Dear Annie,

please have a look at the iron diffractogram at the link.

Iron has got only three peaks in the whole 2theta space.

You have got all three peaks; congratulations.

With respect to peak height, you may suffer from internal stress and too small crystallites. Stress and crystallite size will affect XRD peak widths and therefore also peak height.

Small crystallite size leads to larger peak width and thus to smaller peak height. Your peak at around 83° is very broad (FWHM compared to the 43° one). So you should not wonder that its peak height is small.

http://www.chegg.com/homework-help/questions-and-answers/shows-x-ray-diffraction-pattern-iron-taken-using-diffractometer-monochromatic-x-radiation--q3601279

There are 3 things that need to work for you at small sizes that control the strength of the signal:

• Sufficient concentration of sample (for example a supported iron catalyst may only have 5% mass of iron on the support.  A thin or small sample).  This can somewhat be corrected for by extending the irradiation time but it many circumstances may increase the noise as well
• Size of particulate matter - more signal from larger material.  Sharper peaks from larger material and no Scherrer broadening (typically < 100 nm).  As Gerhard points out there are other forms of broadening (instrument and stress)
• X-ray contrast of the material - Fe should be excellent though

Hi Annie

Your XRD pattern shows the three characteristic peaks of metallic iron, i.e. the (110), (200) and (211) reflections. The (110) peak is typically much more more intense than the (200) and (211) reflections, as is the case in your XRD pattern.

Best regards

Geoff

@Professor Waterhouse

I was being doubted that the concentration was not strong enough which caused the other two peaks were too low to convince that it's typical iron pattern. And I could not explain the reason either.

Is there any explanation to tell why the other two peaks were such low?

Thank you so much for your helping.

Peak broadening was mentioned above.

Please have a look at the link; especially at the section 'size and strain broadening'.

Here you will see that the peak broadening B increases with theta when strain (eta) is present.  But peak broadening is always related to reduction in peak height. Thats why your higher indexed peaks (at higher 2theta values)  have got lower peak heights as expected.

Additional remark: Your background in your diffractogram is quite large.

This is most propably due to the presence of Fe-K-fluorescence which mainly is excited via Cu K-alpha incoming radiation. For iron as part of an XRD sample it is recommended to take a Co based x-ray tube. Co K alpha is at 6,93keV and thus does not excite Fe K fluorescence (Fe K-edge is at 7,1keV).

https://en.wikipedia.org/wiki/Powder_diffraction

It does not showed one peak, but multiple peaks and just one of these peaks has a high intensity comparing with the other less values peaks, it depends on Miller indices and the dominated number of crystal lattice faces orientations.

Regards, Emad

Dear Annie, locations of Fe signals shown in the graph are correct. But, I think, you should decrease diameter of your sample. You should reanalyse the sample. Because, signal-noise ratio of the sample is so high. After than this operation, you can see iron peaks, clearly.

Maybe your sample is oriented, like nanowire or nanosheet. Therefore, the peaks in some dimensions are decayed or even disappeared.

Hi Annie

As Qing Wang points out, preferential orientation in your iron nanoparticles is one possible reason why the (110) reflection in your XRD pattern is so intense relative to the other reflections. See Fig. 3 in the attached paper, which shows the XRD pattern for hexagonal Fe nanoplates. The XRD pattern looks very similar to yours in terms of the relative intensities of all the reflections (the signal-to-noise ratio is obviously much better).

Thus, I think your next step should be to do SEM or TEM on your Fe nanoparticles to see if they have a platelet or nanosheet morphology.

Best regards

Geoff

Dear Annie, 

you might have an epitaxial growth or zero valent iron

Dear Annie,

Try to  extend the analysis time  with scan speed 0.1 deg/min  because the signal-to-noise ratio is obviously high in the XRD spectrum. 

Best regards

Eman

Its the shape of monocrystalline material, and having one intense peak means that the atoms are gathering in the site with lowest surface energy, which explains the highest density of crystallites at this direction.

If your compound is not characterized with one peak, then you should verify the experimental tools and try again.

i am suspecting  that  your products contain a high portion of amorphous materials which gave strong noise-like signals 

 I also feel that amorphous component of the material is dominating in your sample. Try to understand the techniques to improve the degree of crystallinity. of the sample-heat treatment is one of the ways. There could be more relevant to your compound.

What type of powder holder are you using in the XRD analysis? Pl confirm

Dear Annie,

There are many factor involved in the picture you have observed. In my opinion, I see huge fluorescence rather than diffraction (too high background).

1. Be sure that you're using "proper" X-ray source. For example, if you use Cu-anode than such elements as Fe, Cr, Mn will significantly absorb your radiation and be fluorescent (link).

2. If you use not Cu-anode, than you need to check:

   a) amount of sample

   b) level of sample is equal to sample-holder

   c) if sample holder correctly placed

These will ensure that you are in good diffraction conditions.

3. Next will be playing with XRD machine settings, but it's another long story...

Hope it helps!

https://www.researchgate.net/post/Why_mainly_Cu_Kalpha_radiation_is_used_in_XRD_why_not_other_elements_and_what_is_the_reason_for_using_Kalpha_radiation_why_not_Kbeta

Dear Annie, From the answers and explanations given above, there are many different parameters to be considered for,: amorphous state?; position of the sample holder,? fluorescence effect? quasi-single crystal? counting time? etc..

In my opinion the main question is: what is the chemical composition of your sample?

What are the elements in the samples? how it was synthesized... ? After that one has to consider the question of the analyser instrument!

However, from the 4 lines I like distinguished on you pouur quality XRD pattern, I suggest you are studying a fcc type material..

Please guide us with the chemical formula!!

Best regards

Daniel

the problem is due to high background caused by X-ray florescence of Fe. when collecting XRD of materials containing some elements such as Fe and Mn, the secondary X-ray emitted by the elements causes high background levels that ruins the pattern. increasing the scanning time slightly improves the quality of diffraction pattern but the problem can be completely overcome by replacing the copper tube with a cobalt tube X-ray tube (if available)   

Dear all,

My sample was first fabricated in the di water with 99.99% iron string and made it become nano size. Except for exposing in the air for a while, there was nothing else added.

After placing for a long time, it had condensation. The analyzed sample was the condensation collection. (without any water)

Thank you all so much for helping and giving advice, I have learned so much from you.

Hi Annie

Few point may add to the above info. 

You can rotate the sample holder during data acquisition to increase the intensity of the peaks if they have some preferred orientation.

Changing the source x-ray radiation is also important as pointed out by @Gerhard Martens. It can strikingly change your intensity. 

Lastly you were right in your first guess! Increasing time of data acquisition can improve the data quality. It would be better if you run your scan in Line detector than a point detector as it will shorten the time with a better signal to noise ratio.

Dear all:

I did the same analysis again but this time the concentration of the sample was much more stronger and the surface was wider. Yet I still received only one peak the same as the picture attached to my question.

Is there any explanation for this kind of result?

Thank you so much.

Have you extended your measurement time to 24 hours?

From your providing x-ray pattern I am seeing three peaks in the pattern , and one peak is more stronger than others. It could be hapen due to (i) sample may be anisotropic nature i.e., it has been grown in a cetrain direction or plane ( among x. y, and z) which has lower surafce energy than the other two planes, (ii) sample concentration and uniformity is not sufficient for getting good dffraction peaks.

As pointed out before , the problem is Fe in Cu radiation. If you have a 1d detector, you can remove the flourescense by removing the lower band of the discriminators in "detector settings". 0.5 should be enough

use xrd rasante and try to increase the thickness