Electrical properties of high density PZT and PMN–PT/PZT thick films produced using ComFi technology

To achieve high actuation forces in piezoelectric film actuators and transducers it is desirable to have relatively thick films. Sol-gel derived films are often limited in the maximum thickness that is obtainable due to the increased probability of cracking and delamination during processing. Composite film (ComFi) technology combines conventional sol-gel processing with ceramic powder processing to enable thick (>2 μm) ferroelectric films to be deposited onto silicon substrates at temperatures as low as 710 °C. Ten micrometre thick films have been fabricated using three different piezoelectric powders [hard doped PZT, soft doped PZT and PMN–PT(85–15)]. The resultant films have high densities with relative permittivities of 800, 900 and 1800, respectively. The d₃₃ piezoelectric coefficients were found to be lower than corresponding values for the bulk material. This has been attributed to a combination of small grain size and the clamping effects of the rigid substrate. Hysteresis loop measurements show that greater fields are required to achieve a similar degree of polarisation to that of the bulk material. This indicates that the presence of the substrate also affects the ability to pole the material so further reducing the observed piezoelectric coefficient.     

Study of sintering behavior of PAN–PZT using dilatometry and co-relation with piezoelectric properties

The sintering behavior of Pb(Al_0.5Nb_0.5)O₃–Pb(Zr_0.52Ti_0.48)O₃ (PAN–PZT) ceramics was investigated. The sintering process of PAN–PZT was divided into four stages based on the amount of in-situ linear shrinkage: (Stage 1) initial stage at sintering temperature RT≤T_s≤ to 770 °C, (Stage 2) perovskite formation stage at 770≤T_s≤990 °C, (Stage 3) densification stage at 990≤T_s≤1265 °C and (Stage 4) Pb-loss stage at T_s>1265 °C. During stage 1, heating of PAN–PZT compact did not cause structural changes except the thermal expansion. During stage 2, the PZT-perovskite structure was formed by rearrangement of crystals. During stage 3, the specimen was rapidly densified with two peaks of strain rate. During stage 4, Pb was volatilized and this loss resulted in sudden increase of shrinkage. On analyzing the sintering stages, the optimized sintering conditions were considered as 1250 °C just before of Pb-loss stage. The effects of T_s on the crystal structure, microstructure and the piezoelectric performance were analyzed and documented.     

The microstructure and characteristics of 0.875PZT–0.125PMN ceramics with addition of Pb-based flux

The paper tries to prepare dense piezoceramics by way of reactive liquid phase sintering. Technique concerning a low-temperature sinterable process is developed by incorporating 4PbO.B₂O₃. The host system is a perovskite type piezoceramics, 0.875Pb(Ti,Zr)O₃–0.125Pb(Mg_1/3Nb_2/3)O₃. It is clear that PbO deficiency of PMN-based relaxor can result in an excessive amount of pyrochlore phase which causes poor densification and greatly degraded dielectric properties. Additives, such as the Pb-based flux, 4PbO·B₂O₃, that increase the amount of PbO also reduce the fraction of pyrochlore phase of PMN-based. If small amounts of 4PbO·B₂O₃ glass powder are added to the calcined 0.875PZT–0.125PMN ceramics, the liquid pase is formed during sintering. Hence, the piezoelectric and dielectric properties are enhanced and the sintering temperature can be reduced. Grain growth in ceramics with sintering time and amounts of 4PbO·B₂O₃ dopants was also studied. The grain growth was analyzed from the kinetic grain growth equation: Rⁿ=k×t.     

Characterization and X-ray peak broadening analysis in PZT nanoparticles prepared by modified sol–gel method

Lead zirconate titanate nanoparticles (PZT-NPs) were synthesized by a modified sol–gel method and were calcinated at temperatures of 600, 650 and 700 °C. Fourier transform infrared (FTIR), powder X-ray diffraction (XRD) and thermal analysis (TGA/DTA), indicate that single-phase perovskite PZT-NPs are obtained after heat treatment at a temperature of 650 °C. The TEM results obtained from the PZT-NPs confirm that the morphology of the PZT nanoparticles is spherical, with an average diameter size of 17 nm. We also investigated the crystallite development in the nanostructured PZT by X-ray peak broadening analysis. The individual contribution of many small crystallite sizes and lattice strains to the peak broadening in the PZT nanoparticles prepared at different temperatures were studied using Williamson–Hall (W–H) analysis in the range of 2θ = 15–80°.     

