Re: Size Strain in GSAS
Title: Message Dear Bob, Perhaps I was not enough clear. Let me be more explicit. It's about one sample of CeO2 (not that from round-robin) that we fitted in 4 ways. (i) by GSAS with TCH-pV (ii) by another pV resulted from gamma distribution of size (iii) by Lorentz - (the limit of any "regular" pV - eta=1) All these 3 variants given bad fits. For example (ii): Rw=0.144, similarly the rest. (In principle if one pV works (TCH for example) any other kind of pV must work.) (iv) by the profile resulted from lognormal distribution of size; this time the fit was reasonably good: Rw=0.047. It resulted c=2.8, that means a "super Lorentzian" profile (I remember that the Lorentzian limit for lognormal is c~0.4 - JAC (2002) 35, 338). Attention, this "super Lorentzian" profile is not constructed as a pV with eta>1. Sure, such samples are rare, or, perhaps, not so rare. A Jap. group (Ida,, Toraya, JAC (2003) 36, 1107) reported "super Lorentzian" on a sample of SiC. They found c=1.37 Best wishes, Nic Popa Nic, This is true for the internal math but the TCH function was assembled to reproduce the true Voigt over the entire range of differing Lorentz and Gauss FWHM values so it works as if the two FWHM components are independent. As for your question, I'm not aware that anyone has actually tried to do the fit both ways on a "super Lorentzian" (eta>1 for old psVoigt) sample to see if a) the fit is the same and b) the eta>1 was an artifact. Any takers to settle this? Bob R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -Original Message-From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Thursday, April 14, 2005 9:11 AMTo: rietveld_l@ill.frSubject: Re: Size Strain in GSAS Dear Bob, If I understand well, you say that eta>1 (super Lorenzian) appeared only because eta was free parameter, but if TCH is used super Loreanzians do not occur? Nevertheless, for that curious sample of cerium oxide we tried GSAS (with TCH) and the fit was very bad. Best wishes, Nicolae PS. By the way, TCH also forces FWHM of the Gaussian and Lorenzian components to be equal, but indeed, eta is not free and cannot be greater than 1. Nic, I know about "super Lorentzians". Trouble is that many of those older reports were from Rietveld refinements "pre TCH" and used a formulation of the pseudo-Voigt which forced the FWHM of the Gaussian and Lorentzian components to be equal and allowed the mixing coefficient (eta) to be a free variable (n.b. it is not free in the TCH formulation). Thus, these ought to be discounted in any discussion about the occurence of super Lorentzian effects in real samples. Bob R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -Original Message-From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Thursday, April 14, 2005 8:10 AMTo: rietveld_l@ill.frSubject: Re: Size Strain in GSAS Right, is rare, but we have meet once. A cerium oxide sample from a commercial company, c=2.8. I don't know if they did deliberately, probably not, otherwise the hard work to obtain such curiosity is costly and the company risks a bankruptcy. On the other hand superlorenzian profiles were reported from a long time, only were interpreted as coming from bimodal size distributions. And third, you see, people have difficulties to extract size distribution from the Rietveld codes as they are at this moment. Nicolae Popa A word from a "provider" of a Rietveld code (please don't call me a "programmer"). "But if c>0.4 any pV fails" - OK, for what fraction of the universe of "real world" samples is "c">0.4? I suspect, given the general success of the TCH pseudoVoigt function, that it is exceedingly small and only occurs when one works hard to deliberately make a sample like that. R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -Original Message-From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Thursday, April 14, 2005 7:14 AMTo: [EMAIL PROTECTED]Cc: rietveld_l@ill.frSubject: Re: Size Strain in GSAS >Dear Nicolae, >Maybe ya ploho chitayu i ploho soobrazhayu, but even after your>explanation I can't see a way to calculate from the results of>fitt
Re: Size Strain in GSAS
