The effect of defect field on dielectric ageing of lead magnesium niobate-lead titanate relaxor ferroelectrics

The ageing effect on the temperature dependence of the dielectric permittiv ity and loss angle tangent was examined for Pb(Mg1/3Nb2/3)(0.9)Ti0.1O3 and 0.1 wt% MnO-Pb(Mg Nb-1/3(2/3))(0.95)Ti-0.05 O-3 ceramics. A Debye-like diel ectric relaxation process was clearly observed in the higher temperature ra nge for the latter composition, but not for the former. It is stressed that the metastability of the ferroelectric domain structure is due to the pres ence of defect dipoles in perovskites. Compared with the dielectric poling behaviour of the compositions, a pin effect was introduced to analyse the d ifferences and similarities of reorientation and alignment of microdomain w ith macrodomain. Defect dipoles are formed from pairs of vacancy and positi vely charged dopant sites and they provide pinning centres to ferroelectric microdomain walls. As a consequence, microdomains re-establish along a cer tain direction over time, and the microstructure changes from a disordering to an apparent ordering. Thus a perovskite relaxer ferroelectrics with acc eptor dopants exhibits a significant time dependent decrease in the complex dielectric response.