Dielectric properties of lead zirconate titanate thin films seeded with barium strontium titanate nanoparticles

A low temperature synthetic method recently proposed by the authors was applied to the fabrication of lead zirconate titanate (PZT) thin films containing crystalline seeds of barium strontium titanate (BST) nanoparticles. PZT precursor and the BST particles were prepared with complex alkoxide methods. Precursor solution suspending the BST particles was spin-coated on Pt/Ti/SiO₂/Si substrate to film thickness of 500–800 nm at particle concentrations of 0–25.1 mol%, and annealed at various temperatures. Seeding of BST particles prevented the formation of pyrochlore phases, which appeared at temperatures above 400 °C in unseeded PZT films, and induced crystallization of PZT into perovskite structures at 420 °C, which was more than 100 °C below the crystallization temperature of the unseeded PZT films. Measurement of dielectric properties at 1 kHz showed that the 25.1 mol% BST-seeded PZT films annealed at 450 °C had a dielectric constant as high as 300 with a dissipation factor of 0.05. Leakage current density of the film was less than 1×10⁻⁶ A/cm² at applied electric field from 0 to 64 kV/cm.     

Effect of compositional modifications on the piezoelectric properties of spray dried lead zirconate titanate ceramics

Lead zirconate titanate powders of different compositions varying from 50 to 55 atomic percent zirconium in the solid solution have been prepared by spray-drying technique. The compositions were varied by changing the zirconium-to-titanium ratio in the solid solution and also with the addition of strontium. The amorphous character of the as-prepared powders and the formation of single phase lead zirconate titanate during calcination were also confirmed by x-ray diffraction technique. These powders were then converted to piezoelectric ceramics by compaction and sintering followed by electroding and poling. Effect of the variation of zirconium to titanium ratio and strontium additions on the piezoelectric properties of the finished ceramics have been explained on the basis of improved sintering, uniform grain size, formation of morphotropic phase boundary and subsequent shift to rhombohedral structure.     

Effects of addition of MnO on piezoelectric properties of lead zirconate titanate

The effects of manganese addition on the piezoelectric properties, microstructure, sintering characteristic and Curie temperature have been studied for Pb(Zr,Ti)O₃ (PZT) ceramics. The valence states of manganese are measured by Electron Spin Resonance (ESR). Those studies show that manganese coexist mainly in the way of Mn₂₊ and Mn₃₊ in PZT ceramics. When the concentration of Mn ion is below 0.5 mole%, it is preferentially incorporated in the lattice Pb site in Mn₂₊ or Mn₃₊, which gives rise to the increase of K_p and d₃₃. In the intermediate concentration region of 0.5–1.5 mole%, Mn ion will be incorporated in the lattice of (Ti, Zr) site in Mn₃₊ acted as acceptor, which increases Q_m without causing large changes of K_p and d₃₃. When the concentration of Mn ion is larger than 1.5 mole%, it will accumulate at the grain boundaries and give rise to the decrease of piezoelectric properties of PZT ceramics. Small amount of Fe may decrease the solubility limit of Mn ion in PZT ceramics and it may also prevent the oxidation of Mn₂₊ and Mn₃₊.     

Piezoelectric and mechanical properties of ceria-doped lead zirconate titanate ceramics

Phases, microstructures and properties of lead-zirconate-titanate (PZT) ceramics with the compositions Pb(Zr_0.535– Ce Ti_0.465) O₃ where =0.0, 0.001, 0.01, 0.02 and 0.05 were studied. Rhombohedral and tetragonal phases were present at =0.0. The amount of the rhombohedral phase increased with increasing , and only the tetragonal phase was present for >0.001. Thec/a ratio of the tetragonal phase also increases with increasing . Particles of CeO₂ were found to be present in compositions with >0.01, indicating that the solubility of CeO₂ is less than 1a/o on the metals basis. The piezoelectric and electromechanical constants achieved maximum values for =0.001. The hardness increased monotonically with increasing . The modulus of rupture and the fracture toughness, however, went through a minimum and both stayed lower than their values for =0.     

