RE: Preferred orientation?
You can check for texture effects (preferred orientation) by obtaining multiple patterns of the material. It's realistic to expect some differences, but preferred orientation is manifest by not being able to replicate the pattern. That's the simple test. Let us know what you find. Another issue for "improper intensities" is when the specimen is not sufficiently wide enough at low angles (typically below 20-degrees 2-Theta with copper radiation) and the x-ray beam does not fully impinge on the specimen. The observed reflections in the low angle region will be less than calculated by a modelling program. Frank May Research Investigator Department of Chemistry and Biochemistry University of Missouri - St. Louis One University Boulevard St. Louis, Missouri 63121-4499 314-516-5098 From: Gerard, Garcia S [mailto:[EMAIL PROTECTED] Sent: Wed 5/7/2008 8:57 AM To: rietveld_l@ill.fr Subject: Preferred orientation? Dear all, I have a laboratory Bragg-Brentano X-ray (Cu) pattern that shows intensity mismatches only at low angles, ie 20-50 2theta or 1.8 to 4 Angstroms. There are overestimated peaks and also underestimated peaks.I have tried to discard factors that might cause this problem: The thermal parameters look sensible. Moreover, the data at high angle looks ok, so intensity transfer from low angle to high angle or vice versa does not seem to be the cause. Atomic positions also look sensible. And again, data at high angle looks ok. Is the scattering angle dependence of the atomic positions the same as for the thermal parameters? (I cannot remember that, but i am pretty sure it is not). Following the advice published in J. Appl. Cryst. 32, 36 (1999), the other factor that might cause this problem is preferred orientation: I have tried to find a hkl dependence in the overestimated and underestimated peaks but i could not find any. If i try to model preferred orientation with spherical harmonics the problems disappears nicely. The problem is how to justify the existence of preferred orientation. The crystal system is orthorhombic. But i have no other information that supports the existence of preferred orientation. Is there any other problem that I cannot think of?Is the preferred orientation correction masking any of these other problems I cannot think of? Regards Gerard Heriot-Watt University is a Scottish charity registered under charity number SC000278.
Re: Article
José Carlos Cordeiro said: > I would like to get the article: > "Polymorphism of tricalcium silicate in Portland cement: a fast visual > identification of structure and superstructure" This 2003 Powder Diffraction article is available from ICDD on-line for those with a subscription at: http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PODIE218010701&idtype=cvips&gifs=yes __ Dr Alan Hewat, NeutronOptics, Grenoble, FRANCE <[EMAIL PROTECTED]> +33.476.98.41.68 http://www.NeutronOptics.com/hewat __
Article
I would like to get the article: "Polymorphism of tricalcium silicate in Portland cement: a fast visual identification of structure and superstructure" I search this article in the Internet but without success, can anybody help me?? thanks === José Carlos Cordeiro Votorantim Cements Brazil === DISCLAIMER: Esta mensagem e seus anexos são destinados exclusivamente ao(s) destinatário(s) identificado(s) acima e contêm informações confidenciais ou privilegiadas. Se você não é o destinatário destes materiais, não está autorizado a utilizá-los para nenhum fim. Solicitamos que você apague a mensagem e seus anexos e avise imediatamente o remetente. O conteúdo desta mensagem e de seus anexos não representa necessariamente a opinião e a intenção da empresa, não implicando em qualquer obrigação ou responsabilidade adicionais. Este mensaje y sus anexos son destinados exclusivamente a los destinatarios identificados arriba y contiene información confidencial o privilegiada. Si no es el destinatario de este mensaje, o una persona autorizada para recibirlo, usted no está autorizada a utilizarlo para ningún fin. Cualquier revisión, difusión, distribución o copiado de este mensaje está prohibido. Si ha recibido este e-mail por error por favor bórrelo y envíe un mensaje al remitente.El contenido de este mensaje y de sus anexos no necesariamente representa la opinión o intención de la empresa, ni implica ninguna obligación legal o responsabilidad para la empresa. This message and its attachments are addressed exclusively to identified addressee and contain confidential and/or privileged information. If you are not the addressee or an authorized person to receive this, you must not use, copy, disclose or take any action based on this message or any information herein. If you have received this message by mistake, please, advise the sender immediately by replying the e-mail and delete this message. The contents of this message and its attachments do not necessarily express the opinion or the intention of the company, and do not implies any legal obligation or responsibilities from this company.
Re: Preferred orientation?
Dear Gerard, The low-angle intensity problem might come from disordered regions, like water or solvent molecules occupying some voids. Also, poor modeling of weakly scattering atoms, like hydrogen, may lead to the similar problem. Best regards, Yaroslav http://filinchuk.com ===8<==Original message text=== Dear all, I have a laboratory Bragg-Brentano X-ray (Cu) pattern that shows intensity mismatches only at low angles, ie 20-50 2theta or 1.8 to 4 Angstroms. There are overestimated peaks and also underestimated peaks.I have tried to discard factors that might cause this problem: The thermal parameters look sensible. Moreover, the data at high angle looks ok, so intensity transfer from low angle to high angle or vice versa does not seem to be the cause. Atomic positions also look sensible. And again, data at high angle looks ok. Is the scattering angle dependence of the atomic positions the same as for the thermal parameters? (I cannot remember that, but i am pretty sure it is not). Following the advice published in J. Appl. Cryst. 32, 36 (1999), the other factor that might cause this problem is preferred orientation: I have tried to find a hkl dependence in the overestimated and underestimated peaks but i could not find any. If i try to model preferred orientation with spherical harmonics the problems disappears nicely. The problem is how to justify the existence of preferred orientation. The crystal system is orthorhombic. But i have no other information that supports the existence of preferred orientation. Is there any other problem that I cannot think of?Is the preferred orientation correction masking any of these other problems I cannot think of? Regards Gerard -- Heriot-Watt University is a Scottish charity registered under charity number SC000278. ===8<===End of original message text===
Preferred orientation?
Dear all, I have a laboratory Bragg-Brentano X-ray (Cu) pattern that shows intensity mismatches only at low angles, ie 20-50 2theta or 1.8 to 4 Angstroms. There are overestimated peaks and also underestimated peaks.I have tried to discard factors that might cause this problem: The thermal parameters look sensible. Moreover, the data at high angle looks ok, so intensity transfer from low angle to high angle or vice versa does not seem to be the cause. Atomic positions also look sensible. And again, data at high angle looks ok. Is the scattering angle dependence of the atomic positions the same as for the thermal parameters? (I cannot remember that, but i am pretty sure it is not). Following the advice published in J. Appl. Cryst. 32, 36 (1999), the other factor that might cause this problem is preferred orientation: I have tried to find a hkl dependence in the overestimated and underestimated peaks but i could not find any. If i try to model preferred orientation with spherical harmonics the problems disappears nicely. The problem is how to justify the existence of preferred orientation. The crystal system is orthorhombic. But i have no other information that supports the existence of preferred orientation. Is there any other problem that I cannot think of?Is the preferred orientation correction masking any of these other problems I cannot think of? Regards Gerard -- Heriot-Watt University is a Scottish charity registered under charity number SC000278.