Evidence of macro–micro domain transition in poled PMN–PZT ceramics

The dielectric properties of unpoled and poled Pb_0.88Ba_0.06Sr_0.06(Mg_1/3Nb_2/3)_0.37Zr_0.375Ti_0.255O₃ (modified PMN–PZT) ceramics were investigated. It was found that the dielectric constant increased while the loss tangent decreased after poling. A frequency independent abrupt transition in the dielectric constant and loss tangent responses was observed for the poled ceramics. This abnormal behavior was believed to be correlated with the macro–micro domain transition and the corresponding pyroelectric measurement exhibited a narrow peak at the normal-relaxor transition temperature T_nr. Furthermore, the presence of double-loop-like hysteresis and two types of current peaks at a temperature slightly higher than T_nr showed another strong evidence of this transition.     

Phase,microstructure and ferroelectric properties of new complex-structured ferroelectric ceramics in the PZT–SBN system

This study aimed to fabricate and characterize new complex-structured ceramics with formula (1-x)Pb(Zr_0.52Ti_0.48)O₃–xSrBi₂Nb₂O₉ or (1-x)PZT–xSBN (where x=0, 0.1, 0.3 and 0.5 weight fraction). The ceramics were prepared by a solid-state mixed-oxide method and sintered at temperatures between 1000 and 1250 °C. Optimum sintering temperature for this system was found to be 1050 °C for 3 h dwell time. X-ray diffraction patterns of (1-x)PZT–xSBN powders showed peak intensities of two-phase mixture corresponding to the relative amount of each phase as a result of SBN addition. Microstructure of (1-x)PZT–xSBN ceramics showed a variation in grain shape and grain size. The small addition of SBN (x=0.1) was also found to improve ferroelectric properties of pure PZT ceramic.     

Effects of ZnO/Li2O codoping on microstructure and piezoelectric properties of low-temperature sintered PMN–PNN–PZT ceramics

Pb(Mg_1/3Nb_2/3)O₃–Pb(Ni_1/3Nb_2/3)O₃–Pb(Zr_1/2Ti_1/2)O₃ (designated as PMNT) piezoelectric ceramics codoping with Zn²⁺/Li⁺ were prepared and the effects of ZnO/Li₂O (Z/L) additive on microstructure, piezoelectric and dielectric properties were investigated. The results show that the pure perovskite phase is formed and the phase structure changes from tetragonal to rhombohedral with different Z/L weight ratios. The Curie temperature T_c, dielectric constant ?, electromechanical coupling factor k_p and piezoelectric constant d₃₃ decrease, whereas mechanical quality factor Q_m increases with Z/L weight ratio changing from 1:1 to 1:8. The optimized Z/L weight ratio is 1:1. It is revealed that k_p and d₃₃ first increase then decrease, whereas Q_m changes opposite with increasing content of Z/L additive. The PMNT ceramic with Z/L ratio 1:1 and the amount of 1 wt% has excellent piezoelectric properties: k_p = 0.60, d₃₃ = 397 pC/N, T_c = 251 °C, Q_m = 150, ? = 2628 and tan δ = 0.0296, when sintered at 960 °C. Finally, multilayer piezoelectric actuator is prepared using optimal composition by tape casting. The actuator shows the displacement characteristics of 3.3 μm under electric field 100 V/mm.     

低温烧结PZT–0.5%PbO·WO_3压电陶瓷

以固态氧化物为原料,采用一次合成工艺制备锆钛酸铅(leadzirconatetitanate,PZT)–0.5%PbOWO3压电陶瓷,研究摩尔比n(Zr)/n(Ti)、烧结温度对陶瓷性能的影响。结果发现:合成温度900℃保温2h可以得到钙钛矿结构压电陶瓷。n(Zr)/n(Ti)=1.08时,烧结温度为1100℃保温2h,压电陶瓷的综合性能在准同型相界处达最佳:介电常数ε3T3/ε0=1593,介电损耗tg?=0.019,压电系数d33=363.5×10-6C/N,机电耦合系数Kp=0.596,机械品质因数Qm=88.4。     

Shift of morphotropic phase boundary in high-performance fine-grained PZN–PZT ceramics

