An approach for probing dynamic phenomena during hysteresis loop measurements in piezoresponse force microscopy (PFM) is developed. Dynamic PFM (D-PFM) necessitates development of 5-dimensional (5D) data acquisition protocols and associated methods for analysis and visualization of multidimensional data. Using a combination of multivariate statistical analysis and phenomenological fitting, we explore dynamic behavior during polarization switching in model ferroelectric films with dense ferroelastic domain structures and in ferroelectric capacitors. In polydomain films, multivariate analysis of the switching data suggests that ferroelectric and ferroelastic components can be decoupled and time dynamics can be explored. In capacitors, a strong correlation between polarization dynamics and microstructure is observed. The future potential of D-PFM for probing time-dependent hysteretic phenomena in ferroelectrics and ionic systems is discussed.
The effects of bipolar pulse poling on the ferroelastic domain structure and their contribution to the electrical and piezoelectric properties of Pb(Ti0.7Zr0.3)O3 films are investigated. Micro x-ray diffraction measurements clearly show that the volume fraction of the c-domain increases irreversibly as the poling field is increased, leading to changes in the remanent polarization, dielectric constant, and piezoelectric coefficient. Theoretical estimations well explain the changes of remanent polarization and dielectric constant, but the increase in piezoelectric coefficient is much larger than the theoretical estimation. In-situ x-ray diffraction analysis under an electric field reveals that this disagreement is due to the unexpected activation of the ferroelastic domain wall motion. Our results provide new insight into the poling effect on the electric and piezoelectric properties of ferroelectric films.
Piezoelectric materials based on ferroelectrics with a perovskite structure are among the most useful materials because they can convert electrical energy into mechanical energy and vice versa. Although piezoelectricity strongly depends on ferroelastic domain density, there are no general methods to controllably fabricate dense domain structures in ferroelectric films. Here, we report a mechanism to achieve a large piezoresponse based on an electrically induced dense ferroelastic domain structure in ferroelectric films. We demonstrate a large piezoelectric coefficient of 310 pm/V under both bipolar and unipolar electric fields, which is about 3 times larger than that in epitaxial single-crystalline thin films of tetragonal PbZr 0.4 Ti 0.6 O 3 grown on silicon substrates. Analysis by a combination of in situ Raman and piezoresponse force microscopy suggests that the large piezoelectric response can be explained by the motion of dense ferroelastic domain walls. This mechanism provides a general method to enhance the piezoelectric properties of ferroelectric materials.
Crystal structure change with an applied electric field was investigated by Raman spectroscopy and X-ray diffraction (XRD) for the 1 m-thick (100)/(001) one-axis oriented tetragonal Pb(Zr 0.3 Ti 0.7 )O 3 films prepared on Pt-covered (100) Si substrates by chemical solution deposition technique. As-deposited films were under the strained condition in good agreement with the estimation from the thermal strain applied under the cooling process after the deposition from the Curie temperature to the room temperature. This strain was ascertained to be relaxed by an applied electric field in accompanying with the dramatic increase of the volume fraction of (001) orientation. These results demonstrate the importance of the crystal structure measurement not only as-deposited films, but also after applied electric field, such as after poling.
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