RE: Size/Strain Round Robin - 1st Report
Hello to all! When will be the next Round Robin on size and strain? Thanks Miguel Hesiquio
RE: Size/Strain Round Robin - 1st Report
Well, although the specimen was nearly strain-free, strictly speaking this was still a size-strain round robin; all the participants extracted (or refined) strain parameters, didn't they :-) Before to start, the Round Robin participants were said : "Although the first sample selected for the Round Robin shows isotropic line broadening, future samples will exhibit anisotropic line broadening." Another option would have been to not give that assumption of isotropic line broadening, which certainly bias the possibility for more spread results (and personally, I have proposed 2 sets of results : with isotropic and anisotropic line broadening). A third option could have been to give 2 assumptions : Although the first sample selected for the Round Robin shows isotropic line broadening and size-effect only, future samples will exhibit anisotropic line broadening and/or both size/strain effects. Then the participants would have extracted only the size, isotropic, and the spread on the results would have been even narrower. Round Robin organizers have some latitude, fortunately. The participants measured strain because you did not say that the sample was almost strain-free. The participants used isotropic line broadening because you told them to do so. Anyway, in a manuscript submitted for publication, the authors could well say : we tried anisotropic and size/strain effects, and concluded that the sample shows isotropic line-broadening and is strain-free, so that calculations were made again assuming isotropy and no strain effect. The R factors were similar in both cases. That paper would be accepted for publication (if I was the reviewer ;-). Best, Armel
RE: Size/Strain Round Robin - 1st Report
-Original Message- From: Armel Le Bail [mailto:[EMAIL PROTECTED]] Sent: Tuesday, April 17, 2001 8:19 AM To: [EMAIL PROTECTED] Subject: RE: Size/Strain Round Robin - 1st Report If the Round Robin stops on that first sample, it will be a Size Round Robin, not a Size/Strain Round Robin. I think that, even if some Fourier methods needing at least 2 well separated harmonics would disqualify, a more "difficult" sample should be introduced in the Round. Well, although the specimen was nearly strain-free, strictly speaking this was still a size-strain round robin; all the participants extracted (or refined) strain parameters, didn't they :-) I have one with a small orthorhombic cell, volume ~300 A**3... It is up to you to receive 300g of that sample, self evolution of a commercial product (no heating, no human intervention, just aging). "Only" 350 reflections in the 15-150 3-theta degrees range, wavelenght 1.54056 Angstroms. The plan is to continue with other samples, but I think it is a good idea to take some time, finish up the first phase and hopefully learn something from the results, referees, etc. to make the second phase better? But the problem will certainly be : if the reference methods cannot be applied, then which result will be recognized as the good answer... In other words, even if Rietveld-derived methods for size-strain analysis have shown some efficiency in a basic and simple case, can we consider that they will systematically work with the same efficiency in a complex case (i.e. a normal case ;-). Remember that most Size/Strain experts disqualified these Rietveld-derived methods as giving dubious results, in their opinion. My feeling is that a comparison of different methods would not make much sense any more. Why? Because majority of methods that can be applied in that case (Rietveld, pattern decomposition followed by integral-breadth methods, etc.) are based on similar premises (Scherrer for the size and Stokes and Wilson relation for the strain). Therefore, they might lead not to very different but similar (!) results, but we would never know how serious are systematic errors. Several notable exceptions to this rule that are based on a different approach (ARIT, for instance, has a potential to give different strain values, thank you Armel:-). However, who is to say which one gives a correct answer, because the bottom line for all is that some sort of analytical model is presumed for size and strain-broadened profiles. Of course, there is also problem of a true background, which would tend to be overestimated in a cluttered pattern and consequently systematically affecting both size and strain values. Davor Balzar
RE: Size/Strain Round Robin - 1st Report
Davor Balzar wrote : I believe that the reason for the former is absence of strain and a simple specimen (cubic symmetry, spherical crystallites with isotropic broadening) that was chosen. Some people objected to this, but I think that was the only possibility to give the round robin a fair chance that results won't be wildly different. Besides, more "difficult" sample would disqualify most of the Fourier methods of analysis that could not be applied. If the Round Robin stops on that first sample, it will be a Size Round Robin, not a Size/Strain Round Robin. I think that, even if some Fourier methods needing at least 2 well separated harmonics would disqualify, a more "difficult" sample should be introduced in the Round. I have one with a small orthorhombic cell, volume ~300 A**3... It is up to you to receive 300g of that sample, self evolution of a commercial product (no heating, no human intervention, just aging). "Only" 350 reflections in the 15-150 3-theta degrees range, wavelenght 1.54056 Angstroms. But the problem will certainly be : if the reference methods cannot be applied, then which result will be recognized as the good answer... In other words, even if Rietveld-derived methods for size-strain analysis have shown some efficiency in a basic and simple case, can we consider that they will systematically work with the same efficiency in a complex case (i.e. a normal case ;-). Remember that most Size/Strain experts disqualified these Rietveld-derived methods as giving dubious results, in their opinion. Best, Armel Le Bail SSRR local results at : http://sdpd.univ-lemans.fr/microstruct/ssrr/
