Ni and Co are neighbours in periodic system. Since Ni has a higher atomic scattering factor, Co3O4 should show a (slightly) smaller intensity. However, as mentioned before, there are many factors. However, let's assume we keep them all constant (inclusive grain size) then the unit cell volume mainly determines the resulting (absolute) intensity since it displays the scattering power (periodic number dependend) per volume.

The other problem is the intensity...and where it disappears. It is clear that you shouldn't use the intensity maximum since if you consider the area below the peak it won't change at all in case of small grains or strain. The peaks only become broader...and since the intensity is constant the maximum needs to be decreased (because of the intensity constancy). With less and less perfection of your peaks more and more radiation will be scattered without  diffraction and you will find this intensity in the background of your measurement. Also the above mentioned structure influence is not that important since intensity will be simply transfered from one interefernce into another. This is not that dramatic here since the atomic positions are practically unchanged. I only want  express that you cannot (e.g. by another structure) annihilate or generate intensity.

On the other hand, we shouldn't forget the opposite case: the measured crystal is too perfect, like for Si. In this case the intensity description does not follow anymore the kinematic model (I proportional to |F|²) but the is dynamical theory where I~|F| . This means, also for perfect crystals we observe a decrease of intensity. A part of the x-rays penetrates the sample that deep that it will be absorbed from the sample and is not detectable anymore.

High intensity or sharp peak is an indication of more order, crystallization and arrangement. the obtained  pure cobalt oxide XRD  chart higher in order, crystallization and arrangement.than nickel cobaltite. you can confirm the this suggestion by using the FWHM to calculate crystallite size using Sherrer equation. for guidance check (Optik 126 (2015) 1352–1357) :on this web site 

http://www.sciencedirect.com/science/article/pii/S0030402615002685

While you've probably considered this, if the average grain sizes are within 10% of each other and the Ni is ~100% in the former Co site, the XRD intensity for cobalt in the mixed metal cobaltite should be close to half what it is in the pure cobalt oxide. A use of mixed powder oxide standards may allow you to separate the Ni sites from the Co.

I am agree with the suggestion given by Dr. Adel Eldenglawey.  Higher intense peak is an indication of good crystallinity.

This is not a question to be answered because the peak intensity of each peak depend on many factors : the molecular composition of each sample , the crystallite size of each sample , the X-ray voltage of the machine used , the step scan and the time of scan at which the diffraction patterns are taken , the plane of diffraction used for  measurement. . Each factor of these  affect the intensities. At last this question should not be asked if originally you have two sample of different chemical composition.

It is better to attach ur data and give more details about the experiment.

Thanks to all of them for yours valuable suggestions and providing yours appreciable time.....

Yours sincerely

The intensity of a powder pattern depends from intrinsic parameters but also from many experimental parameters (together with those already cited there is also the amount of sample packed in the sample holder). So, a simple comparison of the intensities of two different patterns in many cases has no meaning.

A broadening of the mixed compound can also be associated with the solid-solution formation compared to the other sample, which alters the lattice constant.

As mentioned above usually the decrease in XRD peak intensity is an indication of less degree of crystallinity and may be a decrease in the crystalite size (peak broading effect). I am a assuming that all the other parameters are constant. Good luck

Both oxides have spinel structure, the problem is which of the atoms occupy tetrahedral and wich - octahedral sites and what is the oxidation states of cobalt and nickel. All these factors can also influence the crystallinity of the product. I think the solution is complicated and requires additional studies (Rietweld refinement, magnetic measurements etc.)

As mentioned suggestions are more valuable to refine my doubts regarding peak intensity of two compounds and these suggestions helps alot to me.

Thanks to one and all for their valuable suggestions and time.

Ni and Co are neighbours in periodic system. Since Ni has a higher atomic scattering factor, Co3O4 should show a (slightly) smaller intensity. However, as mentioned before, there are many factors. However, let's assume we keep them all constant (inclusive grain size) then the unit cell volume mainly determines the resulting (absolute) intensity since it displays the scattering power (periodic number dependend) per volume.

The other problem is the intensity...and where it disappears. It is clear that you shouldn't use the intensity maximum since if you consider the area below the peak it won't change at all in case of small grains or strain. The peaks only become broader...and since the intensity is constant the maximum needs to be decreased (because of the intensity constancy). With less and less perfection of your peaks more and more radiation will be scattered without  diffraction and you will find this intensity in the background of your measurement. Also the above mentioned structure influence is not that important since intensity will be simply transfered from one interefernce into another. This is not that dramatic here since the atomic positions are practically unchanged. I only want  express that you cannot (e.g. by another structure) annihilate or generate intensity.

On the other hand, we shouldn't forget the opposite case: the measured crystal is too perfect, like for Si. In this case the intensity description does not follow anymore the kinematic model (I proportional to |F|²) but the is dynamical theory where I~|F| . This means, also for perfect crystals we observe a decrease of intensity. A part of the x-rays penetrates the sample that deep that it will be absorbed from the sample and is not detectable anymore.

I concern this question in terms of the crystallinity. For pure mono metal spinel oxide, it is easier to crystallize than binary metal. Because crytallization into spinel type involves metal ion migration into tetrahedra and octahedra sites. It is obviously easier for mono metal ion than binary metal ion to accomplish the process.

High intensity or sharp peak is an indication of more order, crystallization and arrangement. When other experimental parameters are constant and identical ordering would produce more intense peaks. Hope the former is more ordered one.

As Prof A. El-Denglawey has mentioned the High intensity or sharp peak is an indication of ordered arrangement. When other experimental parameters are constant and identical ordering would produce more intense peaks. Hope the former is more ordered one.