I have a few suggestions:

     Don't forget the ratio of surface to volume atoms.  At the surface you have atoms that are not fully coordinated (missing half of their nearest neighbors).  Without those nearest neighbors, the lattice parameters of the unit cell can be distorted.  This in turn would affect your XRD spectra.

1)  If the ratio of surface to volume atoms is low, then you can expect the diffraction of x-rays with volume atoms to hide/overshadow the diffraction of x-rays by surface atoms.  A low surface to volume ratio is indicative of large crystallites (> 1 micron).  In this case you can expect XRD peaks to be very well defined and narrow.

2)  But, with a high surface to volume atom ratio the diffraction of x-rays  at the surface of a crystallite is significant enough to be seen against the volume x-ray diffraction 'background'.  Since lattice parameters are off true unit cell values, you can expect some diffraction just below or just above an expected XRD peak.  This leads to a widening of the XRD peak.  Which is typically seen in crystallites < 1 micron.

      Another thing, the low angle 2-theta data is de-emphasizing your crystalline peaks.  So perhaps try a 2-theta range starting at 25 degrees.   That way you cut out the high cps of the low angle data (which is useless anyway UNLESS you are specifically setting up the XRD for low angles).  That will emphasize the 100%, near 100% peaks you are looking for.

     My GUESS (I must strongly emphasize 'guess' is that the surfactant is significantly hindering crystalline growth.  Without the low angle data, you might also interpret the data as looking partially amorphous.

Q1)  Are you SURE the commercial powder is composed of nano-crystallites?  Ronald Reagon (past US president) once said: "Trust but verify".  So, trust the commercial source's valuation of crystallite size, but verify it for yourself (SEM, TEM, etc.)  You can even try to determine crystallite size (

Hello Mohamed,

What if the surfactant molecule is about 4 nm long and the crystalline particle is about 40 nm in diameter? You think that the influence of the surfactant still might be negligible? 

Thank you for the answer.

Best regards,

Michał W.

the red curve is obviously not a nano-crystalline material since the peaks are too sharp. If your particle size is 40 nm you would expect to get very broad peaks with lower peak intensity. a 4nm layer would not be observable using conventional xrd.

even if the 4nm layer is perfectly crystalline you will not see it with conventional xrd. The broadening would be so large that it would be below the signal to noise. The black pattern does not show less crystalline order, it just shows the large peak broadening due to the 40nm crystallite size. If there were less order then you would not expect to see the broad peaks perfectly corresponding to the most intense peaks due to long range order.

Is that so? I'd expect to observe fairly sharp peaks for 40 nm nanocrystalline particles... (not as sharp as for a single crystal for sure, but still). In fact you can see 4 nm particles by XRD. Or at least that's my experience with SnO2 nanoparticles, embedded in a thin film or inside a mesoporous carbon material, with average size from 5 to 7 nm. Surely these would be broad peaks, with maybe a FWHM of 1.5 to 2, but you will see peaks. The black pattern looks to me like what would be the result of crystalline 4 nm particles, not of 40.

If you have enough 4 nm sized grains then you will get a pattern that will look very similar to an amorphous pattern. If you have 40 nm particles with a 4nm outer layer then any signal from the 4nm phase will be washed out by the signal from the 40 nm phase.

I think Michal's issue is that the 40 nm nanoparticles peaks are very broad, and he wonders whether the surfactant of 4 nm plays a role or not. If the 40 nm are single crystals, I'd expect to observe them as relatively sharp peaks, and not see the 4 nm crystals response. Since he does not observe relatively sharp peaks, I suspect the particles are either (i) smaller than 40 nm or (ii) are in fact agglomerates of much smaller nanocrystals. Can the surfactant enhance the formation of these smaller nanocrystals?

I suspect, my personal opinion, that the 40 nm particles are agglomerates of smaller particles covered with surfactant. This would explain the peak broadening of the phase.

Excellent discussion! Here are some of my suggestions to deconvolute individual contributors to the diffraction pattern (reciprocal space image):

Obtain XRD patterns with identical sample loading methods for each of the items individually. Meaning,

This will reduce the "hand waving". Based on the comments, there seem to be two possible competing effects:

• Nano "grain size/shape"
• Crystallinity or Amorphous Content 

Let us temporarily disregard the "strain effect" or presence of "preferred orientation" in this case.

