Researching Domain Structure And Electrical Properties Of Low–Dimensional Ferroelectric Materials Based On Piezoresponse Force Microscopy

Ferroelectric materials have great potential in high-speed,stable and low-power memory devices in the future.With the development of miniaturization and high integration of device,micro-ferroelectric properties play an important role in device applications.Therefore,it is very necessary to study the micro ferroelectric properties of ferroelectric materials,especially low dimensional ferroelectric materials.Micro ferroelectric properties are usually closely related to the complex domain structure and boundary conditions of ferroelectric materials,and the analysis of the micro-domain structure and the regulation of the micro-piezoelectric response need to be further explored.The piezoelectric micro-technology with high spatial resolution and abundant expansion modules can characterize the micro domains of ferroelectric materials on three-dimensional scale,which with high spatial resolution,and it is a powerful tool to accurately characterize the microscopic properties of low dimensional ferroelectric materials.At the same time,it also provides the possibility for exploring the regulation of field,such as force field,temperature field and electric field.In this paper,PFM technology is used to realize the characterization of ferroelectric domain structure,piezoelectric properties with temperature changes and electrostrictive coefficient combined with several modules.The specific work includes the following aspects:?1?BiFeO₃ ferroelectric thin films with unique domain structure were prepared by pulsed laser deposition,and BiFeO₃ thin films with vertically aligned domain structures were regulated by the strain of substrates.The results of X ray diffraction show that BiFeO₃ thin film is a high-quality epitaxial film.By PFM,the BiFeO₃ films of different thicknesses and interfaces are rotated and scanned in-plane or out-plane,respectively.With MATLAB data processing,the 3D ferroelectric domain structure is reconstructed and the influence of film thickness and interface on the evolution of BiFeO₃ micro-domain structure is analyzed.?2?Ba(Ti_0.8Zr_0.2)O_0.5(Ba_0.7Ca_0.3)Ti O₃lead-free composite nanofibers were prepared by electrospinning.X ray diffraction and Raman spectrum analysis indicated that the tetragonal phase is coexisted with the orthogonal phase in BTZ-0.5BCT,and BTZ-0.5BCT is in good crystallinity,and transmission electron microscopy?TEM?tests show that fibers are confined within one-dimensional boundaries.Based on temperature changed PFM,two maxima of the piezoelectric response are observed at120 and 180?,which is matched with the diffusion point temperature on 120?and180?.It is proved that the size effect of ferroelectric/piezoelectricity and the constraint effect of one-dimensional boundary have an important effect on the phase transition of the whole nanofibers.?3?Flexible Pb(Zr_0.2Ti_0.8)O₃ films were prepared on mica substrate by pulsed laser deposition.X ray diffraction and morphology tests show that the films have good crystallinity and smoothness.Electrical hysteresis loop test of ferroelectric analyzer show that Pb(Zr_0.2Ti_0.8)O₃ films have unique characteristics of double hysteresis loop,which is possibly a large electrical strictive material.Based on PFM system,on the one hand,we analyze the flip characteristics of the film micro-region in detail through the phase flip test of multi-point;on the other hand,the strain of the films is measured on the microscopic scale,and the electrostriction coefficient M₃₃=1.2×10^-15 m²/V² is obtained by using the relation between strain and the square of electric field/polarization.