La를 도핑한 비납계 세라믹 Na½Bi½TiO₃(NBT)의 유전 및 강유전특성

Abstract

A most widely used piezoelectric materials, such as PZT families, contains a great deal of lead. For environmental protection, it is necessary for lead-free ferroelectric and piezoelectric materials. Recently, a lead free ceramics have been studied as an important ferroelectric and piezoelectric materials. One of them, Na1/2Bi1/2TiO3(NBT) based composition is an important lead-free piezoelectric materials, which was discovered by Smolenskii et al. The NBT showed two phase transitions, which one is antiferroelectric phase below 200℃ and another ferroelectric phase at 320℃. The NBT has a relatively large polarization, however, pure NBT has a high coercive field and relatively high conductivity. Thus, it is difficult for a poling treatment as an electronic material. To improve the ferroelectric and piezoelectric properties, many research groups have been studied. Recently, the effects of ion doping and several solid solutions have been investigated. Especially, the dielectric and ferroelectric properties of the ion doped NBT systems are not fully understood. In this study, we have prepared pure NBT and La doped NBT ceramics. The effects of La doping on the dielectric and ferroelectric properties were investigated. The phase formation and crystal structure were investigated by XRD. The surface morphology were confirmed by SEM. The electrical properties were measured by a dielectric spectrometer from 40℃ to 600℃. The remanent polarization(Pr) and coercive electric field(Ec) were obtained from ferroelectric P-E hysteresis loop by using a Sawyer Tower circuit.