Some pieces of advice would lead to spending to much time for nothing, I'm afraid. First of all, Arya does not mention whether the synthesis concerns an inorganic or an organic substance. This is a very important distinction since there are considerably more organic compounds than inorganic ones and less often already characterised crystallographically.
Dr. Quinn's remark concerning the appearance of the diffraction pattern is very important. Do the the lines tend to be "equally spaced" or are there clusters (even overlaps)? The latter scenario shows signs that the symmetry is low (and is extremely seldom cubic for organic compounds because of an unrealistic demand to fullfil a molecular packing that allows for the automatic constraint of four threefold axes simultaneously of molecular entities). Again, if there are many peaks (more than 30, say) within the first 45 degrees (theta) the symmetry is most likely to be less than cubic.
In order to index a completely unknown pattern the first thing is the ensure that it comes from a the sample that is single phase. The next thing is to test for mathematical relations between Q-values to get a fair picture of the difficulty. In general, the task is not one should gladly start with without experience, so I recommend to look for a single crystal. Even that may be a difficult thing to find, but if you have a single crystal pattern, the indexing is more or less straightforward.
Good hunt!
Sir,
From XRD data, we will get 2theta values. From that, how can we calculate the (h,k,l) values? What i am thinking is, if we get the (h,k,l) values, we can easily find out whether it is FCC, BCC or cubic. ( if h+k+l= even means it is BCC and if (h,k,l) values are all odd or all even means it is FCC otherwise it may be cubic). Is there any method to calculate the (h,k,l) values without having any information other than XRD data ?
Addition
The microstructural parameters crystallite size‘t’ and lattice constant a=b=c are found using the formulae,
t = 0.89 λ/βcosθ-----(i)
Where β is the full width half maxima (FWHM) in radians, λ is the wavelength of incident CuKα X-Rays (1.54Å) used in the experiment, d is the inter-planer spacing, θ is the angle of diffraction and h,k,l are Miller indices.
All the Best.
What is the name of your material? There are many software can do this. You can use 'Match' .
Hi,
As Thomas Breuer mentioned, you can use the ICSD (Inorganic Crystal Structure Database) to identify possible crystal structures. While there are too many possibilities to check them all, you can input the elements you used for synthesis to narrow down the different options. If you have synthesized something that has already been reported in literature, there is a good chance that it is in the ICSD. Additionally, the more XRD peaks in the pattern, the less symmetric the structure. If you only have a few peaks, there is a high chance that your structure is cubic. You can possibly use this info to even further narrow your options in the ICSD.
Best,
Eric
Some pieces of advice would lead to spending to much time for nothing, I'm afraid. First of all, Arya does not mention whether the synthesis concerns an inorganic or an organic substance. This is a very important distinction since there are considerably more organic compounds than inorganic ones and less often already characterised crystallographically.
Dr. Quinn's remark concerning the appearance of the diffraction pattern is very important. Do the the lines tend to be "equally spaced" or are there clusters (even overlaps)? The latter scenario shows signs that the symmetry is low (and is extremely seldom cubic for organic compounds because of an unrealistic demand to fullfil a molecular packing that allows for the automatic constraint of four threefold axes simultaneously of molecular entities). Again, if there are many peaks (more than 30, say) within the first 45 degrees (theta) the symmetry is most likely to be less than cubic.
In order to index a completely unknown pattern the first thing is the ensure that it comes from a the sample that is single phase. The next thing is to test for mathematical relations between Q-values to get a fair picture of the difficulty. In general, the task is not one should gladly start with without experience, so I recommend to look for a single crystal. Even that may be a difficult thing to find, but if you have a single crystal pattern, the indexing is more or less straightforward.
Good hunt!
Since I read that overlapping peaks are present, one has to conclude that it cannot be cubic (if single phase), all the more since the building-blocks cannot be considered as single carbon atoms arranged in a 3-D manner. It is more probable that it is (pseudo-) 2-D with graphite-like sheets leading to other lattice choices.
However, the most important thing is to ensure that the overlaps are not an effect of more than one phase being present. A quick test of mathematical relations between the Q-values (= 1/d^2) of the 5-6 first reflections should give hint -- but indexing is in general not an easy problem.
I give as a supplement a more detailed view of the crucial but extremely easy calculations to perform.
Test for cubic system from Q-values:
Primitive lattice gives ratios 1:2:3:4:5:6:8:9:10... (7, 15, 23, 28... are mathematically impossible values)
I-centred lattice gives ratios 1:2:3:4:5:6:7:8:9.. (typical appearance for a pattern of a bcc lattice is that lines come almost equally spread out)
F-centred lattice gives ratios 3:4:8:11:12:16:19:20 ...(typical appearance for a pattern of a fcc lattice is thus that the lines come alternately as two or single lines).
In your case, I sincerely doubt that this piece of information is helpful, as it is very unlikely that your substance has cubic symmetry!
Indexing can be somewhat challenging, especially when the XRPD pattern contains impurity peaks and/or the peaks are very broad and overlapped. Could you share the XRPD pattern, to judge/test if it is possible to find a solution (or to improve the data) ? .
Actually for Indexing and refinement purpose the rule of thumb is to have at least 10000 cts on the highest peak because that will give you 1% relative counting statistical error. So a longer measurement time to improve the data quality would not harm. Still the pattern looks simple enough (enough peaks are resolved) to be indexed, if its not containing additional impurities.
Can you share the raw data file ? Because digitization of the picture into scan data will further decrease the data quality.
Based on on the digitized/converted bitmap (a procedure with many flaws, it is a low resolution bitmap only) and the assumption of Copper radiation the first indexing solution that explained all lines in a Pawley fit is Tetragonal: a = 18.8 Å, c= 8.1 Å. But again, to really confirm the unit cell and the lattice centering good XRPD data is required.
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