Study On The Sintering Characteristics And Electrical Properties And Of Relaxor-PZT Quaternary Piezoelectric Ceramics

In order to satisfy the requirements of the multilayer piezoelectric transformers, piezoelectric actuators, and other multilayer piezoelectric ceramic device, the properties of piezoelectric ceramics should combine a low sintering temperature and high electrical performances such as a high piezoelectric constant (d33), a high electromechanical coupling coefficient (kp), a high relative dielectric constant (εT33/ε0), a moderate mechanical quality factor (Qm) and a low dielectric loss (tanδ), etc. In this thesis, ZnO/Li2CO3and Bi2O3were used as low temperature sintering aids, to study the effect of different sintering aids on the microstructure, density, dielectric and piezoelectric properties of PZT-based quaternary piezoelectric ceramics.Firstly, the influence of the proportion and the amount of ZnO/Li2CO3on the sintering characteristic and electrical properties was studied. The results show that the addition of ZnO/Li2CO3did not change the crystal structure of PZT-based quaternary piezoelectric ceramics, and the formed liquid phase promoted densification and reduced the sintering temperature during the sintering process. It was found that when ZnO:Li2CO3=1:2, ZnO/Li2CO3=3.75mol%, high-density and excellent electrical properties could be obtained at a lower sintering temperature, satisfying the requirement of the multilayer ceramic capacitor. For example, after sintering at820℃/2h, the electrical properties are as follows:d33=545pC/N, kp=0.52, Qm=56, εT33/ε0=3174, tanδ=0.047, which satisfy the requirement of pure Ag paste as an inner electrode. After at980℃/2h, the sample can have d33=715pC/N, kp=0.59, Qm=53, εT33/ε0=4153, tanδ=0.031, which can satisfy the requirement of90Ag-10Pd paste. And at1020℃/2h, the sample can have d33=690pC/N, kp=0.58, Qm=56, εT33/ε0=373O, tanδ=0.035, which allows the85Ag-15Pd paste as inner electrode.Then, the effect of the sintering temperature and holding time on microstructure and electromechanical properties was investigated in ZnO/Li2CO3doped PZT-based quaternary piezoelectric ceramics. The experimental results show that when the sintering temperature is1020℃, the sample can have a high grain boundary migration, a large and uniform grain size, and a high-density structure. When the holding time is2h, the formed liquid could infiltrate grain boundary fully, make the grain growth completely, and a own small grain boundary gap. Generally speaking, the optional sintering condition could be that the sintering temperature is1020℃, and the holding time is2h, which could make the sintered sample own a dense, homogeneous microstructure and excellent electrical properties.Finally, in order to further reduce the sintering temperature, which can match with the requirement of low cost Ag-Pd electrode, a small amount of Bi2O3was added into ZnO/Li2CO3(ZnO:Li2CO3=1:2, ZnO/Li2CO3=3.75mol%) modified PZT-based quaternary piezoelectric ceramics. The experimental results show that a small amount of Bi2O3did not change the main crystal structure, could clearly improve densification, and further enhance the dielectric relaxation. The sample doped with0.1mol%Bi2O3could exhibit excellent electrical properties of d33=533-742pC/N, kp=0.56-0.64, Qm=42-68, εT33/ε0=3122-4251, as they were sintered in the temperature range of820℃-1020℃for2h. They might have larger potentials for the application in the multilayer piezoelectric ceramic devices using different Ag-Pd inner electrodes.