Role of point defects in the formation of relaxor ferroelectrics

Relaxor ferroelectrics are engineered by doping a large amount of point defects into normal ferroelectrics. The point defects create nanoscale compositional heterogeneity, which in turn lead to local Curie temperature (T_C) variation and random local electric and strain fields. However, it is still unclear about the individual roles played by each of these effects in converting a normal ferroelectric into a relaxor. In this study we distinguish these effects by carryout computer simulations using the phase field method. We find that although both the local-field and local-T_C effects could lead to the formation of nanodomains in relaxors, it is the former that leads to the appearance of Burns temperature T_B, the latter that leads to the appearance of the intermediate temperature T*, and a combination of the two allows one to model all three characteristic temperatures of a relaxor reported in experiments: T_B, T* and the freezing temperature T_f. This work unravels the roles of point defects in the formation of relaxor ferroelectrics and offers deep microscopic insight into relaxors.