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 according to the formula Pb_0.85-Ba_0.15[(Zn_1/3Nb_2/3) _0.7Ti_0.3]_1-xW_xO₃ 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 (T_m). The frequency dispersion of T_m 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, induces an increase in the tendency towards Curie-Weiss behavior above T_m, which is associated with the growth of ferroelectric domains.