Effect of milling time and pH on the dispersibility of lead zirconate titanate in aqueous media for inkjet printing

Micrometre-sized Pb(Zr_0.53Ti_0.47)O₃ (PZT) powder was dispersed in water, stabilized with the ammonium polyacrylate (PAANH₄) and milled to reduce the particle size. The influence of the pH, the amount of PAANH₄, and the milling time on the zeta potential, the PZT particle size and the particle size distribution was studied. The agglomeration took place regardless the milling time at pH 3. The suspension, containing 5 vol.% of PZT and 5 wt.% of PAANH₄, milled at pH 10 for 240 min, was stable and contained particles with a narrow, log-normal particle size distribution with the median size of 160 nm. The dissociated carboxyl groups from the PAANH₄ interacted with the PZT particles as evidenced by Fourier transform infrared spectroscopy and electrosterically stabilized the particles in water at pH 10. The PZT particle size and the stability of the suspension fitted the requirements for the ink, suitable for ink-jet printing.     

Thickness effects on structures and electrical properties of lead zirconate titanate thick films

PbZr_0.52Ti_0.48O₃ thick films with thickness of 1–6 μm have been prepared by a polymer-assisted MOD process. The polymer, poly(vinyl acetate) (PVAc) was introduced into PZT precursor solutions. The grain size increased from 30 nm to 100 nm with an increase of the additive amount of PVAc. Meanwhile, the grains grew larger (in a range of 100–500 nm) and the surface of the films became rougher with increasing film thickness. This promotes the structural relaxation and prevents cracking formation. The critical thickness at which the film begins to crack increases significantly. The dielectric constant and remanent polarization (P_r) increased from 1070 to 1490 and from 36.1 μC/cm² to 52.4 μC/cm², respectively, and the coercive field (E_c) decreased from 57.3 kV/cm to 41.3 kV/cm as the film thickness increased from 0.95 μm to 6.02 μm. PZT thick films prepared in this study are promising materials for MEMS applications.     

Electrical and mechanical properties of ferroelectric lead zirconate titanate/tungsten oxide ceramics

Ferroelectric PZT/xWO₃ ceramics (when x = 0, 0.5, 1, 3 and 5 vol%) were fabricated from PZT and nano-sized WO₃ powders by a solid-state mixed-oxide method. Phase characterization suggested that the reaction between PZT and WO₃ occurred during the sintering. This reaction seemed more pronounced with increasing the content of WO₃. The maximum density at approximately 97% of the theoretical value was achieved at 1 vol% of WO₃ addition. The grain size was reduced with an addition of WO₃ particles from 7.8 μm for PZT to 1.8 μm for 0.5 vol% WO₃ and 0.8 μm for 1–5 vol% WO₃. Mechanical properties of PZT could be improved with an addition of WO₃ nano-particulates. The addition of 0.5 vol% WO₃ could maintain good electrical properties while increasing WO₃ significantly reduced dielectric and piezoelectric constants of the PZT.     

Optimization of pH and dispersant amount of Y-TZP suspension for colloidal stability

In this article, the amount of dispersant agent [i.e., polyethyleneimine (PEI)] and pH was optimized to achieve high colloidal stability in yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) suspension. Rheological properties of aqueous Y-TZP suspension in the presence of different amounts of PEI were evaluated via viscosity tests to identify the optimal amount of dispersant agent. Zeta potential and particle size measurements were employed to determine the suitable pH that can establish good colloidal stability. Mechanical properties (e.g., density and hardness) and morphological properties were also considered in determining the optimal pH. Rheological tests showed that Y-TZP suspension with 0.4 wt% PEI had the lowest viscosity, which is suitable for colloidal processing. pH 2 and 4 were recorded to have the lowest particle size and highest zeta potential, respectively. Characterization tests and morphological analysis showed that pH 2 had the highest density (92.5%), highest hardness (10.36 GPa), and homogeneous microstructure with fine average grain size (486 nm). Thus, the dispersant amount of 0.4 wt% PEI and pH 2 were selected as the optimal parameters for colloidal processing of aqueous Y-TZP suspension. Y-TZP suspension with excellent colloidal stability and reliable final products was produced under these parameters.     