Effects of sol infiltration on the screen-printed lead zirconate titanate thick films

Ferroelectric PZT(60/40) thick films were fabricated by the screen-printing method and the PZT precursor solution was spin-coated on the thick films to obtain a densification. Structural and electrical properties of the thick films with the treatment of sol coating were investigated. The lattice constant of PZT thick films was 0.4073 nm and there is no dependence on the number of sol coatings. The thickness of PZT films obtained by one screen-printing was approximately 16 μm. The relative dielectric constant increased and dielectric loss decreased with the increase in the number of sol coatings, and the values of the 15-coated PZT-15 film were 369 and 2.16% at 1 kHz, respectively. The remanent polarization, coercive field, and breakdown strength of the PZT-15 thick film were 23.2 μC/cm², 18.03 kV/cm and 78 kV/cm, respectively.     

Temperature-dependent ferroelectric hysteresis properties of modified lead zirconate titanate ceramics

Temperature-dependent ferroelectric hysteresis properties of modified lead zirconate titanate ceramics have been investigated in a wide temperature range from 300 to 433 K. It is observed that remnant polarization, saturation polarization, and coercive field are increasing with an increase of the temperature in a low-field region and decreasing in a high-field region. Such behavior is explained by the competition between switching and backswitching mechanisms. A three-stage dependence of the logarithm of the hysteresis loop area on the logarithm of the electric field is identified. The temperature dependence of backswitching properties has been studied. The obtained results indicate that the temperature dependence of the polarization backswitching can be well described by the Arrhenius law. The activation energy for the domain switching determined from the fitting results exhibits decreasing tendency with the increase of the electric field.     

Direct precipitation of lead zirconate titanate by the hydrothermal method

Direct precipitation of fine powders of lead zirconate titanate (PZT) in the complete range of solid solution, is investigated under hydrothermal conditions, starting from lead oxide and titania/zirconia mixed gels. The perovskite phase is formed in the temperature range of 165 – 340°C. Sequence of the hydrothermal reactions is studied by identifying the intermediate phases. The initial formation of PbO: TiO₂ solid solution is followed by the reaction of the same with the remaining mixed gels giving rise to X-ray amorphous PZT phase. Further, through crystallite growth, the X-ray crystalline PZT is formed. This method can be extended for the preparation of PLZT powder as well. The resulting powders are sinterable to high density ceramics.     

Preparation and ferroelectric properties of Bi-modified lead zirconate titanate thin film

We have studied the structural and electrical properties of bismuth-modified lead zirconate titanate thin films. Specimens with various Bi contents, (Pb1−3/2xBix) (Zr0.52 Ti0.48) O3 (PBZT) thin films, were prepared on a Pt-coated Si wafer by the sol–gel method. Ferroelectricity confirmed by the measurement of dielectric constant and P–E hysteresis loop was found for specimens below x = 0.25, in which the values of both dielectric constant and remanent polarization were decreased with increasing Bi contents. The behaviors of the electrical properties with Bi content corresponded to the structural changes by increasing non-ferroelectric cubic phase with increasing Bi contents, which was thought to be due to the vacancies in Pb-sites created by the substitution of Bi into Pb.     

Influence of solution rate and substrate temperature on the properties of lead iodide films deposited by spray pyrolysis

Polycrystalline lead iodide (PbI₂) thin films have been deposited by spray pyrolysis method using N,N-dimethylformamide (DMF) as solvent as a function of several deposition parameters. DMF is used as an alternative to water due to the larger solubility limit of PbI₂ in this solvent. In this work, the solution rate during the deposition time of 3 h was varied in the range of 0.11 cm³/min up to 0.30 cm³/min. A growth rate varying from 19 Å s^?1 up to 47 Å s^?1 was obtained as a function of solution rate. Dark current as a function of temperature for the final films reveals that for larger solution rates smaller values of electrical resistivity is obtained. For a solution rate of 0.30 cm³/min, an electrical transport activation energy (E _a) of about 0.65 eV was measured for the whole temperature range. On the other hand, for the sample deposited with a solution rate of 0.11 cm³/min, two main transport mechanisms can be observed with an activation energy of about 1.23 eV for temperatures above 50 °C. The effect of substrate temperature is also discussed. Samples were deposited in the temperature range of 170 °C up to 250 °C with a fixed solution rate of 0.16 cm³/min. In addition, the films were exposed to X-ray irradiation in the mammography diagnosis region, using a molybdenum (Mo) anode and a peak tube potential between 26 and 36 kV (equivalent photon energies between 10 keV and 15 keV).     

