Search

Electromechanical properties have been measured by a resonant method for "very soft" (APC856), "soft" (APC850), and "hard" (APC840, APC841, and APC880) lead zirconate–lead titanate (PZT) ceramics as a function of poling temperature and poling electric field. Quantitative results are presented for piezoelectric coefficients d33, d31, k31, kp, and kt; for elastic stiffness c33E, elastic compliance s11E, and dielectric permittivity e33T. An elevated temperature has a significant effect on the poling efficiency for hard PZT ceramics – in particular, piezoelectric coefficients could be substantially (by 50% of their saturated value) increased by the appropriate choice of poling temperature. A similar effect is observed for the poling electric field for hard PZTs at lower temperatures, but the electric field intensity is less significant at higher poling temperatures. The longitudinal and transversal components of material tensors change in different extent as a result of poling.

Domain switching behaviors of sol-gel derived lead zirconate titinate (PZT) films have been characterized for ferroelectric memory applications by measuring P-E hysteresis curves as a function of frequency, temperature and electrode size. The coercive field (Ec) of PZT films strongly depended on the measuring frequency, nevertheless their remanent polarization (Pr) was almost independent of it. The frequency dependence of Ec could be explained based on the nucleation-controlled model of domain switching. A linear relation was obtained between logarithmic frequency and 1/Ec2. The slope of the line was subject to temperature and the interception of that, at 1/Ec2=0, was subject to electrode size. A guideline was proposed to enable ferroelectric memories to operate at higher speeds and lower voltages.

Barium titanate zirconate (Ba(Ti1-xZrx)O3) films in the range of x=0 to 1.0 were prepared on (100)Pt/(100)MgO substrates at 973 K by metalorganic chemical vapor deposition (MOCVD). The effects of zirconium content (x) on the microstructure and dielectric properties of films were investigated. At x≤0.15, the Ba(Ti1-xZrx)O3 films showed highly crystallized and significant (001) orientation. The (001) orientation of the films decreased with increasing x, and the orientation became random at x>0.36. The dielectric constant of Ba(Ti1-xZrx)O3 films changed with x from 35 to 689 and showed a maximum at x=0.15. The remanent polarization (2Pr) and the coercive field (2EC) of Ba(Ti0.85Zr0.15)O3 film were 3 µCcm-2 and 14 kVcm-1, respectively. The onset electric field for nonohmic conduction of Ba(Ti1-xZrx)O3 film increased from 10 k to 1 MVcm-1 with increasing x.

The ultrasound transducers of which center frequencies are lower than 10 MHz are commonly used in low frequency photoacoustic (PA) imaging systems. However, the improvement of their sensitivity is still needed to detect weak PA signals. In this study, a circular array transducer was constructed by using 120 needle hydrophones made of piezoelectric single crystal lead magnesium niobate–lead zirconate titanate (PMN–PZT). The needle hydrophone was designed to have high sensitivity and wide bandwidth through the Krimtholz–Leedom–Matthaei (KLM) simulation of receiving impulse response. The sensitivity of the fabricated PMN–PZT hydrophone was compared with a commercial poly(vinylidene fluoride) (PVDF) needle hydrophone. The usefulness of the circular array transducer was demonstrated by applying it to a PA system for obtaining images.

A noncontact self-running ultrasonically levitated two-dimensional (2D) stage is discussed. The proposed 2D stage was fabricated from a rectangular aluminum plate and four vibrating plates were integrated. The vibrating plates are cantilever-type plates and piezoelectric zirconate titanate (PZT) elements are attached on their fixed ends. To isolate the performance of each vibrating plate, the four vibrating plates have different lengths of 27, 28, 29, and 30 mm. The 2D stage could be levitated at several frequencies from 60 to 80 kHz. The stage could move in the negative x-direction at 71 kHz, at which the flexural vibration mode was excited on the 30-mm-long vibrating plate. Likewise, the stage could move in the negative y-, positive x-, and positive y-directions at 72, 74, and 77 kHz with the flexural vibration mode on the 29-, 28-, and 27-mm-long vibration plates, respectively. A maximum thrust of 6.3 mN could be obtained at 74 kHz with 70 Vpp.

In this work, high-κ cerium zirconate (CeZrO4) was successfully fabricated by RF magnetron cosputtering with a postannealing temperature of 850 °C. The amount of Zr in CeO2 can be well controlled by adjusting the DC power of the Zr target. X-ray photoelectron spectroscopy (XPS) shows that CeZrO4 becomes amorphous with increasing DC power. The intensity of the CeZrO4 phase increases with increasing oxygen content in the plasma. The crystalline phases were confirmed using X-ray diffraction (XRD). The dielectric constant and flatband voltage shift (ΔVFB) as functions of DC power and oxygen gas flow rate were investigated. The optimum balance between leakage and dielectric constant was considered. The leakage current densities were 3×10-3 and 3×10-5 A/cm2 obtained at +2 and -2 V biases, respectively. A relative dielectric constant (er) of 24.3 and an effective oxide thickness (EOT) of 1.7 nm were achieved.

