How big is the difference to cubic?

Crystal structures are always related to a specific stochiometry. If this is changing as in your case it would be highly accidental that exactly this composition has been investigated and published with structure data. Often only lattice parameters are available and they are only an indication about space group or  the symmetry, i.e. any symmetry can have a cubic metric.

For your case I would start with the simple perowskite replacing La and Sr, and Co and Fe. If someone should help you post the diffraction data. 

Hi, Ajith!

LSCF6428 (i.e. La0.6Sr0.4Co0.2Fe0.8O3-d) has Rhombohedral crystal structure at room temperature, for sure! It is a very well studied compound, for example, see for reference: J.N. Kuhn, U.S. Ozkan, Catal Lett (2008) 121:179–188. The transition to cubic phase occurs continuously upon heating and finishes at about 550 C in air. This compound has only slightly rhombohedrally distorted cell, therefore, depending on the XRD-instrument you use or depending on the size of the particles in your powder, the XRD pattern may look very similar to cubic phase but with broader picks.

Hope it will help you!

Good luck!

Thanks, Prof. Nolze and Dimitry

I have got the xrd pattern with broad peaks as you suggested.  Based on the reference, It is noted that the TEC of Co is low  (upto 500C) for the Fe rich composition. So possibly the structure will be a Rohobohedral. 

Thanks much once again for your valuable replies.

Hi, 

the rhombohedral structure will cause no broadening for all reflections, only for those which become independent due to the transition cubic-rhombohedral. Thus, reflection hhh  (or 000l) will not change i.e. these reflexes are unchanged and should be more narrow. If all reflections are broadened you possibly have a defect structure, i.e. containing both or more modifications.

Best greetings

G. Nolze 

Prof. Nolze, you're absolutely right! Thank's for the correction.

Thanks a lot Prof. Nolze and Prof. Dimitry for your valuable answers which were very helpful.

Regards

S. Ajith Kumar