Re: GSAS informations
Dear Christophe, The coefficients Lij in the formula you wrote have no significance. This formula is a naive representation of strain anisotropy that falls at the first analysis. It is enough to change the indices hkl into equivalent indices and you obtain other Gamma. As a consequence, in cubic classes for example, the microstrain anisotropy doesn't exist, which is a nonsense. The correct formulae are indeed in Peter Stephens paper (at least for a part of Laue classes) but also in a paper by Popa, J. Appl. Cryst. (1998) 31, 176-180, where the physical significance of coefficients is explicitly stated. Hence, if denote by Eij the components of the microstrain tensor in an orthogonal coordinate system related to crystallite, then the coefficients are some linear combinations (specific to every Laue class) of the averages . Best wishes, Nicolae Popa - Original Message - From: Christophe Chabanier To: [EMAIL PROTECTED] Sent: Wednesday, April 07, 2004 6:45 PM Subject: GSAS informations Hello everybody,i have a question about the GSAS software. Indeed, i would like to know what are exactly the L11, L22, L33L23 parameters. I saw that these parameters represent the anisotropic microstrain in material. Moreover, there is an empirical _expression_ which uses these parameters as following : Gamma(L) = L11*h^2 + L22*k^2 + L33*l^2 + 2*L12*hk + 2*L13*hl + 2*L23*kl I would like to know and understand the physical representation of these parameters and this _expression_.Thanks in advance Christophe ChabanierINRS-Énergie, Matériaux et Télécommunications 1650 Blvd. Lionel Boulet C. P. 1020, Varennes Qc, Canada J3X 1S2Tél: (450) 929 8220Fax: (450) 929 8102Courriel: [EMAIL PROTECTED]
Re: GSAS information (anisotropic microstrain)
Andreas, What you say is good to know. Nonetheless, the type 4 profile model has built-in constraints according to the cell class -- so it is easy to use and refines with far greater stablility that the Lxx terms. My advice to non-experts is still the following: If you suspect that you have some reflection classes having peak widths wider than others, try out the type 4 model -- refining the Sxx terms and then eta. If the fit improves significantly, you likely have anistotropic peak broadening. If not, you don't & go back to using the type 3 model and ignore the L tensor. The Stephens model is correct only for strain broadening -- but my experience is that it does a pretty good job fitting other types of anisotropic broadening, for example anisotropic crystallite size broadening. In the cases where pretty good is not good enough, then it would make sense to check out the Lxx terms -- but only after trying the Type 4 model to confirm that the observed broading indeed does vary by reflection class. Brian Andreas Leineweber wrote: Dear Brian, recently it was pointed out (J. Appl. Cryst. 37 (2004) 123-135) that the approach proposed by Von Dreele can have indeed - under certain circumstances and restrictions to the parameters - a physical meaning, e.g. concentration fluctuations can show up like this, and the type of anisotropy constitutes a special case of the Stephens model. Best regards Andreas Leineweber Brian H. Toby wrote: My advice on this question is that one should not use this approach. The Stephens formalism, coded in profile type 4, is better founded by theory. See the GSAS manual and reference to Peter Stephen's J. Appl. Cryst paper from a few years back. Brian Christophe Chabanier wrote: Hello everybody, i have a question about the GSAS software. Indeed, i would like to know what are exactly the L11, L22, L33L23 parameters. I saw that these parameters represent the anisotropic microstrain in material. Moreover, there is an empirical expression which uses these parameters as following : Gamma(L) = L11*h^2 + L22*k^2 + L33*l^2 + 2*L12*hk + 2*L13*hl + 2*L23*kl I would like to know and understand the physical representation of these parameters and this expression. Thanks in advance Christophe Chabanier INRS-Énergie, Matériaux et Télécommunications 1650 Blvd. Lionel Boulet C. P. 1020, Varennes Qc, Canada J3X 1S2 _Tél:_ (450) 929 8220 _Fax:_ (450) 929 8102 _Courriel:_ [EMAIL PROTECTED]
Re: GSAS information (anisotropic microstrain)
Dear Brian, recently it was pointed out (J. Appl. Cryst. 37 (2004) 123-135) that the approach proposed by Von Dreele can have indeed - under certain circumstances and restrictions to the parameters - a physical meaning, e.g. concentration fluctuations can show up like this, and the type of anisotropy constitutes a special case of the Stephens model. Best regards Andreas Leineweber Brian H. Toby wrote: My advice on this question is that one should not use this approach. The Stephens formalism, coded in profile type 4, is better founded by theory. See the GSAS manual and reference to Peter Stephen's J. Appl. Cryst paper from a few years back. Brian Christophe Chabanier wrote: Hello everybody, i have a question about the GSAS software. Indeed, i would like to know what are exactly the L11, L22, L33L23 parameters. I saw that these parameters represent the anisotropic microstrain in material. Moreover, there is an empirical expression which uses these parameters as following : Gamma(L) = L11*h^2 + L22*k^2 + L33*l^2 + 2*L12*hk + 2*L13*hl + 2*L23*kl I would like to know and understand the physical representation of these parameters and this expression. Thanks in advance Christophe Chabanier INRS-Énergie, Matériaux et Télécommunications 1650 Blvd. Lionel Boulet C. P. 1020, Varennes Qc, Canada J3X 1S2 _Tél:_ (450) 929 8220 _Fax:_ (450) 929 8102 _Courriel:_ [EMAIL PROTECTED]
