Nuclear Microanalysis Research Articles

The structure and electrical properties of lithium doped pyrochlore Gd2Zr2O7

The lithium-doped phases Gd1.7Li0.3Zr2O6.7 and Gd2Zr1.7Li0.3O6.55 with a pyrochlore structure were prepared by the modified Pechini method using citric acid and glycerol. Monitoring of the lithium content by using a nuclear microanalysis showed that a significant loss of lithium occurred after heat treatment above 1200 °C. Dense ceramics with a stoichiometric lithium content can be prepared by a low temperature microwave sintering (1100 °C). The introduction of lithium in the Gd-sublattice was accompanied by a decrease in the unit cell parameter (a = 10.5208 (1) Å vs 10.5346 (2) Å for Gd2Zr2O7) and during doping at the Zr-sites with lithium, the cell parameter increased (10.5720 (1) Å). The doping in both cases led to an increase in the free cell volume. The impedance spectroscopy results showed that the bulk conductivity can be enhanced by the Li+-doping at the Gd3+-site by almost an order of magnitude. The sample Gd2Zr1.7Li0.3O6.55 had a conductivity lower than that of Gd1.7Li0.3Zr2O6.7 due to the possible trapping of oxygen vacancies by a high-charged acceptor defect LiZrʹʹʹ. The conductivity−pO2 measurements showed that the Li-containing phase was a pure oxide-ion conductor at T < 800 °C.

Study of oxygen content in titanium alloys after exposure at elevated temperature

Isothermal oxidation testing of near α titanium alloys VT18U, VT20, Ti6Al7Nb and Ti6242S was performed in air at 560 °С for 1000 hours. Parameters of diffusion layer on the alloy surfaces were studied by microhardness indentations, optical microscopy, X-ray diffraction analysis and nuclear microanalysis. It was established that concentration of oxygen in diffusion layer of tested alloys after oxidation differs significantly. An approach was demonstrated and validated by nuclear microanalysis data that allows comparative evaluation of the total concentration of interstitial impurities in the diffusion layer by the X-ray diffraction method.

Hydrogen content in proton-conducting perovskites CaZr1 − x Sc x O3 − x /2 (x = 0.0–0.2)

The hydrogen content in CaZr1 − xScxO3 − x/2 (x = 0.00–0.20) and BaZr0.9Y0.1O3-α (for comparison) was studied by powder nuclear microanalysis. The samples were saturated with heavy water (D2O) vapors at 350 and 400°C in air. The chemical expansion of the CaZr0.95Sc0.05O3-α and BaZr0.95Y0.05O3-α samples at 700°C was measured at different water vapor pressures. A model was suggested to explain the lowered hydrogen content in oxides based on CaZrO3.

Isotope Exchange between &lt;sup&gt;18&lt;/sup&gt;O&lt;sub&gt;2&lt;/sub&gt; Gas and Mechanoactivated Oxide NdMnO&lt;sub&gt;3+δ&lt;/sub&gt;

sotope exchange of oxygen 18О2 with oxides NdMnO3+δ was investigated. The oxide was obtained from oxides Nd2O3 and Mn2O3 using a ceramic technology with annealing in air at 1400°C for 90 hours followed by cooling in a furnace. A planetary mill AGO-2 with a centrifugal factor of g = 60 was used for mechanical treatment of oxides. The study of isotope exchange was carried out by nuclear microanalysis. The concentration of the isotopes 18O and 16O in oxides was determined using a Van de Graaff accelerator and 18O(p, α)15N and 16O(d, p)17O* reactions at the energies of incident beams 762 and 900 keV. Isothermal annealing of powders was carried out in oxygen, enriched to 80% by the isotope 18O. It was established that the concentration of the isotope 18O in mechanically activated powders was several times higher than in the initial micropowder under the same conditions of annealing. The effect increased with increasing of mechanical activation time (30 - 300 s). The isotope exchange parameters connected with the processes at the boundaries of the particles of mechano-activated powder and within their volume were analyzed.

