Control of ferroelectric and linear piezoelectric response of PZT films through texture

The high and low field ferroelectric response of freestanding PbZr_0.52Ti_0.48O₃ (PZT) films, with texture varying from 100% (001) to 100% (111) was investigated via 500 nm thick PZT unimorphs deposited on the same substrate. It is shown that the ferroelectric and piezoelectric properties depend strongly on texture, and the effective transverse strain and stress coefficients vary linearly with %(001) and %(111) texture factors. PZT films with 100% (001) orientation displayed 150%, 140%, and 80% larger linear piezoelectric strain coefficient, saturated strain coefficient, and saturated stress coefficient, respectively, compared to films with 100% (111) orientation. As a result, pure (001) textured PZT films with 20% higher dielectric constant have 50% higher figure of merit in sensing than films with pure (111) texture. The piezoelectric and ferroelectric properties of all but one combinations of (001) and (111) texture were shown for the first time to be bounded by the values for 100% (001) and 100% (111) texture. A notable exception was PZT films comprised of 73% (001) and 27% (111) texture which showed stable piezoelectric coefficients at all electric fields, with major technological implication to low power microdevices. Finally, the coercive field was shown to decrease with (001) texture factor and excess‐Pb in the PZT and the PbTiO₃ seed layer.     

Mechanics-aided digital image correlation for the investigation of piezoelectric and ferroelectric behaviour of a soft PZT

The strain response of a polarised PZT was characterised using Digital Image Correlation (DIC). The DIC algorithm is based on a global approach and regularises the displacement field using the balance equations of solid mechanics. The measurement error is reduced by correcting the displacements that are mechanically not admissible. A ferroelectric test showed that the standard deviations of strain fields remain mostly under 1.2 × 10^?4 for an element size of 64 px. The standard deviation on the average value is 3 × 10^?6. The strain field is homogeneous and its average value is consistent with the strain obtained from a CCD laser measurement device. The longitudinal strain, transverse strain and polarisation response of the PZT were measured for bipolar and unipolar loadings ranging from 50 to 5000 V/mm. Material properties were extracted from these measurements. This work shows the advantages of a novel 2D-DIC algorithm for piezoelectric strain characterisation.     

Poling of soft piezoceramic PZT

The properties of piezoelectric ceramic materials are strongly dependent on the degree of polarization as set by the poling process. In the present work a soft piezoceramic PZT material was polarized at different poling conditions. The hysteresis loop, the polarization current and pyroelectric current measurements were used to evaluate the polarization state of the material. The hysteresis loop was monitored using a home-made computer controlled Sawyer–Tower circuit. The polarization current was recorded during the poling process at different applied electric fields, poling time and temperature. The pyroelectric coefficient and the polarization were calculated from the pyroelectric current. The polarization calculated from these data was in excellent agreement with the polarization as calculated from the poling current. The relative permittivity and loss factor were measured as a function of temperature after different poling conditions. The effects of the various poling conditions on the dielectric and ferroelectric properties of the soft PZT are discussed. It is shown that, contrary to common practice, poling at a field slightly larger than the coercive field is adequate to reach full polarization at room temperature.     

Temperature dependent ferroelectric and ferroelastic behaviour of PZT wafers

A study is carried out to understand the temperature dependent non-linear behaviour of PZT wafers under electrical and mechanical loading. Experiments are conducted on PZT wafers at room and elevated temperatures under a high cyclic electric field to examine their behaviour. Experimental characterization is also extended to pure mechanical loading (uni-axial compressive stress) condition at room and elevated temperatures. A temperature dependent micro-mechanical model is proposed based on internal energy to evaluate the ferrolectric and ferroelastic behaviour of PZT wafer. The developed model is incorporated into a 3D finite element framework and numerical simulations are performed. The simulated results for electrical loading are compared with experimental observations which show a significant decrease in dielectric response at elevated temperature and it is also observed that the operating temperature influences the electrical displacement and strain along poling direction (thickness direction) under mechanical loading. A parametric study has also been conducted to understand the performance of PZT wafer in which macro-state variables such as remnant polarization, remnant strain, maximum polarization, and maximum strain are extracted and discussed as a function of temperature.     

Bottom electrode crystallization of PZT thin films for ferroelectric capacitors

The bottom electrode crystallization (BEC) method was applied to the crystallization of PZT thin films deposited by laser ablation over Si/SiO₂/Ti(Zr)/Pt structures, with the platinum films being deposited at two different temperatures. The results were compared with those obtained by rapid annealing with halogen lamps and furnace annealing. PZT films crystallized over Pt made at lower temperature with Ti adhesion layers tend to have a (1 1 1) preferential orientation, while those deposited on platinum made at higher temperature tend to have a (1 0 0)/(1 1 1) mixed orientation. When Zr adhesion layers are used, the PZT films crystallized over Pt have a preferential (1 0 0) orientation, except for films deposited over Pt made at 500 °C and crystallized with a high heating rate. The ferroelectric properties of the films crystallized with the BEC method are good, being similar to those obtained with the other crystallization methods using the same parameters.     

