I observed that V2O3 compound is gradually changing its color from black towards greenish as time goes on. V2O3 and VO2 both come in black color whereas V2O5 come as yellow/orange colored compound. Moreover, the color for V3+ oxidation state is green, V4+>blue, V2+>violet etc.If anyone has any knowledge about the reason of gradual color change in V2O3 please help me to sort out the doubt.
See the answer at
https://www.reddit.com/r/askscience/comments/2frl8a/why_do_different_oxides_of_the_same_metal_have/
Best regards.
I worked with vanadium quite a lot. Most vanadium(IV) compounds with oxygen and nitrogen donor ligands came with a green color. An example is VO(acac)2. Some V(IV) compounds have a blue color, however, like VOSO4.
Vanadium(III) is very easily oxidized, so apparently V2O3 gets oxidized to V(IV) and that is why it turns greenish. Note that very dark green appears black.
Also take into account that if you have a mixture of blue V(IV) and yellow V(V) on the surface, the visual result will probably be green.
Thank you very much sir Yuri Mirgorod, Khaleel Abu-Sbeih and Emanuel Cooper for sharing your knowledge. I still have one more doubt about the stability of V2O3 phase. I took XRD of the V2O3 commercial sample and found that the peaks are surprisingly showing a matching probability towards V2O3 rather than V2O5 and VO2 using x'Pert HighScore Plus software. What do you suggest then Sir ? Is it still V2O3 phase or a mixture of +4 and +5 state?
Maybe the oxidation went to a small extent in your samples, that's why you still see V2O3.
First, I advise you to use XPS technique to determine V oxidation state.
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