Could anyone tell the possible reason for the strange-sharpest peak in observed Raman spectra of LLTO material at ~ 726 cm-1. (This peak does not belong to any second order peak.) I can not find any appropriate references to assign this region too. XRD of this sample confirms the cubic structure. But raman spectra of the same sample do not coincide with cubic/ tetragonal structure reported by others.
Dear colleague Lakshmi Devaraj ,
Have a nice time and good day.
You may need to make EDS for your sample to know and confirm the constituents of the produced materials. It may has contamination. also may need to make TEM to help you to confirm the XRD results.
I wish this is useful and help you.
Yours
A. El-Denglawey
Thank you sir, El-Denglawey for the suggestion. The samples have been already analyzed for ICP and it is free from impurities.
My doubt is, Do these peaks by any chance indicate defect concentration present in the sample.?
Since your material is a mixed crystal, it may be due to the below reason also.
In perfect crystals, only the zone-centre optical phonons can be observed using optical techniques such as Raman spectroscopy. However, the k = 0 selection rule is relaxed as a significance of the interruption of lattice periodicity in nanocrystalline materials. In analogy with electron confinement, phonon confinement has also
been found to give rise to interesting changes in the vibrational spectra. The changes in the Raman spectral parameters are expected to be larger as the dimensionality of the system reduces below the critical size. The presence of zone boundary phonons in crystals with high defect concentration and in mixed crystals has been reported. This arises because of the relaxation of the k = 0 selection rule due to the presence of disorder in the crystal. There are numerous reports on the presence of surface phonons in the Raman spectra of nanostructured materials in addition to the confined optical phonons. Surface phonons are expected to have wavenumber between TO and LO phonons. Because the fraction of surface atoms increases as the crystallite size of a nanostructured material reduces, surface phonons are observed with noticeable intensity for ultrasmall size particles.
You can refer this paper and the back references for more details.
http://pubs.rsc.org/en/Content/ArticleHtml/2016/CP/c5cp06214d
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