Lead zirconate titanate behaviors in an LDMOS

The behaviors of lead zirconate titanate (PZT) deposited as the dielectric for high-voltage devices are investigated experimentally and theoretically. The devices demonstrate not only high breakdown voltages above 350 V, but also excellent memory behaviors. A drain current-gate voltage (ID-VG) memory window of about 2.2 V is obtained at the sweep voltages of ±10 V for the 350-V laterally diffused metal oxide semiconductor (LDMOS). The retention time of about 270 s is recorded for the LDMOS through a controlled ID-VG measurement. The LDMOS with memory behaviors has potential to be applied in future power conversion circuits to boost the performance of the energy conversion system.     

Dielectrophoretic assembly of lead zirconate titanate microtubes

Lead zirconate titanate (PZT) microtubes were assembled onto pre-patterned substrates using dielectrophoresis of a colloidal suspension of microtubes dispersed in isopropyl alcohol. High aspect ratio tubes with an outer diameter of 2 μm and length of about 30 μm were prepared by vacuum infiltration of mesoporous silicon templates. An interdigitated electrode structure with gap sizes ranging from 2 μm to 15 μm was patterned on a silicon substrate via conventional lithography. This allowed a non-uniform alternating electric field to be generated. The influence of the electrode gap along with the effects of the waveform, amplitude and frequency of an applied signal on the dielectrophoretic assembly of PZT microtubes was investigated. A square wave signal of 5 and 10 Hz was found to be the most effective in assembling the microtubes on a 12 μm electrode gap. The results show potential for the dielectrophoretic technique in realizing integrated 3D devices using the high aspect ratio piezoelectric tube structures as building blocks.     

Aftereffect relaxation processes in lead zirconate titanate

Relaxation processes in lead zirconate titanate after switching-off perturbations of different physical nature have been considered. The model of the process, which accounts for the partial depolarization during perturbations, the formation of charged F-centers during released charge trapping, and their relaxation, has been proposed.     

Nanostructured heterophase thin films of lead zirconate titanate

The results of a comprehensive study of electrophysical and photoelectric properties of capacitor structures are analyzed within the proposed model of Pb(ZrTi)O₃ (PZT) films with an excess lead content, which is based on the presence of heterophase intergrain boundaries. It is shown that aging of thin-film capacitor structures is accompanied by a significant increase in the oxygen content in submicron PZT films, as well as by the modification of elemental and phase compositions of the interfaces. It is confirmed experimentally that a decrease in the switching charge in the aged PZT films is due to the oxygen sorption at heterophase crystallite boundaries containing lead oxide and to pinning of the polarization in regions adjacent to the charged boundaries. It is demonstrated that the current-voltage characteristics of the capacitor structures are described in terms of the mechanisms of space-charge-limited currents.     

Phase coexistence in lead zirconate titanate solid solutions

This paper discusses the phenomena observed in the vicinity of the morphotropic phase boundary in Pb(Ti_1?x Zr_x)O₃ (PZT) solid solutions. The location of the boundary between the stable tetragonal ferroelectric phase and the stable rhombohedral ferroelectric phase is calculated, and an analytical expression for determining the concentration range of the possible coexistence of these phases is derived. According to the numerical estimates, the concentration range can be as much as 20 mol % lead zirconate. However, reliable experimental data in support of these estimates are as yet unavailable.     

Perovskite barium zirconate titanate nanoparticles directly synthesized from solutions

Perovskite barium zirconate titanate nanoparticles (25–20 nm in diameter) were synthesized at low temperatures and under ambient pressure using titanium alkoxide, zirconium alkoxide and barium hydroxide as the starting materials. Microstructural analyses by X-ray diffraction and transmission electron microscopy indicated that the powders were nano-scaled, well crystallized, and had a perovskite phase. It is proposed that an acid–base neutralization reaction is the key mechanism behind the formation of such nanoparticles.     

