Aging Rates In PZT Ferroelectrics With Mixed Acceptor-Donor Dopants

Open Access
Author:
Scholz, Joseph Robert
Graduate Program:
Engineering Science and Mechanics
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 08, 2009
Committee Members:
  • Michael T Lanagan, Thesis Advisor
  • Clive A Randall, Thesis Advisor
Keywords:
  • PZT
  • PZT-SKN
  • aging
  • mixed dopants
  • domain walls
  • defects
Abstract:
High permittivity Pb(ZrxTi1-x)O3 (designated PZT)suffers from well-documented aging phenomena. The dielectric and piezoelectric properties change over time due to a reduction in domain wall mobility. The specific mechanism causing these changes related to defects in the material and the detailed mechanisms are not well understood. Devices using PZT are used in the automotive, medical, sensor, and electronic industries. The aging phenomena cause these devices to lose accuracy, power storage, efficiency, and long-term performance. This study aimed to correlate the effects of processing and doping on aging rate and link the aging phenomenon to microstructural and point defects. PZT doped in the formula Pb1-(3x/2)SrxK(x/4)[(Zr0.53,Ti0.47)1-3x/4Nb3x/4]O3 (designated PZT-SKN) has been developed for its useful properties to actuators and transducers in automotive applications. Samples of PZT-SKN were produced with x=0.02 to study the effect of mixed acceptor-donor doping on aging. Samples doped with Sr, Nb, and Fe were produced and used along with commercial PZT4 and PZT5H from TRS Technologies for comparison to the mixed-dopant PZT-SKN system. The samples were characterized for microstructure and dielectric properties. Grain sizes were measured with scanning electron microscopy and phase purity was determined from X-ray diffraction analysis. Capacitance and loss were measured versus temperature at several frequencies and polarization hysteresis loops were measured at room temperature. The sintering temperatures and atmospheres were varied along with dopants to produce different defect structures in the PZT. Aging rate was found to be independent of PbO-loss if reoxidation occurred. The aging appeared to be slightly dependent on oxygen vacancies produced through annealing in nitrogen. PZT-SKN showed low-field aging rates that were intermediate between hard and soft material. This aging was affected by potassium and oxygen vacancy concentration. High-field aging of PZT-SKN showed it to act like a soft material. Low-field and high-field aging were equally significant for iron doped PZT. In mixed dopant systems, aging is highly dependent on the defect structure and field levels applied.