Short-range order in electron-irradiated Cu-Pd: Fluctuations in a nonequilibrium steady state

We present electron diffraction results on specimens of Cu-Pd alloys under irradiation with 1.5-MeV electrons at temperatures from 200 to 400 K. The irradiation induces atomic mobility through the production of point defects but maintains the system in a disordered state despite a long-range-ordered phase being the equilibrium state. The presence of short-range order (SRO) is detected in electron diffraction data. SRO in Cu-Pd is characterized by peaks of intensity that flank the 100 and equivalent positions in the Brillouin zone, removed from those positions by a distance $q_m$. The quantity $q_m$ varies with Pd content and also with the temperature at which the system is irradiated. An analogy is drawn with an equilibrium statistical model.