How XRD identify different phases in a material?

Phase identification:

XRD pattern is just like "fingerprint," and phases having similar chemical compositions can have drastically different XRD diffraction patterns.

For instance, anatase - TiO2, Brookite TiO2, and Rutile- TiO2 are all composed of the same chemicals (Ti & O), but the XRD pattern varies dramatically due to their different phases.

Use peak position and relative intensity of the experimental XRD to match the reference patterns in the database. Both peak positions and relative intensities for at least three peaks must fit

There are three platforms we can match the XRD pattern of our synthesized materials

i. Commercially purchased databases
The International Centre for Diffraction Data (ICDD) and the diffraction data are provided as a powder diffractions file (PDF). ICCD, previously called the Joint Committee for Powder Diffraction Standards (JCPDS), maintained the following PDF

PDF 1 lists d-spacings and relative intensities.
PDF 2, all data indexed such as cell parameters, the chemistry, and density of the materials.

ii. Online open access databases
iii. Literature
In many cases, very newly developed materials will not yet appear in these databases, so the best place to find these spectra is in the original publication.