This is a common question, look at:

https://www.researchgate.net/post/Peak_splitting_at_high_2_theta_angle-can_anyone_help

and

https://www.researchgate.net/post/What_is_the_reason_for_peak_splitting_in_XRD_Can_reitveld_refinement_be_done_for_the_same

How about higher angle peaks, the spitting also occurs? Your case looks like Kalpha1 and Kalpha2 because the intensity of the second peak is about a half of the first one but more detailed answers you can find in mentioned links.

Gevorg,

A 2nd material (element B) that alloys with the 1st material (element A) in the same crystal structure (i.e. BCC to BCC) will simply shift the peak positions. So if you look at the XRD pattern of only element A, and the (211) peak is at 74 degrees, and you look at the XRD pattern of only element B, and the (211) peak is at 76 degrees, then the alloy of the two materials will be somewhere between the two peak positions depending on how much of element B is present. As for the data you have shown, I think that Grzegorz is correct in his assessment that the peak splitting of the alloyed data of such a narrow scanning range is showing K_alpha 1 and K_alpha 2. Also, the pure Mo card looks like calculated values to me instead of actual data. Real data will have some peak broadening due to -- well lots of variables both in the material and the measurement system, but that is a different discussion -- as well as the peak splitting as shown in the alloyed data.

So to help you identify what the alloy is, limit yourself to BCC materials that would have a (211) peak (If I identified the Mo peak accurately, I am going off of my memory for the rules of BCC allowed Bragg conditions) slightly higher than Mo.

Hope this helps,

George

Looking to the diffraction patterns, the first one is calculated and the second one is experimental. The first peak of experimental seems to coincide with the third one of theoretical. The second peak seems to come from the unknown element, since, if the unknown element alloyed with Mo is soluble (only one phase is present), you don't have any way to know what´s the element. It is very possible that the second element (which also crystalize in a bcc structure) has the lattice parameter very close to Mo, maybe is Nb which also crystallize in bcc.

Best regards

Pedro

Gevorg Ter-Isahakyan,

Grzegorz Cios, George Glenn Peterson, P. Grima Gallardo,

I agree with the explanation of these expertise. The XRD pattern after adding an alloy, it seems FWHM decreased due to the adding an alloy and appeared in XRD pattern as the splitting the original peak, known as the satellite peak of unknown material. This peaks should be very much similar lattice constant of that Mo. However, the crystallinity of the original material has been decreased after adding the unknown material, which to be noted. So that identify the elements having closer lattice constant of Mo and that should be answer to your question (may be similar to the suggested by P. Grima Gallardo). You are welcome to more queries !

Obviously there is some information missing concerning the homework. I agree that the top pattern belonging to Mo is a calculated one, seemingly from using copper radiation, but the angular resolution is too low to deduce whether it is well monochromatized or is a weighted average of Kalpha-1 and Kalpha-2. The second pattern only shows a blowup from the (211) contribution, and it seems (as has been commented on) that it is due to the two wavelengths. (When showing data, one should include essential information as to radiation used and on what angular scale.) If that is so, it is easy to confirm that the two peaks belong to the same d-value from calculating the ratio between the values of the sine-function and compare with the ratio of the wavelengths.

The second pattern cannot contain only one reflection, so it is rather strange to present a problem like that to be solved by a student without proper information. Again, if we assume that the 2nd pattern is only part of a corresponding full pattern based on a molybdenum alloy, every one of the reflections would show a splitting (as commented upon earlier by others) but increasingly so by increasing angle, and the only conclusion to be drawn is that the element addition results in a cell edge decrease (seemingly an accompanying angular increase). However, you cannot know which elements caused this, since it is then the effect of solid solubility conserving the parent phase. The same effect would be obtained from any element that is soluble in molybdenum that has a radius less than on the Mo (the structure of the pure solute is irrelevant). You cannot even say whether that element is a metal or a non-metal! For instance, silicon (not at all bcc) would give that effect as well as a whole bunch of metals. The solution to your problem to find (from XRD) what the element can be is impossible if the two peaks are indeed a resolved alpha-1/alpha-2 contribution of the (211) reflection.

If, on the other hand, the "satellite" peaks belong to another bcc-element, the alloy is a mechanical mixture of two bcc-type phases and an identification might succeed as Pedro Gallardo indicated.