To be more clear, how can you explain that the Raman spectrum of a bulk glass sample features some other variations than that of the powder of the same bulk glass?
In general, sharp intense peaks in glass powders (or salts) are indicative of presence of crystalline structures. Upon annealing, the powder is transformed to amorphous material, the glass. Usually, glasses don't exhibit such sharp or intense peaks and show broad bands instead. However, some glasses may demonstrate some weak peaks due to low content of crystalline inclusions. All these effects manifest different properties of phonons in crystalline and amorphous phases.
Thank you Serge Grabtchak for your reply.
I guess that you are considering the corresponding powder as crystalline. In fact, the powder is amorphous since no heat treatment is performed after grinding the bulk glass.
I see, sorry didn't catch it. Do you have any ideas about typical sizes of particles in the powder?
No, I don't have any information about the particle size in the powder. Otherwise, can you please explain how could such data demonstrate the difference between the two spectra?
I was thinking more along nanoparticle related aspect. Having a mixture of nanoparticles would change Raman spectra - it's a known fact, and there are plenty of articles on this subject. However, I have to admit that simple mechanical grinding is unlikely to produce such fine nanoparticles, more like micron size. What exactly do see - more narrow and distinct peaks (for the powder) or still broad bands with additional broad features?
It's very interesting that Raman spectra vary in terms of particle size.
In fact, the only difference between the two spectra of powder and bulk is the asymmetrical shape of one broad band at approximately 600 cm-1, and in contrast, the same broad band in the bulk's spectrum is slightly narrow and more particularly quite symmetrical.
Not all the sizes - you've got to affect bulk phonons which happens when one would approach the nanoscale...
Very interesting comments, I made Raman spectra of commercial silicate at different molar ratio and I found these bands.
Thank you M. Farooq for your interesting comment.
In fact, despite that the glass in question is a TeO2-based glass I'll try to dry the powder as you suggested.
In the other hand, I think that the noticed difference may be assigned to grinding which probably alters the initial amorphous structure of the glass i.e. the structural units of tellurium atoms and the distances of Te-O bonds.
Compared with the bulk glass Raman spectrum, the first two broad bands in the powder's spectrum are distinctly more intense.
As a matter of fact, I believe that the understanding of the origin of the significantly different shape of the band in the region 600-650 cm-1 is way more important as part of the amorphous structure determination.
I propose a very simple explanation.The observed effect may be caused by a higher light scattering efficiency of the powder sample.
Thank you Dr. Balter for your comment!
Apart from the optical properties of the both samples, do you think that this observed difference could be related to the structure features of bulk and powder? In other words, is there any reason that structural modifications could occur during grinding the bulk glass?
Thank you again M. Farooq for your valuable contribution! Definitely, it is a very interesting step to reveal the origin of the disagreement in terms of peak intensities. But I think that there's probably another factor behind the shape difference of the band in the region 600-650 cm-1.
Definitely, I will try this!
In this regard, I am thinking about sandblasting as a technique to increase the surface roughness of bulk glass. Do you have any recommendation for how to perform this experiment?
Quartz has its main feature at ~450-500.Maybe normalise to this.
Has there been any background subtraction?
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