The domain reorientation process in polycrystalline materials was investigated through hysteresis loop measurements in soft and hard lead zirconate titanate (PZT) bulk ceramics. In order to investigate the degree of alignment of domains with the electric field the ferroelectric characterizations were performed in two perpendicular directions for each sample. It was found that for the soft PZT, the kinetics of the fatigue process due to space charges in a specific direction is not affected by the previous fatigue story induced in the other perpendicular one thus showing a fatigue anisotropy. This fact was attributed to no displacement of part of space charges during the electric field switching. However, for the hard PZT, an influence of the previous electric story could be observed due to the continuous realignment of the complex defects perpendicularly to the electric field.

Domain reorientation anisotropy in ferroelectric polycrystals

Domain structure of ferroelectric ceramics

From XRD and integrated charge measurements in a tetragonal PLZT 12/40/60 ceramic the 90° and 180° domain percents contributions to P as a function of poling are de duced. A remanence of oriented 90° domains is observed even heating well above the Curie point.

A XRD study of 90° domains in tetragonal PLZT uncer poling

Grinding and polishing affected the orientation of 90° domains at the surface of lead zirconate titanate (PZT) ceramics. This was quantified by using changes in the intensity ratio of the {002} and {200} X-ray reflections. Grinding unpoled PZT with 600-grit SiC paper gave X-ray intensity ratios similar to those of poled material. This implies that 90° domain realignments had occurred in the near surface region probed by the X-rays. Grinding poled samples with 600-grit SiC further increased the X-ray intensity ratio beyond that caused by poling, indicating that additional surface reorientation of 90° domains had occurred. The effects of diamond polishing depended on the size of the diamond particles. The use of 6-μm diamond had no effect on the {002}/{200} intensity ratio of either poled or unpoled samples, while polishing with 15- or 45-μm diamond significantly enhanced the 90° domain rotation. In unpoled samples, the increase in the X-ray intensity ratio then approached that induced by poling or grinding with 600-grit SiC paper. While the observed increase in X-ray intensity ratio upon grinding is attributed to the rotation of 90° domains, the simultaneous formation of 180° domains appears to minimize or reduce the increase in electrical polarization.

Modification of surface texture by grinding and polishing lead zirconate titanate ceramics

Preferred domain orientation of a piezoelectric ceramic develops through domain switching under electric poling. In previous investigations the critical free energy required for domain switching has been assumed as a constant. This assumption leads to overestimation of the poling-induced texture and provides no explanation for the switching reversal in ferroelectric ceramics after the poling field is removed. In this paper, the contribution of intergranular stress to critical energy for 90° domain switching is investigated. A criterion including intrinsic threshold energy and an interaction energy, which is related to the intergranular stress and the intergranular depolarization field, is proposed. The texture evolution during poling process is simulated using a computational model starting from an initial random domain orientation distribution. The resulted domain orientation distributions under and after poling are predicted. The remanent domain switching after poling is the result of the balance between the interaction energy and intrinsic threshold energy. The final texture is much weaker than that under the electric field. Pole figures of poled Navy VI lead zirconate titanate measured by x-ray diffraction are consistent with the predicted textures.

Modeling of electric field induced texture in lead zirconate titanate ceramics

A simple method for obtaining the space distribution of domains by measuring the X-ray diffraction pattern has been put forward in this article. The relation between the diffraction intensity (in (hkl)) and the polar axis [001] density distribution is discussed. While there is only one angle between (hkl) and (001), the distribution function of the polar axis [001] with respect to the zenith angle could be obtained as soon as the intensity of X-ray for the samples prior to and after polarization is measured. The space distribution of the domains in the sufficiently polarized ceramic PZT (Zr/Ti=50/50) has been calculated according to the technique as mentioned above, and the results were treated by the least square method. Generally, it has been previously shown that most of the distribution functions are Gaussian type, that is Wφ = W0exp (−φ2/2δ2). However, our results show that W(φ) = 1/(1+α2 φ2)2 gives the best fit. Using the DEG (degree) unit system, the distribution function is Wool(φ) = 1/[1...

The measurement of space distribution of domains in polarized PZT ceramic

The domain structure of ferroelectric ceramics changes in the process of polarization and in the course of application. This kind of change has a direct influence on the macroscopic properties of the materials. A simple method for determining quantitatively the fraction of 90°domain-rotation in the tetragonal ferroelectric phase by measuring the changes of the intensity of X-ray diffraction has been put forward in this article. The percentage of 90° domain-rotation in the process of polarization could be obtained directly as soon as the intensity ratios of I200 and I002 of the nonpolariza-tion and polarization are respectively measured out correctly. The structure factors and preferred orientation which may exist have been taken into account in the deduction of the formula. For PZT ceramics of 50/50(Zr/Ti), the fraction of 90° domain-rotation under different conditions of polarization has been calculated by using the above method. The result obtained are parallel to the changes of the macroscopic properties. A comparison with the indirect method was used previously in the mechanical strain experiments has been made. In addition, the problem of determining the internal stress prior to and after polarization by measuring the broadening of the diffracted X-ray lines has also been discussed.

Li Cheng-cui

Papers

The measurement of space distribution of domains in polarized PZT ceramic

X-RAY INVESTIGATION BEFORE AND AFTER POLARIZATION OF PZT CERAMICS (Zr/Ti = 50/50)