Characterization of Radiation Damage at the Nb Site in Natural Pyrochlores and Samarskites by X-Ray Absorption Spectroscopy

ABSTRACTX-ray absorption spectroscopy has been used to investigate the Nb B-site in pyrochlores (A1.2B2O6Y0–1, Fd3m, Z=8) and samarskites (A3B5O16) in both metamict and annealed condition. The XANES and EXAFS measurements indicate significant changes in pyrochlore and smaller changes in samarskite as a result of radiation damage. In the metamict state the Nb site in both pyrochlores and samarskites is similar to Nb in Nb2O5. Short Nb-O (1.65Å) bonds are not disrupted by alpha-decay/recoil-nuclei events as much as longer bonds (2.00Å). This increases the asymmetry and static disorder at the local Nb site while long range order is greatly diminished resulting in considerable distribution in Nb-M distances and bond angles.

Download Full-text

Studies on Nanostructured M50 Type Steel Using X-Ray Absorption Spectroscopy and NMR

MRS Proceedings ◽

10.1557/proc-351-195 ◽

1994 ◽

Vol 351 ◽

Author(s):

Mahalingam Balasubramanian ◽

Y.D. Zhang ◽

J.I. Budnick ◽

K.E. Gonsalves ◽

T.D. Xiao

Keyword(s):

Magnetic Properties ◽

Long Range ◽

Absorption Spectroscopy ◽

Near Neighbor ◽

Long Range Order ◽

X Ray ◽

Type Steel ◽

Disordered Phase ◽

Structural And Magnetic Properties ◽

X Ray Absorption

ABSTRACTWe have investigated the local structural and magnetic properties of Fe in nanostructured Fe-Cr-Mo-V-C M50 type steel. Experimental techniques which we used include XAFS and NMR. NMR results on as-synthesized M50 type steel shows that the material contains a small amount of bcc Fe plus some other highly disordered phase(s). XAFS measurements indicate that the near neighbor coordinations around Fe are not simply well ordered bcc or fcc Fe and that the sample doesn't have long range crystalline order. XAFS measurements on the consolidated sample show that Fe is predominantly in the form of bcc Fe with good long range order.

Download Full-text

Characterization of the Local Titanium Environment in Doped Sodium Aluminum Hydride using X-ray Absorption Spectroscopy

MRS Proceedings ◽

10.1557/proc-837-n2.4 ◽

2004 ◽

Vol 837 ◽

Cited By ~ 1

Author(s):

J. Graetz ◽

A.Yu. Ignatov ◽

T.A. Tyson ◽

J.J. Reilly ◽

J. Johnson

Keyword(s):

Absorption Spectroscopy ◽

Interatomic Distance ◽

Aluminum Hydride ◽

Titanium Atom ◽

Long Range Order ◽

X Ray ◽

Fine Structures ◽

X Ray Absorption ◽

Exafs Spectra

ABSTRACTTi K -edge x-ray absorption spectroscopy was used to explore the local titanium environment and valence in 2–4 mol% Ti-doped sodium alanate. An estimate of the oxidation state of the dopant, based upon known standards, revealed a zero-valent titanium atom. An analysis of the near-edge and extended fine structures indicates that the Ti does not enter substitutional or interstitial sites in the NaAlH4 lattice. Rather, the Ti is located on/near the surface and is coordinated by 10.2±1 aluminum atoms with an interatomic distance of 2.82±0.01 Å, similar to that of TiAl3. The Fourier transformed EXAFS spectra reveal a lack of long-range order around the Ti dopant indicating that the Ti forms nano-clusters of TiAl3. The similarity of the spectra in the hydrided and dehydrided samples suggests that the local Ti environment is nearly invariant during hydrogen cycling.

Download Full-text