Preparation of lead zirconate titanate nano-powder by electrohydrodynamic atomization

A lead zirconate titanate (PZT) sol was subjected to electrohydrodynamic atomization in the stable cone-jet mode. The droplets generated were sized by laser diffraction before deposition and heating to 600 °C. The droplets were 20–35 m in size and transmission electron microscopy showed that their relics consisted of PZT powder particles, <10 nm in size. Thus, a novel method of preparing nano-powders of functional advanced materials, such as PZT, has been pioneered. PACS 81.20.Ev; 81.20.Rg; 77.84.-s; 81.07.Bc     

Lead zirconate titanate cantilever for noncontact atomic force microscopy

Noncontact atomic force microscopy with frequency modulation detection is a promising technique for surface observation with true atomic resolution. The piezoelectric material itself can be an actuator and sensor of the oscillating probe simultaneously, without the need for additional electro-mechanical transducers or other measurement systems. A vertical resolution of 0.01 nm rms has been achieved using a microfabricated cantilever with lead zirconate titanate thin film in noncontact mode frequency modulation detection. The cantilever also has a sharpened pyramidal stylus with a radius of about 10 nm for noncontact atomic force microscopy.     

Crystallization of lead zirconate titanate films by laser annealing

The structure of lead zirconate titanate Pb(Zr _x Ti_{1 ? x} )O₃ thin films grown by chemical solution deposition on Si-SiO₂-Ti-Pt substrates has been studied using transmission electron microscopy and energy-dispersive analysis. Films crystallization has been performed using laser annealing. It has been found that, in contrast to isothermal annealing where nucleation on the platinum layer dominates, crystallization and growth of spherical perovskite crystals occur in the film bulk. The perovskite phase crystal size increases from 10 to 120 nm with increasing laser beam energy.     

Pressure-temperature phase diagrams for several modified lead zirconate ceramics

Using dielectric constant and loss measurements we have determined the pressure-temperature phase diagrams of four ferroelectric ceramics based on lead zirconate (PbZrO₃). The materials chosen for study all have pressure-induced ferroelectric to antiferroelectric transitions at ∼0.3 GPa. In all four materials, five phases were identified by comparing our results with studies, previously published by other workers, of the phase behavior of modified PbZrO₃ materials as a function of composition and temperature. The observed phases are the ideal cubic perovskite paraelectric phase, two rhombohedral ferroelectric phases, and two antiferroelectric phases, one orthorhombic and one pseudotetragonal. Comparison is made with previous temperature-composition studies of modified PbZrO₃ materials.     

Ferroelectric photonic crystals based on nanostructured lead zirconate titanate

The first results obtained in the synthesis of one-dimensional ferroelectric photonic crystals based on nanostructured lead zirconate titanate and porous silicon are reported. The samples synthesized are studied using linear reflection and second optical harmonic spectroscopy.     

Stochastic ferroelectric switching of lead zirconate titanate thin films

We investigate the repolarization phenomenon in a ferroelectric film. Our ferroelectric sample was lead zirconate titanate (PZT) obtained by sol-gel synthesis and deposited by spin coating on ITO/glass substrate. A series of repolarizations were induced in the ferroelectric film by applying a triangular wave and the current peaks related to the switchings of the ferroelectric domains were acquired for statistical analyses. It is shown that the dynamics and statistics of polarization switchings are well simulated by a simple mean-field model in which a double-well, asymmetric potential is included to describe the asymmetry at the PZT-ITO interface.     

Polarization switching process of soft lead zirconate titanate bulk ceramics

The domain switching dynamics was investigated in Nb-doped Pb(Zr_0.52Ti_0.48)O₃ bulk ceramics through observing systematically the evolution of the hysteresis loops at frequencies ranging from 0.01 to 100 Hz and in a field of 7.5–35 kV/cm. The experimental results indicate that the hysteresis loops are remarkably dependent on the fields and the frequencies. The data are analyzed by the Merz equation. The analysis results reveal that the requirement to satisfy the Merz equation is saturated loops. Based on these results, we divided the polarization switching process into three regions.     

Internal field and self-polarization in lead zirconate titanate thin films

It has been shown that 300-nm-thick polycrystalline films of lead zirconate titanate (PZT), the compositions of which correspond to the region of morphotropic phase boundary, undergo anomalous changes in the composition and the microstructure as the annealing temperature increases. This causes substantial variations in the dielectric and piezoelectric responses, the spontaneous polarization and the internal field value. It has been demonstrated that the self-polarization varies nonmonotonically with increasing the internal field and is characterized by a threshold effect. The role of excess lead oxide and its influence on the formation of the self-polarization and the change in the effective permittivity of the ferroelectric layer has been discussed.     