Nuclear microanalysis of lithium dispersion in LiFePO4 based cathode materials for Li-ion batteries

This paper provides original characterization of battery electrodes by means of nuclear microanalysis. It presents a non-invasive method to investigate simultaneously the concentrations and the distributions of the different constituent elements of a C-LiFePO4 positive electrode as a function of its state of charge (SOC). Since the technique used here is able to identify lithium element, a direct visualization of the possible solid electrolyte interface (SEI) layer can be envisioned. Results obtained open new investigation schemes to a better understanding of mechanisms leading to electrode capacity fading and consequently to improve electrode building processes.

Oxygen isotope exchange in nanosized powders of the Al2O3 oxide

Oxygen isotope exchange (OIE) between nanosized powders of the aluminum oxide Al2O3 and oxygen-containing gases 18O2 and C18O2 has been studied in a temperature range of 100–500°C. The concentration of the oxygen isotope 18O in the powders was determined by nuclear microanalysis technique (NRA). It has been shown that for this oxide the OIE exhibits a significant size effect. It has been established that the OIE of the Al2O3 nanopowder is characterized by a specific time dependence of the concentration of the 18O isotope at the surface of grains and by a low level of the content of 18O in the oxide. A linear dependence of the concentration of 18O in the nanopowders on the specific surface of the nanoparticles has been revealed. The experimental data are discussed in terms of several models of the process of isotope exchange.

Oxygen atomic displacement waves in the lattice of the Bi,Pb-2223 phase composite annealed in an atmosphere with a low oxygen (O2 + N2) content

After annealing of Bi,Pb-2223/Ag composites in a nitrogen-oxygen atmosphere with a low oxygen content in the 2223 phase, cross-polarized waves of oxygen atomic displacements have been revealed by electron diffraction in the [010]2223 direction. It has been demonstrated using the methods of X-ray photo-electron spectroscopy and nuclear microanalysis that nitrogen does not interact with the 2223 lattice and that the oxygen index (9.67 ± 0.20) becomes less than the stoichiometric index (x = 10). It has been found that the generation of atomic displacement waves is due to the deficiency of oxygen in the double Bi-O layers.

Identification of the sources of gas-containing metallurgical defects during the smelting of titanium alloys

A method for identifying the sources of gas-containing metallurgical defects during the industrial smelting of Ti-6Al-4V titanium alloy using vacuum arc remelting technology was developed. The defect database that was obtained during long-term monitoring of an industrial process and the diffusion mechanism of the modification of defect sources in smelting underlie the development of this method. The results of metallographic studies and measurements of the microhardness and the oxygen, nitrogen, and aluminum concentrations in defects were used for identification. The concentrations of light element atoms in defects were measured by the nuclear microanalysis. This method allowed identification at an 80.0% level of efficiency.

Diffusion of insoluble carbon in zirconium oxides

The diffusion coefficient of insoluble carbon in zirconium oxides has been obtained for the temperature range of 900–1000°C. There are no published data on the diffusion of insoluble impurities; these data are of current interest for the diffusion theory and nuclear technologies. Tracer atoms 13C have been introduced into oxides by means of ion implantation and the kinetics of their emission from the samples in the process of annealing in air has been analyzed. The measurements have been performed using the methods of nuclear microanalysis and X-ray photoelectron spectroscopy. The diffusion activation energy is 2.7 eV and the carbon diffusion coefficient is about six orders of magnitude smaller than that for oxygen self-diffusion in the same systems. This result indicates the strong anomaly of the diffusion properties of carbon in oxides. As a result, zirconium oxides cannot be used in some nuclear technologies, in particular, as a material of sources for accelerators of short-lived carbon isotopes.

H/D isotope effect for solubility of hydrogen in doped perovskites

A novel method for studying the H/D isotope separation effect in the “nonstoichiometric oxide-gas” system is suggested. The theoretical scheme of this method is represented for doped perovskites of the ABO3 family, but this approach is also applicable to other compounds where the solubility of hydrogen is determined by the content of oxygen vacancies. The suggested approach is used to determine the H/D isotope effect in hydrogen solubility from the experimental data for proton-conducting oxides. The measurements have been taken using the nuclear microanalysis of fine-grain BaZr0.9Y0.1O3 − y powders. The method is based on the study of the products of the 2H(d, p)3H nuclear reaction. The observed pronounced isotope effect is in quantitative agreement with our theoretical predictions.