Metastable ferroelectric phase in lanthanum-doped lead zirconate titanate stannate antiferroelectric ceramics

Metastable ferroelectric phase induced by electric field in lanthanum-doped lead zirconate titanate stannate antiferroelectric ceramics near morphotropic phase boundary were studied as a function of electric field, temperature and hydrostatic pressure. Upon application of an electric field to the antiferroelectric ceramics, the rhombohedral FE phase can be induced from tetragonal AFE phase when the induced field was larger than the critical field E_AEF-FE, and the induced FE phase can remain metastable state when the electric field was removed. The metastable FE phase was unstable, which recovered to AFE phase again with the increasing of temperature at about 80 °C and the increase of hydrostatic pressure at 150 MPa, respectively. Large charge release from remanent polarization of metastable FE phase was accompanied with phase transition. The relationships of critical parameters of field-induced phase transition were also shown.     

Roles of polymeric dispersant charge density on lead zirconate titanate aqueous processing

Poly(acrylic acid) (PAA) and poly(acrylic acid-co-maleic acid) (PACM) were used as dispersants in preparation of lead zirconate titanate (PZT) aqueous suspensions. The effects of dispersant structure on particle stabilization were investigated through properties of the suspensions. Viscosity and sedimentation height measurements showed that addition of the dispersants improved particle stabilization. The dispersant concentrations to obtain the lowest viscosity were 0.4 wt% for PAA and 0.2 wt% for PACM based on powder dried weight basis. Furthermore, effects of pH were studied on the suspensions prepared with 0.2 wt% dispersants. Viscosity and sedimentation behaviors indicated the improvements of particle dispersion and suspension stability with an increasing pH. Particle dispersion revealed by laser light scattering and scanning electron microscopy supported an improvement of particle dispersion at alkaline pHs. Detailed analysis of these data indicated that the PACM exhibited higher dispersant efficiency for PZT aqueous suspension in all conditions. The results were discussed based on the concentrations of anionic –COO^? groups at various pHs and charge density along polymeric backbone of the dispersants.     

Electric field inhomogeneity as a cause for fatigue in lead zirconate titanate ferroelectrics

The profile of ferroelectric fatigue in lead zirconate titanate ceramic in the thickness direction was investigated by thinning the fatigued samples continuously from both sides symmetrically. The electrical properties of fatigued samples exhibited a gradual recovery with the samples being thinned and then remained nearly unchanged, however, well below the values at fresh state. The results revealed that fatigue was not limited to the near-electrode regions, but throughout the ceramic samples in the thickness direction. The electric field inhomogeneity in ferroelectric ceramics during bipolar switching was proposed to be responsible for ferroelectric fatigue and the fatigue profile through phase decomposition.     

Effects of temperature on aging degradation of soft and hard lead zirconate titanate ceramics

This paper aims to study the effects of heat treatment temperatures on the aging degradation of piezoelectric properties, i.e. piezoelectric coefficient (d₃₃) and planar electromechanical coupling factor (k_p), in soft and hard PZT ceramics. Aging degradations of d₃₃ and k_p of the samples were measured for 192 h prior to heat treatments. The samples were then treated at various temperatures equivalent to 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8 times of the materials' Curie temperatures. Aging degradations of d₃₃ and k_p of the heat-treated samples were observed continuously for 1128 h. The piezoelectric properties of the un-treated samples gradually decreased with aging time. Attenuation of d₃₃ and k_p in the samples immediately after heat treatment increased with increasing heat treatment temperature. Moreover, aging degradation rate and relaxation time of the samples measured after heat treatments increased with increasing heat treatment temperature. Comparing to hard PZT ceramics, soft PZT demonstrated greater change of d₃₃ and k_p immediately after heat treatments. Soft PZT also showed greater aging rate and aging time than those of hard PZT. From the overall results, it can be concluded that both material type and heat treatment temperature have effects on aging behaviors of PZT materials. Aging degradation was more pronounced in soft PZT and the samples treated at high temperatures. The observed aging behaviors of PZT materials were explained by the interaction between domains and defects of oxygen vacancies that leads to volume, domain and grain boundary effects.     

