I confirm all above beside

peak shift maybe attributed to

1-     changes in stoichometric composition by doping.

2-     Instrumentations (Doppler effect during counts)

3-     Microstructure parameters (crystallize size and lattice strain"

4- Thermal annealing

this is happening because your dopant ions have been incorporeted into the lattice and changed the lattice constant of your host. that is the evidence that your dopant incorporeted sucessfully 

The main reason in your case is the increase/decrease in the lattice parameters that is reflected by the shift of diffraction peaks. This effect is mainly due to the difference in ionic radii between the main element and the dopant ion 

This effect is mainly associated with dopant ions.

As all have mentioned. the inclusion of other ions (such as dopants) will cause a shifty due to changes in lattice parameters.  I have seen that in TiC when small amount so of oxygen was present in the lattice

 Due to the change in lattice parameters.

If we modify the original system by using a dopant, it affect the lattice/unit cell of the material. Change in lattice parameters result in shift in XRD peaks. You can also calculate the lattice strain by using the broadning of the XRD peaks.

is the effect of dopant. 

One possible effect of dopant atoms incorporated into the lattice is decreasing (or increasing) of residual stress. When nanocomposites are in tension stress all peaks are shifted to higher angles (in compression to lower angles). 

change in the parametre cristallin

Dear Amin,

The shift in the peak during the XRD analysis is due to (i) due to linkage between host and doped particle (ii) due to change in the size of the host particle (iii) change in the binding energy and due to change in mechanical properties.

Dear Amin,

The dopant atoms are being taken into the host structure substituting for some of the host atoms and thus causing the structure to either contract or expand. If the peak shift is to higher angles the host structure is contracting and vice-versa. Clearly if the particles are of n.m. size the diffraction peak will be very diffuse and broad as the structure of particles will be strongly reflected in their surface structure which is highly disordered.

In powder diffraction, a change of effective depth (position) of the diffracting sample surface with absorptivity of the power-material in a powder-mount is a major artifact causing peak shifts.

With small particles, actual intrinsic peak shifts are due to crystal-particle size and shape. Here is a major work on that topic: https://www.researchgate.net/publication/270473313_Constraints_on_structural_models_of_ferrihydrite_as_a_nanocrystalline_material

Also, undetected phase mixtures and/or compositional inhomogeneity for a given crystal phase can be the source of an apparent shift.

Article Constraints on structural models of ferrihydrite as a nanocr...

I confirm all above beside

peak shift maybe attributed to

1-     changes in stoichometric composition by doping.

2-     Instrumentations (Doppler effect during counts)

3-     Microstructure parameters (crystallize size and lattice strain"

4- Thermal annealing

How can we differentiate or how can we identify the reasons? because if this could be the reason in peak shift what would be the main factor than, what are the circumstances in which we could identify the shift factor? Essam R. Shaaban

I was leaving out the trivial cause of change in lattice parameter in my partial answer.

Regarding strain effects, look at the underlying theory of the William-Hall plot method, as described here (discussion around Fig. 10): https://www.researchgate.net/publication/225956583_Interplay_of_surface_conditions_particle_size_stoichiometry_cell_parameters_and_magnetism_in_synthetic_hematite-like_materials

Article Interplay of surface conditions, particle size, stoichiometr...

Some of the motives for the shif of the diffractions peaks are:

1. When the surface of the sample doesn´t coincide with the surface of the holder. This effect produce a systematic shift of the peaks.

2. Uniform strain or compression produce systematic shift of the peaks.

3. Doping the sample with an element of different atomic or ionic size than that which is sustituted. This sustitution can be systematic in all directions or along one direction or plane.

Dear Naveed,

Actually, research means to identify the all possible causes either physical or chemical. Yes, you point out very important criteria that the cause is due to one factor or several factors indulge in it. Nano-physics based on Quantum mechanics and that part always tells possibilities.

Ok, come in to your question. The main cause is change in the lattice structure. The all other causes arises due to change in the lattice structure in XRD measurements. If the lattice size increases the peak shift arises before the peaks of host particle and if lattice size decrease the peak shift after the peak of the host particle. 

With best regards.

1. Random Stress due to intercalation of foreign atoms.

2. Stoichiometric inhomogeneity

3. Polytypic structure changes  

  are the key factors for the peak shifts. For X-M-X type structures these reasons are prominent.

Firstly, due to dopant, secondly instrument,  and may be due to change in lattice structure

It may change due to annealing at higher temperature, at high temperature the crystal may start to grow

Among  the parameters mentioned for shifting the XRD peaks, I think doping changes the lattice parameters and the XRD peak shifts in the opposite direction. That is, if the dopant leads to an increase in the lattice constant then the diffraction angle 2θ decreases and vice verse. Annealing can shift the XRD peaks but not too much it will have higher effect on the FWHM.

The shift may be due to the difference in the ionic radii of the main element and the dopant.

The shift of the peak position in x-ray diffraction can be attributed to the change of the lattice constants of the unit cell of the investigated crystal system.  This may result in expansion or shrinking of the unit cell depending on the ionic radius of the dopant. 

I confirm the explnations from Prof Saleh Heniti

Please post your XRD data along with reference scan and describe the composition of your material better.

due to different ionic radii

You can find a good summary of possible reasons for peak shift in the attached pdf.

Best regards

because due to different atomic radii

how can we account for a broader peak?? means large fwhm???

Broadining of the diffraction peak can be due to the small nano size of the crystalline sample, strain and instrumental factors. Fitting of the peak can provide you with the FWHM from wich the particle size and strain can be deduced after elimination broading due to instrumental factors by considering diffraction standard material such as silicon.

If it is a bulk sample, the primary reason could be attributed to the change in the orientation of the crystal lattice with respect to an inertial frame of reference. That means the miller indices would be different, and that can be caused due to either different ways of sample preparation, or due to different sample thickness where the orientation of the crystal planes vary with the thickness.