Lead zirconate (PbZrO3) thin films are grown on Pt(111)/Ti/SiO2/Si(100) substrates by sol–gel using precursor solutions with stoichiometric and 20 mol % excess Pb. Films with no preferred orientation and [111] pseudocubic texture (denoted as [111]pc) are obtained by changing the drying temperature at the pyrolysis stage. Randomly oriented films were found to have a two-phase microstructure consisting of large rosette-type perovskite regions with a nanocrystalline phase located in between. The ratio of the rosettes increase to cover the entire surface of the films with the increase of Pb content. The films with [111]pc orientation have a uniform microstructure with micron size grains. The electrical properties of the films were influenced markedly by the microstructure and orientation of the films. The [111]pc oriented films exhibit a square-like double hysteresis loop with maximum polarization (P max) reaching 61×10-6 C/cm2 under 550 kV/cm, whereas stoichiometric films with no preferred orientation have a P max of 36×10-6 C/cm2 with slimmer hysteresis curves.

Lead zirconate (PbZrO3) thin films doped with Ce, Cr and Er were grown on Pt(111)/Ti/SiO2/Si(100) substrates by sol–gel spin coating process. Polycrystalline films with a phase-pure perovskite structure and a random orientation were obtained regardless of doping materials. Microstructural examinations of the films revealed a two-phase microstructure consisting of large rosette-type perovskite regions with a nanocrystalline phase located in between. Perovskite rosettes were found to be of polycrystalline in nature with grain size ranging between 50–250 nm. Increasing number of annealing cycles and temperature were found to improve the microstructure, crystallinity and electrical properties. Doping elements were also found to increase electrical properties with a saturation polarization (P sat) reaching 65 ×10-6 C/cm2 in Ce- and Cr-doped coatings compared to 39 ×10-6 C/cm2 for undoped PZ films.

A diaphragm-type (100)-dominant-oriented tetragonal phase lead zirconate titanate (PZT) film actuator was fabricated. The ferroelectric properties of the texture-controlled PZT film were comparable to those of bulk PZT ceramics. The displacement property of the PZT film actuator driven at ±20 V exhibited a butterfly-like hysteresis. However, this butterfly shape showed an opposite direction to that of the typical displacement curve of bulk PZT ceramics. This depressed displacement property of the PZT film appears to indicate bend motion in the vertical direction on the film surface since the film is not clamped, and it does not reflect the genuine piezoelectric property. For a unipolar drive, the value of the displacement was about 220 nm at 20 V. The deflection amplitude of the diaphragm actuator showed a peak at 77.5 kHz. Therefore, the diaphragm of the texture-controlled PZT film is considered to be applicable to microactuators.

The relationship between crystal structure and nonlinear piezoelectric coefficient was investigated in lead zirconate titanate-lead antimony niobate ceramics with various Zr/(Zr+Ti) ratios and MnO contents, using rectangular-bar-shaped samples. The electromechanical coupling factor k 31 and 3rd nonlinear piezoelectric coefficient ξ31 were measured near the resonance frequency of length-extensional 1/2 λ mode vibration. Among the ceramics having various Zr/(Zr+Ti) ratios, the minimum ξ31 was observed when the crystal structure of the sample was just on the morphotropic phase boundary, at which k 31 showed the maximum value. The ξ31 also decreased with the increase of MnO additive.

We investigated the crystalline and electrical properties of heteroepitaxial lead zirconate titanate (PZT) films grown on Si covered with epitaxial (100) (ZrO2)1-x(Y2O3)x(YSZ) buffer layers. The PZT films were prepared by reactive sputtering. When the substrate temperature was between 400 and 485°C, we obtained a heteroepitaxial (110) oriented monoclinic PZT (m-PZT) film which was metastable. The lattice parameters were as follows:a=b=0.379 nm,c= 0.521 nm and γ=81.3°. The m-PZT film had a larger oxygen composition ratio O/(Zr+Ti) of 3.2 to 3.8 than the perovskite phase. Although the resistivity of the as-grown m-PZT film was much lower than that of the normal perovskite phase, it was increased by two to five orders of magnitude by a step-annealing process of 300°C for 120 min, 325°C for 120 min and 350°C for 180 min in sequence. From theC–Vcharacteristics of the step-annealed m-PZT/YSZ/Si structure, the relative dielectric constant was estimated to be about 45.

