Is it possible the presence of a new Raman peak in a composite sample? If so, what could be the reasons?
Yes, that's possible. In the easiest case in which vibrations are localized you could imagine that one material would have an A-B-A and one a C-B-C group vibrating and in the composite you also get an A-B-C group vibration. In general, the assignments are not that straightforward because vibrational modes are generally delocalized, so for a final explanation you would require theoretical support, e.g. by DFT.
Jürgen Weippert Thank you for your detailed response. It helps to understand that new Raman peaks can arise from the interaction of different groups within the composite. Your explanation about localized and delocalized vibrations is quite insightful. In my specific case, I observed new peaks at 132 cm⁻¹, 202 cm⁻¹, 309 cm⁻¹, 351 cm⁻¹, 386 cm⁻¹, and 663 cm⁻¹ in an In₂O₃-SnO₂ composite sample. The individual components, SnO₂ and In₂O₃, show peaks at different positions, with SnO₂ having peaks at 130, 196, 570, and 625 cm⁻¹, and In₂O₃ having peaks at 192, 308, 480, and 602 cm⁻¹. Notably, the peak at 132 cm⁻¹ is close to the SnO₂ peak at 130 cm⁻¹, and the peak at 309 cm⁻¹ is close to the In₂O₃ peak at 308 cm⁻¹.
Could you please provide more insights on how to differentiate between new phase formations and other possible reasons for these new peaks?
If your composite is now a ternary SnxInyOz compound and there is no literature available yet (I haven't searched), I can't give you much hope of getting around supporting it with a quantum chemical calculation, which will probably have to be DFT.
If you can make a series of concentration ratios, you may observe that peaks shift as a function of concentration. For the compound I personally work with, yttria-stabilized zirconia, Hemberger et al. made such a calibration curve:
Article Quantification of Yttria in Stabilized Zirconia by Raman Spectroscopy
So maybe such a thing can also be done in your case, but that's also a lot of work and phase changes by the concentrations may heavily affect that.
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