Volume 86, Issue 1, 01 July 1999
Index of content:
- DIELECTRICS AND FERROELECTRICITY (PACS 77)
Longitudinal piezoelectric coefficient measurement for bulk ceramics and thin films using pneumatic pressure rig86(1999); http://dx.doi.org/10.1063/1.370771View Description Hide Description
A pneumatic pressure rig was designed to measure the effective coefficient of thin film piezoelectrics by applying a known stress and monitoring the induced charge. It was found that the stress state imposed included components both perpendicular and parallel to the film plane. The later were due to friction and could largely be relieved through sliding of the O-rings to their equilibrium positions for a given pressure. The induced charge stabilized as equilibrium was reached and most of it was produced by the normal component of the stress. By minimizing the surface friction and compensating for the remnant in-plane stress, very good agreement was obtained among the values measured by the Berlincourt method, double-beam interferometry and this method for a bulk lead zirconate titanate(PZT) sample. The value of PZT thin films made by sol-gel processing was also measured. The as deposited films usually showed very weak piezoelectricity with values ranging from 0 to 10 pC/N, indicating little pre-existing alignment of the domains. With increasing poling field, the value also increased and saturated at poling fields exceeding three times the coercive field. Typically, films with thicknesses around 1 μm had values of 100 pC/N. Good agreement between double-beam interferometry and this technique was also obtained for thin films. The small difference between the two measurements is attributed to the effect of mechanical boundary conditions on the effective coefficient.
Thickness dependence of structural and electrical properties in epitaxial lead zirconate titanate films86(1999); http://dx.doi.org/10.1063/1.370772View Description Hide Description
We have studied the effect of misfit strain on the microstructure and properties of ferroelectriclead zirconate titanatethin films. We have changed the misfit strain by varying the film thickness and studied the thickness effect on the domain formation of epitaxial(PZT)filmsgrown by pulsed laser deposition on (001) substrates with (LSCO) electrodes. The nominal thickness of the PZT films was varied from 60 to 400 nm with the LSCO electrode thickness kept constant at 50 nm. X-ray diffraction experiments show that the films relax via the formation of a domains, the fraction of which increase with the ferroelectricfilm thickness. The c-axis lattice constant of PZT films calculated from the 002 reflection decreases with increasing film thickness and approaches the bulk value of ∼0.413 nm in the films thicker than 300 nm. Cross-sectional transmission electron microscopy images reveal that the a-domain fraction and period increase with increasing film thickness. The relaxation of misfit strain in the film is accompanied by systematic changes in the polarization properties, as well as the switching fields, quantified by the coercive field and the activation field.
86(1999); http://dx.doi.org/10.1063/1.370773View Description Hide Description
The electrical response during indentation of a piezoelectric ceramic-polymer 1-3 composite has been investigated. The current (quasistatic charge increment) induced in the indentor due to the polarized layer on the contact surface increases with load as the contact area increases. Good agreement was found between the measuredcurrents as a function of load with those predicted using an analytical model. In addition, the current increases with increasing indentation velocity and indentor diameter. It uses known analytical results to develop a new tool for characterizing the electrical response of piezoelectric composites. As such, linear elastic indentation with simultaneous measurement of load and electric current is shown to be a new, fast, and nondestructive technique that can be used for quality assurance and to study the effect of aging and development/presence of damage/microcracking in monolithic piezoelectric and 1-3 piezoelectric composites.
High resolution study of domain nucleation and growth during polarization switching in ferroelectric thin film capacitors86(1999); http://dx.doi.org/10.1063/1.370774View Description Hide Description
The domain nucleation and growth during polarization switching in (PZT)ferroelectric thin filmcapacitors with Pt top (TE) and bottom electrodes (BE) were studied by means of atomic force microscopy(AFM). The experimental configuration used in this study differs from that conventionally used (AFM tip/PZT/BE) where the AFM tip acts as a positionable TE. A small ac voltage was applied between the electrodes with a step by step increasing dc bias voltage. The induced piezoelectric vibration was detected by the AFM tip, its amplitude and phase determined with the lock-in amplifier. The phase difference between the applied ac voltage and the piezoelectric signal as a function of the x-y position was nearly locked at 0 or 180, representing film regions with parallel (in-phase) and antiparallel (antiphase) polarization direction, respectively. The polarization reversal was induced by application of a step by step increasing dc bias field opposite to the polarization of the prepoled sample. At each bias step 10 μm×10 μm images of the amplitude and the phase were collected. By approaching the coercive field a rapid decrease of the amplitude with a small change in phase was observed, first in preferential sites for reversed nucleation, then over the whole studied area. The first regions with reversed polarization were observed at about 3.2 MV/m and the switching was completed at 5.5 MV/m. The results were interpreted using both the forward and the sideways domain growth models that are named by their rate-limiting kinetics. It was concluded that under the assumption of a sufficient resolution of domain imaging in our study, the forward domain growth being the rate limiting mechanism prevails in our PZTthin film.