Re: GSAS informations
>From my experience both functions #3 and #4 work fine when broadening anisotropy is >not significant. I found #4 more works better when anisotropy is large (up to 2 times); in this case improvement is substantial Peter Zavalij -Original Message- From: Maxim V. Lobanov [mailto:[EMAIL PROTECTED] Sent: Wednesday, April 07, 2004 11:05 AM To: [EMAIL PROTECTED] At least, in the classical article by Peter Stephens (J. Appl. Cryst., 32, 281) it is written about this and similar approaches that "these methods have been successful in producing improved line-shape fits, even though no theoretical justification or microscopic model has been given". The description is given in the GSAS manual. I asssume this is a phenomenological treatment, which appears quite reasonable and convenient... By the way, GSAS has Stephens' formulation as well. Sincerely, Maxim. > > i have a question about the GSAS software. Indeed, i would like to know >what are exactly the L11, L22, L33L23 parameters. I saw that these >parameters represent the anisotropic microstrain in material. Moreover, >there is an empirical expression which uses these parameters as following : > > L22*k^2 + L33*l^2 + 2*L12*hk + 2*L13*hl + 2*L23*kl > > I would like to know and understand the physical representation of these >parameters and this expression. > __ Maxim V. Lobanov Department of Chemistry Rutgers University 610 Taylor Rd Piscataway, NJ 08854 Phone: (732) 445-3811
Re: GSAS information (anisotropic microstrain)
My advice on this question is that one should not use this approach. The Stephens formalism, coded in profile type 4, is better founded by theory. See the GSAS manual and reference to Peter Stephen's J. Appl. Cryst paper from a few years back. Brian Christophe Chabanier wrote: Hello everybody, i have a question about the GSAS software. Indeed, i would like to know what are exactly the L11, L22, L33L23 parameters. I saw that these parameters represent the anisotropic microstrain in material. Moreover, there is an empirical expression which uses these parameters as following : Gamma(L) = L11*h^2 + L22*k^2 + L33*l^2 + 2*L12*hk + 2*L13*hl + 2*L23*kl I would like to know and understand the physical representation of these parameters and this expression. Thanks in advance Christophe Chabanier INRS-Énergie, Matériaux et Télécommunications 1650 Blvd. Lionel Boulet C. P. 1020, Varennes Qc, Canada J3X 1S2 _Tél:_ (450) 929 8220 _Fax:_ (450) 929 8102 _Courriel:_ [EMAIL PROTECTED]
Re: GSAS informations
At least, in the classical article by Peter Stephens (J. Appl. Cryst., 32, 281) it is written about this and similar approaches that "these methods have been successful in producing improved line-shape fits, even though no theoretical justification or microscopic model has been given". The description is given in the GSAS manual. I asssume this is a phenomenological treatment, which appears quite reasonable and convenient... By the way, GSAS has Stephens' formulation as well. Sincerely, Maxim. > > i have a question about the GSAS software. Indeed, i would like to know >what are exactly the L11, L22, L33L23 parameters. I saw that these >parameters represent the anisotropic microstrain in material. Moreover, >there is an empirical expression which uses these parameters as following : > > L22*k^2 + L33*l^2 + 2*L12*hk + 2*L13*hl + 2*L23*kl > > I would like to know and understand the physical representation of these >parameters and this expression. > __ Maxim V. Lobanov Department of Chemistry Rutgers University 610 Taylor Rd Piscataway, NJ 08854 Phone: (732) 445-3811
GSAS informations
Hello everybody, i have a question about the GSAS software. Indeed, i would like to know what are exactly the L11, L22, L33L23 parameters. I saw that these parameters represent the anisotropic microstrain in material. Moreover, there is an empirical _expression_ which uses these parameters as following : Gamma(L) = L11*h^2 + L22*k^2 + L33*l^2 + 2*L12*hk + 2*L13*hl + 2*L23*kl I would like to know and understand the physical representation of these parameters and this _expression_. Thanks in advance Christophe Chabanier INRS-Énergie, Matériaux et Télécommunications 1650 Blvd. Lionel Boulet C. P. 1020, Varennes Qc, Canada J3X 1S2 Tél: (450) 929 8220 Fax: (450) 929 8102 Courriel: [EMAIL PROTECTED]
trns value in GSAS