The phase formation and field-induced strain properties of the Pb0.97Y0.02[(Zr0.6Sn0.4)1-y Ti y ]O3 ceramics have been investigated as a function of Ti4+ content (0.08 ≤y ≤0.09). With increasing Ti4+ content, the specimens showed a structural transition from the orthorhombic to the rhombohedral phase. The specimen of y=0.08 represented a double hysteresis loop, while the specimen of y=0.09 represented a single hysteresis loop. The strain of digital-type shape was observed in the specimens of y=0.08 and y=0.085. The strain at the shape memory state was about 2.8 ×10-3 in the specimens of y=0.085.

The elastic strain behavior associated with the field-induced antiferroelectric-to-ferroelectric phase transition has been investigated for Pb0.99Nb0.02[(Zr1- x Sn x )1- y Ti y ]0.98O3 ceramics (PNZST) by means of dielectric, polarization and strain hysteresis measurements. As the applied electric field intensity increased, a sudden increase in the strain was observed along with a corresponding change in polarization that is attributable to the phase transition. PNZST ceramics with optimized composition exhibit a huge strain value of 0.44%, which may make the development of a new functional transducer device possible.

A major emerging market for ferroelectric non-volatile memories is the RF tag. In that application, low power and low voltage memory operation is essential. Historically, the lead zirconate titanate (PZT) family has not been noted for low voltage hysteresis loops but this is a function of process and not a property of the material. The authors have reduced the saturation voltage for a PZT sol gel process to less than 2.5 V while achieving greater than 40 µ C/cm2 δP for 20/80 PZT using platinum electrodes. Niobium doped PZT has also been fabricated with the low saturation voltage while producing greater than 30 µ C/cm2 δP. The authors report on the electrical properties of these films.

The hydrothermal method to deposit lead zirconate titanate (PZT) thin film is a new method reported by Tsurumi et al.. in 1991. This method consists of two linked processes. We have found that the film deposited by the first process is not PZT but separated lead zirconate (PZ) and lead titanate (PT). In this paper, we report that a PZT thin film was successfully deposited by a single process. The chemical construction and composition of the film were analyzed. The Zr/(Zr+Ti) ratio of the PZT film was controlled by changing the ionic composition of the solution.

The dependence of the bulk photovoltaic effect (BPE) on illumination intensity and wavelength has been studied in (Pb0.97, La0.03)(Zr0.52, Ti0.48)1-0.03/4O3 ceramics normally sintered at 1200° C for 2 h and then heat-treated in various atmospheres such as nitrogen, air and oxygen at 900° C for 1 h to investigate the enhancement of the BPE in the nitrogen-treated sample. The values of the Glass constant and the photoconductivity increased with decreasing oxygen partial pressure (p O2) during the heat treatments, whereas that of the dark conductivity decreased, indicating the creation of oxygen vacancies. No significant change was observed in ion oxidation states in the heat-treated samples by X-ray photoelectron spectroscopic analysis. The wavelength showing the maximum value of the photovoltaic current became shorter with decreasing p O2 during the heat treatments and simultaneously the value of the maximum current notably increased. At the same time broadening of the current curves was also noted in the spectral responses. It is proposed that some of the electrons originating from the formation of oxygen vacancies can be expected to contribute to the enhancement of the BPE.

Ferroelectric properties of lead-zirconate-titanate (PZT) films formed by the sol-gel deposition technique have been discussed from the standpoint of ferroelectric random-access memory (FRAM) and dynamic random-access memory (DRAM) applications. PZT films with -preferred orientation and random orientation were formed on Pt/Ti/SiO2/Si substrates by optimizing fabrication conditions. Remanent polarization of the -preferred film was 23.5 µ C/cm2 which is somewhat higher than that of the randomly oriented one. An abrupt saturation of remanent polarization was observed only for the -preferred film. The voltages which provide saturations of remanent polarization densities for the -preferred films are almost constant between 3.5 V to 4 V independent of thickness. The dielectric constant of the randomly oriented film was 730 which is larger than that of the -preferred one and gradually decreased depending on the applied electric field. The -preferred PZT film is appropriate for FRAM application, and the randomly oriented one is preferred for DRAM application.

Piezoelectric and dielectric responses were investigated for doped lead zirconate titanate (PZT) ceramics under strong electric field (1.6 MV/m). Displacements and polarization changes were measured and the effects of dopants were discussed. Doping of 2% Nb significantly increased the displacement of (Pb0.875Sr0.125)(Zr0.55Ti0.45)O3 ceramics. Doping of 2% Fe suppressed 90° domain rotation and decreased displacement. Results were discussed by dividing displacement and polarization change into two components, i.e., a piezoelectric or dielectric contribution and a 90° domain rotation contribution.

