[Ifeffit] Debye-Waller factors for metal oxides ?

[Ian James Drake]

Hi,

There is little discussion over the significance of fitted Debye-Waller factors (ss2) found for 
metal centers in metal oxides of heterogeneous catalysts.  I am searching for a better way of 
determining how reasonable these values are in the fits I get.

1.  Are phenomenological models like the correlated Debye model and Einstein model appropriate? 
 It seems that Debye temperatures are hard to find for oxides.

2. Is there an equivalent value for ss2 in x-ray crystallography data that I can refer to for 
comparison in these materials?  What should I look for in reviewing published x-ray 
crystallographic data?

3. Is the temperature dependence reported for the ss2 for some metals (like Cu and Al) similar to 
their respective oxides?  For example, in Debye-Waller factor calculations reported for Al metal 
by R.C.G Killean (in J.Phys.F: Metal Phys., v. 4, pg. 1908, 1974), the ss2 changes by a factor of 
three between  25C and 300C.  Would I expect a factor of three increase in crystalline zeolites 
(AlO4 structural units).

4.  Specific to my work:  I have studied Al containing oxides at temperatures between 25 and 300 
C.    I would like to quantify coordination changes by doing EXAFS fitting of the Al K-edge data. 
 The EXAFS was taken at temperature and I observe no change in the broadening of the data. 
 Likewise, the fitting shows no sensitivity in the Debye-Waller factor.  It is nearly constant at 
0.001 A over the temperatures of interest.  Since ss2 and the coordination number (CN) are 
correlated, I would like a way to bind the error on the fitted CN by modeling real physical 
changes in the Debye-Waller factors.  Do you have any suggestions?

Looking forward to your thoughts.

Ian Drake
Graduate Student
UC Berkeley