RE: Size/Strain Round Robin - 1st Report
Dear Leonid and others: Let me comment on two points that were, I think, raised in your message: (i) Whether to keep round-robin results anonymous or not; (ii) How "good" the results actually are. First of all, if anyone chooses to publish his own results on the Web or otherwise, he/she, of course, has every right to do so. However, my firm belief is that I cannot and should not do it for at least two reasons: The first one is obvious; I don't want to put anyone in a position to be (potentially) embarrassed. We had a variety of researchers with different level of experience in line-broadening field (as it should be for a real round robin) and I am particularly thankful to the participants who sent in results, although it was their first time to evaluate size and strain from diffraction data. Second reason: several participants were using commercial software to evaluate size-strain values and/or were from companies that sell XRD equipment or software. I can imagine a situation where a potential customer could take these results (either good or bad, it does not matter) into the consideration when making purchasing decision, which would be unwarranted and a potential liability for the round-robin organizers. Saying all this, I am not arguing that the individual results should be kept secret. We hope to write a full publication where the individual results will be, of course, available (or deposited with IUCr, depending on the editor, I suppose). The report that was posted on the Web is just a condensed (preliminary) version, as I understood from previous postings on this mailing list that some people are eager to see the results as soon as possible. I can also try to "extract" the original results from the e-mails and post them on the Web page, but please, be patient; this takes some time and according to my work plan, I can spend no more than 10 % of my time on the round robin:-) Next issue is about the results. I am asking myself the same thing: Most of the people probably have expected less agreement in size-strain kind of analysis, so "if results are so good, why did you undertake the round robin in the first place?" :-) However, the full publication will hopefully give a more balanced picture of overall results and then everyone will be able to judge whether they are really "impressive" or not. For instance, in the Conclusions it was pointed out that the mean was changed for 73 % if strain was detected. Or even worse, if one considers the scatter of results in domain-size values reported by the participants (among those included in the averages reported on the Web site), say, of volume-weighted domain size: minimum number reported to me was 21.1 and maximum 57.4! Now, I would call that impressive but not exactly with the same connotation:-) However, I think that this kind of scatter was expected. What was a nice result and what, I believe, Leonid is referring to, is a comparison of averages obtained by different methods and especially obtained by different instruments. I believe that the reason for the former is absence of strain and a simple specimen (cubic symmetry, spherical crystallites with isotropic broadening) that was chosen. Some people objected to this, but I think that was the only possibility to give the round robin a fair chance that results won't be wildly different. Besides, more "difficult" sample would disqualify most of the Fourier methods of analysis that could not be applied. The fact that different instruments with very different resolutions gave similar results for size and strain is particularly encouraging. Again, if a specimen with smaller line broadening were selected, probably it would have favored higher-resolution instruments, and the results might have been vastly different. The bottom line, as it looks to me, is: Yes, there was a substantial scatter of results that we expected, but there is a nice agreement between different instruments and methods, which is very encouraging. Especially interesting is a comparison between different instruments because everything else was al ready known from the literature. I hope this justifies why we tried to have measurements collected on different instruments in the round robin, although it might have been a problem for some participants. Best regards, Davor Balzar ** National Institute of Standards and Technology Materials Science and Engineering Laboratory Div. 853, 325 Broadway Boulder, CO 80305-3328 Tel: 303-497-3006 Fax: 303-497-5030 E-mail: [EMAIL PROTECTED] Web: http://www.boulder.nist.gov/div853/balzar European mirror: http://www.ccp14.ac.uk/ccp/web-mirrors/balzar/div853/balzar/ ** -Original Message- From: Leonid Solovyov [mailto:[EMAIL PROTECTED]] Sent: Friday, April 13, 2001 11:14 PM To: [EMAIL PROTECTED] Subject: Re: Size/Strain Round Robin - 1st