The fine-grained xPb(Zn_1/3Nb_2/3)O₃–(1 − x)Pb(Zr_0.47Ti_0.53)O₃ system has been prepared from submicron precursor powders obtained by high-energy ball milling method. The addition of PZN induces a decrease of grain size from an initial micron scale to a submicron scale, accompanying with the phase transition from tetragonal to morphotropic phase boundary (MPB), and then rhombohedral side. Interestingly, compared to the former published data for coarse-grained ceramic, the MPB has shifted from 50% to 30% PZN content side due to the enhancement of the internal stress for fine-grained ceramic. The enhanced electrical and mechanical performances are closely associated with the phase structure and grain size. A high piezoelectric property (d₃₃ = 380 pC/N and k_p = 0.49) as well as mechanical performance (H_v = 5.0 GPa and K_IC = 1.33 MPa m^1/2) were obtained simultaneously for the MPB 0.3PZN–0.7PZT ceramics with an average grain size of 0.65 μm.     

Effect of ZnO nano-particulate modification on properties of PZT–BLT ceramics

This research was conducted to study the effect of ZnO nano-particulate modification on properties of Pb(Zr_0.52Ti_0.48)O₃ (PZT)–(Bi_3.25La_0.75)Ti₃O₁₂ (BLT) ceramics prepared by a mixed-oxide solid-state sintering method. ZnO nano-particulate was added into PZT–BLT ceramics to obtain PZT–BLT/xZnO (x = 0, 0.1, 0.5 and 1.0 wt%). The PZT–BLT/xZnO ceramics were investigated in terms of phase, microstructure, physical, electrical, and mechanical properties. Tetragonality of PZT–BLT crystal structure tended to increase with increasing ZnO content. ZnO addition obviously increased the density of PZT–BLT ceramics while the grain size slightly decreased. Intergranular fracture mode was observed for pure PZT–BLT ceramic while the samples contained ZnO nano-particles showed a mixed-mode inter-/trans-granular fracture. Addition of ZnO also affected hardness and fracture toughness values. Addition of ZnO nano-particulate into PZT–BLT ceramics was found to improve room temperature dielectric constant but did not have a significant effect on ferroelectric properties. These observed results were expected to be caused by the behaviors similar to a donor-doped system.     

Effect of PMN modification on structure and electrical response of xPMN–(1−x)PZT ceramic systems

The structural and electrical properties of xPb(Mg_1/3Nb_2/3)O₃–(1−x)Pb(Zr,Ti)O₃ ternary ceramic system with the composition near to the morphotropic phase boundary (MPB) and of xPb(Mg_1/3Nb_2/3)O₃–(1−x)Pb(Zr_0.47Ti_0.53)O₃ ceramics were investigated as a function of the Pb(Mg_1/3Nb_2/3)O₃ (PMN) content by scanning electron microscopy (SEM), X-ray diffraction (XRD), dielectric and piezoelectric spectroscopy and polarization-electric field measurement technique. Studies were performed on the samples prepared by a columbite precursor method for x=0.125, 0.25 and 0.5. Room temperature SEM investigations revealed common trends in the grain structure with increasing PMN content. XRD analysis demonstrated that with increasing PMN content in xPb(Mg_1/3Nb_2/3)O₃–(1−x)Pb(Zr_0.47Ti_0.53)O₃, the structural change occurred from the tetragonal to the pseudocubic phase at room temperature. Changes in the dielectric and ferroelectric behavior were then related to these structural trends and further correlated with the piezoelectric properties. The results of ferroelectric hysteresis measurements, in conjunction with dielectric spectroscopy, demonstrated an intermediate, relaxor-like behavior between normal and relaxor ferroelectrics in the solid solution system, depending on the PMN content.     

Characterisation and modelling of CNT–epoxy and CNT–fibre–epoxy composites

Abstract

This research presents an experimental and theoretical investigation on the effects of carbon nanotube (CNT) integration within neat epoxy resin (nanocomposites) and a carbon fabric–epoxy composite (multiscale composites). An approach is presented for the prediction of mechanical properties of multiscale composites. This approach combines woven fibre micromechanics (MESOTEX) with the Mori-Tanaka model which was used for the prediction of mechanical properties of nanocomposites in this research. Nanocomposite and multiscale composite samples were manufactured using cast moulding, resin infusion, and hand lay-up process. The CNT concentrations in the composite samples were from 0 to 5 wt-%. The samples were characterised using tensile, shear and flexural tests. The discrepancy between the theoretical predictions and the experimental observations was hypothesised to be due to dispersion and bonding issues and SEM images are presented in support of the hypothesis.     

