Re: Sources of standard reference materials
Hi! You can try with ZnO, annealed at 950ºC, 72 h h, ( from works of Langford and Louêr) best wishes Miguel Hesiquio Hi All, Does anyone know an appropriate source of standard reference materials for a line profile standard, like NIST SRM 660a (LaB6) - other than NIST, as they are out of stock and ...is expected to become available by November 2009. Thanks, Ross Miguel Hesiquio-Garduño Profesor Titular A Departamento de Ciencia de Materiales Academia de Ciencias de la Ingeniería ESFM-IPN. tel 57 29 60 00 ext. 55003, ext. 55011
Re: Le Bail vs Rietveld for crystallite size and cell parameters?
Hi ! I have worked with both methods in ZnO, I have found that it is easier work with Le Bail or Pawley when you are looking for size strain and lattice parameters, because you just need some data about the crystal structure. But this is just an specific case. Best wishes Miguel Hesiquio-Garduño Profesor Titular A Departamento de Ciencia de Materiales Academia de Ciencias de la Ingeniería ESFM-IPN. tel 57 29 60 00 ext. 55003, ext. 55011 Dear All, I was wondering if there are any advantages of using Rietveld vs Le Bail refinements when crystallite size and cell parameters are the only variables of interest? Thank you, Sergey -- Sergey Ushakov PhD Staff Research Associate Peter A Rock Thermochemistry Laboratory and NEAT ORU University of California at Davis One Shields Avenue, Davis, CA 95616 phone (530) 754-5863 Fax (530) 752-9307 __ This message was written entirely with recycled electrons.
Re: Peak shape
Hi Vengadesh you can adjust the profile ( just single peak ) with pseudo-Voigt function ( I have done it) , but if you want do a whole pattern fitting I think a pearson VII should be better best wishes Miguel Hesiquio Dear All, We took an x-ray diffraction data using Vantec detector in Bruker. What the peak shape one should consider in the refinement, as it is not fitting well with pseudo-voigt. Thank you in advance. With regards, vengadesh Send free SMS to your Friends on Mobile from your Yahoo! Messenger. Download Now! http://messenger.yahoo.com/download.php
Re: wavelenght issue!
Hi! following Daniel's comment, Fullprof and the other programs calulate a profile taking in account ( among other parameters)the doublet k-alpha, not an average wavelength, perhaps the WL ratio is not exactly 0.5 but 0.475 is a good value,yn powdercell there is a list for WL ratios. And in order to calulate lattice parameters you can use Rietveld refinement or wpf, best wishes Miguel Hesiquio Tamas Dragos schrieb: Perhapse I did not make myself clear so Ill just try again. I know how to set up the wavelengths in FullProf and I also know how to setup the ratio, but a ratio of 0.5 seems so far away from the real physical value. It is not so easy to calculate a mean wavelength and I do not think that FullProf just takes the simple mean of the two wavelengths meaning wavelenght1 + wavelength 2 / 2. So I want to know if I wanna calculate the values for the cell parameters with another method, how do I do to find out which value FullProf uses as a mean for the kalpha1 and kalpha2 wavelenghts. There seems to be a misconception here: Fullprof does not use an average wavelength; at least not for the standard applications, if at all. If you give two different wavelengths, the programm will calculate two corresponding peaks for any given Bragg reflection, using the intensity ratio given. Daniel Toebbens Institute of Mineralogy and Perography University of Innsbruck, Austria Miguel Hesiquio-Garduño Profesor Titular A Departamento de Ciencia de Materiales Academia de Ciencias de la Ingeniería ESFM-IPN. tel 57 29 60 00 ext. 55003, ext. 55011
Re: integrated intensity
Hi Joy! you can use Fullprof ( The interface Winplotr), but i think that in first place you should made a qualitative analysis, in order to know the crystalline phases, best wishes Miguel Hesiquio-Garduño Profesor Titular A Departamento de Ciencia de Materiales Academia de Ciencias de la Ingeniería ESFM-IPN. tel 57 29 60 00 ext. 55003, ext. 55011 Dear all may anyone write me in elaborate the steps for finding out the integrated intensity for the diffraction peaks due to the different hkl planes for a crystalline material. what are the useful softwares available for this. warm wishes, j. mukherjee FSD, Central Fuel Research India India-828108 __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
Re: integrated intensity
Hi Joy! you can use Fullprof ( The interface Winplotr), but i think that in first place you should made a qualitative analysis, in order to know the crystalline phases, best wishes Miguel Hesiquio-Garduño Profesor Titular A Departamento de Ciencia de Materiales Academia de Ciencias de la Ingeniería ESFM-IPN. tel 57 29 60 00 ext. 55003, ext. 55011 Dear all may anyone write me in elaborate the steps for finding out the integrated intensity for the diffraction peaks due to the different hkl planes for a crystalline material. what are the useful softwares available for this. warm wishes, j. mukherjee FSD, Central Fuel Research India India-828108 __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
Re: Size Strain in GSAS
Hi, maybe I'm late in the discussion, but what about if we use a Rietveld ( or whole pattern fitting) refinement in order to extract data for the profile and use it to make the extraction of size and strain effects? thanks and greetings Miguel Hesiquio-Garduño Profesor Asociado C Departamento de Ciencia de Materiales Academia de Ciencias de la Ingeniería ESFM-IPN I guess, this discussion has already died down but I couldn't find a moment for reply soon enough:-) As Prague was already mentioned, let me try to summarize what I think about this subject and have said there (let's hope I actually remember it:-): 1. A careful line broadening analysis (at this point in time) is better done outside Rietveld refinement 2. A physical model is better and preferred to a phenomenological model for analyzing line broadening However, because we discuss the Size-Strain analysis in Rietveld here: 3. Rietveld obviously needs some kind of line-broadening modeling in order to at least correct for sample broadening effects (especially anisotropic ones) to extract correct integrated intensities for crystal-structure refinement. Thus, any model that works is good. 4. Rietveld needs to have a line-broadening model that works for an arbitrary crystal structure (up to triclinic) and arbitrary sample (i.e. many possible sources of broadening could be present in a given sample). Therefore, a phenomenological model is the only one available at this point, as physical models are still struggling with cubic (or hexagonal) structures and a very limited spectrum of physical sources causing broadening. In conclusion: 5. I think that the work done by Nick Armstrong and others is definitely a way to go, but also a long way to go before we get to the level mentioned under 4 (I certainly won't live to see it:-). 