Study On The Properties And Microwave Sintering Of The Doped PZT Piezoelectric Ceramics

Piezoelectric materials, which can convert mechanical energy and electrical energy, have been widely used in various electronic components and devices. For example sensors, actuators, ultrasonic transducers, resonators, filters, buzzers, electronic ignition devices and so on. Piezoelectric materials include piezoelectric crystals, piezoelectric ceramics, piezoelectric polymers and piezoelectric composite materials. Because of simple preparation and low cost, the piezoelectric ceramic materials, in particular, lead zirconate titanate-based ceramic materials （referred to as PZT）, which exhibit excellent piezoelectric properties and adjustable composition, have dominated the main markets of piezoelectric materials for decades. To further enhance its piezoelectric activity and meet the special requirements of piezoelectric properties in the practical application, the present studies of the PZT piezoelectric ceramics include two aspects: Firstly, it is the dopants; Secondly, it is the improvement of the preparation process. At the same time, the quality of PbO （or Pb3O4） is about 70% in the PZT, and it is easy to evaporate during the sintering process, because the temperature of the volatile is low. These not only affect the performance of PZT ceramics, but also can cause environmental pollution. Therefore, the purpose of this study was also to improve the quality of PZT ceramic materials by the way of speeding up the firingrate, lowering sintering temperature and reducing the volatilization of lead oxide.Pb（Zr0.52Ti0.48）O3+xwt%BaO+ywt%Sb₂O₃+zwt%CeO₂ ceramics were synthesized by traditional sintering process and effects of the amounts of BaO, Sb₂O₃ and CeO₂ on phase structure, density, microstructure and electric properties of PZT piezoelectric ceramics were investigated. The results show: With the substitution of BaO, tetragonal phases reduce and rhombohedral phases increase; When the amount of BaO is 1.6wt%, the phase is in the morphotropic phase boundary, which exist rhombohedral and tetragonal phases; the samples densities reach a minimum 7.3g/cm³, d33（172） andεr（779） reach maximum, and tanδ（0.5%） reaches its lowest value. The results of the co-doping of BaO、Sb₂O₃ into PZT piezoelectric ceramics show: With the amount of Sb₂O₃ increasing, the materials crystal structure trends to tetragonal phase of perovskite type, when the amount of incorporation is 1.3wt%, the perovskite phase is in the morphotropic phase boundary, the maximum density of the samples is 7.6g/cm³, d33,εr are 435, 1763, but the tanδincreases to 2%. The results of the doping of BaO, Sb₂O₃, CeO₂ into PZT piezoelectric ceramics show: With the addition of CeO₂, the material system has phase transition from rhombohedral phases to tetragonal phases, but the change is little; When the doping amount is 1.1wt%, the maximum density reaches 7.5g/cm³, d33,εr and tanδare 411, 1910 and 2%. The effects of conventional electric synthesis temperature, sintering temperature and holding time on the microstructure, electrical properties by the optimum doping ratio were studied, the results of the optimum sintering process of the doped PZT piezoelectric ceramics, show: When the electric temperature reaches 850℃, the pyrochlore phases disappear, and the powders have completely formed pure perovskite phases; While the samples are sintered at 1250℃for 2h, the volume density of 7.5g/cm³, the lowest porosity of 0.68%, the maximum piezoelectric constant d33=411, the maximum dielectric constantεr=1910, and the dielectric loss of 2% are gotten.In this paper, the doped PZT piezoelectric ceramics were sintered by microwave methods. The influences of sintering process of conventional electric and microwave methods on the microstructure and electrical properties of PZT ceramic tapes were studied. The results show: The suitable synthesis temperature of the perovskite PZT powders by the microwave method is 750℃. Compared to the electric synthesis method, the synthesis temperature of the microwave is lowered 100℃, the holding time is cut down to nearly 1/6; Powders which obtained smaller size of about 0.5μm exhibit uniform granularity、less reunion and fine morphology of the PZT particles by the way of the microwave synthesis, this is the role of non-thermal effects of microwave. Compared with the electric sintering, the samples with distribution of smaller size grains are gained by the microwave sintering method; The dielectric constant and the piezoelectric constant of the samples sintered by the microwave method at 1000℃for 40min, reach the maximum values ofρ=7.1g/cm³,εr=1616, d33=360, and are slightly lower than density （ρ=7.5g/cm³）, dielectric constant （εr=1910）, piezoelectric constant （d33=411） of the samples sintered by the electric sintering at 1250℃for 120min, it may be due to the rapid speed of microwave sintering, the pores can not be completely filled; Comparison of the two firing methods show, under the little difference in the electrical properties, the microwave sintering temperature is lower 250℃than the electric sintering, and the holding time shorten for 1/3.