Bias Electric Field Dependence of High Power Characteristics in PZT Piezoelectric Ceramics

Open Access
Author:
Bansal, Anushka
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
April 12, 2017
Committee Members:
  • Kenji Uchino, Thesis Advisor
  • Joan Marie Redwing, Committee Member
  • Qiming Zhang, Committee Member
Keywords:
  • Piezoelectrics
  • DC Bias Field
  • PZT
  • High Power Characterization
  • Losses in Piezoelectrics
  • Burst Drive Method
Abstract:
Lead Zirconate Titanates (PZT’s) have been overwhelmingly concentrated on and have commanded the most recent 60 years in piezoelectric applications. Even though material constants for piezoelectric ceramics are for the most part described under free conditions, these measured properties are not legitimate specifically when devices work under externally applied high mechanical or electrical loads. The properties of these materials are liable to the conditions in which they are measured. In this way, an essential point of examination right now is the behavior of these ceramics under such external conditions. DC bias stress and electric field are of specific significance for study because the actuators and transducers are frequently utilized as a part of these conditions to balance out or improve the operation performance. Apart from working under externally applied loads, piezoelectric materials are utilized as a part of diverse high power applications, for example, ultrasonic motors and submerged sonar transducers. In these devices, the piezoelectric materials are driven under high voltages and currents. At high power conditions, the materials go astray from their linear constitutive conditions because of non-linearity and hysteresis in physical parameters. The hysteresis manifests in terms of loss and consequently, heat generation in piezoelectric materials. In this way, the properties must be measured in practically identical high power testing situations to accomplish significant estimations. Thus, investigation of the loss mechanisms is essential for the determination of heat generation. This thesis means to illuminate the loss mechanisms in piezoelectric ceramics in the perspective of the late advancements in high power piezoelectric devices affected by externally applied DC bias field. Under a high mechanical excitation condition at the resonance of a piezoelectric specimen, measured by edge vibration velocity (RMS), the mechanical quality factor Qm degraded by 22% per 0.1 m/s of the vibration velocity increment for the soft PZT, while 17% per 0.1 m/s for the hard PZT under a DC bias field of 300 V/mm. However, it increased by 3.1% per 100 V/mm for the soft and 1.7% per 100 V/mm for the hard PZT with the applied positive DC bias field under a constant vibration velocity of 0.3 m/s. The high-power properties deviated significantly from the ones measured under low power conditions (15% increase in elastic compliance whereas Qm degraded by a factor of 2 under a DC bias field of 100 V/mm). Therefore, this study concludes that the deterioration of the mechanical quality factor Qm with an increase in vibration velocity can be recovered by externally applying positive DC bias field. The DC bias field 200 V/mm exhibits an almost equivalent “opposite” change rate to the vibration velocity of 100 mm/sec. Also, to investigate the loss mechanisms, the three losses (dielectric, elastic and piezoelectric losses) were determined under low and high power conditions. Mechanical loss tan φ’ displayed a change of 2.5% per 100V/mm for soft PZT and 1.1% per 100V/mm for the hard PZT, whereas the dielectric loss showed a change of nearly 1.5% per 100V/mm for soft PZT and 0.4% per 100V/mm for hard PZT. It is notable that the piezoelectric loss tan θ’ can be decreased most effectively under the positive DC bias field (3.1% per 100 V/mm for the soft PZT and 1.9% per 100 V/mm for the hard PZT), than the elastic or dielectric losses. Another noteworthy point is the two-step mechanism observed in hard PZT, a bend of the slope is observed in the elastic loss tan φ’ on the vibration velocity change, while a bend of the slope in the dielectric constant is observed on the DC bias field change. This may suggest a sort of threshold value in terms of mechanical stress or electrical field for stabilizing/unstabilizing the domain wall motions.