Effects of defect dipoles on tunable dielectric response in relaxor ferroelectric ceramics

Tunable dielectric materials have drawn much attention due to their wide applications including capacitors and microwave tunable devices. Ferroelectrics materials have special spontaneous polarization which can be reversibly switched by an external electric field. Therefore, tunable dielectric constant can be easily achieved in ferroelectrics. However, the study of nonlinear dielectric response induced by defect dipoles is rarely concerned. Here, we report the effects of defect dipoles on tunable dielectric response under alternative current (AC) and direct current (DC) electric field in defect dipoles introduced Pb(Lu_1/2Nb_1/2)O₃–PbTiO₃ ceramics. A modified Rayleigh model is proposed to successfully characterize dielectric nonlinearity and reveals the interaction between domain walls and defect dipoles. The defect dipoles had more sensitive effect on dielectric response under AC field than that of defect dipoles-free samples. The drop of intrinsic dielectric contribution under AC field results from the detriment effect of defect dipoles. The irreversible contribution is altered by the movements of defect dipoles under AC field, subsequently inducing the nonlinearity of dielectric response. Samples with defect dipoles have larger tunable scope of dielectric properties than that of defect dipoles-free samples. The present work discovers the potential of application of defect dipoles-tuned dielectric response ferroelectrics in devices which requires both high AC and DC biases, and help to better understand the complex dielectric response of ferroelectrics.     

Effect of sol composition on dielectric and ferroelectric properties of PZT composite films

Crack free calcium modified PZT composite films have been synthesized using modified sol-gel process by depositing the slurries prepared by mixing powder of composition PbZr_0.52Ti_0.48O₃ and sol of composition Pb_(1−x)Ca_xZr_0.52Ti_0.48O₃ (where x = 0, 0.06, 0.1) on Pt(1 1 1)/Ti/SiO₂/Si substrate. The infilteration process has also been employed which resulted in dense microstructure of the films. Thickness of the films as measured by SEM of cross section of the films was more than 25 μm. The XRD patterns of the resultant films consisted of pure perovskite phase and no peak related to either pyrochlore phase or Pt substrate was observed. The room temperature dielectric constant and loss were compared. The temperature dependence of dielectric constant revealed that T_C of all the films was same, i.e., 351 °C, in spite of different compositions of the sol used. Well saturated PE-loops of the films show that the films were ferroelectric in nature.     

The shifting of P-E hysteresis loop by the asymmetric contacts on ferroelectric PZT thin films

Ferroelectric PZT thin films were fabricated by metal-organic decomposition (MOD) onto Pt/Ti/SiO₂/Si substrates. Different metals (i.e., noble metals: Pt, Ag, and non-noble metals: Al, Cr, In) were selected for top electrodes on PZT thin films. Capacitors with noble metals as top electrodes exhibited symmetric P-E hysteresis loops, whereas capacitors with non-noble metals as top electrodes exhibited asymmetric P-E hysteresis loops. Equivalent energy-band diagrams for these two different capacitor structures are proposed based on that noble metals form Schottky contacts and non-noble metals form ohmic contacts with ferroelectric PZT thin films. The internal field built up by the band bending in the bottom PZT/Pt Schottky contact results in the shifting of P-E hysteresis loop for capacitors with non-noble metals as top electrodes.     

Experimental and theoretical study of the ferroelectric and piezoelectric behavior of strontium-doped PZT

Theoretical data using ab initio perturbed ion calculation were compared with ferroelectric and piezoelectric experimental data of strontium doped PZT. Various concentrations of SrO in PZT at constant temperature and sintering time were carried out. Experimental results, such as the remanent polarization, P_R of 6.9–8.9 μC/Cm², the coercive field, E_C of 6.6–7.8 kVcm, and the planar coupling factor, Kp of 0.45–0.53, were compared with the energy of Zr⁴⁺ and Ti⁴⁺ ion dislocation and the lattice interaction energy which show that strontium increment in PZT alter the energies and increase the values of piezoelectric and ferroelectric variables. Calculations of lattice energy of the rhombohedral phase show that a phase non-stability is coincident with increasing experimental values of the P_R, E_C and Kp.     

Dielectric constants of bulk ferroelectric PZT measured by terahertz time-domain spectroscopy

The complex permittivity of bulk ceramic ferroelectric of nominal composition PbZr_0.4Ti_0.6O₃ was measured in the range 0.2–2?THz using transmission time-domain spectroscopy. The results indicate strong absorption and dispersion in this frequency range as often seen in highly disordered and polar materials. The results are compared to equivalent thin film data in the literature, and significant differences in the real and imaginary permittivity suggest that substrate clamping and degree of polarisation of the ferroelectric thin film materials affect dielectric properties even at these high frequencies.     

