Dear Anne

I hope you can upload the xrd pattern of the spinel zinc ferrite to let experts give you more accurate suggestions. The diminish of the highest peak intensity of zinc ferrite may indicate that there is a sever preferred orientation along 311 plane. You may have to check out the crystal shape of the synthesized product using TEM. If the shape of the crystal is needle-like or plate like this may confirm the presence of preferred orientation.

Good luck

Dear Anne,

Mohammed is probably right, the diffraction pattern of your sample may suffer from preferred orientation.

When scanning the literature, for example :

Data 6. HYoon-MnZnFeO-Nanoscale Research Letters-8-530-2013

and

Article Magneto-resistive coefficient enhancement observed around Ve...

you will find a lot of Zn ferrite XRD pattern exhibiting the 311 peak. So the absence of that peak is no general property of Zn ferrite.

Isn't there any tiny peak showing up at about 35°?

You should share the XRD pattern, as Mohammed suggested above, and please share a bit more about your sample. Is it a film for example?

ZnFe2O4 is a normal spinel structure. There should not have any inverted spinel structure because of octahedral site selection energy rule. I don't know your synthesis technique, however if possible you may calcine your material at higher temperature and perform the XRD to check the presence of 311 peak.

Additonal remark:

In fig. 2 of the following link, you can see an example of preferred orientation for Zn ferrite:

Article Synthesis, Magnetic Anisotropy and Optical Properties of Pre...

There is a huge difference in 311 peak height with respect to the powder case.

Many thanks for your help and kind comments. Unfortunatly with all the references sent to me, the 331 diffraction of the spinel unit-cell was absent.

Can you be so kind as to send to me a reference in which this specific diffraction peak is observed?

Enclosed the diffractogram recorded on one of your samples (hematite impureties, porous ZnFe).

Sorry Anne,

you are right.

We all focussed on the 311 peak not on the 331 one, as you already mentioned in the your primary question.

So lets go the the 331 peak:

In Fig. 1 curve e) of the following link a tiny 331 peak shows up:

https://arxiv.org/ftp/arxiv/papers/1203/1203.3924.pdf

In addition please see the first few sentences of section 3.1 (page 4) of that document.

Also in Fig. 3 curve b and Fig. 8 run#1 of the next link a tiny 331 peak shows up:

Article ZnFe2O4 nanoparticles and a clay encapsulated ZnFe2O4 nanoco...

You should perhaps perform a very long run in order to see the 331 peak above noise (at about 50° in 2theta) combined with a decrease in step size (if possible).

In your pattern above also a tiny peak shows up around 50°.

Remark: you may use a Co tube for reduction of Fe fluorescence background of your XRD pattern. So the 331 peak will show up more pronounced and is not affected by the Fe fluorescence noise contribution to the background.

Unfortunately the XRD pattern shown in both links mentioned above were taken via Cu k-alpha radiation ( Cu tube ) and not Co k-alpha.

Co k-alpha is not able to excite Fe-K fluorescence radiation in the sample

Additional remark:

In the papers mentioned above a tiny 331 peak shows up. In many other papers this peak is burried in the noise of the huge background, which is due to Fe fluorescence radiation.

One might expect a somewhat larger 331peak, but according to the ZnFe2O4 lattice (JCPDS card no. 82-1049) the 331 peak is really a tiny one.

Its height is a bit less than 1/10 of the 311 peak.

See for example the expected peak height distribution of the no. 82-1049 (for powder sample) in:

Article Magnetocaloric Effect and Universal Curve Behavior in Superp...

Preferred orientation may also reduce the relative peak heights as well as residual stress.

Thus a reduction of backgound is unevitable when looking onto the 331 peak.

Please use a Co tube (or even a Fe based tube).