Application of INAA and XRF to the analysis of a basic alkaline rock

A study of a basic alkaline rock has been carried out using instrumental neutron activation (INAA), X-ray fluorescence (XRF) and wet chemical analyses techniques. Elemental composition and major oxides have been reported. The rock is found to be rich in K₂O, Na₂O, MgO, CaO, Al₂O₃, and Ti–Fe minerals. The transition elements are also fairly concentrated in the rock. The analyses show the igneous nature of the rock from a high potassic origin.     

ESCA study of fractional monolayer quantities of chemisorbed gases on tungsten

X-ray photoelectron spectroscopy (ESCA) has been used in a study of CO and O₂ chemisorbed on a polycrystalline tungsten sample. Working under ultra-high vacuum conditions, the surface was cleaned and then covered with known monolayer and fractional monolayer quantities of adsorbed CO and O₂. The O(ls) and C(ls) spectral features were detected, and the influence of an adsorbed layer on the tungsten spectral features was determined. A chemical shift of 3.4 eV in the O(ls) line from chemisorbed CO is related to the different modes of bonding of CO to tungsten. A model calculation of the photoelectron yields expected from an adsorbed monolayer is in good agreement with the experimental results.     

Structure of H(D)TaO3 determined by powder X-ray and neutron diffraction

Pure crystalline samples of HTaO₃ and DTaO₃ have been prepared. The crystal structure has been solved using powder X-ray and neutron diffraction (at 2 K and room temperature) and has been shown to consist of Ta(O,OH)₆ octahedra sharing vertices with the oxygen atoms displaced toward the vacant perovskite A sites. The compound is isomorphous with HNbO₃, D_xWO₃, and D_xReO₃ and contains hydrogen atoms as hydroxide groups.     

Plasma reactions of self-assembled monolayers to model oxygen atom effects on polymers

The plasma treatment of self-assembled monolayers of octadecyl mercaptan on gold substrates has been investigated as a model for oxygen atom effects on polymers. Both O₂ and H₂O low pressure gas plasmas have been used. X-ray photoelectron spectroscopy has revealed that the two plasma treatments differ from each other in the extent of oxidation and etch rate with O₂ being the more aggressive plasma. The results have confirmed that the plasma modification of organic surfaces involves a balance between surface oxidation and surface etching. The well-defined structure of the monolayer enables quantitation of these atom-substrate reactions. © 1998 John Wiley & Sons, Ltd.     

Evidence for the two-dimensional hybridization in Na0.79CoO2 and Na0.84CoO2

The electron density distributions of Na_0.79CoO₂ and Na_0.84CoO₂ have been obtained by the maximum entropy method and the Rietveld analysis using powder X-ray diffraction data at room temperature. In the Rietveld refinement, there are good agreement between x=0.79(4) and x=0.84(9), except for (008) and (108) peaks. The deviations of the two reflections are very large relative to those of other reflections, and the change in X-ray diffraction data is clearer than that in neutron diffraction data. This indicates that electron density distributions in Na_xCoO₂ are slightly modulated with increasing x. In fact, there are an obvious overlapping of the electron density between Co and O due to the Co–O hybridization in the CoO₂ layer, but the two-dimensional networks in the electron densities of x=0.84(9) are suppressed by the existence of the O–O network on (008) plane. This is direct evidence of decrease of two-dimensional hybridization in the CoO₂ layer with increasing a sodium content.     

Preliminary synchrotron radiation characterization of first multilayer mirrors for the soft X-ray water window

The development of high-reflectivity devices for soft X-rays at quasi-normal incidence is a challenging research for the development of synchrotron radiation optics, particularly for soft X-ray microscopy and X-ray microprobe spectroscopy. Here we present data concerning the deposition of the first Ni/Ti and Ni/TiO₂ multilayers grown at the INFN Legnaro Laboratories (LNL). These multilayers have a lattice spacing in the order of 14 Å and more than 100 of bilayers. Experimental tests on these multilayers have been performed by a vacuum compatible θ–2θ reflectometer, set up at the INFN Frascati Laboratories (LNF), where their characterization has been accomplished by means of synchrotron radiation.The first multilayer mirrors tailored in order to work at quasi-normal geometry have been measured in the lower X-ray energy domain using both white-beam and monochromatic radiation at about 1 keV.     

