I am working through a paper in which the chemical diffusion coefficient is related to the self-diffusion (or tracer) through the following derivation, on which I am a little hung up. AB2 metal. Overall diffusion D= XADB+XBDA meaning the chemical diffusion of B is: DCB=XADB=XADTB(1+∂lnγ/dlnXB) and the chemical potential of B is: μA=μ00.5B2+RTlnγBxB=μ00.5B2+RTlnp0.5B2 finally the mole fractions of XB and XA vary accordingly: XB = (2+x)/(3+x) XA = 1/(3+x) and then DCB is: DCB=DTB(2+x/2) ∂ln(pB2)/dx I am confused as to where the (2+x)/2 term comes from. I believe it is from the mole fraction XA in the overall diffusion equation combined with a derivation including the mole fraction XB from the chemical potential, but can't work it out exactly. Thank you in advance for any clarification on this topic!