by Yu, Yongjian

Abstract (Summary)
Lead zirconate titanate (PZT) materials are used widely as transducers and actuators in a variety of applications. The phase diagram of PbZrO3-PbTiO3-SrTiO3-SrZrO3 system (called PSZT) shows a long AFE-FE phase boundary suitable for field-induced phase transition study. Initially, the phase transitions in PSZT ceramics are studied to assist in understanding the effects of compositional modification on the relative stabilities of the AFE and FE phases. This yielded modified AFE-FE phase boundary for the PSZT family based on the polarization and structural information. The stabilization of the AFE phase by increasing Sr 2+ and Zr4+ content produced increased AFE-FE transition field and decreased polarization. Phase transitions with respect to temperature are investigated by means of polarization hysteresis and dielectric properties measurements. These observations are discussed in terms of Goldschmidt’s tolerance factor and soft-mode theory. The entropy difference (DS) during AFE-FE phase switching is calculated using a modified Clausius-Clapeyron approach. The dependence of the switching field on temperature (dE/dT) is found to be greater for the reverse switching than for forward phase transition. An explanation is provided in terms of the relative coupling strength of the domains. The longitudinal field-induced strain in the PSZT systems is in the range of 0.2%-0.5% indicating possibilities for creating large strain actuators using selected compositions. However, PSZT ceramics displayed degradation in polarization and field-induced strain with increasing number of the switching cycles. In order to increase the field-induced strain and reduce the remnant strain, composition PSZT 15/80/20 is doped with various amounts of La3+ or Nd3+ (1-3 atom%). The stabilization of the AFE structure by La3+ or Nd3+ doping resulted in increased AFE-FE phase transition field and decreased temperature of the maximum dielectric constant. The induced strain is maximized at 2 atom% La3+ or Nd3+ doping with negligible remnant strain. Using innovative in situ x-ray diffraction technique, direct observations of the unit cell parameters of the AFE phase and subsequent electric field-induced FE phase of selected PSZT ceramics are preformed. This volume increase accounts for most of the large field-induced longitudinal strain during AFE-FE phase transition.
Bibliographical Information:


School:University of Cincinnati

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:ceramics lead zirconate titanate ferroelectric phase switiching antiferroelecrtic


Date of Publication:01/01/2000

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