6. I also believe that (even when 5 is fulfilled) diffraction will often need some additional information provided by complementary characterization methods (i.e. TEM, SEM,...) to completely and accurately characterize defects in a sample, as we may calculate the most probable solution but won't often be able to discriminate between other very likely solutions, that is, the most probable is very often not significantly different from other physically plausible solutions (lognormal and gamma examples already mentioned). 7. Previous point implies that trying to do too much with only diffraction data might actually be dangerous. One can find too many dead-wrong numbers in the literature using some of the physical models (for instance, dislocation densities, etc.), as a real physical cause of broadening was probably different and/or there was a strong correlation between refinable parameters that depend on the diffraction angle in a similar way. Considering the above: 8. The simple modified TCH model (triple-Voigt), used in most major Rietveld programs these days, is surprisingly flexible. It works well for most of the samples (super-Lorentzian is an example when it fails, as well as many others, but this is less frequent that one would expect) and gives some numbers for coherent domain size and strain. If we are lucky to know more about the sample (for instance, the information is available that a lognormal size distribution, certain type of dislocations, etc., is most likely to be prevalent for majority of grains in the sample), those numbers will let us calculate real numbers that relate to the real physical parameters (say, the first moment and dispersion of the size distribution, etc.) in many cases, as discussed here previously. Davor P.S: 9. The fact that a certain physical model does not yield a particular analytical function as a physically broadened profile does not mean that the function cannot successfully approximate that profile, as any such calculation includes many approximations of different kinds. There were numerous examples in literature showing that a simple Voigt function was able to approximate quite different cases. Of course, that is not true in general. -Original Message- From: Matteo Leoni [mailto:[EMAIL PROTECTED] Sent: Tuesday, March 29, 2005 4:59 AM To: rietveld_l@ill.fr Subject: RE: Size Strain In GSAS Leonid (and others) just my 2 cents to the whole story (as this is a long standing point of discussion: Davor correct me if I'm wrong, but this was also one of the key points in the latest size-strain meeting in Prague, right?) Your recipe for estimating size distribution from the parameters of a Voight-fitted profile is clear and straightforward, but I wonder have you, or someone else, tested it on, say, simulated data for the model of spherical crystallites having lognormal size distribution with various dispersions? done several times... if you start from a pattern synthesised from a lognormal and you analyse it using a post-mortem LPA method (i.e. extract a width and a shape parameter and play
Re: question about the Scherrer method
Hi I think that is very difficult obtain a free-strain material, and we can not neglect this effect, and it is very useful work with integral breadth rahter tan FWHM, and you should use a reference material in order to obtain the breadth due the instrument, because if you only take in account the broadening observed in your sample, how do you know if the broadening observed is really due to microstructural effects or is due completely to the instrument?. Some years a go I did that, and when I measured a standardin the diffractometerand Iobserved that the broadening was too big and I had tochange the slits in order to reduce the broadening. Best regards Miguel Hesiquio - Original Message - From: Angel L. Ortiz To: rietveld_l@ill.fr Sent: Friday, April 01, 2005 5:44 AM Subject: question about the Scherrer method Dear users of the Rietveld method: I would like to launch a question regarding the use of the Scherrer method of line-broadening analysis. When estimating the crystallite size in a undistorted material (free of lattice microstrains) using Scherrer method, should I use the integral breadth of the pure profile or its full width at haft maximum (of course, both corrected by instrumental broadening)?. Why?. Thanks in advance. Angel Luis.
Re: Occupation in Fullprof
Hi , When I have refined atomic occupation, I have wrote the same codeword, ( integer part) for both atoms in the same site and changing the decimal part, in 0.5,( in order to do a small variation) , in this way you can correlate the values for the elements present in the crystallographic site, I hope this help you. Miguel Hesiquio-Garduño Profesor Asociado C Departamento de Ciencia de Materiales Academia de Ciencias de la Ingeniería ESFM-IPN Hello to everybody. I'm trying to rifene the mixed phase Y1-xLaxBa2Cu3O7 with fullprof. For the YBaCu2O7 phase the occupation factor for Y site is 0.125 (Pmmm group). For x=0.5 in the mixed phase, the occupation factor at Y and La site is 0.0625 respectively. Can everybody tell me how can i use the codewords in order the refined site have the appropriate sum 0.125? Thanks. Dr. Tasos Gadis Physics Department - Athens University. --