Transparency of the sample causes negative shift of the high angle peaks. The sign of the transparency coefficient in GSAS depends how the formula for error is written (Is the error added or subtracted from calc. angle) but it should be always negative or always positive. How it is realized in GSAS can be found in the bible (GSAS Manual.pdf) that has explanation for everything. Peter Zavalij -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Wednesday, April 07, 2004 12:53 AM To: [EMAIL PROTECTED] Dear All rietvalders, a question about sample transparency in GSAS is asked. is there any physical meaning when its value is positive or negative? Is the sample density correlated somehow with it? since my sample becomes less dense and the neg. trns value was obtained. Hope that it won't be too silly to ask. Thank you for your advice stephen
Space group and constraints
Hi, All, 1) According to A. David Rae’s paper, Acta Cryst. (1990), B46, 474-487, B1a1 can be transformed to P1c1 using new axes (a+c)/2, b, c and origin relocated to put the glide at y=0." Please help me to convert B1a1 (non-standard setting) into P1c1 (standard setting). In particular, how to convert atomic coordinate? 2) If an atom (a1) partly occupy four different sites (b1, b2, b3 and b4) and the total amount of a1 have to keep 1.0, how to define constraints for a1 and b1~ b4 atoms in GSAS? Please give me an advice about two things. Sincerely yours, Yong-Il Kim -- School of Chemistry, University of Nottingham Nottingham NG7 2RD, UK -- _ 고.. 감.. 도.. 사.. 랑.. 만.. 들.. 기.. MSN 러브 http://www.msn.co.kr/love/ Spam detection software, running on the system "lima.ill.fr", has identified this incoming email as possible spam. The original message has been attached to this so you can view it (if it isn't spam) or block similar future email. If you have any questions, see [EMAIL PROTECTED] for details. Content preview: Hi, All, 1) According to A. David Rae¡¯s paper, Acta Cryst. (1990), B46, 474-487, B1a1 can be transformed to P1c1 using new axes (a+c)/2, b, c and origin relocated to put the glide at y=0." Please help me to convert B1a1 (non-standard setting) into P1c1 (standard setting). In particular, how to convert atomic coordinate? [...] Content analysis details: (5.7 points, 5.0 required) pts rule name description -- -- 3.2 CHARSET_FARAWAY_HEADER A foreign language charset used in headers 2.5 MIME_CHARSET_FARAWAY MIME character set indicates foreign language
Re: density of dislocations from the lattice microstrains
Dear Angel L., the bible is: Krivoglaz, M. A. (1969). Theory of X-ray and Thermal Neutron Scattering by Real Crystals. New York: Plenum. and for useful formula you can have a look on some of the following publications (the list is definitely not complet): Wilkens, M. (1970). Phys. Status Solidi A, 2, 359-370. Klimanek, P. & Kuzel, R. Jr (1988). J. Appl. Cryst. 21, 59-66, 363-368. Klimanek, P. & Kuzel, R. Jr (1989). J. Appl. Cryst. 22, 299-307. Dragomir & Ungar (2002) J. Appl. Cryst. 35, 556-564. Dragomir & Ungar (2002) Powder Diffraction. 17, 104-111. and some applications can be found in: Wu, E., Kisi, E. H. & Gray, E. Mac. A. (1998). J. Appl. Cryst. 31, 363-368. Cerny R., Joubert J.-M., Latroche M., Percheron-Guégan A. and Yvon K. J. Appl. Cryst. 33(2000)997-1005 Hope it helps Radovan [EMAIL PROTECTED] a écrit: Dear colleages, Could any of you give the details about the procedure (equations, methods) to deduce the density of dislocatins from the lattice microstrains obtained from the Stokes and Wilson or variance or integral breadth methods. Thanks in advance. Sinverely yours, Angel L. -- Radovan Cerny Laboratoire de Cristallographie 24, quai Ernest-Ansermet CH-1211 Geneva 4, Switzerland Phone : [+[41] 22] 37 964 50, FAX : [+[41] 22] 37 961 08 mailto : [EMAIL PROTECTED] URL: http://www.unige.ch/sciences/crystal/cerny/rcerny.htm
Re: density of dislocations from the lattice microstrains
Dear Angel, there is a vast number of publications about this, and each one will give you a different formula. There is some physics behind the different methods, but it is not a straightforward procedure. Most methods rely, however, on the analysis of Fourier coefficients. Look at Kamminga&Delhez, J. Appl. Cryst 33 (2000) 1122 (for a recent work), and also at works by M. Wilkens (mostly of older dates) or T.Ungar (quite recent). However, if you want to get reliable dislocation densities, you have to know that much about your dislocations that there is no sense any more to determine them by X-ray powder diffraction. (perhaps an exteme statement). Andreas Leineweber [EMAIL PROTECTED] wrote: Dear colleages, Could any of you give the details about the procedure (equations, methods) to deduce the density of dislocatins from the lattice microstrains obtained from the Stokes and Wilson or variance or integral breadth methods. Thanks in advance. Sinverely yours, Angel L.
density of dislocations from the lattice microstrains
Dear colleages, Could any of you give the details about the procedure (equations, methods) to deduce the density of dislocatins from the lattice microstrains obtained from the Stokes and Wilson or variance or integral breadth methods. Thanks in advance. Sinverely yours, Angel L.