Novel forming of columnar lead zirconate titanate structures

The present study is focused on the processing of columnar lead zirconate titanate (PZT) structures on Ti/Pt-coated silicon substrates using electrohydrodynamic deposition. It was found that the as-deposited PZT structure is highly dependent on the concentration of the sprayed precursor, which is believed to be the characteristic of electrohydrodynamic deposition. 0.01, 0.03, 0.06, 0.12, 0.3 and 0.6 M PZT sols were used to prepare as-deposited structures. Columnar PZT structures, which are important for the processing of 1-3 composites, were obtained with the 0.6 M sol. As-deposited and heat-treated columnar PZT structures were investigated using scanning electron microscopy and X-ray diffraction. The development of the PZT columns was studied by observing the cross-section of the structures deposited over different time sprays, revealing a three-stage growth process for these structures. The affect of substrate temperature on the columnar structure was also analysed by studying the density of the columns. Finally, a 1-3 composite was produced by infiltrating photoresists into the columnar PZT structures and the relative permittivity and dissipation factor of such composite were measured as 105 and 0.021. Modelling the structures as a PZT and a polymer capacitor connected in parallel in the PZT/polymer composite suggests that the relative permittivity of PZT columnar material is approximately 154.     

Effect of Ru and LaNiO3 barrier layers on lead zirconate titanate films grown on nickel-based metal foils by sol–gel process

Lead zirconate titanate [Pb(Zr_0.52, Ti_0.48)O₃ (PZT)] films were grown by sol–gel process on nickel and hastelloy foils. PZT perovskite phase was obtained at 650 °C annealing condition and surface topography showed uniform and dense microstructure. The characterization on dielectric properties indicates that diffusion of foil elements into the PZT and the formation of low capacitance interfacial layer occur during process. In order to reduce the diffusion effect of foil element and/or interfacial layer, barrier layers such as Ru(RuO₂) and LaNiO₃ layers were utilized on foil substrates. The increase of grain size was observed in PZT films grown on barrier layers. Dielectric properties are greatly improved without degrading ultimate dielectric breakdown strength.     

Aerosol deposition of dense lead zirconate titanate thin films at room temperature

Lead zirconate titanate (Pb(Zr,Ti)O₃, PZT) films were grown on silicon 1 0 0 substrate by aerosol deposition, using solid-state reacted powder containing donor oxide Nb₂O₅, while the substrate was maintained at room temperature. The PZT films were simultaneously sintered upon deposition on a highly densified ceramic layer. Crystalline phases of the deposited films have been determined by X-ray diffractometry (XRD), and microstructures analysed by transmission electron microscopy (TEM). The cross-section microstructure consisted of several thin layers, including the PZT film and the platinum electrode and titanium-buffered layers on the substrate. High-resolution images revealed that the PZT layer contained a mixture of randomly oriented grains of nanometre size, which were embedded in an amorphous matrix. In contrast to the conventional liquid-phase sintering mechanism, sintering of the PZT films involved amorphised phases generated by pressure-induced amorphisation (PIA) from plastic deformation when the initial powder particles collided amongst one another upon reaching the silicon substrate during aerosol deposition. An analogy may be drawn to the impact of extraterrestrial meteorites in which diaplectic glass, i.e., amorphised phase, was formed and retained metastably at room temperature. The individual PZT grains were joined with the amorphised phase(s) and sintered to become a dense, thin film on the silicon substrate.     

Dielectric characterization of microwave sintered lead zirconate titanate ceramics

Highly reactive lead zirconate titanate powders (PZT) with different compositions were successfully synthesized by the oxidant-peroxo method (OPM) and used to prepare dense ceramic samples with composition near to the morphotropic phase boundary (MPB) sintered at 1000 °C for 2 h using a tubular conventional oven and a commercial microwave system. Crystalline phases were identified in the powder and ceramic samples by X-ray powder diffraction and FT-Raman spectroscopy at room temperature. The fractured surface of the ceramic sample showed a high degree of densification with fairly uniform grain sizes. Dielectric constants measured in the range from 30 to 500 °C at different frequencies (1, 10 and 100 kHz) indicated a normal ferroelectric behavior regardless of the sintering method. Samples sintered by a microwave radiation (MW) method and composition near to the MPB region showed a maximum dielectric constant of 17.911 and an anomalous high Curie temperature of 465 °C.     

