  Reasonable evaluation of composition amplitude in spinodal decomposition is a
challenge to microanalysis of atom probe tomography, especially at early stages
when phase separation is not prominent. This impedes quantitative analysis of
spinodal structure in atom probe tomography as well as comparison with
simulated results from phase field simulations. We hereby report an effective
method to estimate the composition amplitude by constructing an amplitude
density spectrum. This method can sensitively determine the composition
amplitude at early stages. In particular, it substantially bridges experimental
and simulation techniques comprising both discrete and continuum data in the
study of spinodal decomposition. Moreover, it was found that the commonly
adopted Langer-Bar-on-Miller method for atom probe analysis underestimates the
composition amplitude of spinodal decomposition. Case studies have been
performed on the Fe-Cr binary alloys.
