Dear Maxim, I have a large number of structures refined with single crystal data collected at 100 K with Ueq parameters very close or even larger than those of your structure (considering Biso=Ueq/(8pi**2). I had never heard of the mentioned hard limits for acceptable thermal parameters in a structure. At least I have never seen a checkcif alert of that kind. The checkcif alert you are getting sounds reasonable for a slightly rotationally disorder PO4.
It looks odd that different Ba atoms may differ by almost 100% in Uiso but having a good fit may justify these values. If you look at the ICSD you will find many structures with refined thermal parameters. I bet there you will find other phosphates with some thermal parameters refined with neutrons data that will give you enough evidence to refute the referee or to think more about your result. If you need help with searching the ICSD please let me know through a personal e-mail. IMHO your Biso are within acceptable values. I hope this helps. Best regards, Leo El mié., 29 ago. 2018 a las 12:25, Максим Молокеев (<msmolok...@mail.ru>) escribió: > Dear Colleagues, > > I need your expert point of view on the complex problem associated with > the thermal parameters. > > *Description:* > New crystal structure contained Ba, Ca, K, P,O elements (with some Mn,Eu > dopants) was solved and refined using Topas 4.2. The Checkcif tool found > only a few Alert C, namely: Low ’MainMol’ Ueq as Compared to Neighbors of > P1. The thermal parameters Biso of Ba ion are in the range of > 1.52(8)-2.84(5) A^2, Biso(Ca)= 2.5(2)A^2, Biso(K) = 1.1(1) A^2, > Biso(P)=1.52(6) A^2, O ions have 3.2(1) A^2 (one parameter for all O ions). > There are 15 independent ions in the asymmetric cell. The pattern was > measured using CuKa in the range of 5-140 deg. Max. Intensity ~200.000 Cps. > > *The Problem:* > The Reviewer wrote that the suggested crystal structure was less than > satisfactory because Biso should be less that 0.7A^2 for cations and less > than 2A^2 for oxygens. > > *The similar published structure with the same problem:* > I have found the cif-file of the similar structure Ba2CaNa3(PO4)3, which > was solved/refined using single crystal method, that Biso(Ba) are in the > range of 1.58-1.75 A^2 which is much bigger than 0.7 A^2 and the Biso(O) > values vary in the range of 1.42-4.3 A^2. > > *So, I have the questions:* > -Where can I get the reliable information about the trustful range for > thermal parameters? > -Who and why decides to involve these maximal values 0.7 A^2 for heavy > ions and 2A^2 for oxygen ions. Maybe do you know the relevant manuscript? > -Whether the Ba2CaNa3(PO4)3 structure [Kim, M., Kobayashi, M., Kato, H., > Yamane, H., Sato, Y., & Kakihana, M. (2015). Dalton Transactions, 44(4), > 1900-1904] with so "big" thermal parameter also was solved/refined using > single crystal experiment less than satisfactory? > > I think the problem will arise several times in the future and answers > will be a great help to many subscribers here. > Sorry for long text. > > Best wishes, > Maxim > > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > Please do NOT attach files to the whole list <alan.he...@neutronoptics.com > > > Send commands to <lists...@ill.fr> eg: HELP as the subject with no body > text > The Rietveld_L list archive is on > http://www.mail-archive.com/rietveld_l@ill.fr/ > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ > > -- Dr. Leopoldo Suescun Prof. Agr (Assoc. Prof.) de Física Tel: (+598) 29290705/29249859 Cryssmat-Lab./Cátedra de Fisica/DETEMA Fax: (+598) 29241906* Facultad de Quimica, Universidad de la Republica. Montevideo, Uruguay Ahora la cristalografía importa más (www.iucr.org) Crystallography Matters more.
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