Title: Message Nicolae, Nick, Bob, Leonid, I have looked at many patterns (recorded by others) and a few cases have shown profiles that are sharper that a Lorentzian; whereby “sharper” means that the integral breadth is smaller than that for a unit area lorentzian. To put a figure on it would be difficult but at a guess I would say < 3% of patterns fall into this category in a noticeable manner. I have no doubt that the work of Nick Armstrong and co. is mathematically sound but a simulated data round robin as suggested by Leonid Solovyov may be useful – and I am not generally a fan of round robins but this s different as the data is simulated. A pure peak fitting approach shows that two pV’s (or two Voigts) when added with different FWHMs and integrated intensities but similar peak positions and eta values can almost exactly fit Pearsons II functions that are sharper that Lorentzians. This is not surprising as both profiles comprise 6 parameters. Thus from my observations two pVs added together can fit a bimodal distributions quite easily. In fact my guess is that two pVs can fit a large range of crystallite size distributions. Thus distinguishing whether a distribution is not monomodal is of course possible especially if the two pV approach is taken. Attempting to determine more than that however takes some convincing as two pVs seem to fit almost anything that I have seen that is symmetric. Thus introducing more pVs seems unnecessary. Thus yes GSAS can determine if a distribution is not monmodal if you were to fit two identical phases to the pattern except for the TCH parameters. If the Rwp drops by .1% then I wont be convinced. Forgive me Nick but I have not yet read all of your work and I am certain that it is sound. Outside of nano particles (and maybe even inside) my reservation are that we may well be analyzing noise and second order sample and instrumental effects. Thus to show up my naive ness can you categorically say that there are real world distributions that two pseudo Voigts cannot fit because I have not come across such a pattern. Once you have done that then it would be time to concentrate on strain, micro strain, surface roughness and then disloactions all the best alan -Original Message-From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Friday, April 15, 2005 9:30 AMTo: rietveld_l@ill.frSubject: Re: Size Strain in GSAS Dear Bob, Perhaps I was not enough clear. Let me be more explicit. It's about one sample of CeO2 (not that from round-robin) that we fitted in 4 ways. (i) by GSAS with TCH-pV (ii) by another pV resulted from gamma distribution of size (iii) by Lorentz - (the limit of any "regular" pV - eta=1) All these 3 variants given bad fits. For example (ii): Rw=0.144, similarly the rest. (In principle if one pV works (TCH for example) any other kind of pV must work.) (iv) by the profile resulted from lognormal distribution of size; this time the fit was reasonably good: Rw=0.047. It resulted c=2.8, that means a "super Lorentzian" profile (I remember that the Lorentzian limit for lognormal is c~0.4 - JAC (2002) 35, 338). Attention, this "super Lorentzian" profile is not constructed as a pV with eta>1. Sure, such samples are rare, or, perhaps, not so rare. A Jap. group (Ida,, Toraya, JAC (2003) 36, 1107) reported "super Lorentzian" on a sample of SiC. They found c=1.37 Best wishes, Nic Popa Nic, This is true for the internal math but the TCH function was assembled to reproduce the true Voigt over the entire range of differing Lorentz and Gauss FWHM values so it works as if the two FWHM components are independent. As for your question, I'm not aware that anyone has actually tried to do the fit both ways on a "super Lorentzian" (eta>1 for old psVoigt) sample to see if a) the fit is the same and b) the eta>1 was an artifact. Any takers to settle this? Bob R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -Original Message-From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Thursday, April 14, 2005 9:11 AMTo: rietveld_l@ill.frSubject: Re: Size Strain in GSAS Dear Bob, If I understand well, you say that eta>1 (super Lorenzian) appeared only because eta was free parameter, but if TCH is used super Loreanzians do not occur? Nevertheless, for that curious sample of cerium oxide we tried GSAS (with TCH) and the fit was very bad. Best wishes, Nicolae PS. By the way, TCH also forces FWHM of the Gaussian and Lorenzian components to be equal, but indeed, eta is not free and cannot be greater than 1. Nic, I know ab
Re: Size Strain in GSAS
