  We model a binary mixture of passive and active Brownian particles in two
dimensions using the effective interaction between passive particles in the
active bath. The activity of active particles and the size ratio of two types
of particles are two control parameters in the system. The effective
interaction is calculated from the average force on two particles generated by
the active particles. The effective interaction can be attractive or repulsive,
depending on the system parameters. The passive particles form four distinct
structural orders for different system parameters viz; disorder (D), disordered
cluster (DC), ordered cluster (OC), and poly-crystalline order (P C). The
change in structure is dictated by the change in nature of the effective
interaction. We further confirm the four structures using full microscopic
simulation of active and passive mixture. Our study is useful to understand the
different collective behaviour in non-equilibrium systems.
