| In the research of electronic ceramic components, piezoelectric ceramic materials are essential as their function on information receiving, transforming, handling, and reserving, etc. Though lead-based piezoelectric ceramic materials have occupied a dominate position due to their excellent piezoelectric properties and low price, they contaminate the environment in the process of preparation and application, which urgently need to be solved. Among the study of lead-free piezoelectric ceramic materials, BaTiO3 (BT)-based ceramic, with a perovskite structure (ABO3), can satisfy the electrical properties requirements by suitable preparation technique and doping materials for morphotropic phase boundary (MPB) and polymorphic phase transition (PPT) structure, which have been honored as mainstay in the future electronics industry.The most popular preparation technique of BT-based lead-free ceramics is solid state sintering process with a high sintered temperature (around 1450℃), which might result in energy waste and deteriorate electrical propertities as grain structure distortion. Moreover, BT-based ceramics have a wide distribution of electrical performance by various preparation processes. Facing with those problems, we have studied on the preparation, structure, and electrical properties of BT-based piezoelectric ceramics, which displayed the highlights and characteristics in our study.The main highlights embodied in the study are:(1) The high quality with narrow particle size distribution and homogeneous composition of BT-based nanoparticles were prepared via a modified Pechini method through adjusting the raw materials and controlling reaction temperature, and the experimental mechanism of BT-based nanoparticles were obtained. (2) The high densification of BT-based ceramics with uniform grain size were obtained by optimizing the ceramic preparation process through adjusting the green body preparation process and controlling the sintering process parameters, and the mechanism for generating excellent electrical properties of BT-based ceramics were gained. (3) The innovation system of Ir4+-doped and Er3+-doped BT-based ceramics with La3+ doping were studied in depth.The main characteristics embodied in the study are:(1) Based on the as-prepared nanoparticles, BT-based ceramics were sintered by solid state sintering process under a low temperature of 1260℃. (2) Through investigation on the mechanism between structure and electrical performance with doping materials, the associations of electrical properties and structure with doping materials were established for guiding the actual application in electronic ceramic components.The optimum processes of preparation BT nanoparticles and ceramics were obtained by mechanism analysis and optimization practice. Based on the experience, BT-based nanoparticles doped/co-doped Ca, Zr, La3+, IrO2, Ir4+, and Er3+were prepared, respectively. Then, BCZT-based ceramics of 0.33Ba0.8Ca0.2TiO3-0.67BaTi1-xZrxO3 (BCT-BZT,0≤x≤0.2), 0.5Ba0.9Ca0.1TiO3-0.5BaTi1-xO3 (BCT-BZT’,0≤x≤0.2), 0.5Ba0.9Ca0.1TiO3-0.5BaTi0.88Zr0.12O3-0.12%La-xEr (BCT-BZT-La-xEr,0≤x≤0.5%), 0.5Ba0.9Ca0.1TiO3-0.5BaTi0.88Zr0.12O3-0.12%La-xIr4+(BCT-BZT-La-xIr4+,0≤x≤ 1.25%),0.5Ba0.7Ca0.3TiO3-0.5BaTi0.8Zr0.2O3-xIrO2 (BCT-BZT-xIrO2,0≤ x≤ 1.2%), and Ba0.934Ca0.066Ti1-xZrxO3 (BCZT,0≤x≤0.134) were sintered by solid state sintering process. The crystal structure, farcture surface, and electrical properties were detected by X-ray diffraction, Field emission scanning electron microscope, and electrical insurments, respectively. Moreover, reasons for the excellent electrical properties were discussed in detail.It was found that two-step sintering process was good for promoting crystal growth, improving densification, and elelvating electrical properties when studying on the same component of BCT-BZT and BCZT ceramics. For BCT-BZT’ceramics with the grain size of about 2 μm and relative density, ρr= 96.9%, showing PPT region of coexisted orthorhombic and tetragonal structure when x= 0.10-0.12. With increasing zirconium contents, Curie temperature (TC) of BCT-BZT’ceramic was dropped, but the phase transition temperature from orthorhombic to tetragonal structure (TO-T) dielectric frequency dispersion, ferroelectric relaxation, and diffused phase transition (DPT) were enhanced. The optimum electrical properties of remanent polarization, Pr= 16.40 uC/cm2, piezoelectric coefficient, d33= 237 pC/N, and planar electromechanical coupling factors, kp= 0.23 were found when x= 0.10.For BCT-BZT-xIrO2 ceramics, with increasing IrO2 dopant, pr was elevated to 97.4% and then decreased, but ferroelectric relaxation and DPT had the opposite variation; the grain size was dropping from 0.7 μm. The optimum electrical properties of mechanical quality factor, Qm= 78.2, coercive electric field, Ec= 2.99 kV/cm, Pr= 6.28 μC/cm2, J33= 199 pC/N, and kp= 0.26 were found around PPT region of coexisted orthorhombic and tetragonal structure at room temperature when x around 0.4%. Moreover, the obtained electrical properties could satisfy the requirements for Y5Y and X7R multilayer ceramic capacitor. For BCT-BZT-La-xIr4+ceramics,7c was dropped and To-T was dropped to room temperature sharply, dielectric properties and dielectric frequency dispersion were elevated first and then dropped, but ferroelectric relaxation and DPT had a reverse tendency with increasing Ir4+contents. When x around 0.75%, the highest ρr= 97.3%, and the optimum electrical properties of Qm= 70, Pr= 6.20 μC/cm2, d33= 269 pC/N, and kp=0.28 were found. For BCT-BZT-La-xEr ceramics, the replacement of the A site turn to B site in single ABO3 structure, showing the transformation from donor doping to accepter doping mechanism,TC were dropped but TO-T were elevated, dielectric properties and dielectric frequency dispersion were elevated and then decreased, but ferroelectric relaxation and DPT had the opposite variation with increasing Er3+ contents. When x= 0.2%, the highest pr= 96.8%, and the optimum electrical properties of Qm= 69, Ec= 1.60 kV/cm, Pr= 5.78 μC/cm2, d33=196 pC/N, and kp= 0.30 were found. Moreover, the dielectric properties of the ceramics were elevated through the polarization process. |
PDF Full Text Request