Hi Hana, On Fri, Jun 17, 2011 at 2:30 PM, Hana wrote:

Dear EXAFS experts, I am quite a beginner, and that's might be an ignorant question but really important to my work, so I would be happy to get a direction: what would be the right way to weigh in the effect of temperature in soils samples, since solutions like Debye models will not fit to my understanding? specifically, I am trying to compare my measurements(collected at 10K) to literature data of these metals adsorbed on iron oxides (collected at room temperature).

I would appreciate any advise, Hana

The Debye or Einstein model describes how sigma^2 changes with temperature for a particular bond. That can be helpful in many cases, of course. But for a soil sample or ion sorbed to metal oxide surfaces, there are a few issues with this approach. First, metal-oxygen bonds tend to be stronger than metal-metal bonds, and so don't show a lot of temperature dependence to begin with. Second, the Debye (Einstein) models consider only the thermal component of sigma^2, whereas sorbates and metals substituted in metal oxides are likely to have significant "static" disorder, as they have a range of bond lengths. In addition, it would probably be reasonable to assume that for a metal sorbed on an insulating surface that each bond would have it's own strength and so temperature dependence of sigma^2. Third, soil and sorption samples tend to be heterogeneous, and so average over an unspecified number of local environments, further contributing to static disorder. It's a fine idea to measure any sample at low temperature as the sigma^2 are smaller, and radiation damage reduced. But I'm not sure I've seen a work that compares sigma^2 for different temperatures in soil samples or really even tries to interpret sigma^2 for such samples. I wouldn't expect it to tell you much, but I'd be happy to be shown otherwise. Cheers, --Matt