Order and superlattice reflections: in the disordered state,Cu3âAuhas an fcc structure, with lattice parametera=0.3749 nm. In the ordered state, Au occupies the corners of the cell, whereas the Cu atoms occupy the Gace centers. (Assume that the lattice parameter remains constant.) (a) Compute the structure factor for both the disordered and ordered states and determine which reflections are only present in the ordered state; these are known as superlattice reflections. (b) In the disordered state, the probability of finding a Au atom in the origin of the cell is25%; in the ordered state, it is100%. Write down similar probabilities for the Cuatoms for both types of position in the unit cell. (c) Find an expression for the atomic scattering factor for a partially ordered state, i.e., when the probability of finding Au in the origin of the cell is given by25%â¤pAuââ¤100%. (d) Taking into account all correction factors, plot the ratio of the integrated intensities of the fundamental reflection (200) vs. that of the superlattice reflection (110) as a function ofpAuâ