The structure of the lithium-inserted metal oxide δLiV2O5

Employing neutron and X-ray powder diffraction analysis we have found that the compound at composition LiV₂O₅ formed at ambient temperature on insertion of Li into V₂O₅ has a structure which has been significantly altered from that of the original V₂O₅. The V₂O₅ host acts as a layered compound at high lithium contents: weak VO bonds are broken and neighboring layers both shift and buckle to accommodate the inserted lithium ions. The inserted Li ions are in tetrahedral coordination with oxygen.     

Synthesis and crystal structure of (ThCu3)(Mn3+2Mn4+2)O12, a new ferrimagnetic perovskite-like compound

Single crystals of [ThCu₃](Mn³⁺₂Mn⁴⁺₂]O₁₂, a ferrimagnetic perovskite-like compound, have been synthesized by hydrothermal conditions at 600°C and 2 kbar. They have been found to be cubic, of space group Im3, with a = 7.359 Å, and isostructural with [NaMn₃](Mn³⁺₂Mn⁴⁺₂)O₁₂. The crystal structure has been refined by single-crystal X-ray diffraction data. The Th⁴⁺ cations are surrounded by slightly distorted icosahedra; the ThO distance is 2.556 Å. The Cu²⁺ cations are also surrounded by 12 oxygens, which are arranged as three mutually perpendicular rectangles of different size, the smallest and the largest of which are almost squares. The three sets of CuO distances are 1.973, 2.800, and 3.238 Å. The octahedral MnO distance is 1.950 Å. A test based on neutron diffraction powder data indicated that the square sites are occupied by only the Cu²⁺ cations.     

Crystal structure and spectroscopic properties of A[VO2(SO4)(H2O)2] · H2O (A = K, Rb, Tl, NH4) compounds

The crystal structure of dioxovanadium(V) sulfate trihydrates A[VO₂(SO₄)(H₂O)₂] · H₂O, where A is K, Rb, Tl, or NH₄, has been determined based on a combination of neutron and X-ray diffraction data. The compounds are isostructural and have a monoclinic lattice (space group P2₁, Z = 2) with unit cell parameters a = 6.24535(8), 6.26016(7), 6.25817(5), and 6.2500(1) Å; b = 9.8417(1), 9.99736(8), 9.96217(9), and 9.9742(1) Å; c = 6.52113(8), 6.69303(5), 6.70379(6), and 6.70334(9) Å; β = 106.99(1)°, 107.83(1)°, and 107.83(1)°, 107.99(1)°, respectively. The SO₄ tetrahedra and VO₄(H₂O)₂ octahedra share an oxygen vertex to form infinite isolated chains. Atoms A have CN = 10. IR and Raman spectroscopy data are reported.     

Magnetism and structural chemistry of the n=2 Ruddlesden-Popper phase La3LiMnO7

Polycrystalline samples of the n=2 Ruddlesden-Popper phase La₃LiMnO₇ have been prepared and characterized. X-ray and neutron diffraction suggest that the structure is tetragonal with a disordered distribution of Li and Mn cations over the octahedral sites, but ⁶Li MAS NMR shows that the Li and Mn are 1:1 ordered locally. Electron microscopy shows that the stacking of the cation-ordered, perovskite-like bilayers along the crystallographic z-axis is disordered on the distance scale sampled by X-ray and neutron diffraction. Magnetometry data and neutron diffraction data collected at 2 K together suggest that the Mn cations within each structural domain order antiferromagnetically at 14 K, but that the disorder along z prevents the establishment of long-range magnetic order.     

Localization of hydrogen in the layer oxide HTiNbO5

The structure of HTiNbO₅ at 10 and 300 K and of DTiNbO₅ at 300 K has been investigated by neutron powder diffraction. The TiNbO₅ framework and the octahedral distortions previously found for the alkalititanoniobates by X-ray diffraction are confirmed. The position of hydrogen (or deuterium) has been determined: very strong OH … O hydrogen bonds with O … O distances ranging from 2.51 to 2.63 Å are observed. The similarity of these compounds with acids is shown, explaining their ion exchange properties. The absence of protonic conductivity can be explained from structural arguments. The open character of this structure, which can play a part in intercalation and deintercalation reactions is also discussed.     

