In  region UV-VIS of the electromagnetic spectrum, atoms and molecules undergo electronic transitions. In γ,β -MnO2 basic structural unit is [MnO6] and it is an octahedron. Electronic transitions same.

Best regards.

as Yuri Mirgorod. However, I presume that their spectra will be different under mechanical stress.

Dear Aravindhan

I think XRD and Raman technique can be better than UV-Vis Spectroscopy. 

I suspect that the bandgap is too small for UV-Vis, but in the near IR that you could find distinguishing features. To understand this, you would need to look in the literature for the band gap for the different phases and see if they are distinguishable in your spectrophotometer. If the samples are thin enough, you may able to see higher order band to band transitions, but sample preparation can be an issue.  

In general XRD and Ramen should give you more precise information.

Dear Bilal Yaseen Taher,

We have raman but its not in working condition,xrd  result takes a week but i have review so i want to optimize with what i have thats why i asked this question.

Thank you for your reply.

Dear Aravindhan

I appreciate your problem but it is possible to work on the optical properties as the answer to Dr. John when you can examine samples by XRD or Raman technique.

I wish help you, with my best wishes

Dear,

if we evoke the example of SiC , the band gap of this maaterial is sensitive to it cristalline phase, the band gap of 2.3, 3.0, or 3.2 eV for its main polytypes, 3C, 6H, and

4H, respectively which can be easily determined by UV-Visible spectroscopy, so I think that it will be the same thing for all materials which cristallize in numerous phases.

Dear Dr. Vanangamudi:

Really, Dr. Kaci is correct.

The Greek letters mean that exist one or more polytype of a compound with same chemical formula.

In a broad sense, the cation coordination would be the same but coordination octahedral is distorted from a prototype structure.

Taking in account oxide compounds, each Greek letter indicate a distinct crystalline symmetry. In these cases, each crystallographic structure exhibits a distinct bad gap or optical gap.

The magnitude of distance between valence band and conduction band take in electron-volt is different at each crystalline phase.

If systematic analysis is carried out, in addition to gap values, distinct levels of Absorption can be identified, in a plot absorption x wavelength. Seems that above 400 nm such phenomenon can be clearly observed. Since absorption is dependent of wavelength in a smooth way at significant interval of values higher than 400 nm.

Seems that the absorption intensity of Alpha phase is intermediate to both Beta and Delta. The major absorption intensity at wavelength > 400 nm is shown by Delta phase.

Best regard

Marcos Nobre