Preparation and characterization of ceramic nanocomposites in the PZT–BT system

Nanocomposites of the (1 − x)PZT-xBT system were fabricated by the bimodal particle concept. The effect of fabricating conditions on structural characteristics and dielectric properties of the ceramics was investigated using XRD, SEM, and a standard dielectric measurement. The ceramic–solid solutions and -nanocomposites in the PZT–BT system were comparatively explored. It was clearly seen that the microstructures and the dielectric properties of PZT–BT ceramic-nanocomposites are totally different from those of ceramic–solid solutions. The dielectric behavior of ceramic-nanocomposites displayed superimposition of two phase transitions with a lower maximum value of the dielectric constant than that of the solid solutions.     

Temperature dependence of macroscopic and microscopic PZT properties studied by thermo-mechanical analysis,dielectric measurements and X-ray diffraction

The main objective of the paper is to point out the influence of composition and of poling state (poled and unpoled samples) on the evolution of various parameters (?_r, dilatation coefficients, lattice parameters) at different scales (lattice, bulk) using X-ray diffraction (XRD), thermo-mechanical analysis (TMA) and dielectric methods. The transition temperatures have been determined from the above measurements and compared. The composition has an influence on the transition temperature and not on the dilatation coefficient value. The poling state influences only the macroscopic dilatation evolution and not the value of the transition temperature. A scale effect is only observed on majoritary tetragonal compositions which show different values of transition temperatures from microscopic and macroscopic methods.     

Effects of microwave heating on dielectric and piezoelectric properties of PZT ceramic tapes

Commercial lead zirconate titanate (PZT) perovskite powders were used to fabricate ceramic tape and then sintered by microwave and conventional methods. Both dielectric and piezoelectric properties of PZT ceramic tapes were studied in terms of sintering process. X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) show the PZT perovskite phase with smaller grain size and dense microstructure can be obtained at a lower sintering temperature by microwave process. It was also observed that shrinkage ratio and bulk density of the tapes sintered at 800 °C were obtained about 19% and 7.46 g/cm³ by the microwave heating method, respectively, that is corresponding to those values of sintered PZT tapes at 950 °C by conventional process. Moreover, the dielectric constant and maximum permittivity are increased about 30% as compared with conventional processing method. The experimental results demonstrated that the characteristics of the PZT tapes could be significantly improved by microwave heating method. These results demonstrate that such a simple approach can upswing the piezoelectric and dielectric properties of these tapes by using microwave process with a short heating time.     

Novel P(VDF-HFP)/BST nanocomposite films with enhanced dielectric properties and optimized energy storage performance

Nanocomposites using poly (vinylidene fluoride-co-hexafluoropropylene), P(VDF-HFP), as the matrix, and barium strontium titanium oxide (BST) nanoparticles as the filler were systematically studied. P(VDF-HFP)/BST composite films containing different amounts of BST were prepared using the solution-casting method. The dielectric constant (ε_r), dielectric loss (tan δ), and their frequency and temperature dependence, were characterised for the films under weak electric fields. The behaviour of the films under high electric fields was explored using polarisation-electric field (P-E) loops. The ε_r was found to increase from 14.1 to 42.1 as the BST content increased from 0 vol% to 40 vol%, and the Maxwell-Wagner model showed a good fit with the measured ε_r values, indicating that the microstructure of the fabricated nanocomposites is uniform, which can also be observed in SEM images of all P(VDF-HFP)/BST nanocomposite films. In determining the temperature (T) dependence of the ε_r and tan δ of the composites, P(VDF-HFP) plays a decisive role, while BST plays an influential role. As the BST content increases, the charge/discharge energy density (U_charge/U_discharge) increases, while the breakdown strength (E_b) and charge-discharge efficiency (η) decrease. Notably, the maximal U_discharge 3.79 J/cm³ was obtained when the BST content was 20 vol% at 2100 kV/cm. In addition, from the perspective of practical application, when the applied electric field intensity is lower than 900 kV/cm or between 900 kV/cm and 2100 kV/cm, in order to obtain the maximal U_discharge, the P(VDF-HFP)/BST composite with BST content of 30 vol% or 20 vol% should be selected respectively.     

