Synthesis Of Perovskite PMN-PT And Fabrication Of Its Relaxor Ferroelectric Ceramics

As a new-style functional material with promising applications in many fields, lead-based relaxor ferroelectrics could perform higher dielectric, piezoelectric and electrostrictive properties. In this paper, perovskite ferroelectrics of (l-x)Pb(Mg_1/3Nb_2/3)O3-xPbTiO3 (PMN-PT, O≤x≤l) have been prepared by the precursor method. And relaxor ferroelectric PMN-PT ceramics with compelx perovskite structure have been obtained successfully from the pre-synthesized powders. Combing with d₃₃ test and density measure, the composition, structure and properties of the PMN-PT ceramics have been studied systematically by means of macro-quantity chemical analysis, X-ray diffraction (XRD), scanning electron microscope (SEM), differential thermal analysis (DTA) and thermogravimetric analysis (TGA).The precursor method could solve the problem that the appearance of pyrochlore phase during the synthesis procedure by avoiding the direct reaction between PbO and Nb₂O₅. Furthermore it also could decrease calcination temperature and PbO volatility. The homogenous precursor of MgNb₂O₆ was prepared at l000℃ for 4 hrs with excess 2%( mol) MgO. And then complex perovskite PMN-PT could be synthesized at 850℃ for 4hrs with excess 5%(mol) PbO.The relaxor ferroelectric PMN-PT ceramics have been fabricated from pre-synthesized PMN-PT powders by ball milling, moulding, removing binder and sintering under the atomosphere of PbO. The results of study revealed that 0.65PMN-0.35PT ceramics exhibited maximum piezoelectric coefficient d₃₃640pC/N and density 8.10 g/cm3.The composition of obtained PMN-PT have been analyzed by means of macro-quantity chemical analysis. The analyzed results of the Pb2+ concentration indicated that PbO in the PMN-PT seldom volatilized at 850℃. The PbO volatility loss could be up to 3.9%(wt) when sintered at 1200℃. The loss of PbO was very minute when PMN-PT was sintered at 1200℃ while the samples buried in the powders with the same composition.DTA/TGA analysis indicated that the perovskite PMN-PT could be formed at 650℃. And the loss of PbO would be sharply increased from the temperature of 1200℃. The perovskite PMN-PT was heat-treated under various temperature from 650℃ to 1200℃. The results of XRD analysis demonstrated that the perovskite PMN-PT was rather stable in a large temperature scale.The XRD peak of 2 6 =45 ?was gradually widened with the increasing of PT. It might mean that rhombohedral phase was gradually converted to tetragonal phase in this system. Near x=0.30⁰.35 of the PT content, there was a morphotropic phase boundary (MPB) where the PMN-PT materials could be characterized with remarkable piezoelectric properties. Further study showed that the piezoelectric coefficient d₃₃ could be up to maximum value when the amountof the rhombohedral phase approached to that of the tetragonal phase in the PMN-PT system.