Effect of tungsten doping on the dielectric response of PZN–PT–BT ceramics with the morphotropic phase boundary composition

In this paper, effect of tungsten doping on the dielectric property of the Pb(Zn1/3Nb2/3)O3–BaTiO3–PbTiO3 system around morphotropic phase boundary(MPB) composition is presented. Samples were prepared according to the formula Pb0.85−xBa0.15[(Zn1/3Nb2/3)0.7Ti0.3]1−xWxO3 assuming the compensation for W is achieved via the appearance of the lead vacancies. X-ray diffraction results show that a nearly complete perovskite phase was maintained as W was progressively added up to 5 wt.%. Introduction of W stabilizes the tetragonal phase against the rhombohedral one, resulting in the displacement of MPB composition region towards relaxor end. Moreover, lattice distortion of the tetragonal phase is enlarged, that of the rhombohedral phase is lowered. W- doping leads to an increase in the dielectric permittivity maximum and a decrease in the phase transition temperature (Tm). The frequency dispersion of Tm is succesively weakened as W ions are gradually incorporated, reflecting the strengthened couplings among ferroactive oxygen octahedra. A maximum on the degree of diffuse phase transition is observed at 1 mol% WO3, which can be interpreted in terms of competing effects of chemical inhomogeneity and ferroelectric couplings. W-doping also induces an increase in the tendency towards Curie–Weiss behavior above Tm, which is associated with the growth of ferroelectric domains.