GRAIN SIZE, TEMPERATURE AND FATIGUE EFFECTS OF FIELD-INDUCED ANTIFERROELECTRIC-FERROELECTRIC PHASE SWITCHING BEHAVIOR IN STRONTIUM ZIRCONATE TITANATE CERAMICS
Lead Zirconate Titanate (PZT) ceramics have excellent electromechanical properties for applications such as sensors, transducers, and actuators. Commercially available actuators exhibit strain values of up to 0.1%. Recent research has focused on inducing large strain by adopting a technique of phase transition from an antiferroelectric (AFE) phase to a ferroelectric (FE) phase. Since unit cell volume of AFE is smaller than that of FE, switching from AFE to FE can be associated with large strain values. In recent investigations, Sn-, La- doped PZT systems were found to exhibit strain values as high as 0.5%. Sr-modified PZT system shows a large AFE - FE phase boundary suitable for field - induced phase transition study. Recent work carried out in this laboratory reported that certain compositions along the phase boundary in PbZrO 3 -PbTiO 3 - SrTiO 3 -SrZr0 3 system show promising electro mechanical properties that can be used for potential actuator applications. However, the effect of microstructure on the electromechanical response was not investigated. In this study, two Sr-modified compositions located at the AFE-FE phase boundary were selected. The effect of grain size on the AFE-FE switching behavior was studied. Variation in grain size was achieved by subjecting the samples to different sintering time at a constant sintering temperature. These samples with different grain size were tested for electromechanical properties i.e. polarization and longitudinal strain. In order to understand the thermal stability of the phase switching process, polarization measurements of all samples were carried out in the temperature range of -20°C to 100°C. Also, stability of the properties on prolonged electrical switching was investigated by subjecting the compositions to repeated electrical loading. Grain size was found to increase with increasing sintering time from 4 ?m to 14 ?m .The maximum polarization, Pmax exhibited by samples with different grain sizes ranged from 36 ?C/cm ^2 to 43 ?C/cm ^2 and the longitudinal strain was in the range 0.31% to 0.52%. Both compositions showed AFE-FE transition at room temperature. When the temperature was decreased below room temperature, it was observed that ferroelectric hysteresis loop was exhibited by both composition. At room temperature, AFE - FE phase transition was evident from double-hysteresis loop. When the samples were heated above a critical temperature, losses were found to occur. This was evident from the shape of the P-E loop. Both compositions investigated showed fatigue effect when subjected to repeated electrical loading. Fatigue was found to set-in after about 10 ^5 cycles. Associated with the initiation of fatigue was the small degradation in properties. Maximum polarization, P max decreased in the range of 6% to 7% after subjecting the samples to 10 ^6 cycles.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/2001