A new type of disordered structure of AuCu₃

X-ray diffuse scattering with an intensity distribution of one-dimensionally elongated shape in reciprocal space is observed for a single-crystal of AuCu₃, which is in a transient state around the order-disorder transition point. The analysis is carried out on the basis of Wilson's model for the disordered structure of AuCu₃. The probability that a unit cell at a given position is displaced by half the diagonal of the unit cell cube is derived as a function of the position of unit cell, and is found to be expressed by an exponential function.