Dielectric and light scattering measurements are performed in lanthanum modified lead zirconate titanate (PLZT) (6–8)/65/35 hot-pressed ceramics in order to refine the phase diagram. A relaxor-ferroelectric phase transition takes place in PLZT (6–7)/65/35 at temperature lower than the temperature of the dispersive dielectric constant maximum. At this temperature the size of polar regions “a” essentially increases up to a>λ (=0.63 µ m). The appearence of ferroelectric long-range order in PLZT with decreased concentration of La ions is explained by larger coupling between ferroelectrically active BO6 octahedrons due to the smaller concentration of defects and higher dielectric constant.

Pb(Zr, Ti)O3 (PZT) films with very thin PbTiO3 (PT) and ( Ba0.5Sr0.5)TiO3 (BST) buffer layers inserted between the film and Pt/Ti/ SiO2/Si substrate were synthesized by the sol-gel technique, and effects of variation in thickness upon microstructural and ferroelectric characteristics were investigated. Insertion of buffer layers was found to exert marked effects. PT buffer layers with thicknesses as thin as 2–4 nm yield PZT films with dense, homogeneous microstructure and good ferroelectric properties such as large remanent polarization, small coercive field and low leakage current densities. On the other hand, use of (2–4)-nm-thick BST buffer layers yields PZT films with dense microstructure and good dielectric properties such as increased permittivity, small coercive field and good leakage current characteristics. However, fatigue behavior of PZT films was not improved through insertion of PT or BST buffer layer.

The electric field-induced acoustic emission (AE) in a poled tetragonal lead zirconate titanate (PZT) ceramic was measured at room temperature and related to the polarization switching, field-induced strain, dielectric constant, and piezoelectric constant in the high-voltage electric field. The AE signals became most remarkable when the polarization approached the saturation, while they became minimal when the polarization reversal occurred. The AE count, expressed as a function of electric field, exhibited a hysteresis loop similar to the strain loop. These data suggest that the AE signals were generated by the strain due to 90° domain switching rather than the piezoelectric strain.

Several conditions for the 2-stage sintering method have been refined to improve the optical quality of (Pb, La)(Zr, Ti)O3 (PLZT) ceramics, and electrooptical properties of fabricated PLZT ceramics with the composition of (6–9)/65/35 were examined. Ceramics which were obtained from mixed oxide (MO) powders exhibited better electrooptic characteristics (better transmittance, smaller residual birefringence, larger electrooptic coefficients) than those from coprecipitated (CP) powders under common processing conditions. For several compositions of MO-PLZT, smaller E c was attained, as compared with reported ones. A marked improvement in electrooptic coefficients (R=6.3×10-16 m2/V2, V π=130 V, with 0.30 mm thickness) was also observed for MO-PLZT 9/65/35 ceramics.

Dielectric properties of alkaline-earth-substituted PbZrO3 ceramics up to microwave frequencies were investigated. Although there were no preferable characteristics in the Ba- or Sr-substituted system, the ceramics in a (PbCa)ZrO3 system showed not only high dielectric constants in the range of 100 to 118, but also high Q values of 1000 to 1150 and small temperature coefficients of resonant frequency of 0 to 30 ppm/ °C. The crystal structure of the Ca-substituted ceramics was also investigated by X-ray powder diffraction. The structure changed from PbZrO3-type orthorhombic to CaZrO3-type orthorhombic through cubic and rhombohedral with increasing Ca substitution. Coaxial dielectric resonators made of the selected above material had Q values in the range of 430 to 450 at the 900 MHz band.

The domain structure of a typical antiferroelectric substance, lead zirconate, is examined in detail fori the first time by electron diffraction and electron microscopy. The 90° and 60° domain configurations can be consistently understood on the basis of the pseudo-cubic unit cell. 180° domains, which are characteristic of the antiferroelectric phase, are observed. The displacement vectors between the domains are determined as ¼[21n], ¼[21̄n] and ¼[02n] (n=0 or 2) by the α-fringe theory for off-Bragg settings. Crystal structure images of the domains reveal how the unit cells connect across the domain boundary. 90° and 180° domains are found in the intermediate phase between the antiferroelectric and the paraelectric phases. The fact that 180° domains are observed is important evidence indicating that the phase is ferroelectric.

A new type of bending actuator, “monomorph”, is proposed by using a single plate of semiconductive piezoelectric ceramics. The principle of bending originates from the nonuniform distribution of the electric field in a single plate caused by the semiconductor–metal electrode contact. Monomorph characteristics are exemplified in lead zirconate based and barium titanate ceramics. A bend curvature comparable to that of conventional piezoelectric “bimorphs” can be obtained.

“Monomorph” characteristics, i.e. bending motions of a single ceramic plate have been investigated in the PbZrO3-(K1/2Bi1/2)ZrO3 solid solutions. The composition dependence of the bending deformation measured is explainable on the bases of the semiconductor and field-induced strain properties. Also, the bending mechanism could be analysed by measuring the lattice parameter change with an applied electric field.