Hi, In response to some of this post: There was a move by a bunch of us in the ICDD to hold a profile fitting round robin ( which I think would by quite useful ). But it died when we realized the prodigious level of resources that would be required to make sense of the rather large matrix of data that would arrive. But with regards to a round robin on this question: seems to me some qualified individual could simply do the work and publish a nice paper on it. Regards, Jim At 12:30 PM 4/15/2005 +0200, you wrote: "urn:schemas-microsoft-com:office:office"> Nicolae, Nick, Bob, Leonid, I have looked at many patterns (recorded by others) and a few cases have shown profiles that are sharper that a Lorentzian; whereby sharper means that the integral breadth is smaller than that for a unit area lorentzian. To put a figure on it would be difficult but at a guess I would say < 3% of patterns fall into this category in a noticeable manner. I have no doubt that the work of Nick Armstrong and co. is mathematically sound but a simulated data round robin as suggested by Leonid Solovyov may be useful and I am not generally a fan of round robins but this s different as the data is simulated. A pure peak fitting approach shows that two pV s (or two Voigts) when added with different FWHMs and integrated intensities but similar peak positions and eta values can almost exactly fit Pearsons II functions that are sharper that Lorentzians. This is not surprising as both profiles comprise 6 parameters. Thus from my observations two pVs added together can fit a bimodal distributions quite easily. In fact my guess is that two pVs can fit a large range of crystallite size distributions. Thus distinguishing whether a distribution is not monomodal is of course possible especially if the two pV approach is taken. Attempting to determine more than that however takes some convincing as two pVs seem to fit almost anything that I have seen that is symmetric. Thus introducing more pVs seems unnecessary. Thus yes GSAS can determine if a distribution is not monmodal if you were to fit two identical phases to the pattern except for the TCH parameters. If the Rwp drops by .1% then I wont be convinced. Forgive me Nick but I have not yet read all of your work and I am certain that it is sound. Outside of nano particles (and maybe even inside) my reservation are that we may well be analyzing noise and second order sample and instrumental effects. Thus to show up my naive ness can you categorically say that there are real world distributions that two pseudo Voigts cannot fit because I have not come across such a pattern. Once you have done that then it would be time to concentrate on strain, micro strain, surface roughness and then disloactions all the best alan -Original Message- From: Nicolae Popa [mailto:[EMAIL PROTECTED]] Sent: Friday, April 15, 2005 9:30 AM To: rietveld_l@ill.fr Subject: Re: Size Strain in GSAS Dear Bob, Perhaps I was not enough clear. Let me be more explicit. It's about one sample of CeO2 (not that from round-robin) that we fitted in 4 ways. (i) by GSAS with TCH-pV (ii) by another pV resulted from gamma distribution of size (iii) by Lorentz - (the limit of any "regular" pV - eta=1) All these 3 variants given bad fits. For example (ii): Rw=0.144, similarly the rest. (In principle if one pV works (TCH for example) any other kind of pV must work.) (iv) by the profile resulted from lognormal distribution of size; this time the fit was reasonably good: Rw=0.047. It resulted c=2.8, that means a "super Lorentzian" profile (I remember that the Lorentzian limit for lognormal is c~0.4 - JAC (2002) 35, 338). Attention, this "super Lorentzian" profile is not constructed as a pV with eta>1. Sure, such samples are rare, or, perhaps, not so rare. A Jap. group (Ida,, Toraya, JAC (2003) 36, 1107) reported "super Lorentzian" on a sample of SiC. They found c=1.37 Best wishes, Nic Popa Nic, This is true for the internal math but the TCH function was assembled to reproduce the true Voigt over the entire range of differing Lorentz and Gauss FWHM values so it works as if the two FWHM components are independent. As for your question, I'm not aware that anyone has actually tried to do the fit both ways on a "super Lorentzian" (eta>1 for old psVoigt) sample to see if a) the fit is the same and b) the eta>1 was an artifact. Any takers to settle this? Bob R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -Original Message- From: Nicolae Popa [mailto:[EMAIL PROTECTED]] Sent: Thursday, April 14, 2005 9:11 AM To: rietveld_l@ill.fr Subject: Re: Size Strain in GSAS Dear Bob, If I understand well, you say that eta>1 (super Lorenzian) appeared only because eta was free parameter, but if TCH is used super Loreanzians do not occur? Nevertheless, for that curious sample of cerium oxide we tried GSAS (with TCH) and the fit was very bad. Best wishes, N