Investigation of large signal properties of quasi-static lead zirconate titanate actuators at elevated temperature

Quasi-static multilayer piezoelectric actuators are finding more and more applications, for example, in the field of aerospace; however, their properties are still not fully characterised, in particular at a high temperature. The present study targets the full characterisation of both soft-doped and hard-doped lead zirconate titanate (PZT) up to 200°C. A simple set of tests and test results are presented, focusing particularly on dielectric losses and creep effect. Dielectric losses were found to decrease with the increasing field for soft-doped PZT, while they tend to increase for hard-doped PZT. The interpretation is that soft-doped PZT has less hysteresis at high field. The creep behaviour is also significantly different. While soft-doped PZT follows a logarithmic model with low and stable creep rates, hard-doped PZT exhibits non-logarithmic creep with increasing or decreasing rates depending on the temperature. This behaviour is attributed to the generation of additional poling in the material.     

Effects of thermal strain on electric properties of lead zirconate titanate thin films upon LaNiO3 coated base metal plates

Electric properties for ferroelectric lead zirconate titanate (PZT50/50, 45/55, 40/60, 30/70) thin films on base metal plates with different thermal expansion coefficient (TEC) were calculated by a phenomenological model. Results show that when the TEC of substrates increases, dielectric constant, tunability and piezoelectric coefficient d₃₃ of all PZT thin films with tetragonal phase are decreased due to the larger compressive thermal strain. PZT50/50 thin films deposited on smaller TEC substrates can achieve higher dielectric constant, tunability and d₃₃. The computed dielectric constant of PZT50/50 thin films is in accordance with the measured results from sol-gel experimental process, and the trend of dielectric constant of PZT films adjacent to morphotropic phase boundary (MPB) derived from some references also agrees with that from calculation. These results suggest that higher tunability and d₃₃ of PZT films can be obtained by choosing smaller TEC substrates.     

Rheological properties of nanosized barium titanate prepared by HGRP for aqueous tape casting

The conditions for the preparation of stable nanosized barium titanate suspensions with high solids content for the production of aqueous tape casting are identified. The rheological behavior of colloidal barium titanate suspension with Ammonium polyacrylate (NH₄-PAA) as a dispersant to aid the powder dispersion has been investigated. Nanosized barium titanate powder was synthesized by a continuous high-gravity reactive preparation (HGRP) technique, and then annealed at 900 °C for 2 h. Measuring the zeta potential, the particle size distributions and ball-milling time, assessed the optimum conditions of the suspension with low viscosity and stability. An isoelectric point (IEP) at pH = 2.8 was found. Particle size distribution tests identified an optimum pH value about 10 and an optimum dispersant addition about 1.2 wt.% (based on the dry powder weight). As the ball-milling time was longer than 8 h, the amount NH₄-PAA adsorbed on the barium titanate reached to saturation. The maximum solid content attained during this work was 45 vol.% at pH of 10, with dispersant addition 1.2 wt.%. High green density value (up to ∼55.4% of the theoretical density) in BaTiO₃ sheet was achieved with a solid content 40 vol.%. After sintering at 1200 °C for 2 h a final density of 95% is reached.     

Electrical fatigue behavior of lead zirconate titanate ceramic under elevated temperatures

The electrical fatigue behavior of lead zirconate titanate (PZT) ceramics is investigated under different temperatures. A bipolar triangular electric field with the amplitude of ±1.5 kV/mm and the frequency of 50 Hz is applied to samples up to 1 × 10⁶ cycles. The fatigue rate is found to be temperature dependent, and the fatigue degradation is represented by the loss of remnant polarization, dielectric constant, and piezoelectric constant increased with loading cycle numbers. The degradation, involving surface damage and crack propagation, is more pronounced in samples cycled at lower temperatures, and increases with increasing number of cycles. The temperature effect on fatigue degradation of the properties is described based on the field shielding effect caused by surface damage and fatigue-induced cracks. The effect is more dominant in case of higher cycling numbers and lower temperature fatigue due to higher strain mismatch between switchable and non-switchable domains. Moreover, Raman spectroscopy is used to determine the influence of fatigue on the ferroelectric domains in different areas of the specimens.     

