Investigation on Strain Characteristics of Ferroelectric Ceramics for Micromechatronic Actuator Application

Abstract

Ferroelectric are materials which possess a spontaneous electric polarization and dipole can be reversed by applying an electric field. Ferroelectric materials have good properties such as high induced-strain at low electric fields and reduced hysteresis. Ferroelectric materials are very useful in many applications such as sensor and actuator. Actuator is a transducer where the external input energy changes displacement or force. The strain behavior of ferroelectric materials is related to electric field in two types as piezoelectric and electrostrictive phenomena. This research focuses on lead-free based (BaTiO3) and lead based (PLZT) ferroelectric ceramics at various parameters consisting of grain size, phase, crystal structure and temperature. Strain characteristic and ferroelectric properties of BaTiO3 ceramic sintered at 1350, 1375 and 1400 °C for 2h on grain size effect were observed. It was found that grain size increased when the sintering temperature was increased. The ferroelectric properties of ceramic resulted from the grain size effect. The highest strain was 0.064% and piezoelectric constant of 250.5 pm/V. It can be concluded that dielectric, ferroelectric properties and strain behavior were affected by grain size. Strain characteristic and ferroelectric properties of BaTiO3 ceramic sintered at 1375 °C for 1, 2, 4, 6 and 8h on phase combination and microstructure were observed. It was found that the shape of polarization hysteresis loop changed to slim loop after increasing soaking time resulting from behavior of combination between cubic and tetragonal phase. The ferroelectric properties of ceramic depend on cubic phase in combination phase. The strain characteristic in this work could not be analyzed because the signal from measurement was very bad due to the pores in ceramic. Strain characteristic and ferroelectric properties of commercial BaTiO3 ceramic with temperature dependence were observed. It was found that ferroelectric properties decreased with temperature increase due to the dominant effect from 90o domain rotation than 180o domain. The maximum strain at 120 oC as 0.148% was caused by mix direction of 90o and 180o domain reorientation. The butterfly-like shape change to quadratic shape and reduced area of hysteresis to linear relation of polarization resulted from phase transition from ferroelectric to paraelectric. Strain characteristic and ferroelectric properties of barium zirconium titanate ceramic Ba(Zr0.05Ti0.95)O3 with temperature dependence were observed. It was found that the right shift of transition temperature from orthorhombic phase to tetragonal (between 40 oC and 60 oC) and high depolarization occurred. Slimmer loop and saturated polarization were due to the mix rotation between 90o domain and 180o domain but temperature increase resulted in the decrease of ferroelectric because 90o domains were easier to rotate. The strain characteristic is quadratic relation. At 60 oC, the maximum strain was 0.180%, the maximum of piezoelectric constant was 179.8 pm/V and the highest asymmetry was 0.006% caused by phase transition from orthorhombic to tetragonal. Strain characteristic and ferroelectric properties of PLZT, 9/Zrx/Ti100-x ceramics where x= 70, 65, 60, 55 and 50 mol% were prepared by two-stage sintering. It was found that at room temperature, the results of strain behavior and ferroelectric properties depended on Zr/Ti ratio. The temperature dependence of PLZT 9/Zrx/Ti100-x ceramic at 30-140 oC showed that the decrease of strain and area polarization loop (slimmer loop to linear relation) with increasing temperature was due to the transition from tetragonal to rhombohedral to paraelectric phase.