Preparation and properties on PMN-PT ceramics with fluoride sintering aids

Relaxor ferroelectric 0.68 Pb (Mg_1/3Nb_2/3) O₃-0.32 PbTiO₃ ceramics with fluoride (LiF, MgF₂, CaF₂) sintering aids were prepared by the columbite precursor method. The phase composition and microstructure of ceramic samples was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the dielectric and piezoelectric properties were measured. The results showed that pure perovskite phase was obtained for all the specimens and no other phase was detected. The grain size is larger (about 3-4μm) for the PMN-PT ceramics with LiF and MgF₂ sintering aids, but smaller (approximately 0.5-1μm) for the pure PMN-PT ceramics and that with CaF₂ sintering aids. For the PMN-PT ceramics with LiF and MgF₂ sintering aids, the maximum dielectric constants increase, the piezoelectric properties are improved and the diffusion phase transition become weak. But for the PMN-PT ceramics with CaF₂ sintering aids, the maximum dielectric constants decrease, the piezoelectric properties deteriorate and the diffusion phase transition become strong.