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We present a Monte-Carlo simulation on the dipole alignment configuration and dielectric susceptibility of a defective ferroelectric lattice with randomly distributed lattice defects in the framework of the Ginzburg-Landau theory. These defects are assumed to suppress locally the electric dipoles. It is found that with increasing defect concentration the dipole lattice configuration evolves from a normal ferroelectric state to a two-phase coexisted state, where highly polarized regions are embedded in a paraelectric matrix. The dielectric susceptibility in lattices with various defect distributions is studied. The simulated results are used to explain the measured dielectric response in ferroelectric copolymers containing defects induced by proton irradiation. (c) 2004 Elsevier B.V. All rights reserved.