Glass ceramics generally have well defined Raman peaks in Raman spectrum. However with the increase in modifier content, I observed that intensity of the peaks decreased and ceased to even zero with further modifier content increase. Is is related to the exploitation of center of symmetry of glass network, or some other phenomenon is contributing to it???
If you can compare Raman peak intensity with IR spectra and he whether there is correlation between reduced Raman intensity with increase related IR forbidden modes, then the center of symmetry would most likly be the reason. Otherwise, a correlation with x-ray analysis may help to ansswer the question to see to what extend the glass structure might have "transformed" leading to perhaps new / different Raman signals according to the new symmetry.
Hi,
It should be usefull for helping if you can give the compositions of your glasses.
Thanks Dr. Roughani. I will surely look for comparing IR and Raman spectra of the samples and finding correlation between the two as per your kind advice. I could observe from XRD and Raman spectra that, the glass ceramic samples (having some crystalline phase embedded in glass matrix) are exhibiting Raman peaks, while spectra of pure glass samples consist of no visible peak with naked eye... Can you kindly suggest any other link between x-ray and Raman spectra...
Thanks Dr. Guimbretière for your response. Our samples contain Silica as network former and small amount of oxides of Ca, Mg, K and Al as network modifiers...
To answer the follow up question related to the connection between the Raman and X-ray, considering glass has short term order, unlike single crystal structures with long term order, then Raman peaks reflect symmetry associate with "local crystalline behavior" of glass with short term order. With the addition of modifier, you may disturb the short term order to an extent that Raman peak could vanish. If so, then x-ray diffraction also should show similar behavior in terms of regular x-ray patterns associated with short term order disappearing. On the other hand, if you more or less maintain the short term crystalline glass structure but simply impact the Centro-symmetry (reducing polarizability and enhancing dipole radiation), then it should show an increase in IR intensity accompanying a reduction in Raman intensity.
I am thankful to you Dr. Roughani for that much informative discussion. I have got the base to that concept, and now I can go for the literature to strengthen it.
Small scale ordering during crystallization increases Raman intensity and thus Raman spectrum becomes a very useful tool for identifying early stages of nucleation/crystal precipitation. Modifier ion addition locally disturbs the short range order and thus Raman intensity reduces. I do agree with Bahram Roughani answers.
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