X-ray intensity fluctuation spectroscopy studies of ordering kinetics in a Cu-Pd alloy

Abstract

X-ray intensity fluctuation spectroscopy has been used to examine the coarsening kinetics in the classic long-period superlattice Cu-Pd alloy. The evolution of the speckle intensity was examined near the centers of both a superlattice peak (associated with local $L{1}_{2}$ order) and a satellite peak (associated with one-dimensional antiphase correlations). The decay of the two-time correlation function $C({t}_{1},{t}_{2},q)$ was independent of the direction examined and was similar for the superlattice and satellite peaks. In agreement with published Langevin theory and simulations, the decay time $\ensuremath{\tau}$ of the two-time correlation function increases linearly with average time ${t}_{m}=({t}_{1}+{t}_{2})∕2$. It is relatively independent of the wave vector near the peak centers. However, $\ensuremath{\tau}$ increases much more slowly with increasing ${t}_{m}$ than is expected.