Lanthanum dopant induced transition from the ferroelectric to the relaxor state in 0.7PFW-0.3PT ceramics

In this paper, Pb1-xLax(Fe2/3W1/3)0.7Ti0.3O3 ceramics are synthesized by the conventional reaction method and the dielectric properties are investigated with the empirical law and ordering models. The lattice structure changes from tetragonal to pseudocubic after doping with lanthanum and the pyrochlore phase is induced as the amount of lanthanum dopants exceeds 5%. The effects of lanthanum dopants on the resistivity, the diffused phase transition, the space charge polarization and the dielectric loss are investigated. According to the ordering models, the long range order (LRO) ferroelectric is changed to the short range order (SRO) relaxor with the use of lanthanum dopants. It is suggested that growth of the 1:1 ordered domain is impeded by increasing the amounts of lanthanum dopants since the excess positive charge of the 1:1 ordered domain Pb1-xLax(Fe1/2W1/2)O3 is enhanced. Furthermore, the p-type carriers are neutralized by the electron compensation which is induced by the fewer lanthanum dopants.