A flexible piezoelectric pressure sensor based on PVDF nanocomposite fibers doped with PZT particles for energy harvesting applications

Flexible piezoelectric energy harvesters are a suitable choice for scavenging wasted mechanical energy because of the high demand for sustainable power sources. Flexible pressure sensors based on PVDF-PZT nanocomposite with different PZT volume fractions (0.011, 0.041, 0.096, 0.17, 0.3, and 0.37) were prepared in the form of fibers through an electrospinning method for piezoelectric energy harvesting application. According to the results, dielectric constant and piezoelectric coefficients (e.g. piezoelectric coefficient, and figure of merit) gradually increased with the doping of PZT particles into PVDF fibers. Dielectric constant (ϵ), piezoelectric coefficient (d), and figure of merit (d × g) for PVDF-PZT nanocomposite with 0.011 PZT volume fraction were 37.29, 10.51 pCN⁻¹, and 33.46 × 10⁻¹⁶ m²/N, respectively, and increased to 104.81, 22.93 pCN⁻¹, and 56.68 × 10⁻¹⁶ m²/N for PVDF-PZT nanocomposite fibers with a volume fraction of 0.37. As piezoelectric energy harvesters, piezoelectric sensitivity of PVDF-PZT nanocomposite fibers rose with increasing the PZT volume fraction. The generated output voltage was 184 mV under an applied force of 2.125 N with the piezoelectric sensitivity calculated as 173.507mV/Nμm for PVDF-PZT nanocomposite fibers with 0.37 PZT volume fractions which increased compared to pristine PVDF fibers (generated output voltage = 22 mV under applied force 2.4 N, piezoelectric sensitivity = 29.49 mV/Nμm). The achieved output power density of PVDF-PZT nanocomposite fibers with 0.37 PZT volume fractions was obtained 30.69μW cm⁻² higher than PVDF-PZT nanocomposite fibers with 0.011 PZT volume fractions (18.44μW cm⁻²).     

Development of hard/soft ferrite nanocomposite for enhanced microwave absorption

Nickel and zinc substituted strontium hexaferrite, SrFe₁₁Zn_0.5Ni_0.5O₁₉ (SrFe₁₂O₁₉/NiFe₂O₄/ZnFe₂O₄) nanoparticles having super paramagnetic nature are synthesized by co-precipitation of chloride salts using 7.5 M sodium hydroxide solution. The resulting precursors are heat treated (HT) at 900 and 1200 °C for 4 h in nitrogen atmosphere. During heat treatment, transformation proceeds as a constant rate of nucleation and three dimensional growth with an activation energy of 176.79 kJ/mol. The hysteresis loops show an increase in saturation magnetization from 1.042 to 59.789 emu/g with increasing HT temperatures. The ‘as-synthesized’ particles with spherical and needle shapes have size in the range of 20–25 nm. Further, these spherical and needle shaped nanoparticles tend to change their morphology to hexagonal plate and pyramidal shapes with increase in HT temperatures. The effect of such a systematic morphological transformation of nanoparticles on dielectric (complex permittivity and permeability) and microwave absorption properties are estimated in X band (8.2–12.2 GHz). The maximum reflection loss of the composite reaches −29.62 dB (99% power attenuation) at 10.21 GHz which suits its application in RADAR absorbing materials.     

Effects of foam composition on the microstructure and piezoelectric properties of macroporous PZT ceramics from ultrastable particle-stabilized foams

Porous lead zirconate titanate (PZT) ceramics could be produced by combining the particle-stabilized foams and the gelcasting technique. In this study, the foaming capacity of particle-stabilized wet foams was tailored by changing the concentration of valeric acid and pH values of suspension. Accordingly, porous PZT ceramics with different porosity, microstructure, dielectric and piezoelectric properties were prepared with the respective wet foam. Increase in the porosity led to a reduction in the relative permittivity (ε_r), a moderate decline in the longitudinal piezoelectric strain coefficient (d₃₃) and a rapid decline in the transverse piezoelectric strain coefficient (d₃₁), which endowed porous PZT ceramics with a high value of hydrostatic strain coefficient (d_h) and hydrostatic figure of merit (HFOM). As a result, the prepared samples possessed a maximal HFOM value of 19,520×10^?15 Pa^?1 with the porosity of 76.3%. The acoustic impedance (Z) of specimens had the lowest value of 1.35 Mrayl, which could match well with those of water or biological tissue; accordingly, the material would be beneficial in underwater sonar detectors or medical ultrasonic imaging.     

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 dielectric properties and optical propagation loss of c-axis oriented ZnO thin films deposited by sol–gel process

The c-axis oriented ZnO thin films were prepared on various substrates by sol–gel processes. The stability of solution was examined through solvent and stabilizer. The c-axis orientation and grain size of films were increased with increasing of heat treatment temperature. The optical propogation losses of ZnO films deposited SiO₂/Si(111) substrates were measured using end-coupling method. The losses result in the scattering of the interface of ZnO/SiO₂, and the ZnO grain. Dielectric constant and resistivity of thin films deposited on Pt/SiO₂/Si(111) substrates are, respectively, in the range of 7–13 and 1.7×10⁴9.8×10⁵Ω cm.     