Grain boundary self-diffusion of tracer 18O atoms in nanocrystalline oxide LaMnO3 + δ

Diffusion coefficients of tracer 18O atoms at boundaries of nanograins of LaMnO3 + δ oxide have been measured in the temperature range of 400–500°C. The samples of the nanocrystalline oxide are prepared with the use of the shockwave loading method. The concentration profile of the tracer atoms after diffusion annealing is measured with the use of the nuclear microanalysis method. The activation energies of the grain boundary diffusion amounts to about 2 eV and the boundary width is ∼0.05 nm. The measured coefficients of the grain boundary diffusion at 500°C exceed the corresponding coefficients of the volume diffusion by seven orders of magnitude.

Mechanism of formation of macrodefects in titanium alloys

The mechanism of formation of carbon- and gas-containing metallurgical macrodefects in titanium alloys and the mechanism of modification of these defects in the processes of smelting and heat treatment are established. As the main investigation method, the nuclear microanalysis was used, which allowed measurements of concentration distributions for oxygen, nitrogen, and carbon atoms in the zone of macrodefects. It is found that the source of carbon-containing macrodefects was fragments of a cutting tool. As a source of gas-containing macrodefects, the Ti-O-N particles served, which possess the liquidus temperature exceeding the temperature of smelting.

Study of Distribution of Impurity Atoms in Metallurgical Macrodefects

Using nuclear microanalysis (NRA) and electron probe microanalysis (EPMA), concentrations of carbon, oxygen, nitrogen, aluminum, and vanadium were measured on a large group of macrodefects formed in the course of smelting titanium alloys. A remarkable enrichment of the defect material in oxygen and nitrogen atoms was detected; histograms of defect distribution over the concentrations of oxygen, nitrogen, aluminum, and vanadium were obtained. The above results agree with the concepts according to which the defects are formed from the particles that have the melting temperature higher then the temperature of smelting.

Hydrogen diffusion in high temperature proton conducting ceramics

BaCeO3 or SrCeO3-based perovskites doped with a rare earth are high temperature protonic conductors (HTPC) envisioned as electrolytes for fuel cells working at intermediate temperature (400–600°C). In these ceramics, the proton conductance is hampered by microstructural defects that act as barriers for hydrogen diffusion. Respective contributions of bulk and grain boundaries to overall conductivity is usually evidenced via impedance measurements but further information on hydrogen transport relevant for improvement of microstructure design can be obtained with nuclear microanalysis, based on the use of MeV light ions microbeam. We report here a contribution of ion beam microanalysis to the study of hydrogen transport in BaCe0.9Y0.1O3. ERDA hydrogen profiling performed on partially hydrated samples at 200 and 500°C reveals concentration gradients from which diffusion coefficients have been derived with the help of a simple Fickian diffusion model.

Photoluminescence and composition of amorphous As2Se3 films modified with Er(thd)3 complex compound

The photoluminescence and composition of amorphous As2Se3 films modified with an Er(thd)3 complex compound have been studied. A band centered at 1.54 μm, characteristic of photoluminescence from Er embedded in amorphous matrices, has been revealed at room temperature. The composition of thin amorphous As2Se3 films modified with an Er(thd)3 complex compound has been examined by methods of nuclear microanalysis: Rutherford backscattering and nuclear resonant reactions. Dependences of the concentrations of Er ions, oxygen, and carbon on the growth conditions of the films are obtained. It is shown that the Er concentration in a thin film varies nonlinearly as the relative concentration of the starting complex compound increases. In addition, the increase in the Er content of a film is accompanied by a simultaneous rise in the content of such light elements as oxygen and carbon. Comparative analysis of the nuclear microanalysis data and IR spectra demonstrates that, in modification of As2Se3 with the Er(thd)3 complex compound by the given method, the nearest environment of Er in the complex compound is partly preserved.