Determination of reversible and irreversible contributions to the polarization and strain response of soft PZT using the partial unloading method

Experimental work is aimed at systematically investigating the non-linear ferroelectric and ferroelastic behavior of a commercially available soft lead zirconate titanate (PZT) material. The fast partial unloading method is used to measure the material properties of unpoled soft PZT under pure electric field and of initially pre-poled soft PZT under compressive stress loading. In the first experiment using unpoled PZT, the evolution of piezoelectric constants and dielectric permittivity is determined as a function of electric field. It is found that the piezoelectric constants and dielectric permittivity depend on the electric field history. The results are used to separate the reversible strain and polarization from the irreversible ones caused by domain switching. In the second experiment using initially pre-poled PZT, it is found that the strain response is significantly dependent on the stress loading rate. The elastic moduli and piezoelectric coefficients are evaluated with respect to the compressive stress history. The measured longitudinal and transverse irreversible strains change significantly during both loading and unloading processes. An attempt is made to discuss the use of irreversible strain and irreversible polarization as internal variables for constitutive modeling. This investigation provides valuable information for modeling to predict the performance and for improving the reliability of piezoelectric devices.     

Monte Carlo investigation of hysteresis properties in ferroelectric thin-films under the effect of uniaxial stresses

The uniaxial stress dependence of the hysteresis behavior of ferroelectric films was studied. The DIFFOUR model was modified to include the uniaxial stress effect. Both the uniaxial stress and the external electric field were applied on the out-of-plane direction of the films. The polarization was measured with varying the magnitude of the applied stress and the electric field frequency via the dynamics of the polarization reversal in terms of hysteresis. The study was taken by means of Monte Carlo simulations using the spin-flip Metropolis algorithm. From the results, the district dependence of hysteresis behavior on frequency between low frequency and high frequency was prominent. On the other hand, the remanent and the coercivity significantly decreased with increasing applied stresses. Moreover, the areas under the hysteresis loops also decreased indicating smaller magnitude of energy dissipation. The results agree well with related experiments where applicable.     

MgO掺杂对功率型PZT压电陶瓷性能的影响

通过掺入不同比例的MgO,采用固相烧结法,制备出一种Pb0.95 Sr0.05(Zr0.525 Ti0.475)O3+1.1 mol％ CaFeO5/2+0.3mol％ Fe2O3+0.2mol％ Li2CO3+xmol％ MgO压电陶瓷材料.实验表明:适量MgO掺杂可以改善材料压电介电性能,在保持较高压电性能基本不变的前提下,提高机械品质因数Qm,降低介电损耗tanδ.当x=0.2时,陶瓷的综合性能最佳,具体性能参数为:压电应变常数d33=254 pC/N,平面机电耦合系数Kp=54.5％,相对介电常数εT33/ε0=960,介电损耗tanδ=0.34％,机械品质因子Qm=822.其性能满足大功率压电器件的要求,能较好地应用于压电变压器、超声换能器等器件中.     

Effects of Residual Stress on the Electrical Properties of PZT Films

The effects of the residual stress (either compressive or tensile) induced during the heat-treatment process on the electrical properties of Pb(Zr_0.52Ti_0.48)O₃ (PZT) films were investigated. The PZT films were deposited on platinized silicon substrates by the rf-magnetron sputtering method using a single oxide target. After their deposition, the films were bent elastically by means of a specially designed fixture during the annealing process. Residual stress was induced in the film by removing the substrate from the fixture after annealing. The ferroelectric and piezoelectric properties of the films were markedly changed by the residual stresses; the remnant polarization ( P _r) and saturation polarization ( P _sat) increased when a compressive stress was induced. On the other hand, the piezoelectric properties increased when a tensile stress was induced in the film.     

Poling behaviour at the grain boundaries of ferroelectric PZT thin films investigated by electric scanning force microscopy

The poling behaviour of PZT(53/47) films was investigated separately at the grain boundaries and inside the grain volumes by ESFM. The films were prepared by sol-gel processing on Pt-metallized polycrystalline Al₂O₃, substrates and consisted of columnar grains with mean diameter of 220 nm. It was found that the polarization was decreased at simple grain boundaries in a border zone of 20 nm to 40 nm width, with up to 42% related to the grain volumes. At triple points, the polarization was decreased by the same amount in a border zone of 40 nm to 80 nm width with respect to the grain volumes. An asymmetric poling behaviour of the saturation polarization was found at the grain boundaries. The switchable polarization of the grain boundaries was determined to be 74% of that of the grain volumes. The coercive field was clearly increased at the grain boundaries.     