Effect of the excess of bismuth on the morphology and properties of the BaBi2Nb2O9 thin films

In this study, the effect of bismuth content on the crystal structure, morphology and electric properties of barium bismuth niobate (BaBi₂Nb₂O₉) thin films was explored with the aid of X-ray diffraction (XRD), scanning electron microcopy (SEM), atomic force microscopy (AFM) and dielectric properties. BaBi₂Nb₂O₉ (BBN) thin films have been successfully prepared by the polymeric precursor methods and deposited by spin coating on Pt/Ti/SiO₂/Si (1 0 0) substrates. The phase formation, the grain size and morphology of the thin films were influenced by the addition of bismuth in excess. It was observed that the formation of single phase BBN for films was prepared with excess of bismuth up to 2 wt%. The films prepared with excess of the bismuth showed higher grain size and better dielectric properties. The 2 wt% bismuth excess BBN thin film exhibited dielectric constant of about 335 with a loss of 0.049 at a frequency of 100 kHz at room temperature.     

Annealing-induced changes in the nanoscale electrical homogeneity of bismuth ferrite dielectric thin films

In this study, we investigated the effects of forming gas (7% H₂ + 93% Ar) annealing (FGA) and recovery annealing (RA) in ambient oxygen on the structure and electrical properties of BiFeO₃ (BFO) thin films. X-ray diffraction results indicate that BFO remains in the perovskite phase following FGA. However, the spatial distribution of current maps obtained by conductive atomic force microscopy shows that FGA-treated BFO thin films are less electrically insulating than those without prepared thermal annealing. Recovery annealing improves the structural and chemical homogeneity of the FGA-treated films, thereby increasing the electrical resistance of the films.     

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.     

Micromechanics of domain switching in rhombohedral PZT ceramics

The lattice strain {2 0 0} and diffraction peak intensity ratio R{1 1 1} have been determined in soft rhombohedral PZT ceramics during the application of an electric field up to 2.5 MV m⁻¹ and as a function of the grain orientation ψ, using high energy synchtron X-ray diffraction. The magnitude of both {2 0 0} and R{1 1 1} increased sharply beyond a field level of 1 MV m⁻¹ due to the onset of ferroelectric domain switching. {2 0 0} exhibited a near linear dependence on cos² ψ, in agreement with previous studies of the remanent-poled state. In contrast, the R{1 1 1}–cos² ψ plot showed evidence of saturation in ferroelectric domain switching, particularly for ψ > 60°. The development of lattice strain during poling is discussed in terms of contributions from the intrinsic piezoelectric effect and from residual stress caused by differences in the poling strain of a grain, and the piezoelectric strain of a grain relative to its surroundings.     

Preparation and characterizations of highly transparent UV-curable ZnO-acrylic nanocomposites

A sol–gel chemical route was adopted to prepare the zinc oxide (ZnO) nanoparticles as small as 4 nm. UV-curable ZnO-acrylic nanocomposites were then prepared by employing 3-(trimethoxysilyl)propyl methacrylate (TPMA) as the surface modification agent of ZnO particles. UV–vis analysis revealed a high optical transparency (>95%) in visible light region for nanocomposite thin films with ZnO contents up to 20 wt.%. The addition of ZnO nanoparticles also enhanced the dielectric constants of nanocomposites and the dielectric constants greater than 4 in frequencies ranging from 1 to 600 MHz was obtained in the samples containing 10 wt.% of ZnO nanoparticles. A comparison of experimental results and theoretical calculation indicated that the interfacial polarizations in between ZnO nanoparticles and polymer matrix may play an important role in the enhancement of dielectric properties of nanocomposites.     

Hard/soft effects of multivalence co-dopants in correlation with their location in PZT ceramics

Piezoelectric hard/soft effects of multivalence co-dopants (Sb and Mn) in correlation with their location in the lattice, were investigated in PZT ceramics, prepared by conventional ceramic technology, with the following compositions: Pb_0.98Sr_0.02 ((Ti_0.49Zr_0.51)_1-0.015-xMn_0.015Sb_x)O₃ with x = 0, 0.005, 0.01, 0.02, 0.03, where antimony was initially assumed to substitute for Ti/Zr ions. The antimony valence state was found to be +3 in all samples by X-ray Photoelectron Spectroscopy investigations. The Electron Paramagnetic Resonance spectra evidenced a steep enhancement of the Mn²⁺ concentration upon increasing antimony doping level, explained by a charge compensation mechanism, between the Sb³⁺ ions substituting Pb²⁺ at the A-sites and the Mn²⁺ ions, localized at the B-sites. The incorporation of Sb³⁺ at the A-site of the PZT lattice is also supported by the variation of the lattice parameters, determined by X-ray Diffraction, with the increasing Sb concentration. The investigation of the dielectric, electromechanical and ferroelectric properties evidenced a hard piezoelectric behavior, mainly attributed to the presence of large sized Mn²⁺ ions, localized at B-sites. Our results prove that the piezoelectric hard/soft response is decisively influenced by the interplay between multiple valence states and locations of the co-dopants, on one hand, and the charge compensation mechanisms, on the other hand. This provides indirect information about the location of some co-dopants which can substitute for both cationic sites in the PZT based ceramics.     

