because I prepared magnetite by sol-gel method, I got XRD peaks, but for Raman, I didn't get a peak at the range 600cm-1, should I change the wavelength of the laser, or what do I have to do
XRD ve ramanda pik elde etmek için ikisine uygun dalga boyu lazerle gönderilmeli.
Dear Wedad A. Alwesabi , thanks for your interesting question.
Raman spectra are not dependent on the excitation laser wavelength, sometimes we choose a laser with a wavelength or another to avoid interferences casused by luminiscence, which can mask the Raman bands.
Note, it is always useful for us in order to help you, to know what excitation laser you used and what settings did you choose to obtain your Raman spectra.
Magnetite has five Raman active modes, applying group theory to its spinel structure, according to literature these vibrational bands appear at around: 193, 306, 450-490, 538, and 668 cm-1.
But it happens that two of those five modes (193 and 450-490 cm-1) are really weak, and often they are not reported in many cases, specially when the sample is measured at room temperature and for nanoparticle samples.
Bands at 306 and 538 cm-1 are weak but often they can be seen in a Raman spectrum of magnetite. The more strong band is the one appearing around 668 cm-1, this one is the more characteristic or distinctive of magnetite.
However you cannot find this band in your experiment and from your XRD you know you actually have magnetite.
May be the answer for this question is related to the thermal stability of magnetite, which when heated in air transforms into maghemite and finally into hematite. These transformations can be induced by the laser power used during Raman measurements, due to energy transfer and heating in the sample under the laser spot. Raman spectra of maghemite and hematite do not contain the band at 668 cm-1 characterist of magnetite, while some bands from these materials could appear near the other two bands of magnetite, what together with the XRD results could cause confusion.
Several articles used the laser power variation to observe these transformations.
So it would be a good idea to repeat your Raman experiments with a fresh sample of magnetite and a low laser power. You could start with the lowest possible on your spectrometer and rising it step by step untill you get a good Raman spectrum of your sample.
Here you can find some articles about the topic:
Article Raman Spectroscopic Study of Magnetite (FeFe2O4): A New Assi...
Article Vibrational Spectroscopic Characterization of Hematite, Magh...
https://academic.oup.com/gji/article/177/3/941/627133?login=false
https://pubs.rsc.org/en/content/articlehtml/2019/na/c9na00064j#imgfig2
Hope you find this answer helpful, if you need some extra explanation, please don´t hesitate to contact.
Regards
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