Internal standards
Does anyone have a suggestion for a vendor that has crystalline corundum, zincite and/or rutile to use as internal standards except NIST? The SRM standards are very expensive for very little quantity. Thank you, Maria Chrysochoou Assistant Professor Department of Civil and Environmental Engineering University of Connecticut Storrs CT 06269 E-Mail: [EMAIL PROTECTED] Tel.: (860) 486 3594 Fax: (860) 486 2298
Re: Internal standards
Dear Maria, We are developing standard materials for XRD and can help you. You can write directly to my e-mail for details. Luis Quoting Chrysochoou, Maria [EMAIL PROTECTED]: Does anyone have a suggestion for a vendor that has crystalline corundum, zincite and/or rutile to use as internal standards except NIST? The SRM standards are very expensive for very little quantity. Thank you, Maria Chrysochoou Assistant Professor Department of Civil and Environmental Engineering University of Connecticut Storrs CT 06269 E-Mail: [EMAIL PROTECTED] Tel.: (860) 486 3594 Fax: (860) 486 2298 -- Dr. Luis Gallego Martinez Comissão Nacional de Energia Nuclear Instituto de Pesquisas Energéticas e Nucleares Centro de Ciência e Tecnologia de Materiais Av. Prof. Lineu Prestes 2242 Cidade Universitária - USP São Paulo - SP - Brasil - CEP:05508-000 Tel: + 55 11 3133-9222 Fax: 3133-9276 [EMAIL PROTECTED] www.ipen.br
Question on Rietveld with x-ray
Dear experts on Rietveld with x-ray, When it comes to Rietveld, I have exclusively been working with neutrons. Now I am just trying Rietveld with x-rays, and immediately came up with a question. Since x-ray scatters from electrons, it seems to me that we always have to use, for instance, O-2 instead of O, and so on, for ionic compounds. But I have an impression that O is still used in many examples, including certain example files given in GSAS, such as Y2O3.EXP. Why is it? As a naturally following question, since no material is perfectly ionic, the oxidation numbers may become another refinable parameters. But I suppose they are never refinable in GSAS or in FullProf. Therefore, I suppose the fractional occupation may be compromised instead? Is this in any way discussed among x-ray experts? Thanks a million in advance. Jae-Ho *** Jae-Ho Chung, Assistant Professor Department of Physics, Korea University Anam-dong 5, Seongbook-gu Seoul 136-713, Rep. of Korea tel.) +82-2-3290-3116 fax.) +82-2-927-3292 web.) http://scattering.korea.ac.kr http://scattering.korea.ac.kr ***
Re: Question on Rietveld with x-ray
Jae-Ho Chung wrote: Dear experts on Rietveld with x-ray, When it comes to Rietveld, I have exclusively been working with neutrons. Now I am just trying Rietveld with x-rays, and immediately came up with a question. Since x-ray scatters from electrons, it seems to me that we always have to use, for instance, O-2 instead of O, and so on, for ionic compounds. But I have an impression that O is still used in many examples, including certain example files given in GSAS, such as Y2O3.EXP. Why is it? I suggest that you plot the scattering curves for O and O-2, and then decide how much difference it makes. In addition, you should also postulate a theory concerning the differences. Hint: The electron cloud is not a point object. As a naturally following question, since no material is perfectly ionic, the oxidation numbers may become another “refinable” parameters. But I suppose they are never refinable in GSAS or in FullProf. Therefore, I suppose the fractional occupation may be compromised instead? Is this in any way discussed among x-ray experts? See above. What experiment would you propose to make the oxidation number be refinable? Larry
RE: Question on Rietveld with x-ray
To all: The mathematical description of crystals is valid for the bulk of the volume. However, the description suffers from a physical termination of series effect at the surface of the crystal. For very large crystals, the amount of surface is much greater relative to the total volume of the crystal. However, when the crystalline material approaches what we now refer to as the nano state (perhaps less than 40 Angstroms - 8 to 10 unit cells), the amount of surface becomes significant. The chemical composition - oxidation state of surface atoms - is intuitively different at the surface of a material than within the bulk. How does one deal with that situation? The effects are present in the powder pattern; how does one model them? Frank May Research Investigator Department of Chemistry Biochemistry University of Missouri - St. Louis One University Boulevard St. Louis, Missouri 63121-4499 U.S.A 314-516-5098 - office 314-623-4524 - cell From: Larry Finger [mailto:[EMAIL PROTECTED] Sent: Wed 4/2/2008 9:47 AM To: Jae-Ho Chung Cc: Rietveld_L@ill.fr Subject: Re: Question on Rietveld with x-ray Jae-Ho Chung wrote: Dear experts on Rietveld with x-ray, When it comes to Rietveld, I have exclusively been working with neutrons. Now I am just trying Rietveld with x-rays, and immediately came up with a question. Since x-ray scatters from electrons, it seems to me that we always have to use, for instance, O-2 instead of O, and so on, for ionic compounds. But I have an impression that O is still used in many examples, including certain example files given in GSAS, such as Y2O3.EXP. Why is it? I suggest that you plot the scattering curves for O and O-2, and then decide how much difference it makes. In addition, you should also postulate a theory concerning the differences. Hint: The electron cloud is not a point object. As a naturally following question, since no material is perfectly ionic, the oxidation numbers may become another refinable parameters. But I suppose they are never refinable in GSAS or in FullProf. Therefore, I suppose the fractional occupation may be compromised instead? Is this in any way discussed among x-ray experts? See above. What experiment would you propose to make the oxidation number be refinable? Larry