Structure and phase transitions of lead zirconate hafnate solid solutions

Solid solutions of two antiferroelectrics, namely, lead zirconate and lead hafnate, i.e., PbZr_{1 − x} Hf _x O₃ (x = 0, 0.3, 0.5, 0.7, 1.0), have been prepared by solid-phase synthesis from simple oxides. The elemental composition of the samples and their structure have been studied using X-ray fluorescence and X-ray diffraction analyses. The phase transformations of the solid solutions have been determined in the temperature range 20°C < T < 300°C.     

Humidity effects on calcium zirconate ceramics in electrochemical hydrogen cells

In the eighties, Iwahara discovered that doped Sr and Ba cerates show significant proton conduction, at high temperature, and in hydrogen- or water-containing atmosphere [1]. Begin ‘90 it was proved that also doped zirconates (Sr, Ba, Ca) join this family of proton conducting perovskites [2]. Within this group, indium doped CaZrO₃ is one of the more interesting materials for applications, being mechanically and chemically particularly stable, and producible in very dense form. Specifically, it was already succesfully incorporated in a hydrogen sensor for liquid aluminium [3]. In principle, this sensor works as a simple electrochemical hydrogen concentration cell described by Nernst. However, as already remarked phenomenologically from the beginning [1], a hydrogen concentration cell using these perovskites shows the theoretically predicted emf, only in the presence of humidity. In this paper we want to go deeper into the reasons for this phenomenon. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

Fatigue of lead titanate and lead zirconate titanate thin films

The fatigue of lead titanate and lead zirconate titanate ferroelectric thin films, i.e., a change in the polarization as a function of the number of switching cycles in an external electric field, is investigated experimentally. The threshold numbers of switching cycles are determined to be 10¹⁰–10¹¹ for the lead titanate films and 10⁹–10¹⁰ for the lead zirconate titanate films. It is shown that a change in the temperature does not substantially affect the threshold number of switching cycles at which the switched polarization decreases drastically. However, an increase in the external field strength leads to a noticeable decrease in the threshold number of switching cycles. The process of fatigue is accompanied by an increase in the coercive field and the internal bias field. It is established that, as the number of switching cycles increases, the internal bias field changes more significantly as compared to the coercive field. The absence of a change in the phase composition in repeatedly switched samples indicates that the fatigue processes have a nonchemical nature. The anomaly observed in the frequency dependence of the permittivity in the frequency range 10⁶–10⁷ Hz due to the domain structure disappears after multiple switching cycles. This suggests that the observed fatigue phenomenon has a domain nature.     

强电场作用下反铁电锆钛酸铅的介电行为研究

采用电滞回线方法和偏置直流电场中叠加小交变电场方法研究了锆钛酸铅反铁电陶瓷材料在强电场作用下的介电行为.测量结果显示，锆钛酸铅反铁电材料的介电常数随外加电场强度呈非线性变化，在反铁电 铁电转变的电场区间形成介电峰.表征极化强度随电场强度变化率的微分介电常数εd峰值出现在反铁电 铁电转换电场强度处，最高达到41000.随着偏置电场增加反铁电向铁电体转变过程中，小信号介电常数εc减小；在电场降低铁电回复成反铁电过程中，小信号介电常数εc增大，小信号介电常数εc峰先于微分介电常数εd峰出现.根据电场作用下反铁电 关键词： 锆钛酸铅反铁电陶瓷 介电行为 强电场条件     

Theoretical modelling of infrared spectra of the twinned lead zirconate

The THz-frequency range dispersion of the complex dielectric permittivity tensor of antiferroelectric lead zirconate, associated with its multiple weak infrared active phonon modes, is modelled by the oscillator formula with parameters fully determined from the recently developed atomistic shell model. The resulting realistic dielectric function is used to estimate the far-infrared reflectivity spectra of a twinned lead zirconate crystal in the limit of narrow and wide domains. It is shown that in case of the sufficiently narrow domain widths, the effective-medium average permittivity shows additional modes identified as geometric resonances (i.e. extraneous excitations created by material interfaces), possibly distinguishable in suitable experiments.