Q.R. Yin

Dielectric properties of 65PMN-35PT/P(VDF-TrFE) 0-3 composites

Lead magnesium niobate-lead titanate (PMN-PT with 35 mol.% PT) single crystal powder has been incorporated into a polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE) 70/30 mol.%) copolymer matrix to form 0-3 composites. With 65/35 mol.% composition, PMN-PT has high piezoelectric properties as a result of the enhanced polarizability arising from the coupling between two equivalent energy states. P(VDF-TrFE) ferroelectric copolymer films can be poled to give piezoelectric and pyroelectric performance without prior mechanical stretching. The composites were prepared using solvent casting to disperse the single crystal powder homogeneously in the matrix. Composites with PMN-PT volume fraction φ ranging from 0.05 to 0.4 were fabricated using a hot-press method. The relative permittivity and pyroelectric coefficients of the composites were measured as a function of φ. Good agreement has been obtained between the theoretical and experimental values. Under the same poling condition, the composites have higher pyroelectric coefficient than the pure copolymer films. Hysteresis measurements reveal that the remanent polarization of composites increases as φ increases.

Processing effects on the microstructure and ferroelectric properties of Pb(Zr,Ti)O3 thin films prepared by sol–gel process

Abstract Lead zirconate titanate Pb(Zr 0.53 Ti 0.47 )O 3 (PZT) thin films grown on Pt(1xa01xa01)/Ti/SiO 2 /Si(1xa00xa00) substrates by a simple sol–gel process use various thermally decompose temperatures from 320 to 400 °C. Then PZT films were annealed at various temperatures from 550 to 600 °C in oxygen atmosphere by a rapid thermal annealing process, and highly (1xa01xa01)-oriented PZT thin films have been obtained. The microstructure and surface morphologies, and root mean square (RMS) roughness of the thin films were studied by X-ray diffraction and atomic force microscopy (AFM). AFM images shown that the higher (1xa01xa01) orientation present in the PZT thin films, the smaller grain size, and the lower RMS roughness. PZT films on Pt/Ti/SiO 2 /Si substrates were initially heated at 400 and 320 °C, then annealed at 550 °C, the remanent polarization ( P r ) and coercive electric field ( E c ) were 16.1 μC/cm 2 and 105 kV/cm, 32.2 μC/cm 2 and 79.9 kV/cm; at 100 kHz, the dielectric constant and dissipation factor were 331 and 0.045, 539 and 0.066, respectively. The highly (1xa01xa01) oriented PZT films, have smooth surface, good ferroelectric and dielectric properties.

Scanning electron acoustic microscopy for the evaluation of domain structures in BaTiO3 single crystal and ceramics

As a non-destructive and subsurface detecting technique, the scanning electron acoustic microscopy (SEAM) method has been applied to study the ferrodomain structures in ferroelectric BaTiO3 single crystal and ceramics. The domain arrangements and the orientations of domain walls at different geometry structures in the BaTiO3 single crystal, and the relationships of domain structures with surface grains in the BaTiO3 ceramics, have been discussed by analysing the experimental results obtained at different operation conditions. The distributions of electron acoustic signals with modulation frequencies up to 1 MHz have been obtained. The relationship of the electron acoustic signal with incident electron energy has also been studied. Although the thermal wave coupling mechanism makes a certain contribution to the acoustic signal generations, the image contrast of ferrodomains is dominated by differences in the electrical properties of ferroelectric materials.

Near-field acoustic and piezoresponse microscopy of domain structures in ferroelectric material

Three kinds of near-field microscopy imaging mode including SEAM (Scanning electron acoustic microscopy), PFM (Piezoresponse force microscopy) and SPAM (Scanning probe acoustic microscopy) have been developed to investigate domain structures of ferroelectric ceramics, crystals and thin films in our studies. The domain imaging mechanisms are presented individually in three imaging modes. Sub-surface micro-domain configuration of ferroelectric BaTiO3 ceramics and single crystal and their dynamic behavior under external fields were clearly visualized by SEAM. Ferroelectric domain structures of ferroelectric PZT thin film and PMN-PT single crystal were characterized by PFM. Nanoscale switching behavior and local field-induced nanoscale displacement behavior of domain structures in ferroelectric thin film were studied by PFM. Antiparallel domain patterns in ferroelectric transparent PLZT ceramics were also characterized by SPAM. The combination of SEAM, PFM and SPAM in application to imaging domain structures undoubtedly enrich our understanding of the nature of piezoelectricity and ferroelectricity at submicro-, even nano-meter scale

Scanning electron acoustic imaging of residual stress distributions in ceramic coatings and sintered ceramics

Abstract Scanning electron acoustic microscopy has been used to reveal the residual stress distributions in the subsurface in carbon steel coating with Ti 3 N 4 . The experimental results show that residual stress distributions formed around the cracks are 2-fold, symmetrically butterfly-shaped with similar pattern of interchanging plastic and elastic zones. At the same time, we have observed the same butterfly-shaped residual stress fields surrounding the pores formed by the sintering process in piezoelectric transducer (PZT) ceramics. Moreover, the residual stress fields of the pores have the same orientation.

NANOSCALE PIEZOELECTRIC AND ELASTIC PHENOMENA OF FERROELECTRIC DOMAIN

ABSTRACT Piezoresponse force microscopy (PFM) and scanning probe acoustic microscopy (SPAM) were combined to characterize locally piezoelectric and elastic phenomena of domain structures in lead-free Bi4Ti3O12 piezoelectric ceramics and ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals. The acoustic images of ferroelectric domain were firstly visualized by SPAM at low frequency below 10 kHz. The domain imaging mechanisms are ascribed to the elastic response of ferroelectric domain to local contact stiffness difference of the individual domains in response to local elastic stress fields. An interesting proportional relationship was revealed between the local piezoelectricity and elasticity for ferroelectric domains.

The study of domain rearrangement under external electric fields by scanning electron acoustic microscope

Abstract Compared with other methods, scanning electron acoustic microscope (SEAM) is a convenient, fast and nondestructive technique revealing ferroelectric domain without any special pre-treatment to the sample. It is also a promising technique for the dynamic study of domain structure of ferroelectric materials. In the initial research, detailed images of rearrangement of domains in BaTiO3 ceramics induced by an external electric field were obtained. The results are discussed.

Acquisition of modulated PZT signal and application of SEAM

PZT transducers can be used to measure the characteristics of materials irradiated by laser or electron beams. In order to maintain high measurement resolution, the signal aroused on the transducer is modulated to produce a modulated PZT signal. Signal acquisition is accomplished with a lock-in amplifier and computer technologies. A typical application is SEAM (Scanning Electrical Acoustic Microscopy). The SEAM image reflects the thermal characteristics of materials. Furthermore, the SEAM image can supply subsurface information without destroying the sample.

The origins of image contrast in SEAM of ferroelectric semiconductor, ceramics and single crystal: BaTiO/sub 3/

A relatively new imaging technique, scanning electron-acoustic microscope (SEAM), was used to investigate the ferroelectric semiconductors, ferroelectric ceramics and single crystal: BaTiO/sub 3/. The subsurface defects of ferroelectric semiconductors and the domain structures of ferroelectric ceramics and single crystal were observed without any pre-handling to the samples in the electron-acoustic imaging of these materials. The origins of image contrast in SEAM of these materials have been discussed based on differently experimental conditions.