In order to understand the question that I have, let me walk, you trough it.
I have several WO3 samples, which present two lattice vibration peaks: at ~130 and 150 cm-1. In these samples, the ratio of these lattice vibration changes (increases from 0.75 to 1.05), also their intensity changes - in the first sample, the 130 cm-1 lattice vibration is more intense, but in the others the 150 cm-1 lattice vibration increases and the 130 cm-1 it decreases).
I guess that the crystal structure of the samples changes, or more likely, it shifts from one crystal phase to another.
What do you think about my hypothesis?
Do only the intensities change or is there also a change of the exact peak maximum?
For an actual phase transition, I would expect that parameter to change as well to some extent. If you just have different intensity ratios I would postulate that your samples have a different crystal quality (defect or dislocation density, crystallite size etc.) - maybe you can cross-correlate with XRD which of the peaks is higher for a better crystal?
Dear collegue
you can do the lattice modes in the factor group, starting from the externe vibrations of WO3 in its point group, and making coorelations to get the lattice modes in the facxtor group. then you can have an idea about activity of lattice modes depending on the factor group symmetry.
best regard
Ali OUASRI
Thank you for your answers!
Jürgen Weippert, the peak position does not change, only the intensities. From the ratio of other peaks 700/800, we know that we have surface defects, which have a negative effect upon the photocatalytic activity. We also measured XRD, we have the patterns, and in it, you can see that there is a crystal phase change from partial hydrate to monoclinic and hexagonal partial hydrate. I have attached the Raman spectra and XRD patterns.
Artur Braun, the color of the samples, shifts from bluish to yellow, yellowish, respectively, to green. We have determined the band gap value of each sample, but there is no trend or correlation between the DRS and Raman provided information.
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