The Investigation Of Doping Modification And Preparation Process Of 0.25PZN-0.75PZT Piezoelectric Ceramics

In this paper, 0.25PZN-0.75PZT ceramics were prepared by a conventional mixed oxide method and conventional sintering. Through investigating La doped 0.25PZN-0.75PZT ceramics, some conclusions can be found: La doping promotes a transition from the rhombohedral phase to the tetragonal phase and moves the MPB to the high Zr/Ti ratio. A moderate amount of La doping （≤5mol%） can significantly improve the piezoelectric, dielectric properties, but excessive La doping can promote the formation of pyrochlore phase, thus deteriorating the properties. Besides, La doping will reduce the Curie temperature dramatically and make the sintering range narrow. The MPB of 0.25PZN-0.75PLZT （5mol%La） system was determined in the region of Zr/Ti=52.5/47.5-53.5/46.5 by X-ray diffraction （XRD） patterns. And the optimal formula was determined as 0.25PZN-0.75PLZT （5mol%La,Zr/Ti=53/47）.Based on the optimal formula, the effects of the preparation process such as calcining temperature, the forming pressure, firing silver technology and poling technology on the properties were studied and a basical optimal technology was confirm: calcining at 900℃,forming under 400MPa, firing silver at 600℃or 850℃for 5-10min, poling in a silicon oil at 140℃under 2kV/mm field for 10min. A rapid cooling process has been carried out in this paper before the poling field was revoked to study the effect of the poling conditions on properties with avoiding the disturbance of the temperature factor.The effects of lead content on the properties of pure, La doped and Mn doped 0.25PZN-0.75PZT ceramics have been also investigated in the paper. The research indicates that: The optimal properties were attained with lead content of 1.00 for pure 0.25PZN-0.75PZT. For La doped one, the excess of 2mol% lead can get the better properties. And when an excess of 4mol% even more lead was added, the properties of Mn doped 0.25PZN-0.75PZT were better. Excessive PbO will inhibit the generation of lead vacancies and oxygen vacancies at the same time. For the“soft”piezoelectric ceramics with lead vacancies as majority, the inhibition effect of excessive PbO on the generation of lead vacancies dominates, thus the piezoelectric properties will decrease; nevertheless, for the“hard”piezoelectric ceramics with oxygen vacancies as majority, the suppression effect of excessive PbO on the generation of oxygen vacancies is dominant, therefore the piezoelectric properties will increase in certain scope.In addition, the influence of Sb₂O₅ doping on the properties of 0.25PZN- 0.75PZT ceramics was studied by two doping ways: adscititious and B site. The conclusion is that the increase effect of Sb₂O₅ doping on the piezoelectric properties of 0.25PZN-0.75PZT ceramics is not notable.The optimal formula was obtained in this paper: 0.25PZN-0.75PLZT （5mol%La, Zr/Ti=53/47）. Through optimizing the process: calcining at 900℃,forming under 400MPa, firing silver at 850℃for 10 min, poling in a silicon oil at 80℃under 3.3kV/mm field for 15min, the optimal properties were achieved:ε33T/ε0=4535, tgδ=1.83%, d33=622pC/N, kp=0.626, Tc=204℃.