. Polyethyleneterephtalate with methylalcohol showed contradictory results. The measurements were completed with a magnetic study of adsorption of natural air and pure oxygen on cellulose and PP 5506.As far as the interpretation is concerned, the measurements of magnetic susceptibility are in good agreement with experiments on high resolution nuclear magnetic resonance (NMR). From the experimental results the authors draw up conclusions as to the character of mutual interaction of polymers with given adsorbates, to the location of an adsorbed molecule on the polymer surface, and to the contribution of Van Vleck polarization paramagnetism and other susceptibility components on the experimental results.Toluene C₆H₅.CH₃, adsorbed on polypropylene, showed two more peaks beside a NMR signal of C₆H₅; they were identified as the signals of CH₃ adsorbed on non-equivalent parts of a polypropylene macromolecule.     

X-ray photoelectron study of some silicon-oxygen compounds

More than fifty specimens of silicon-oxygen compounds have been studied by X-ray photoelectron spectroscopy. Due to the insulating properties of these specimens the measured binding energies of the various atomic levels were corrected using the C (1s) line due to hydrocarbon contamination as a reference. A statistical treatment of the experimental results has been used to verify the validity of the reference and to discuss the differences in binding energy of the Si (2p) line in various samples. Three different steps of oxidation have been found for silicon; the chemical shifts with respect to unoxidised silicon are 3.2, 4.1 and 5.0 eV for surface oxidised silicon, silicates and quartz, respectively. The influence of atoms other than oxygen in the neighbourhood of silicon, such as fluorine or alkaline cations is discussed.     

X-ray diffraction and Raman spectra of merrillite at high pressures

ABSTRACT

The compressibility and effect of pressure on the vibrations of merrillite, Ca₉NaMg(PO₄)₇, were studied by using diamond anvil cell at room temperature combined with in-situ synchrotron X-ray diffraction and Raman spectroscopy up to about 18 and 15?GPa, respectively. The pressure-volume data was fitted by a third-order Birch–Murnaghan equation of state to determine the isothermal bulk modulus as K₀ ?=?87.2(32) GPa with pressure derivative K₀′?=?3.2(4). If K₀′?=?4, the isothermal bulk modulus was obtained as 81.6(10) GPa. The axial compressibility was estimated and an axial elastic anisotropy exists since a-axis is less compressible than the c-axis. The Raman frequencies of all observed modes for merrillite continuously increase with pressure, and the pressure dependences of stretching modes (v ₃ and v ₁) are larger than those of the bending modes (v ₄ and v ₂) and external modes. The isothermal mode Grüneisen parameters and intrinsic anharmonicity of merrillite were also calculated.     

An X-ray photoelectron spectroscopic study of some bis(diamine)-copper (II) complexes

XPS data for a series of octahedral copper(II) diamine tetrafluoroborate and perchlorate complexes are interpreted in the following terms; (i) the inductive effect of diamine substituents; (ii) the degree of cation-anion interaction; (iii) the effect of progressive increase in diamine chelate ring size; and (iv) the Jahn-Teller effect in these complexes.