The effect of Nb doping on dielectric and ferroelectric properties of PZT thin films prepared by solution deposition

Niobium (Nb)-doped lead zirconate titanate thin films (PNZT) were produced by solution deposition with nominal compositions, Pb_(1?0.5x)(Zr_0.53Ti_0.47)_1?xNb_xO₃ where x = 0.00–0.07. The effects of sintering temperature, sintering time, variation of thickness in the films and change of niobium content were investigated with regard to phase development, microstructure, and ferroelectric and dielectric characteristics. The best results were obtained in double-layered films (390 nm) sintered at 600 °C for 1 h. Optimum doping level was found in 1% Nb-doped films. For 1% Nb-doped [Pb_0.995(Zr_0.53Ti_0.47)_0.99Nb_0.01O₃] films, remanent polarization (P_r) of 35.8 μC/cm² and coercive field (E_c) of 75.7 kV/cm have been obtained. The maximum dielectric constant was achieved in 1% Nb-doped films which was 689. Ferroelectric and dielectric properties decreased at higher Nb doping levels because of the changes in the grain size and perovskite lattice parameters.     

烧结温度对多孔陶瓷压电性能的影响

研究了烧结温度对海藻酸钠离子凝胶法制备3-1型多孔PZT压电陶瓷和凝胶注模法制备3-3型多孔PZT压电陶瓷性能的影响.结果表明:当烧结温度从1150℃升至1250℃,多孔PZT陶瓷的孔隙率降低,晶粒尺寸、介电常数、压电系数、厚度机电耦合系数和抗压强度增大,静水压压电系数与静水压品质因数随之降低.3-1型PZT陶瓷具有定...     

Comparative studies of dynamic hysteresis responses in hard and soft PZT ceramics

Lead zirconate titanate (PZT) is a ferroelectric material with very interesting and useful dynamic hysteresis properties. Normally, PZT is doped with donors or acceptors to yield better electrical properties. Soft and hard PZT ceramics are respectively donor- and acceptor-doped PZT, which are commercially available and widely employed in various applications. Previous investigations have mainly been focused on the dynamic hysteresis at room temperature and under stress-free condition. However, when used, these ceramics are normally subjected to stress. More importantly, the ambient temperature is usually not at room temperature. Therefore, this study was to investigate dynamic hysteresis behavior of both hard and soft PZT ceramics with varying compressive stress and temperature. The results clearly revealed the influence of external stress and temperature on the dynamic hysteresis of both types of PZT ceramics. Increasing stress and temperature resulted in a decrease of the hysteresis area of the two types of PZT ceramics.     

Effects of uniaxial drawing on the performance and structure of filled polytetrafluoroethylene

Based on the phenomenon of softening under drawing, the filled polytetrafluoroethylene (PTFE) composites were studied. Short glass fibers (SGFs) were added into PTFE and drew at room temperature uniaxially in different draw strain ratios. As the result showed, porosity and tension strength increased, whereas the hardness decreased during orientation. Tensile softening provided an opportunity for taking the composite as gasket material. It could be detected from the tests of compressibility and recovery that both compressibility and resiliency were improved with the increasing draw ratio, and when draw strain ratio reached 80%, resiliency was nearly three times as the nondrawn one. There were two phenomena in the filled composite: first, SGFs were debonded from PTFE resin and second, small voids and fibrils were formed, which brought unique properties such as softening and high strength to the composite. It was also found that crystals divided into smaller ones and after that rearranged at an early stage of tension. When the draw ratio reached 35%, degree of crystallinity started to increase and fibrils began to be formed. It was believed that fibrils were imperfect crystal, and kept increasing the draw ratio, fibrils grew and crystalline grain became smaller gradually. POLYM. ENG. SCI., 54:1427–1435, 2014. © 2013 Society of Plastics Engineers     

Microstructure,electrical and mechanical properties of MgO nanoparticles-reinforced porous PZT 95/5 ferroelectric ceramics

Porous Pb (Zr_0.95Ti_0.05) O₃/xMgO (PZT/MgO, x=0, 0.1, 0.2, 0.5 and 1.0 wt%) ferroelectric ceramics were prepared with MgO nanoparticles as reinforcing phase. The effects of MgO nanoparticles on the phase, microstructure, electrical and mechanical properties of as-prepared ceramics were investigated. The results show that the grain size is reduced obviously when increasing the amount of MgO. Compared with pure porous PZT, T_C of MgO-added PZT ceramics shifts to higher temperature. Moreover, dielectric, ferroelectric and piezoelectric properties show no much degradation. Further, PZT/MgO ceramics possess enhanced mechanical properties compared to pure porous PZT ceramics, the largest increment of the fracture toughness and hardness being 31.3% and 19.8%, respectively. The optimal electrical and mechanical properties are obtained with the addition of less than 0.5 wt% MgO nanoparticles.