Reaction Mechanism of the Exchange Reaction between CuCl and BaO Studied by Time-Resolved X-ray Absorption Spectroscopy

The solid state reaction 2CuCl+BaO→Cu₂O+BaCl₂ has been examined in situ using energy-dispersive X-ray absorption fine-structure spectroscopy (DXAFS). A high time resolution on the order of seconds between two Cu K-XANES spectra has been achieved by this experimental setup. The spectra suggest that the transformation of CuCl to Cu₂O is preceded by an unidentified, intermediate state. Fingerprint methods as well as principal component analysis have been applied, which confirm the formation of exactly one new intermediate phase. The nature of this phase remains unidentified and could not be elucidated by the experimental investigations.     

Crystal structure of a high‐pressure phase of magnesium chloride hexahydrate determined by in‐situ X‐ray and neutron diffraction methods

A high‐pressure phase of magnesium chloride hexahydrate (MgCl₂·6H₂O‐II) and its deuterated counterpart (MgCl₂·6D₂O‐II) have been identified for the first time by in‐situ single‐crystal X‐ray and powder neutron diffraction. The crystal structure was analyzed by the Rietveld method for the neutron diffraction pattern based on the initial structure determined by single‐crystal X‐ray diffraction. This high‐pressure phase has a similar framework to that in the known ambient‐pressure phase, but exhibits some structural changes with symmetry reduction caused by a subtle modification in the hydrogen‐bond network around the Mg(H₂O)₆ octahedra. These structural features reflect the strain in the high‐pressure phases of MgCl₂ hydrates.     

Alkali metal suboxides: Intermediates between salts and metals

Rubidium and cesium form stable metal-rich oxides (suboxides) which have been investigated by thermal and structural analysis. The compounds Rb₉O₂, Rb₆O (? Rb₉O₂Rb₃), Cs₁₁O₃, Cs₄O (? Cs₁₁O₃Cs₁₀), Cs₁₁O₃Rb, and Cs₁₁O₃Rb₇ contain the characteristic ionic clusters Rb₉O₂ and Cs₁₁O₃. A simple model for the chemical bonding in alkali metal suboxides is described and proved by measuring the electrical properties and optical reflectivities as well as photoelectron spectra of these compounds. It is found that cesium suboxides play an important role in widely used photocathodes and image converters of type S1. The IR sensitivity of these devices is explained on the basis of surface plasmon-enhanced photoemission.     

A new phase in the Ag−O−S system

The investigations of reaction between Ag₂SO₄ and Ag₂S in air atmosphere have been carried. Results of DTA and X-ray phase powder diffraction of a reaction mixture have confirmed that in the Ag?O?S system exists a new phase. A formula of the phase is Ag₂SO₂.     

Neutron self-shielding in hydrogenous samples

Measurements performed in the past to determine sensitivity enhancements (later identified as neutron density increases) in PGNAA as a function of hydrogen concentration in slab-shaped samples are described. The results are compared to the results of Monte Carlo computations. It is concluded that, like H₂O, D₂O can also cause substantial neutron density increases. In one concentrated salt solution, however, D₂O seems to cause a neutron density decrease that cannot be explained from the macroscopic neutron scattering and absorption cross sections in the model used.     

X-ray reflectivity study of polymer assembly at air-water interface

X-ray reflectivity (XR) measurements were carried out for amphiphilic diblock copolymer monolayers on water surface. From XR data, the layer thickness, and surface and interface roughnesses could be determined as a function of surface pressure. The XR experiments were performed using an ‘Air–Water Interface X-ray Reflectometer’ with conventional X-ray source (Cu target) in our laboratory. LB trough was equipped to the reflectometer, so the in situ measurements could be carried out for spread monolayers on water surface at different surface pressures. Kiessig fringes were observed for specular measurement for amphiphilic diblock copolymer, poly(α-methylstyrene)-poly(decyl 4-vinylpyridine) (P(α MSt)-b-P(4VP-C₁₀H₂₁I)) monolayers on water surface. It was observed that the thickness of the monolayer became thicker with increasing surface pressure. By curve fitting for the data obtained for the monolayer at surface pressure of 37 mN m^-1, the thicknesses of P(αMSt)₅₀ and P(4VP-C₁₀H₂₁I)₅₀ layers was determined to be 21 and 22 Å, respectively. Because the chain length of P(αMSt)₅₀ is calculated to be 126 Å in all-trans conformation, it was indicated that the molecules did not get aligned even when they were pressedto become such a dense state.     

