The influence of defects on first-order structural phase transitions

When studying the influence of quenched defects on first-order structural phase transitions, one has to take into account the elastic deformations which are induced by heterogeneous nucleation of the new phase. In the present paper the influence of both 'random local transition temperature' and 'random local field' defects are considered within a first-order perturbation Landau theory. Both the order parameter (o.p.) fluctuations and the defects are treated perturbatively, which is consistent for structural phase transitions close to a tricritical point and for low enough defect concentrations. in such systems the o.p. fluctuations tend to induce the first-order character of the transition, whereas both types of defect play the opposite role and tend to decrease the jump of the o.p. at the transition. Estimates of the concentration of defects which can lead to complete smearing of the transition are given.