I made some regenerated cellulose films which were characterized by XRD to study the crystallinity, scan speed used was 1.8°/min. The XRD pattern I obtained is not identical to what has previously been reported (see attached pic, left side-literature & right side- my result)
Lit.showes that the diffraction peaks for RC appear at 21.6◦ (2 0 0), 19.9◦ (1 1 0) and 12.0◦ (11 0), however my sample is only showing two peaks, one at 12.1◦ and another one at 21.2. I am rather confused as to whether the missing peak diffused withe the other peak and resulted in just one broad peak or what?
Another questions is as you can see in my result I have two peaks, if I calculate the crystallinity using the deconvulation method I consider the peak at 12.1◦ to be the crystalline peak due to its sharpness and the other peak at 21.2 to be the amorphous peak due to its broad nature, is this correct? I mean to just use peak shape as a means to determine whether the peak is crystalline or not?
Could you explain please, is this exactly the same sample measured (for both pics)?
About your 2nd question, you cannot tell (at least in this case) is it (pic. 2) effect of sample's amorphous structure or just imposition of two broad peaks. What you can try to do is the RDF function plot for both samples (aka. my question number one).
If both of XRD patterns are taken from the same sample (which was heat/chemically treated somehow, or is very old and is falling apart), this phenomena in fact could mean progressive amorphization.
Konrad.
It is a similar pattern. It looks like you have lower signal/noise ratio and, more importantly, broader peaks than the reported compound. This usually indicates that your average crystallite is smaller, and/or lower degree of crystallinity, i.e. more defects. Another option is that your diffractometer is not as good as the one they have used in the report, but it should not matter to such extent.
The broad peak around 20 2theta is probably two peaks that appear merged due to said broadening. You should take that into account when you fit the peaks, but with only 3 peaks the uncertainty will be huge anyway... Have you measured background independently?
From what I see, I would assume the material is not as crystalline as the one reported.
Notice that your second peak position is at the average positions of the (110) and (200) peaks appearing in the reference pattern. The two peaks in this angular range are not resolved in your pattern. Further, the first peak in your pattern and the standard pattern exhibit similar breadth. If you recall that the crystallite size determined from the breadth of a given reflection is a measure of the crystal dimension in a direction perpendicular to the corresponding reflecting crystal planes, you can deduce that your crystallite size is similar to that of the reference sample in the direction perpendicular to the planes responsible for the first reflection. However, crystallization along the [110] and [200] directions in your sample is poor compared to that in the reference sample, resulting in broadened peaks which overlapped due to their proximity. Further, the fact that your overlapped double peak profile rests on top of a very broad, amorphous-like hump could indicate that there is a broad distribution of crystallite size in the [110] and [200] directions, extending down to the regime of short range order. The appreciable reduction of the intensity of the double peak profile compared to that of the first peak in your pattern is consistent with this interpretation. As a conclusion, crystallization in your sample is not uniform in all crystal directions.
In fact, as already suggested, your material seems less crystalline than that reported in the literature. Also in your case there are three peaks, but the last one is less evident because it is very large and overlapped to the previous one. You should verify if the preparation method is the same, the eventual thermal treatment and so on, to be sure that a pattern similar to those reported in the literature should be expected. But I think that you can be satisfied, there is a good similarity
Thanks.
Regarding the preparation method, yes it is exactly the same, the only thing different is that in the lit. they ground the film sample into powder form and then did the XRD, whereas I did it for the film directly. Could that be the reason?
I don't think this difference in preparing the XRD sample would lead to the observed difference in XRD patterns. The observed difference is clearly a matter of quality of crystallization along certain crystal directions. In fact, the grinding process could lead to mechanical-induced defects, which would lead to poorer crystal quality. The only advantage of the grinding is to obtain randomization of the crystallite directions in space, and avoid preferred orientation in certain directions, which would lead to stronger reflections corresponding to such directions. Therefore, the greater relative intensity of the first peak in your pattern could be partially due to preferred orientation (texture), and partially due to the reason mentioned in my previous answer. To examine the effect of texture in your film, I would grind the film into fine powder and carry out XRD measurement on the powder. The relative intensity of the first peak in the powder compared to that in the film should, in principle, shed light on the contribution of preferred orientation to the intensity of the first peak. .
Dear Fatima,
Your problem seems to be connected with azimuth orientation of the sample.
What is the condition of your tissue sample? Usually it is a thin film.
It is impossible to get an unstressed film! It must be elongated – fiber material.
Your film has 2 lateral directions: elongated and perpendicular. You can put the sample into the equator plane center of the diffractometer in two positions.
So you will obtain different diffraction pictures when the sample is placed in the elongation direction and in the perpendicular one.
If you study a rotating sample you are to obtain mixed picture with widened peaks.
Do your use the transmission or reflection mode?
SY,
Michael
Two variables that would affect conventional equatorial scan XRD patterns of fibrous samples are:
Both these are nearly impossible to detect with a single conventional "equatorial" scan diffractogram using the ubiquitous 0D "point counter" as illustrated in the query.
Suggestions:
"Preferred orientation" is an inevitable consequence of even "bunching" several fibers together for the sample holder.