Re: Size Strain in GSAS
Nic, Well, I have been tempted from time to time to implement a "log normal" type distribution in on eof the profile functions. A "nice" math description ameanable to RR would help. Bob From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Fri 4/15/2005 2:30 AM To: rietveld_l@ill.fr Dear Bob, Perhaps I was not enough clear. Let me be more explicit. It's about one sample of CeO2 (not that from round-robin) that we fitted in 4 ways. (i)by GSAS with TCH-pV (ii) by another pV resulted from gamma distribution of size (iii) by Lorentz - (the limit of any "regular" pV - eta=1) All these 3 variants given bad fits. For example (ii): Rw=0.144, similarly the rest. (In principle if one pV works (TCH for example) any other kind of pV must work.) (iv) by the profile resulted from lognormal distribution of size; this time the fit was reasonably good: Rw=0.047. It resulted c=2.8, that means a "super Lorentzian" profile (I remember that the Lorentzian limit for lognormal is c~0.4 - JAC (2002) 35, 338). Attention, this "super Lorentzian" profile is not constructed as a pV with eta>1. Sure, such samples are rare, or, perhaps, not so rare. A Jap. group (Ida,, Toraya, JAC (2003) 36, 1107) reported "super Lorentzian" on a sample of SiC. They found c=1.37 Best wishes, Nic Popa Nic, This is true for the internal math but the TCH function was assembled to reproduce the true Voigt over the entire range of differing Lorentz and Gauss FWHM values so it works as if the two FWHM components are independent. As for your question, I'm not aware that anyone has actually tried to do the fit both ways on a "super Lorentzian" (eta>1 for old psVoigt) sample to see if a) the fit is the same and b) the eta>1 was an artifact. Any takers to settle this? Bob R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -Original Message- From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Thursday, April 14, 2005 9:11 AM To: rietveld_l@ill.fr Subject: Re: Size Strain in GSAS Dear Bob, If I understand well, you say that eta>1 (super Lorenzian) appeared only because eta was free parameter, but if TCH is used super Loreanzians do not occur? Nevertheless, for that curious sample of cerium oxide we tried GSAS (with TCH) and the fit was very bad. Best wishes, Nicolae PS. By the way, TCH also forces FWHM of the Gaussian and Lorenzian components to be equal, but indeed, eta is not free and cannot be greater than 1. Nic, I know about "super Lorentzians". Trouble is that many of those older reports were from Rietveld refinements "pre TCH" and used a formulation of the pseudo-Voigt which forced the FWHM of the Gaussian and Lorentzian components to be equal and allowed the mixing coefficient (eta) to be a free variable (n.b. it is not free in the TCH formulation). Thus, these ought to be discounted in any discussion about the occurence of super Lorentzian effects in real samples. Bob R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -Original Message- From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Thursday, April 14, 2005 8:10 AM To: rietveld_l@ill.fr Subject: Re: Size Strain in GSAS Right, is rare, but we have meet once. A cerium oxide sample from a commercial company, c=2.8. I don't know if they did deliberately, probably not, otherwise the hard work to obtain such curiosity is costly and the company risks a bankruptcy. On the other hand superlorenzian profiles were reported from a long time, only were interpreted as coming from bimodal size distributions. And third, you see, people have difficulties to extract size distribution from the Rietveld codes as they are at this moment. Nicolae Popa A word from a "provider" of a Rietveld code (please
Re: Size Strain in GSAS