Microstructural development and electrical properties of lead zirconate titanate composite films

Dihydroxyalcohols (DIOL route) and 2-methoxyethanol (MOE route) are two of the most commonly used solvents in preparing sol-gel lead zirconate titanate (PZT) films. The employment of the PT(MOE) film as a buffer layer for PZT(DIOL) films not only offers advantages of more precise film thickness and better adhesion to substrate, but also reduces the crystallization temperature, improves the surface smoothness, and increases the grain size of the PZT(DIOL)/PT(MOE) composite films. The PT (MOE) buffer layer also improves electrical properties, such as polarization-electric field behavior, fatigue endurance, and leakage behavior, of PZT films.     

Effect of Gd-substitution on dielectric and transport properties of lead zirconate titanate ceramics

The gadolinium (Gd)-modified lead zirconate titanate (i.e., Pb_1?xGd_x (Zr_0.65Ti_0.35)_1?x/4O₃; x = 0, 0.07, 0.10 and 0.12) ceramics have been synthesized using a high-temperature (~1,100 °C) solid-state reaction route. Preliminary X-ray structural studies show the formation of single-phase compounds in the tetragonal crystal system. Scanning electron micrographs of the surface of pellet samples show uniform distribution of grains of different shape and size with few voids. It is interesting to observe the significant effect of Gd-substitution on the nature, size, and distribution of grains, and the density of samples. Detailed analysis of dielectric properties of the materials indicates that the materials are non-relaxor but have diffused ferroelectric phase transition. The temperature and frequency dependence of conductivity follows Jonscher’s universal power law.     

Improved fatigue properties of lead zirconate titanate films made on oxygen-implanted platinum electrodes

Pb(Zr_0.3Ti_0.7)O₃ (PZT) thin film capacitors fabricated on an oxygen-implanted Pt bottom electrode were studied. Oxygen was implanted at a low acceleration voltage (40 kV) and dose (1×10¹⁵ cm⁻²). Structural examination by grazing-incident X-ray diffraction (GIXD) and chemical analysis by X-ray photoelectron spectroscopy (XPS) revealed that the implantation generated a very thin amorphous top surface layer (approx. 20 nm), which contained approximately 7% of oxygen that stayed in the film in the form of PtO bonding. The amorphous layer, however, resumed the crystalline structure accompanied by the dissociation of PtO under the rapid thermal annealing at 600 °C for 5 min. The remnant polarization of sol–gel derived Pb(Zr_0.3Ti_0.7)O₃ (PZT) films fabricated on the oxygen-implanted Pt was slightly reduced from 11.92 μC/cm² for the PZT capacitors fabricated on a Pt electrode without implanted oxygen to 9.07 μC/cm². Nevertheless, the fatigue endurance was significantly increased. The switching polarization of PtO_x/PZT/Pt (O-implanted) capacitors remained within 95% of the starting value after 4×10¹⁰ switching cycles, which is comparable to that of PZT capacitors made with other conducting oxides.     

Electromechanical properties of lead zirconate titanate piezoceramics under the influence of mechanical stresses

In lead zirconate titanate piezoceramics, external stresses can cause substantial changes in the piezoelectric coefficients, dielectric constant, and elastic compliance due to nonlinear effects and stress depoling effects. In both soft and hard PZT piezoceramics, the aging can produce a memory effect that will facilitate the recovery of the poled state in the ceramics from momentary electric or stress depoling. In hard PZT ceramics, the local defect fields built up during the aging process can stabilize the ceramic against external stress depoling that results in a marked increase in the piezoelectric coefficient and electromechanical coupling factor in the ceramic under the stress. Although soft PZT ceramics can be easily stress depoled (losing piezoelectricity), a DC bias electric field, parallel to the original poling direction, can be employed to maintain the ceramic poling state so that the ceramic can be used at high stresses without depoling.     

