Hello Shan: The high correlation between SO2 and the Debye-Waller parameter is not surprising at all since they both act to change the intensity of the peaks in Chi(R). With an estimated standard deviation of +-0.3, a change of 0.5 in the coordination number is quite reasonable too since ESDs are not really "error bars" but tend to be lower. Unless you have other information which can help to pin down one of the two parameters, I am afraid that you are stuck with this ambiguity. You have not said what the ss value does when you do not restrain it. That might help you to figure out an interpretation. If it goes way out to a non-physical value then you _have_ to restrain it and make sure that you report the fact. In any case the CN is always one of the most difficult values to pin down. Without actually seeing the data, it is difficult to give you more than generalities. Cheers, Carlo On Tue, 19 Dec 2006, Shantanu Behera wrote:

Hi Folks

I have a small doubt. I work on the structural features of Y that are segregated to Alumina grain boundaries (very dilute amounts of Yttrium in polycrystalline alumina).

In some of my fits, I find a correlation ~0.85 between SO2 and ss. If I restrain the ss, from 0.004 to 0.007, the CN changes by ~0.5 (not considering +/-0.3). I would appreciate if someone can explain me how to interpret the results from a structural point of view.

Warm regards Shan

-- Carlo U. Segre -- Professor of Physics Associate Dean for Special Projects, Graduate College Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://www.iit.edu/~segre segre@debian.org