Chemical analysis of heavy elements by identification of fission fragments through X-ray coincidence measurements

INTRODUCTIONThe prospect of performing chemical analysis of thin specimens at any desired level of resolution is particularly appealing to the materials scientist. Commercial TEM-based systems are now available which virtually provide this capability. The purpose of this contribution is to illustrate its application to problems which would have been intractable until recently, pointing out some current limitations.X-RAY ANALYSISIn an attempt to fabricate superconducting materials with high critical currents and temperature, thin Nb3Sn films have been prepared by electron beam vapor deposition [1]. Fine-grain size material is desirable which may be achieved by codeposition with small amounts of Al2O3 . Figure 1 shows the STEM microstructure, with large (∽ 200 Å dia) voids present at the grain boundaries. Higher quality TEM micrographs (e.g. fig. 2) reveal the presence of small voids within the grains which are absent in pure Nb3Sn prepared under identical conditions. The X-ray spectrum from large (∽ lμ dia) or small (∽100 Ǻ dia) areas within the grains indicates only small amounts of A1 (fig.3).

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Long-period modulated superstructures in Pd-12.5 at.%Ce and Pd-15 at.%Ce alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100173959 ◽

1990 ◽

Vol 48 (4) ◽

pp. 164-165

Author(s):

Noriyuki Kuwano ◽

Masaru Itakura ◽

Kensuke Oki

Keyword(s):

Electron Microscopy ◽

Mean Value ◽

Heavy Elements ◽

Arc Furnace ◽

X Ray ◽

Long Period ◽

Ultra High Purity ◽

Heat Treated ◽

Atomic Scattering ◽

The Mean

Pd-Ce alloys exhibit various anomalies in physical properties due to mixed valences of Ce, and the anomalies are thought to be strongly related with the crystal structures. Since Pd and Ce are both heavy elements, relative magnitudes of (fcc-fpd) are so small compared with <f> that superlattice reflections, even if any, sometimes cannot be detected in conventional x-ray powder patterns, where fee and fpd are atomic scattering factors of Ce and Pd, and <f> the mean value in the crystal. However, superlattices in Pd-Ce alloys can be analyzed by electron microscopy, thanks to the high detectability of electron diffraction. In this work, we investigated modulated superstructures in alloys with 12.5 and 15.0 at.%Ce.Ingots of Pd-Ce alloys were prepared in an arc furnace under atmosphere of ultra high purity argon. The disc specimens cut out from the ingots were heat-treated in vacuum and electrothinned to electron transparency by a jet method.

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Microdomains in BaFeO3-y (0.35 < y < 0.50)

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100177039 ◽

1990 ◽

Vol 48 (4) ◽

pp. 780-781

Author(s):

M. Vallet-Regí ◽

M. Parras ◽

J.M. González-Calbet ◽

J.C. Grenier

Keyword(s):

Electron Diffraction ◽

Chemical Analysis ◽

Monoclinic Phase ◽

Orthorhombic Phase ◽

Total Iron ◽

Zone Axis ◽

Electron Micrograph ◽

X Ray Diffraction ◽

X Ray ◽

Compositional Variations

BaFeO3-y compositions (0.35<y<0.50) have been investigated by means of electron diffraction and microscopy to resolve contradictory results from powder X-ray diffraction data.The samples were obtained by annealing BaFeO2.56 for 48 h. in the temperature range from 980°C to 1050°C . Total iron and barium in the samples were determined using chemical analysis and gravimetric methods, respectively.In the BaFeO3-y system, according to the electron diffraction and microscopy results, the nonstoichiometry is accommodated in different ways as a function of the composition (y):In the domain between BaFeO2.5+δBaFeO2.54, compositional variations are accommodated through the formation of microdomains. Fig. la shows the ED pattern of the BaFeO2.52 material along thezone axis. The corresponding electron micrograph is seen in Fig. 1b. Several domains corresponding to the monoclinic BaFeO2.50 phase, intergrow with domains of the orthorhombic phase. According to that, the ED pattern of Fig. 1a, can be interpreted as formed by the superposition of three types of diffraction maxima : Very strong spots corresponding to a cubic perovskite, a set of maxima due to the superposition of three domains of the monoclinic phase along [100]m and a series of maxima corresponding to three domains corresponding to the orthorhombic phase along the [100]o.

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