In our series of glasses and glass ceramics (silicate with minor alkali content), the raman spectra exhibits bands in glass-ceramics but the bands are absent in glasses. The prepared glass-ceramics have higher modifier ions Ca2+, Na+ etc. than glass samples.
From literature, I came to know that NBOs (formed due to modifier ions) are more polarizable. Also, raman bands appear when change of polarization occurs. Hence, we expected glass samples to be more raman active due to higher NBOs, and ceramics to be relatively raman inactive. However, reverse happened in the present case. How can I explain this anomaly?
Dear Satwinder Singh,
Firtly, The components of silicate host including? having Te, Pb or Bi...components? Do U know, What is a big change of structure from glasses to glass-ceramic? Raman spectroscopy is
Secondly, the different of material structure between glass and glass-ceramic is amorphous and amorphous+micro crystals, respectively. After thermal-annealed process (optimal temprature depend on Tc in DTA curve), the glasses changes to glass-ceramics, that means micro-crystals are formed in main glass host. In order to know what kind of micro-crystals formed, the glass-ceramics can be measured by XRD (structure study).
In your case, the raman spectra bands exhibits in glass-ceramics only, which may be corresponding to vibration energies of NBOs but may be corresponding to vibration energies of formed micro-crystals also. To exactly detemind this, U should check these vibration energy values for each from documents about your materials, beside check FWHM of exhibited raman bands, peaks... (normaly, narrowing, strong and clearly for crystals,). More difficulties, if U explain this base on polarizable of NBOs. Because, according theory, raman active modes base on the polarization changing of moleculars or atoms group. However, the polarization changing happens only during vibration process of moleculars (when excitation by laser). Therefore, more or less NBOs in glass may not relative to exhibit or absent of raman bands above.
Good luck!
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