Alan, Ah - the "rocks & dust" model. It works well. Bob From: alan coelho [mailto:[EMAIL PROTECTED] Sent: Fri 4/15/2005 5:30 AM To: rietveld_l@ill.fr Nicolae, Nick, Bob, Leonid, I have looked at many patterns (recorded by others) and a few cases have shown profiles that are sharper that a Lorentzian; whereby "sharper" means that the integral breadth is smaller than that for a unit area lorentzian. To put a figure on it would be difficult but at a guess I would say < 3% of patterns fall into this category in a noticeable manner. I have no doubt that the work of Nick Armstrong and co. is mathematically sound but a simulated data round robin as suggested by Leonid Solovyov may be useful - and I am not generally a fan of round robins but this s different as the data is simulated. A pure peak fitting approach shows that two pV's (or two Voigts) when added with different FWHMs and integrated intensities but similar peak positions and eta values can almost exactly fit Pearsons II functions that are sharper that Lorentzians. This is not surprising as both profiles comprise 6 parameters. Thus from my observations two pVs added together can fit a bimodal distributions quite easily. In fact my guess is that two pVs can fit a large range of crystallite size distributions. Thus distinguishing whether a distribution is not monomodal is of course possible especially if the two pV approach is taken. Attempting to determine more than that however takes some convincing as two pVs seem to fit almost anything that I have seen that is symmetric. Thus introducing more pVs seems unnecessary. Thus yes GSAS can determine if a distribution is not monmodal if you were to fit two identical phases to the pattern except for the TCH parameters. If the Rwp drops by .1% then I wont be convinced. Forgive me Nick but I have not yet read all of your work and I am certain that it is sound. Outside of nano particles (and maybe even inside) my reservation are that we may well be analyzing noise and second order sample and instrumental effects. Thus to show up my naive ness can you categorically say that there are real world distributions that two pseudo Voigts cannot fit because I have not come across such a pattern. Once you have done that then it would be time to concentrate on strain, micro strain, surface roughness and then disloactions all the best alan -Original Message- From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Friday, April 15, 2005 9:30 AM To: rietveld_l@ill.fr Subject: Re: Size Strain in GSAS Dear Bob, Perhaps I was not enough clear. Let me be more explicit. It's about one sample of CeO2 (not that from round-robin) that we fitted in 4 ways. (i)by GSAS with TCH-pV (ii) by another pV resulted from gamma distribution of size (iii) by Lorentz - (the limit of any "regular" pV - eta=1) All these 3 variants given bad fits. For example (ii): Rw=0.144, similarly the rest. (In principle if one pV works (TCH for example) any other kind of pV must work.) (iv) by the profile resulted from lognormal distribution of size; this time the fit was reasonably good: Rw=0.047. It resulted c=2.8, that means a "super Lorentzian" profile (I remember that the Lorentzian limit for lognormal is c~0.4 - JAC (2002) 35, 338). Attention, this "super Lorentzian" profile is not constructed as a pV with eta>1. Sure, such samples are rare, or, perhaps, not so rare. A Jap. group (Ida,, Toraya, JAC (2003) 36, 1107) reported "super Lorentzian" on a sample of SiC. They found c=1.37 Best wishes, Nic Popa Nic, This is true for the internal math but the TCH function was assembled to reproduce the true Voigt over the entire range of differing Lorentz and Gauss FWHM values so it works as if the two FWHM components are independent. As for your question, I'm not aware that anyone has actually tried to do the fit both ways on a "super Lorentzian" (eta>1 for old psVoigt) sample to see if a) the fit is the same and b) the eta>1 was an artifact. Any takers to settle this? Bob R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -Original Message- From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Thursday, April 14, 2005 9:11 AM To: rietveld_l@ill.fr Subject: Re: Size Strain in GSAS Dear Bob,
request
Dear all, Can anyone please send me the following articles. The electrodeposition of precious metals; a review of the fundamental electrochemistry ARTICLE Electrochimica Acta, Volume 18, Issue 11, November 1973, Pages 829-834 J. A. Harrison and J. Thompson Electrochemistry of electroless plating ARTICLE Materials Science and Engineering A, Volume 146, Issues 1-2, 25 October 1991, Pages 33-49 Izumi Ohno Electrolytic bath for the electrodeposition of noble metals and their alloys PATENT REPORT Metal Finishing, Volume 102, Issue 4, April 2004, Page 71 Electrodeposition of metals and alloysnew results and perspectives ARTICLE Electrochimica Acta, Volume 39, Issues 8-9, June 1994, Pages 1091-1105 René Winand Our place doesn't subscribe these journals... thankyou venkat