BTW what method did you use to determine the "size"? How do you define "size"? 4 nm, 40 nm, 7 nm etc. Just making sure I'm on the same page as you erudite folks :-)

Thank you all for your comments.

First of all, I have to say that I used the term: "particle", so the diameter of 40 nm is determined based on SEM and nanoparticle tracking analysis system. I never stated that I must have crystals with the size of 40 nm. The dimensions of the surfactant I estimated by assumption that there is only one layer of molecules bonded to the particles surface, and surfactant molecule is about 4-6 nm long. This is what I mean when I use therms: dimension or diameter. I never described in this way any of the crystallites in my samples.

I beginning to think, that I probably have nanoparticles of 40 to about 100nm in diameter, but composed of crystallites with smaller dimensions (about few nanometers) and that is why the broad peeks are present. Also, there is a possibility, that my black sample is more amorphous than crystalline... 

Thank you all for the discussion, and if you have more comments I will be more than happy to see them.

Also, thank you for the suggestions of other experiments, but unfortunately, my department does not posses its own XRD machine, so it might be tricky for me to do more tests. But I will decidedly try!

Best regards,

Michał W.

i think a TG/DTA test will help you to understand at least if there is a huge difference between the two powders in terms of crystallinity.

Sharp peaks looks remained. So it can be said that surface totally covered by surfactant.

I have a few suggestions:

     Don't forget the ratio of surface to volume atoms.  At the surface you have atoms that are not fully coordinated (missing half of their nearest neighbors).  Without those nearest neighbors, the lattice parameters of the unit cell can be distorted.  This in turn would affect your XRD spectra.

1)  If the ratio of surface to volume atoms is low, then you can expect the diffraction of x-rays with volume atoms to hide/overshadow the diffraction of x-rays by surface atoms.  A low surface to volume ratio is indicative of large crystallites (> 1 micron).  In this case you can expect XRD peaks to be very well defined and narrow.

2)  But, with a high surface to volume atom ratio the diffraction of x-rays  at the surface of a crystallite is significant enough to be seen against the volume x-ray diffraction 'background'.  Since lattice parameters are off true unit cell values, you can expect some diffraction just below or just above an expected XRD peak.  This leads to a widening of the XRD peak.  Which is typically seen in crystallites < 1 micron.

      Another thing, the low angle 2-theta data is de-emphasizing your crystalline peaks.  So perhaps try a 2-theta range starting at 25 degrees.   That way you cut out the high cps of the low angle data (which is useless anyway UNLESS you are specifically setting up the XRD for low angles).  That will emphasize the 100%, near 100% peaks you are looking for.

     My GUESS (I must strongly emphasize 'guess' is that the surfactant is significantly hindering crystalline growth.  Without the low angle data, you might also interpret the data as looking partially amorphous.

Q1)  Are you SURE the commercial powder is composed of nano-crystallites?  Ronald Reagon (past US president) once said: "Trust but verify".  So, trust the commercial source's valuation of crystallite size, but verify it for yourself (SEM, TEM, etc.)  You can even try to determine crystallite size (

Dear Jason,

About Q1. I never stated that commercial powder is composed of nano-crystallites. I have just stated that it is a nano powder, and I have checked that. From nanoparticle tracking analysis it is clear that we have particles with size

In my opinion sample preparation also effects the XRD pattern. To obtain more conlcusive opinions a SEM with "broken agglomerates" (40 nm agglomerates?) may be helpful.

Ronald Reagan's malapropism was "Doviyai nu proviyay", it should really have been, "Доверяй, но проверяй" (Doveryay, no proveryay). It is probably one of my favorite quotes considering the political turmoil in parts of the world today. However, in science this should be the basic principle, shouldn't it?

Just curious, what about Jason's analysis was objectionable enough to "Down Vote". We are not in a beauty contest here. So, it would be much appreciated if the objectionista can explain the technical demerit in Jason's conclusions and suggestions. That would be educative at least. I hope it is not some emotional reaction or personal vendetta :-) Bare in mind, I do not give two hoots for the RG score.

Michal!

1. Do you have direct access to the XRD instrumentation or are you also a vicarious user like many others looking to take advantage of XRD data provided to you?

