The study of disordered systems by EXAFS: Limitations

Eisenberger, P.; Brown, G. S.

doi:10.1016/0038-1098(79)90790-7

Cited by 401 publications

(154 citation statements)

References 7 publications

Supporting

Mentioning

148

Contrasting

Unclassified

Order By: Relevance

“…6A, our EXAFS results would be difficult to understand. Namely, if the Ni atoms were distributed over several sites with different geometry and coordination one would expect much larger Debye Waller factors and/or small (apparent) coordination numbers, because of the interference between slightly different coordination distances [23]. But as fig.…”

Section: Discussionmentioning

confidence: 99%

“…Why the M-Mo coordination number approaches 2 for the Co promoted catalysts, while it is about 1 for the Ni promoted catalyst, is not clear. It might be that there is a spread in the Ni-Mo distance, leading to some loss in intensity [23]. It should also be noted that the absolute uncertainties in the coordination numbers of higher shells can be substantial [241.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Exafs study of the local structure of Ni in Ni-MoS2/C hydrodesulfurization catalysts

et al. 1990

View full text Add to dashboard Cite

To study the local structure of the Ni promoter atom, the Ni and Mo K edge EXAFS spectra of Ni-MoSz/C hydrodesulfurization catalyst were measured in an in-situ EXAFS cell at 77 K. The Ni atom is situated in a square pyramid of five S atoms at a distance of 2.21 from the S atoms. In addition an EXAFS contribution due to a Mo atom at 2.82 A from the Ni atom could be identified. This local structure indicates that the Ni atoms are situated on top of the S 4 squares at the MoS 2 edges in millerite-type Ni sites. The Ni atoms are situated in the planes of the Mo atoms and not in the intercalation plane midway between successive MoS 2 sandwich layers.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Exafs study of the local structure of Ni in Ni-MoS2/C hydrodesulfurization catalysts

et al. 1990

View full text Add to dashboard Cite

show abstract

“…Actually, the anharmonic contributions to the pair potential are not negligible (Eisenberger & Brown, 1979), at least for the first coordination shell; bond expansion and third and fourth cumulants can be measured with good accuracy and are far from negligible (Dalba et al, 1999;Fornasini et al, 2004;Abd el All et al, 2013;Ahmed et al, 2013).…”

Section: Pair Potential Energymentioning

confidence: 99%

On EXAFS Debye-Waller factor and recent advances

2015

View full text Add to dashboard Cite

The effects of structural and vibrational disorder on the EXAFS signals are parameterized in terms of the Debye Waller (DW) factor. Here the vibrational contribution is addressed, which for most systems can be singled out by studying the temperature dependence of the EXAFS DW factor, which corresponds to a good accuracy to the parallel mean square relative displacement (MSRD) around the inter-atomic equilibrium distance. By comparing the first-shell EXAFS thermal expansion with the crystallographic thermal expansion one can evaluate the perpendicular MSRD. The results of recent measurements on copper and on several tetrahedral semiconductors are here critically compared and some properties of the MSRDs are discussed, such as the dependence of correlation, force constants and vibrational anisotropy on crystal structure and bond ionicity as well as the relative merits of the correlated Debye and Einstein models. The anharmonic contribution to the parallel MSRD of CdTe has been evaluated and a quasi-harmonic analysis has been attempted, leading to an estimation of the bond Grü neisen parameter.

show abstract

“…Limitations of the EXAFS technique in the study of disordered systems have been discussed, for example, by Eisenberger and Brown (1979), Eisenberger and Lengeler (1980) and Brown et al (1988). For systems in which static disorder is large, (i>0.1 A) a reduction in the EXAFS amplitude and coordination numbers results, and an apparent contraction in the near-neighbour bond distances of up to 0.15 .~ can be expected.…”

Section: Spectral Analysismentioning

confidence: 99%

An EXAFS study of cation site distortions through the P2/c-P1̄ phase transition in the synthetic cuproscheelite-sanmartinite solid solution

et al. 1994

View full text Add to dashboard Cite

EXAFS spectroscopy has been used to monitor changes in divalent cation site geometries across the P2/c-Pi phase transition in the sanmartinite (ZnWO4)-cuproscheelite (CuWO4) solid solution at ambient and liquid nitrogen temperatures. In the ZnWO4 end member~ Zn occupies axially-compressed ZnO6 octahedra with two axial Zn--O bonds at approximately 1.95 A and four square planar Zn-O bonds at approximately 2.11 A. The substitution of Zn by Cu generates a second Zn environment with four short square planar Zn~O bonds and two longer axial Zn-O bonds. The proportion of the latter site increases progressively as the Cu content increases. Cu EXAFS reveals that the CuO6 octahedra maintain their Jahn-Teller axially-elongate geometry throughout the majority of the solid solution and only occur as axially-compressed octahedra well within the stability field of the Zn-rich phase with monoclinic long-range order.KEVWORDS: EXAFS spectroscopy, sanmartinite, cuproscheelite, phase transition. In~oducfionREciter powder X-ray diffraction studies on the complete solid solution between sanmartinite, ZnWO4, and cuproscheelite, CuWO4, have revealed the existence of a displacive ferroelastic phase transition Redfern, 1992, 1993). The spontaneous strain, calculated from the lattice parameters, was used as a measure of the order parameter for the transition which, at room *Present Address: Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK temperature, appeared continuous as a function of composition and with a critical composition of Cu0.22Zn0.78WO4 . With increasing Cu-content and temperature, the transition was found to become more first-order in character with a tricritical transition occurring at about Zn0.32Cuo.68WO 4 and 650~The observed critical transition temperature varied non-linearly as a function of composition indicating a coupling between X, the molar fraction CuWO4, and the order parameter, Q, of the form ~IXQ 2 + ~2XQ 4. The resulting Landau potential successfully modelled the transition as a function of both composition and temperature.

show abstract

The study of disordered systems by EXAFS: Limitations

Cited by 401 publications

References 7 publications

Exafs study of the local structure of Ni in Ni-MoS2/C hydrodesulfurization catalysts

Exafs study of the local structure of Ni in Ni-MoS2/C hydrodesulfurization catalysts

On EXAFS Debye-Waller factor and recent advances

An EXAFS study of cation site distortions through the P2/c-P1̄ phase transition in the synthetic cuproscheelite-sanmartinite solid solution

Contact Info

Product

Resources

About