I remember that the peaks in this range are due to vibrations of M-O groups. In your spinel together with Fe, you also have Mn-Zn on tetrahedral sites that contribute to the spectrum with their own vibrations. You can search in the literature, there are many IR spectra of spinels to be used for a right attribution. You can also use Raman spectroscopy, in some cases it is better than IR

Dear Dr. Shahedi:

There aren’t sufficient data for a proper assignment of the absorption bands.

However, the number of bands for normal spinels is distinct of inverse spinel both case with bands below 1000 cm-1.

There is a great number of data at Zn ferrite, which provide further insight at about MnZn spinels. Both, normal (A)[B2 ]O4 or (A+2 )[B+3B+3 ]O4 ; and inverse spinels (A)[AB]O4 or (A+3 )[B+2A+3]O4 exhibit two intense bands assigned to existence of tetrahedral sites and octahedral sites.

Tetrahedron is typically occupied by Zn.

Octahedron is typically occupied by Fe (+3).

In a broad sense, inverse spinel, can exhibits Zn at tetrahedral and octahedral coordination.

Wavenumber of each band is function of the temperature of calcination of precursor powder. However, the distribution of cations depending on the chemical formula does MnZn ferrite.

Take in account normal spinels, two intense e defined bands area expected band with high wavenumber has been assigned to Zn-O stretching vibration for tetrahedral coordination, Fe-O

Vibration appears at a low wavenumber.

If MnZn ferrite is further considered as an inverse spinel the cation Zn2+ occupy site A, while 80% of Mn2+ cation occupy A site and 20% occupy B site (inverse spinel)

Well, shoulder or shoulders are common. Here, two hypotheses can be further considered:

I) Cation with distinct valence state occupying more than one site of coordination. Ex.: Fe2+ in both tetrahedral and octahedral coordination

II) During powder calcination atmosphere wasn’t homogeneous along sample, surface powder has high oxidation with high crystallinity, one portion of the powder with low oxygen level exhibit a lower crystallinity. See, above, was mentioned that in an infrared spectrum profile and position of the absorption band of spinel depending on the crystallinity degree.

See, typically a single spectrum is insufficient to a precise assignment of metal-oxygen bands in spinel.

Suggestions: calcination of precursor-powder in a plate, instead a crucible, insert air flux in the furnace. Verify if parts of calcined powder exhibits distinct colors, if yes re-homogenize and reach new thermal process at same temperature and time. Find further references with spectral analysis of a material of similar chemical composition synthesized by other classical or chemical routes.

See, some interval can be considered as (MnO)4 (Mn at tetrahedral coordination) can exhibit band at interval 562- 550 cm-1, (MnO)6 (Mn at octahedral coordination) can present a band at interval 420 – 385 cm-1.

With best regards

Marcos Augusto Nobre

=> Vibrations of Mn-Zn-O bonds in the ferrite structure may cause the peaks.

=> Observe peaks associated to C-H stretching vibrations if the synthesis process includes organic chemicals or contamination with C-H bonds.