Research On The Preparation Of Lead-free Piezoelectric Thick Films

As is well known, traditional piezoelectric materials (lead zirconate titanate) containing much lead can cause environmental pollution and damage people's health during manufacture and use. In order to protect our environment from lead pollution, investigation of lead-free piezoelectric materials to replace traditional piezoelectric materials is the latest trend in piezoelectric development. Among all these materials, Na0.5Bi0.5TiO3- K0.5Bi0.5TiO3(NBT-KBT) performan high piezoelectric properties. With the development of electronic component, the characteristic of miniaturization, integration, multifunction of devices demands piezoelectric thick films for the low operating voltage and less interface reaction. Compared with other existing methods, screen printing and tape casting are successful methods for fabrication of piezoelectric thick films. In this thesis, NBT-KBT thick films was successfully prepared by water-based gel-taping method and screen printing method.NBT-KBT powder was prepared successfully by sol-gel method. NBT-KBT powder was obtained at the condition aging time 36 hour and calcining at 650℃for 2 hours. The average particle size was 200 nm.The process of fabrication was studied, Factors that have effect on the properties of the powder were discussed.Powders synthesized from sol-gel method and conventional solid state reaction method was used to form NBT-KBT thick films by gel-taping method respectively. The thickness of the films is 300μm. It was found that the powder synthesized from sol-gel method can decrease sinter temperature and increase piezoelectric properties. The properties of NBT-KBT thick films sintered at 1120℃for 2h are as follows:εr=919, tanδ=4.9%(1kHz, 25℃), d33=102 pC/N, kt =20%, Pr=24μC/cm2, Ec=56 kV/cm2.NBT–KBT thick films doping with Mn was prepared by screen printing method. MnO2 doping resulted in transition from rhombohedral to tetragonal. Its dielectric, piezoelectric and ferroelectric properties were studied. It was found that manganese doping increases the electrical properties of NBT-KBT efficiently. When the quantity of manganese is 1.0mol%, the properties are as follows:εr=735, tanδ=2.2%(10kHz,25℃), d33=88 pC/N, Pr=28μC/cm2, Ec=86 kV/cm2.