Effect of pH on the properties of barium titanate slurries with an aniomic dispersant

The colloidal stability of barium titanate (BT) aqueous suspensions with poly(acrylamide/4‐carboxylamino‐4‐oxo‐2‐butenate) (PAAM/COB) at pH 7, 9, and 12 has been investigated by means of ζ potential, adsorption, sedimentation, and particle size measurements. The isoelectric point of BT powder is at pH 4.6 and the value of ζ potential decreases as the pH of suspensions increases. The adsorption of PAAM/COB onto BT particles follows the Langmuir adsorption isotherm. The saturated amount of adsorbed polymer decreases with increasing pH. In general, BT particles in basic solutions with PAAM/COB are more stabilized, and less agglomerated than those without any dispersant present. As pH is increased, the resulting ζ potential becomes more negative, although lower polymer concentration is required for monolayer coverage of particle surface. Consequently, the resulting suspensions become more stabilized, and contain powder with smaller particle size. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1082–1088, 2006     

A study of the electric power generation properties of a lead zirconate titanate piezoelectric ceramic

Electric power generation characteristics of lead zirconate titanate (PZT) piezoelectric ceramic have been investigated experimentally and numerically. A thin PZT ceramic plate attached to a thin brass plate was used to examine the electric voltage generated during cyclic loading. On increasing the number of PZT ceramic plates combined together in the longitudinal direction, the electric voltage increases with the highest electric voltage being obtained for four PZT ceramic plates; and the maximum electric voltage becomes almost constant even if the number of PZT ceramic plates combined together increases more than four. This is attributed to the low strain level and the mixed strain (compressive and tensile strain). The effect of strain characteristic on the electric voltage value was analyzed numerically using our strain definition, and a clear correlation between the extent of compressive strain and generated electric voltage is clarified. A different electric generation characteristic was further observed depending on the stress conditions: generation of positive and negative electric voltage occurs when the PZT ceramic is subjected to mainly compressive and tensile stress, respectively.     

Effect of holmium substitution on structural and electrical properties of barium zirconate titanate ferroelectric ceramics

The holmium substituted Ba_1−3x/2Ho_xZr_0.025Ti_0.975O₃ (x=0.01, 0.02, 0.025, 0.05) compositions were synthesized by the solid state reaction technique. The synthesized specimens were characterized for their structural and electrical properties using X-ray diffractometer, scanning electron microscopy, impedance analyzer and loop tracer. Phase analysis shows the formation of secondary phase Ho₂Ti₂O₇ for Ho≥2.5 mol% substitution. The microstructural investigation shows that the holmium substitution significantly reduces the grain size. The substitution of holmium increases the Curie temperature for x≤0.02 whereas Curie temperature decreases for x≥0.025. The maximum dielectric constant at transition temperature is observed for x=0.02. The solubility limit is 2 mol% and for x≥0.025 some of the holmium atoms enter B-sites and forms the secondary phase. An increase is observed in the coercive field of the specimens with the increasing holmium content.     

Influence of tensile vs. compressive stress on fatigue of lead zirconate titanate thin films

Novel applications of ferroelectric films require a variety of different substrates, which exert different mechanical stress on the film. This raises the question of reliability of differently stressed films. This work compares the cycling-induced fatigue of the polarization hysteresis of PZT films in different stress states. A tensile stress of +270 MPa, for PZT on fused silica glass, causes gradual degradation, while degradation sets in abruptly under compressive stress of −100 MPa, for PZT on sapphire. The main fatigue mechanism is domain wall pinning on charged defects. Reversible and irreversible domain wall processes in the small- and large-signal permittivity reveal that the fatigue behavior results from a variation of the ferroelectric domain structure. Films under tensile stress contain more 90° domain walls, which get pinned continuously on isolated defects. Compressive stress creates more 180° domain walls, which require formation of defect agglomerates during a certain threshold cycle number for pinning.