Piezoresponse force microscopy characterization of rare-earth doped BiFeO3 thin films grown by the soft chemical method

The multiferroic behavior with ion modification using rare-earth cations on crystal structures, along with the insulating properties of BiFeO₃ (BFO) thin films was investigated using piezoresponse force microscopy. Rare-earth-substituted BFO films with chemical compositions of (Bi_1.00−xRE_xFe_1.00O₃ (x=0; 0.15), RE=La and Nd were fabricated on Pt (111)/Ti/SiO₂/Si substrates using a chemical solution deposition technique. A crystalline phase of tetragonal BFO was obtained by heat treatment in ambient atmosphere at 500 °C for 2 h. Ion modification using La³⁺ and Nd³⁺ cations lowered the leakage current density of the BFO films at room temperature from approximately 10⁻⁶ down to 10⁻⁸ A/cm². The observed improved magnetism of the Nd³⁺ substituted BFO thin films can be related to the plate-like morphology in a nanometer scale. We observed that various types of domain behavior such as 71° and 180° domain switching, and pinned domain formation occurred. The maximum magnetoelectric coefficient in the longitudinal direction was close to 12 V/cm Oe.     

Impact of ionizing radiation on structural,dielectric, and piezoelectric properties of Sr modified PZT

Ion irradiation effects on piezoceramic (Pb_0.94 Sr_0.04) (Zr_0.52 Ti_0.48)O₃ (PSZT) are investigated by using 4 MeV carbon (C), 9 MeV copper (Cu), and 20 MeV gold (Au) ions. The energies of incident ions are selected in order to target the same range of all incident ions in the material, while producing different amounts of vacancies. The ion irradiation is performed with fluences of 1×10¹³, 1×10¹⁴, and 1×10¹⁵ ions/cm² using Tandem Pelletron accelerator (5UDH-2). Post irradiation changes in PSZT are investigated via various structural, dielectric, and piezoelectric measurement techniques. Results divulge that the irradiation process disturbs the crystallinity along with reduction in X-ray diffraction (XRD) peak intensities owing to strain induced structural defects. A small decrease in dielectric constant is observed due to trapped charges, which screen the depolarization after irradiation. However, a significant decrease is detected in piezoelectric charge coefficients (d₃₃) and piezoelectric voltage coefficients (g₃₃) due to switching of micro domains of PSZT as a result of energy observed during irradiation process. These results indicate that ion irradiation has damaging effects on the properties of PSZT. The discussed information may be utilized to assess performance of PSZT based devices under radiation rich environments such as space.     

Microstructural, electrical and magnetic properties of multiferroic CoFe2O4/0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 nanocomposite thin films

Bilayered CoFe₂O₄/0.68Pb(Mg_1/3Nb_2/3)O₃-0.32PbTiO₃ nanocomposite films are successfully prepared on Pt/Ti/SiO₂/Si substrate via simple sol-gel process. X-ray diffraction result reveals that there exists no chemical reaction or phase diffusion between the CoFe₂O₄ and 0.68Pb(Mg_1/3Nb_2/3)O₃-0.32PbTiO₃ phases. The microstructure is characterized by scanning/transmission electron microscopy (STEM). The composite thin films exhibit both strong ferroelectric and ferromagnetic responses at room temperature. The maximal magnetoelectric coupling coefficient of the nanocomposite films reaches up to 25 mV/cm Oe, occurs at a lower bias magnetic field (H_dc) of 550 Oe.     

Raman scattering, electronic structure and microwave dielectric properties of Ba([Mg1−xZnx]1/3Ta2/3)O3 ceramics

Effects of Zn substitution for Mg on the crystal structure, lattice vibrations and microwave dielectric properties of Ba(Mg_1/3,Ta_2/3)O₃ (BMT) ceramics were investigated. Raman scattering spectra for Ba([Mg_1−xZn_x]_1/3Ta_2/3)O₃ (BMZT) ceramics, with x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0, were measured at room temperature. The Raman result shows a dominance of 1:2 ordered structure at all Zn substitution contents. All Raman modes shift to lower frequencies with increasing Zn substitution. Higher Qf value correlates well with narrower width of the breathing Raman mode A_1g(4) and larger relative intensity of 1:2 long-range-ordered mode E_g(2) in BMZT solid solution. First-principle calculation was performed to investigate the electronic structure of 1:2 ordered BMT and Ba(Zn_1/3,Ta_2/3)O₃ (BZT). Covalent bond between Zn and O in BZT is much stronger than that between Mg and O in BMT due to the Zn 3d orbital. Zn substitution for Mg leads to longer and weaker Ta-O bonds, which may be one reason for the variation of Raman spectroscopy and microwave dielectric properties of BMZT system.