Vegard's law.

Dear Isaac,

using Vegard's law is the way to resolve this issue.

In the base PDF4 + 2016 from the ICDD, I have been able to find the case Cu0.25Ni0.75 04-004-4502, the cases that you are looking for, you can obtain them by means of the Vegard's law from the pure cases (Cu 04-004-0386, Ni 04-004-0850),  representing the combination of phases in % of the position of the peaks of the pure phases for example with Excel or Origin.

I hope it helps.

Santiago Medina

Vegards rule is a rule and no law. There are several mixtures which do not match to a simple linear interpolation between two constituents. One famous example is Au-Ag. In case of Cu and Ni it seems to be not critical.... see the attached link, however I have to admit that if you take the shown diagram and add the lattice parameter of Ni = 3.524A, the derived slope in the diagram will finally end in a lattice parameter for Ni which is considerably smaller than the correct one. Therefore, it might be that there is also a small deviation from vegards rule. I would suggest to look for some experimental data. Look e.g. the attached pdf. 

or the last reference.

Article Pulsed electrodeposition of nanocrystalline Cu–Ni alloy film...

Article Cu–Ni materials prepared by mechanical milling: Their proper...

The TOPAS or LEPTOS (BRUKER) software packages are useful for the simulation of such kind of coatings or alloy formation. TOPAS & LEPTOS are the curve fitting softwares of Bruker which considers all the instrument parameters as well as the provided crystal structure parameters in . str format for the curve fitting. After the curve fitting it will directly give you the percentage of the specific phase in the given powder sample. Topas is mainly used for powder samples & LEPTOS is used for the Thin films.  In Leptos thickness of multilayered thin films, stress generation in it and surface morphology of the sample can be studied. I have used TOPAS mainly so I don't have that much idea about the Leptos, please google Bruker's webinar presentations related to Leptos &  Topas for more info. 

For simulating the patterns corresponding to the question, DIFFRAC.EVA must be enough, is posible to do with DIFFRAC.TOPAS also, both from Bruker. There are others software available, for example Expert HighScore from Panalytical, Rigaku software,Match!...

Try Power Cell, a very useful free software for simulation of diffraction patterns

http://www.ccp14.ac.uk/ccp/web-mirrors/powdcell/a_v/v_1/powder/e_cell.html

Best regards,

Pedro

The point is: do you know the structure of the alloy or not?

In the first case, if you have a reasonable idea of the structure (because you found it in the literature or you can estimate it using Vegards rule to determine the lattice parameter) you can easily simulate the diffraction pattern using FullProf Suite. It’s not the most user-friendly software I’ve used but it’s free, very powerful and very versatile. For example you can also compare several patterns, one for an ordered structure and another for a disordered one.

If you need to determine the structure it’s much harder. You can start from a reasonable approximation of the structure (i.e. that of one for the two materials) and relax it using an ab initio calculation software. It moves the atoms in the structure until it finds a stable position, very likely the equilibrium one. For this I know you can use VASP, but it’s difficult, very power consuming and probably it’s expensive. There are other less accurate software that are easy and free, but I don’t know them. However, it’s really better to ask so some colleague who does ab initio simulation! You can easily have a result but its accuracy depends a lot on the parameters of the simulation you chose.

https://www.ill.eu/sites/fullprof/