Improved dielectric properties of lead lanthanum zirconate titanate thin films on copper substrates

Thin films of lead lanthanum zirconate titanate (PLZT) were directly deposited on copper substrates by chemical solution deposition and crystallized at temperatures of ~ 650 °C under low oxygen partial pressure (pO₂) to create film-on-foil capacitor sheets. The dielectric properties of the capacitors formed have much improved dielectric properties compared to those reported previously. The key to the enhanced properties is a reduction in the time that the film is exposed to lower pO₂ by employing a direct insertion strategy to crystallize the films together with the solution chemistry employed. Films exhibited well-saturated hysteresis loops with remanent polarization of ~ 20 μC/cm², dielectric constant of > 1100, and dielectric loss of < 0.07. Energy densities of ~ 32 J/cm³ were obtained at a field of ~ 1.9 MV/cm on a ~ 1 μm thick film with 250 μm Pt electrodes.     

Effects of rapid thermal annealing on nucleation, growth, and properties of lead zirconate titanate films

The nucleation and growth behavior of solgel-derived lead zirconate titanate (PZT) films was investigated at different rapid thermal annealing (RTA) processes. The effects of RTA on PZT film surface morphology, crystal orientation, residual stress, and properties were also studied and are discussed. PZT nucleation and growth behavior were found to be more sensitive to heating rate than to hold time during RTA. Higher heating rates were preferred for uniform PZT nucleation and grain growth, which resulted in dense microstructures, smooth surfaces, and better film ferroelectric properties. Lower heating rates led to strong PZT (100) orientation, better film piezoelectric properties, and low residual stress, but at the risk of film cracks caused by arbitrarily distributed large crystallites with diameters of approximately 300 nm among crystallites with diameters of approximately 30 nm. Furthermore, the residual stress of the PZT film was found to be effectively reduced by extending the hold time.     

Improvement of sintering and piezoelectric properties of soft lead zirconate titanate ceramics

Niobium-doped Pb(Zr_0.53Ti_0.47)O₃ (PZTN) ceramics were prepared by the conventional(mixed oxides) method, modified by the addition of a PZT colloid of the same composition. The colloidal precursor was prepared using a coprecipitation method. Such an addition produced a significant improvement in the sinterability of a conventionally prepared PZTN powder and the sintering temperature was reduced, achieving a density 98% theoretical density at 1075 °C for 2 h. The measured piezoelectric properties were as high ask _p = 0.62 andd ₃₃ = 330 ×10^–12CN^–1.     

Densification of sintered lead zirconate titanate by hot isostatic pressing

The effects of hot isostatic pressing (HIPing) on sintered lead zirconate titanate are presented. Densities up to 98% were obtained by HIPing for 1 h at 1300°C with argon gas pressures of either 20.7 or 138 MPa. The microstructural changes observed after HIPing, and the rapid initial kinetics for densification and pore shrinkage, indicate that prssure-enhanced grain rearrangement and solution-precipitation processes are primarily responsible for densification. The persistance of large voids after HIPing suggests that it may be impossible to completely eliminate gross processing-related defects in lead zirconate titanate by HIPing.     

Dielectric and pyroelectric properties of Ba-modified lead lanthanum zirconate stannate titanate ceramics

(Pb_0.97−xLa_0.02Ba_x)(Zr_0.75Sn_0.12Ti_0.13)O₃ ceramics in the composition range 0.1 ≤ x ≤ 0.16 were prepared by conventional solid state reaction process. On increasing Ba content from 0.1 to 0.16 mol, the specimens underwent phase transition from the first order to the second order and the Curie temperature decreased from 85 to 35 °C. With x = 0.16, the specimen showed good pyroelectric properties for practical applications. When a 500 V/mm dc bias field was applied, the specimen showed the maximum pyroelectric coefficient of 5800 μC/m² K and figure of merit of 58 × 10⁻⁵ Pa^−0.5 at Curie temperature.     

Performance characteristics of smart-materials based on lead zirconate titanate

This paper deals with the characterization of smart-material combinations based on the principle of phase transformation; that may provide drastic change in resistance with a small change in pressure. Lead zirconate titanate (PZT) has been selected as a base material for the development of smart-material combinations and pressure-sensitive devices were fabricated using the same. The devices have been characterized with change in pressure. Both dynamic and static pressures were used for characterization of the devices. Fast switching action i.e. large change in resistance with pressure has been observed and discussed. The reliability tests on the devices have also been performed to establish their long-term stability.