The amorphous impurity will add up to the background in form of hump (if there is a short range order). No, it will not shift the peak position of the crystalline phase. It will not affect the absolute intensities of the crystalline phase. However, don't forget that the final pattern is convolution of both amorphous and crystalline phase.

I cannot answer your question in general, but I can add some information on the situation in polymers. I believe, however, that the general features are universal. First of all: "amorphous" and "(perfectly) crystalline" states are two theoretical extremes, between which there is almost a complete continuum of states.

If you start from the perfectly crystalline state of, say NaCl, you will have almost Dirac-delta like reflection peaks (even that is not true, as there are lattice vibrations causing finite linewidth and even at absolute zero you have zero point vibration), and if you go up with temperature, you will gradually have vacancies, interstitials etc. these imperfections will cause line broadening. If you use e.g. high energy irradiation or neutron irradiation, you will have more and more broadening. If the defect concentration exceeds a certain limit, the lattice may even collapse. In inorganic or low molecular organic materials another reason of line broadening is the finite size of the crystllites (polycrystalline materials). The atoms situated at the inter-crystalline surfaces may be considered as beonging to the "amorphous" state in that sense that their scattering is more liquid-like.

If you move to inorganic glasses, where the crystllization is hampered by kinetic effects (high viscosity), you will again have a whole continuum between the completely amorphous and crystalline states. Annelaing close to the glass temperature may induce crystallization (especially in vitro-ceramics). In this case the phase structure may be described as a mixture of crystalline and amorphous phases. (One or more of these phases my be metastable in the thermodynamic sense, described by pseudo-variables).

In polymers the structure can be such that no crystallization is possible (e.g. atactic vinyl polymers), here you will have an almost ideally amorphous structure. If the structure does allow crystallization (e.g. isotactic or syndiotactic vinyl polymers), you will have partial crystallization. The crystalline size will be very small, and the inter-crystalline area is regarded to be amorphous. This is an oversimplification, however, as the observed scatterogram may also be described by perfectly and imperfectly crystlline parts as well. The "amorphous" inter-crystalline phase may also be oriented or partially ordered. Some even use a three phase model to describe the situation: crystalline, amorphous and intermediate or "surface" phase. The situation is further complicated by the fact, that, depending on the crystallization conditions the so-called "folding length" or "large period" of the partially crystalline polymer (which influences not only the diffraction peak width but also the DSC behavior) may be different. Furthermore there is a higher organization level, the so-called spherulite (in the order of micrometers), which may very depending on the crystallization conditions. These three parameters: overall crystallinity, folding length (crystal size distribution) and spherluite size are three independent parameters, exhibitin g complex inter-relations. Therefore if one studies effects such as filler effect, additive efffect, crystallization condition effect, it has to be taken into account that these effects may be completely different at these three levels of structure.

The amorphous impurity will add up to the background in form of hump (if there is a short range order). No, it will not shift the peak position of the crystalline phase. It will not affect the absolute intensities of the crystalline phase. However, don't forget that the final pattern is convolution of both amorphous and crystalline phase.

How can you add an amorphous impurity in a crystalline material? Ultimately, after homogenization,it will be either amorphous or a crystalline material. But for the reasoning purposes, we can argue that amorphous material will only add to the background in a diffraction pattern.

Usually, even amorphous materials exhibit some kind of short or medium range order that give rise to (several) broad peaks in the xrd pattern - some people might call it "background".

Since the resulting xrd pattern is a superposition (not a convolution!) of the amorphous and the crystalline phase, it can (under certain conditions!) be possible to determine the amorphous volume fraction present in your sample by evaluating the integrated intensities of these two phases.

If the amount of amorphous phase does not influence the lattice distance, the microstrain or the "crystal size" itself, it has no effect on the position or the width of your crystalline peaks. A plot of these parameters versus the crystalline volume fraction should provide an answer to this question.

I have usually obtained a very wide band (10-20º) in the 15-35 2 theta range. It seams not to be affecting the peaks intensity of the chrystalline phase.

I agree with Mr. Ricardo Rojas and Mr. Florian Koehler and others. Since a very wide band (of 10-20º) in the 2 theta range between 15-35 is usually observed along with crystalline peaks. This wide band does not affect the peaks position/intensity of the crystalline phase.

Amorphous impurity in the crystalline material may cause shift in the peaks of XRD pattern and change in intensity of peaks. There may be change in bond length and bond stretching.

I agree with Mr. Raghavender Medishetty.

Amorphous impurity can be seen in XRD by the formation of very broad peak near the diffraction reflections obtained from the crystalline structure of the sample.

I think Dr. Singh means to say that X-ray diffraction cannot be used as an analytical tool. This is because X-ray diffraction can only determine (detect) crystalline phases and cannot determine any amorphous phases. Thus if X-ray diffraction is utilized to determine, for example the phases during hydrogen absorption or de-sorption (e.g Mg(NH2)2) and if the product after de-hydrogenation disappear from the XRD spectra, one cannot simply concluded that the product disappear because of chemical reaction. It is very possible that the product disappear from the XRD spectra during hydrogen desorption because it became amorphous.