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.     

静水压下锆锡钛酸铅铁电陶瓷相变和介电性能研究

研究了铌掺杂锆锡钛酸铅铁电陶瓷Pb_0.99Nb_0.02[(Zr_0.90Sn_0.10)_0.96Ti_0.04]_0.98O₃(PZST 90/10-4-2Nb)在静水压(0-300 MPa)下的电荷释放量和介电性能. 对压力诱导的低温铁电三方(F_R(LT))→反铁电正交(A_O)相变进行了研究. PZST 90/10-4-2Nb铁电陶瓷分为未极化、极化和压力去极化三种. 极化PZST 90/10-4-2Nb陶瓷F_R(LT)→A_O相变过程中,电荷释放量为29.3 μC/cm²,相变压力为140 MPa. 介电性能表明:极化PZST 90/10-4-2Nb陶瓷相变压力为136 MPa,而未极化陶瓷相变压力为104 MPa,压力去极化陶瓷未表现出明显的相变特征. 关键词： 静水压 铁电陶瓷 相变 介电     

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.     

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.     

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.     

Dynamic fatigue during polarization switching of lead zirconate titanate ceramics with variable ferroelectric hardness

The remanent polarization of lead zirconate titanate ceramics with variable ferroelectric hardness is experimentally studied in a strong ac field. The results obtained suggest that the main mechanism of multiplication of crystal defects that controls the fatigue rate of soft ferroelectric ceramics is the process of twinning and untwinning in crystallites during polarization switching. In hard ferroelectric ceramics, the formation of a hysteresis loop is accompanied by the formation of stable configurations of mechanical twins in crystallites due to secondary twinning. Polarization switching in these configurations does not induce twin-wall motion, and the fatigue rate is low.     

掺铒锆钛酸铅镧陶瓷的上转换动力学分析

测量了掺铒锆钛酸铅镧(Er³⁺:PLZT)陶瓷的吸收光谱和上转换荧光光谱,利用Er³⁺:PLZT的吸收光谱,计算Er³⁺离子的辐射跃迁概率. 分析了980nm 激发下 Er³⁺:PLZT 的上转换荧光光谱,观察到明显的上转换荧光,且峰值位于540,564nm附近的绿色荧光带比 678nm 附近的红色荧光带强. 建立了Er³⁺离子跃迁的速率方程,通过求解速率方程并采用拟合荧光衰减实验曲线的方法,得出 关键词： 频率上转换 3+离子')" href="#">Er³⁺离子 锆钛酸铅镧陶瓷 速率方程     

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.     

Determination of the nanoscale dielectric properties in ferroelectric lead zirconate titanate (PZT) thin films

We report on nanoscale experiments with <100 nm lateral resolution being able to differentiate the effective dielectric polarisation P_z, deposited charge density σ, surface dielectric constant ε_surface, its voltage dependence ε_surface(U), as well as the built-in electric bias voltage U_int in ferroelectric lead zirconate titanate (PZT) thin films. This is possible by combining piezoresponse force microscopy (PFM) and pull-off force spectroscopy (PFS), both methods based on scanning force microscopy (SFM). The differentiation becomes possible since both P_z and σ contribute additively in PFS, while they are subtractive in PFM, hence allowing the two contributions to be separated. ε_surface can be quantified by means of the experimental PFS data and the calculated effective penetration depth of PFM developed in a finite element modelling. Finally, U_int and ε_surface(U) are derived by an absolute matching of the P_z values measured by PFM and PFS.Our nanoscale results obtained on PZT thin films reveal values for the above specified quantities that have the same order of magnitude as those obtained from macroscopic measurements reflecting the integral response using large electrode areas. However, we stress that the data reported here reveal physical properties deduced on the nanometer scale. Furthermore, they are recorded during one single experimental investigation, using one single set-up only.     

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.     

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.     

Effects of microstructure on the properties of ferroelectric lead zirconate titanate (PZT) thin films

Lead zirconate titanate (PZT) thin films were prepared with pulsed laser deposition and sol–gel techniques. The PZT films fabricated by these two techniques have similar randomly oriented single perovskite phases, but the film derived from the pulsed laser deposition exhibits a more compact and flat morphology. The dielectric, ferroelectric, and piezoelectric properties of the two kinds of films are comparatively characterized and discussed. It is observed that a denser microstructure would lead to a significantly higher dielectric constant and remanent polarization and a much lower coercive electric field, but only a relatively slight enhancement on the piezoelectric constant. The film with a looser microstructure could have a substantially higher piezoelectric voltage constant g₃₃ due to the much lower dielectric constant. Our results and discussion provide a better understanding of the relationship between the microstructure and the film properties, which is essential in order to tailor the microstructure and hence determine the performance aiming at a specific application. PACS 68.55.Jk; 77.22.-d; 77.65.-j     

Dynamic magnetoelectric effects in bulk and layered composites of cobalt zinc ferrite and lead zirconate titanate

Low-frequency magnetoelectric (ME) coupling is investigated in bulk samples and multilayers of cobalt zinc ferrite, Co_1-xZn_xFe₂O₄ (x=0–0.6), and lead zirconate titanate. In bulk samples, the transverse and longitudinal couplings are weak and of equal magnitude. A substantial strengthening of ME interactions is evident in layered structures, with the ME voltage coefficient a factor of 10–30 higher than in bulk samples. Important findings of our studies of layered composites are as follows. (i) The transverse coupling is stronger than the longitudinal coupling. (ii) The strength of ME interactions is dependent on Zn substitution, with a maximum for x=0.4. (iii) A weak coupling exists at the ferromagnetic-piezoelectric interface, as revealed by an analysis of the volume and static magnetic field dependence of ME voltage coefficients. (iv) The interface coupling k increases with Zn substitution and the k versus x profile shows a maximum centered at x=0.4. (v) The Zn-assisted enhancement can be attributed to efficient magneto-mechanical coupling in the ferrite. PACS 75.80.+q; 75.50.Gg;75.60.-d;77.65.-j;77.65.Ly;77.84.Dy     

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.     

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     

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.     

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.