2. Was the sample loading similar for both the diffractograms? Flat sample surface or in a capillary?

3. If the sample was flat and the kW used identical, then my suggestion is to normalize the data w.r.t. the total integrated intensity for a more effective comparison of the two diffractograms. In other words, the diffracting volume is identical.

4. Distinguishing between the "amorphous halo" and the "blurring" of the Bragg peak due to "Nano" size of constituents may not be trivial. Anyone know how that may be done?

5. If you were to use a 2D real time XRD detector you would probably already have a better idea. In fact, a simple dental film exposure for any Bragg peak will give you a better clue.

6. The conventional diffractogram that you are showing were obtained using a "spatially blind" 0D or "point counter" (scintillation counter). This technology and method is as old as the Braggs (more than a century). It is antiquated and yet useful to many researcher even today. However, the lack of the perspective from the 2D data is a huge handicap in the interpretation of the conventional data. In the Debye-Scherrer film method the 2D data is convoluted (smudged) by the process of sample rotation.

7. Do you have any micrographs of the two samples? Please post them.

8. SEM will not be able to distinguish particle, grain or crystallite (coherently diffracting domain) unless combined with localized diffraction techniques. SEM will not be able to distinguish crystalline or amorphous nature either, correct?

9.  My hypothesis which is similar to Jason's but needs experimental verification, is that the surfactant is:

• inhibiting crystallinity or
• inhibiting growth of "Nanoparticles" 

10. I notice that you have data fairly close to the SAXS range. Have you considered using SAXS to deconvolute (isolate) and identify the effect of "agglomerate" size distribution? SAXS - Small Angle X-ray Scattering!

Stay open minded to come to the right conclusion. "Доверяй, но проверяй" :-) 

I've attached an image showing one (hkl) from a so called Si powder "standard". A Bruker D8 with Bragg-Brentano focussing optics was used. Notice that instead of the expected continuous Debye-Scherrer arc we are actually seeing large "spots" from the sample. Using a conventional 0D detector it would have been virtually impossible to detect the large particle size or the effect of "preferred orientation" invariably present in most practical situations.

Ravi,

To answer number 4: The best way I know of to differentiate between a nanocrystalline and amorphous sample using xrd is to do a pair distribution function. In order to do this you must measure extremely high in q space (at least 20 inverse angstroms preferably 30+) in order to get a reasonable fourier transform into real space. If the sample is nano-crystalline than you should see peaks in the PDF that correspond to the expected bond lengths in the crystal structure. If it is amorphous than you will only see peaks (and broader) corresponding to the short/medium range order atom-atom distances.This is also a good method for separating contributions from both amorphous and nano-crystalline phases as well as multiple amorphous or nano-crystalline phase. It is a very powerful method for studying structures of nano-crystalline materials, polymers, metallic glasses and such.

Michal,

It is clear that the red X-Ray pattern received for true crystalline material. But the second material is obviously amorphous. Black pattern does not contain any signs of surfactant-ceramic bonding. But, there are some variants. What about the crystallinity of pure surfactant? If pure surfactant is amorphous, than it can't be stated in XRD pattern in any case. On the other hand, if surfactant is crystalline, than it could be stated as individual surfactant phase (surfactant precipitated without any interaction with ceramic components) or it could form some crystalline phase with one of ceramic component. But no: there are no any sharp XRD reflections. Therefore, IF surfactant is presented in this material, than it is in amorphous state. And the only way to influence on roentgenogram consists in decrease of XRD profile intensity. You can find it out by TGA, IR-spectroscopy, CHNS-analysis or else. Or You can heat this material in air above 300°C (2-3 hours) and remove it.

It is important to understand that surfactant presence in synthesis mixture can put obstacles in the way of true crystalline particles formation. It is more precisely to speak about obstacles for crystalline particles growth, because surfactant do can stabilize nanoparticles in reaction mixture forming preventing layer in their surface. So, my answer to “Is it possible that presence of this surfactant may distort the XRD pattern as much as it is visible?” is “NO”. And the answer to “Or maybe other effects cause this differences in XRD patterns of both samples?” presented above and concerned with ceramic formation (particles growth) in reaction mixture, but not with XRD patterning. It can be supposed that ceramic particles are too small.

By the way, what about the ceramic/surfactant molar or weight ratio(s) and both ceramic’s specific surfaces?

I do tender my apologies for my extremely poor English.