A polypseudorotaxane coordination polymer comprising Preyssler-type phosphotungstate and flexible N-donor ligands

A coordination polymer based on Preyssler-type phosphotungstate, {Cu₄(L)₂(HL)(H₂O)₅[HNa(H₂O)P₅W₃₀O₁₁₀]}·2H₂L·4H₂O (1), has been hydrothermally synthesized and characterized by single crystal X-ray diffraction, powder X-ray diffraction, IR spectrum, element analysis, and thermogravimetric analysis. The structure shows that the asymmetry coordination of the N-donor ligands results in formation of chiral sub-building blocks (SBUs). The chiral SBUs were connected by Cu–O bonds and organic ligands to form a two-dimensional (2-D) structure. Furthermore, 1 represents the first 2D + 2D → 2D polypseudorotaxane framework based on the chiral lamellar structure; magnetic properties have been investigated as well.     

Sodium aluminogermanate hydroxosodalite hydrate Na6+x[Al6Ge6O24](OH)x · nH2O (x ≈ 1.6, n ≈ 3.0): Synthesis,phase transitions and dynamical disorder of the hydrogen dihydroxide anion,H3O2−, in the Cubic high-temperature form

Crystalline sodium aluminogermanate hydroxosodalite hydrate Na_6+x[Al₆Ge₆O₂₄](OH)_x · nH₂O with x ≈ 1.6 and n ≈ 3.0 has been synthesized by reacting Al₂O₃, GeO₂ and NaOH solution under hydrothermal conditions, and characterized by means of simultaneous thermal analysis, differential scanning calorimetry, X-ray and neutron diffraction as well as ¹H and ²³Na MAS NMR and IR spectroscopy. The material undergoes a reversible structural phase transition at T_c = 166 K (heating mode), which is actually a complex two-step transformation as detected in DSC measurements. Structure refinements of the cubic high-temperature form (cell constant a = 9.034(2) Å, room temperature) with single-crystal X-ray and powder neutron diffraction data have not yielded overall satisfactory results, probably due to the solid-solution character of the hydrosodalite. The refinements nevertheless demonstrate that (i) the sodalite host framework is a strictly alternating array of corner-linked AlO₄ and GeO₄ tetrahedra, and (ii) most polyhedral [4⁶6⁸] cavities are occupied by four sodium cations and one orientationally disordered hydrogen dihydroxide anion, H₃O₂^?, which possesses a strong central hydrogen bond. Variable-temperature ¹H MAS NMR spectra unambiguously confirm the presence of H₃O₂^? ions and, in addition, reveal a dynamical intraionic exchange between the central and terminal protons and a rotational diffusion of those anions to occur in the high-temperature form. The nature of the guest complexes filling the remaining cages could not be unambiguously determined. Results are compared with those obtained in recent studies on the related sodium aluminosilicate hydrosodalite system of the general formula Na_6+x[Al₆Si₆O₂₄] (OH)_x · nH₂O.     

Development of a combined method to carry out a multielement analysis for environment preser vation

The paper discusses the possibilities of energy dispersive X-ray fluorescence spectroscopy and instrumental neutron activation analysis in the investigation of environmental pollutions. The X-ray fluorescence spectroscopy of samples was performed using the MECA-1044A analyzer (XR-500, LINC SYSTEMS, Great Britain) with a pulsed X-ray tube with a silver target as a source of excitation. Neutron activation analysis was carried out on the basis of two reactors: IBR-2 LNP JINR, Dubna, and TWR ITEP, Moscow. The optimal regimes of measurement for both methods as well as the detection limits corresponding to these regimes are given. To illustrate the perspectives of the methods, the ecological problem of the consequences of introducing into soil of the now available meliorator CaSO₄·2H₂O is solved in the paper. Data on absorption of trace elements in a wide range including rare-earth elements by agricultural plants are presented. This paper may be of interest for specialists in analytical chemistry and ecology.