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.     

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.     

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.     

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.     

Mechanical properties of sol-gel derived lead zirconate titanate thin films by nanoindentation

Lead zirconate titanate (PZT) thin films are deposited on platinized silicon substrate by sol-gel process. The crystal structure and surface morphology of PZT thin films are characterized by X-ray diffraction and atomic force microscopy. Depth-sensing nanoindentation system is used to measure mechanical characteristics of PZT thin films. X-ray diffraction analyses confirm the single-phase perovskite structures of all PZT thin films. Nanoindentation measurements reveal that the indentation modulus and hardness of PZT thin films are related with the grain size and crystalline orientation. The increases of the indentation modulus and hardness with grain size are observed, indicating the reverse Hall-Petch effect. Furthermore, the indentation modulus of (1 1 1)-oriented PZT thin film is higher than those of (1 0 0)- and random-oriented films. The consistency between experimental data and numerical results of the effective indentation moduli for fiber-textured PZT thin films using Voigt-Reuss-Hill model is obtained.     

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.     

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.     

Characterization of lead zirconate titanate ceramics using surface acoustic wave

Lead zirconate titanate (PZT) is widely used as a piezoelectric transducer material for bulk and surface acoustic wave (SAW) devices. In this Paper a novel laser-ultrasound technique for measuring the SAW properties of PZT for quality control purposes is presented.     

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.     

Evolution of the switching current during the accumulation of fatigue in lead titanate and lead zirconate titanate thin films

The fatigue processes caused by repeated cyclic switching of polarization in lead titanate and lead zirconate titanate thin films on silicon substrates by applying rectangular pulse and sine wave fields are investigated. Upon an increase in the cycling number, an increase in the coercive and internal bias fields is observed, along with a reduction in the switching current maximum, the switching time, and the switchable polarization. At the same time, no change in the mobility of domain boundaries is observed.     

AC Poling study of lead zirconate titanate/vinylidene fluoride-trifluoroethylene composites

It is experimentally known that a polymer matrix phase in a composite of ferroelectric particles dispersed in a ferroelectric polymer can be polarized by using a few cycles of an ac field, without causing much disturbance to the state of polarization of the inclusion particles. This paper attempts to investigate this special poling process for a typical ferroelectric composite system of lead zirconate titanate (PZT) ceramic particles in a vinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) copolymer matrix, upon the application of 10 Hz ac fields of various amplitudes. Compared to a copolymer sample, the composite samples can be polarized at a lower field, and hence show a larger remanent polarization at the same poling field. Among the composites, the observed remanent polarization increases with increasing ceramic volume fraction. These experimental observations can be understood by a simple model, in which space charges are allowed to accumulate at the particle-matrix interfaces because of the electrical conductivity of the constituents. At a fast switching poling field of 10 Hz, the calculation shows that conductivity and charge accumulation effects in the composite are only minimal. Accordingly, although the PZT phase as well as the copolymer phase are both polarized under the ac field, the ceramic phase is only polarized to about 10% when the copolymer phase is almost fully polarized. Thus, one can still use an ac field to polarize only the copolymer phase of the composite without altering the polarization state of the ceramic phase significantly. PACS 77.22.Ej; 77.84.Lf     

Fatigue of lead titanate and lead zirconate titanate thin films with various values of coercive and internal bias fields

The dependence of the residue polarization on the number of switching cycles in thin ferroelectric films with various thicknesses and on substrates differing by values of the coercive and internal bias fields was experimentally studied. A model describing the features of the fatigue effect in these films is proposed.     

Phase transitions in polarized heterophase systems based on lead zirconate titanate

Temperature dependences of the depolarization currents have been studied and phase transformations between the R3c, R3m, P4mm, and Pm3m phases have been determined in samples of the five-component heterophase ferroelectric ceramics based on lead zirconate titanate.     

Poling induced higher order nonlinearity changes in lead zirconate titanate ceramic

High order nonlinear behaviors in Pb(Zr_1?x,Ti_x)O₃ (PZT) ceramics were studied using the harmonic generation technique, both before and after poling. It was found that the amplitude of the third harmonic is smaller than that of the second harmonic before poling, but the situation is reversed after poling with a substantial increase of the third harmonic amplitude. Noticeable time dependence of nonlinearities were observed in poled ceramics, which gradually decreased and saturated after about two days. These facts confirmed the generation of microcracks during poling.     

Development of perovskite and phase transition in lead cobalt niobate modified lead zirconate titanate system

Ferroelectric lead zirconate titanate–lead cobalt niobate ceramics with the formula (1 − x)Pb(Zr_1/2Ti_1/2)O₃–xPb(Co_1/3Nb_2/3)O₃ where x = 0.0–0.5 were fabricated using a high temperature solid-state reaction method. The formation process, the structure and homogeneity of the obtained powders have been investigated by X-ray diffraction method as well as the simultaneous thermal analysis of both differential thermal analysis (DTA) and thermogravimetry analysis (TGA). It was observed that for the binary system (1 − x)Pb(Zr_1/2Ti_1/2)O₃–xPb(Co_1/3Nb_2/3)O₃, the change in the calcination temperature is approximately linear with respect to the PCoN content in the range x = 0.0–0.5. In addition, X-ray diffraction indicated a phase transformation from a tetragonal to a pseudo-cubic phase when the fraction of PCoN was increased. The dielectric permittivity is remarkably increased by increasing PCoN concentration. The maximum value of remnant polarization P_r (25.3 μC/cm²) was obtained for the 0.5PZT–0.5PCoN ceramic.     

Quantitative electron energy-loss spectroscopy (EELS) analyses of lead zirconate titanate

Electron energy-loss spectroscopy (EELS) analyses have been performed on a sol-gel deposited lead zirconate titanate film, showing that EELS can be used for heavy as well as light element analysis. The elemental distributions within the sol-gel layers are profiled using the Pb N(6,7)-edges, Zr M-edges, Ti L-edges and O K-edge. A multiple linear least squares fitting procedure was used to extract the Zr signal which overlaps with the Pb signal. Excellent qualitative information has been obtained on the distribution of the four elements. The non-uniform and complementary distributions of Ti and Zr within each sol-gel deposited layer are observed. The metal:oxygen elemental ratios are quantified using experimental standards of PbTiO(3), PbZrO(3), ZrO(2) and TiO(2) to provide relevant cross-section ratios. The quantitative results obtained for Ti/O and Pb/O are very good but the Zr/O results are less accurate. Methods of further improving the results are discussed.