Suppose a A-BxOy composite coating is under investigation. If the weight or atomic percent of A, B and O are known from the EDX analysis, how to calculate the volume fraction of BxOy in the coating layer?
As far as I understand your question correctly you have a two-phase system which allows you to calculate the mass fraction of A and BxOy from EDS. If you want calculate the volume fraction you simply need to know the density (i.e. "X-ray" density) in order to calculate the respective volume and from that the volume fraction.