Investigation of the elemental composition of surrogates of fuel-containing materials by nuclear microanalysis

Nuclear microanalysis was used to determine the elemental composition of individual components of the batch for synthesizing surrogates for the lava-like fuel-containing mass and to determine the composition of the surrogates themselves. The elemental composition of the surrogates obtained is compared with that of the real materials. Brown surrogates are found to contain uranium in amounts exceeding 8 mass %. It is found that the elemental composition of the surrogates is nonuniform in different sections of a slab; this could be an indication of incomplete melting of the batch components or the presence a temperature gradient in the heating facility. The decrease of the initial mass of the batch during vacuum melting is due to silicon, calcium, iron, and oxygen losses.

Nuclear microanalysis of tooth enamel from a community in the Western Cape, South Africa

Extracted teeth collected from a Black African community living in the Gugulethu suburb of Cape Town, South Africa were studied by nuclear microscopy. Analysis by PIXE (with 3.0 MeV protons) of permanent extracted incisor and molar teeth from males and females of different ages showed a homogeneous elemental profile distribution for iron, zinc and strontium, irrespective of gender and/or age. Fluorine content as determined simultaneously from the 110 keV gamma-ray yield from proton bombardment had a similar mean value (females: 1.8% by mass and males: 1.6% by mass) for both genders. However, the mean content of strontium for females (97 μg g −1) was about 40% lower than that for males (69 μg g −1). In addition, a sub-group of children showed a smaller standard deviation on the distribution of zinc and fluorine. Previous results on the trace elemental concentration of the enamel of molar teeth, showed a depletion of up to 50% by mass for strontium after 20 h of exposure in acidic solution. Although the strontium level for the African female group fits this profile it is not certain what the demineralization observed was due too.

Rutherford backscattering spectroscopy and surface morphology of amorphous As 2Se 3 films modified with complex compounds Ln(THD) 3 (Ln=Eu, Tb, Er, Yb)

In this work we report the results on study of amorphous As 2Se 3 films modified with rare-earth dipivaloylmethanates Ln(THD) 3 (Ln=Eu, Tb, Er, Yb) using different diagnostic techniques. The rare-earth, oxygen and carbon concentrations have been determined by Rutherford backscattering spectroscopy and nuclear reaction analysis. The films have smooth surfaces with typical roughness the sizes of which have been changed with chemical modification. According to the results on nuclear microanalysis and IR spectroscopy the assumptions about the local environment of the rare-earth ions in amorphous matrix can be suggested.

Nuclear microprobe local hydrogen measurements in HTPC

High-temperature protonic conducting ceramics (HTPC) exhibit promising protonic conductivities at intermediate temperatures (400–600 °C), with a potential for a broad range of practical applications: electrolytes in electrochemical cells, batteries, sensors, etc. A balance still has to be found between high protonic conductivity and chemical stability in a wet environment. In addition to bulk conductivity measurements, local investigations of protonic transport are recommended to evidence limitations induced by their microstructure, such as the role of grain boundaries or intergranular secondary phases. Methods for local hydrogen concentration measurement with spatial resolution at the micrometer level are scarce. The nuclear microanalysis meets this demand. We report here the first application of a nuclear microprobe technique to the study of HTPC perovskites, synthesized according to a melt-process developed at NASA GRC. Elastic Recoil Detection Analysis (ERDA) combined with Rutherford back-scattering (RBS) was first exploited for perovskites containing very low hydrogen contents. A less common method has been developed for thin samples which utilized 1H(p,p) 1H forward scattering with coincidence detection (ERCS). From the broad compositional and structural range of perovskites, we have limited our efforts to SrCe 0.9Y 0.1O 3− δ and Sr 3Ca 1+ x Nb 1.82O 9− δ , compositions which represent simple and complex perovskite structures, respectively.

Nuclear microanalysis of amorphous As2Se3 films modified with Ln(thd)3 (Ln = Eu, Tb)

The compositions of amorphous As2Se3 thin films modified with the Ln(thd)3 (Ln = Eu, Tb) complexes have been determined by nuclear microanalysis using deuterons provided by an electrostatic accelerator: Rutherford backscattering spectroscopy and nuclear reaction analysis. The rare-earth, oxygen, and carbon contents have been determined as functions of the initial concentration of the complex. The films have been also characterized by IR spectroscopy. Analysis of the nuclear microanalysis and IR spectroscopy results suggests that, in the modified films, the rare-earth atoms retain their local environment, in contrast to thin films of amorphous hydrogenated silicon.