Electromechanical properties of [0 0 1]-textured Mn–PMN–PZT ceramics under uniaxial pressure

Dielectric, ferroelectric, and piezoelectric properties of both random and textured Mn–PMN–PZT ceramics were characterized under uniaxial stress. Textured ceramics exhibit a large piezoelectric response under uniaxial pressure; the bias field piezoelectric constant is higher than 700 pC/N when pressure is below 50 MPa. Moreover, textured ceramics also show better depolarization resistance under uniaxial stress fields; overall, 30% of the origin performance will remain when stress approaches 200 MPa, but for random ceramics, it is only 10%. The ferroelectricity of both random and textured ceramics is suppressed by uniaxial compression. E_c, P_r, E_i, and dissipation energy all decrease with increasing uniaxial stress. In addition, phase-field simulation was used to better understand the polarization-changing effects on piezoelectric and dielectric performance. The uniaxial stress causes polarization rotation and increases the angle between polarization and the electric field, which is an important factor leading to the increase of the dielectric constant.     

Synthesis and characterizations of BNT–BT and BNT–BT–KNN ceramics for actuator and energy storage applications

Dielectric and ferroelectric properties of 0.93Bi_0.5Na_0.5TiO₃–0.07BaTiO₃ (BNT–BT) and 0.93Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–0.01K_0.5Na_0.5NbO₃ (BNT–BT–KNN) ceramics were studied in detail. An XRD analysis confirmed the single perovskite phase formation in both the samples. Room temperature (RT) dielectric constant (ε_r) ~1020 and 1370, respectively at 1 kHz frequency were obtained in the BNT–BT and BNT–BT–KNN ceramics. Temperature dependent dielectric and the polarization vs. electric field (P–E) studies confirmed the coexistence of ferroelectric (FE) and anti-ferroelectric (AFE) phases in the BNT–BT and BNT–BT–KNN ceramics. Substitution of KNN into the BNT–BT system decreased the remnant polarization, coercive field and the maximum strain percentage. The energy storage density values ~0.485 J/cm³ and 0.598 J/cm³ were obtained in the BNT–BT and BNT–BT–KNN ceramics, respectively. High induced strain% in the BNT–BT ceramics and the high energy storage density in the BNT–BT–KNN ceramics suggested about the usefulness of these systems for the actuator and the energy storage applications, respectively.     

The preparation and properties of zirconia-doped Y–Si–Al–O–N oxynitride glasses and glass-ceramics

Two series (N-9 and N-18 series) of zirconia-doped Y–Si–Al–O–N oxynitride glasses and glass-ceramics were designed. Nominal compositions of the glass samples in equivalent percent (eq%) are xZr: (24–0.25x)Y: (15–0.25x)Al: (61–0.5x)Si: 91O: 9 N and xZr: (24–0.25x)Y: (15–0.25x)Al: (61–0.5x)Si: 82O: 18 N (x=0, 2, 4, 6), respectively. The obtained samples were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Densities, Vickers hardness, fracture toughness, glass transition temperature, and thermal expansion coefficient data were established for each sample. Effect of Zr and N content on glass network structure, thermal and mechanical properties was investigated. It was found that the addition of zirconia is effective in preparing Y–Si–Al–O–N oxynitride glasses with lower glass transition temperature and higher hardness.     

Colloidal Stability and Sintering of Yttria–Silica and Yttria–Silica–Alumina aqueous suspensions

The aim of this work was to produce dense yttrium silicate materials by slip casting, with more than 90% of Y₂SiO₅ phase. The rheological behaviour of concentrated aqueous slips was studied considering the effect of the dispersing additives, solids content and pH. The densification kinetics was examined as a function of temperature and time, and the reactions were analysed in the light of the equilibrium phase diagrams. Deflocculation of the slips was achieved by either an electrostatic mechanism using tetraethylammonium hydroxide, thus requiring a high concentration of base, and by a polyelectrolyte through an electrosteric mechanism, which provided more reliable results. In the binary system Y₂O₃–SiO₂, a very low grade of sintering was obtained at 1600°C. The use of alumina allows sintering through a liquid phase, reaching 90% theoretical density.     

Effects of CeO2 addition on the piezoelectric properties of PNW–PMN–PZT ceramics

Temperature stability and electrical properties of the piezoelectric material are very important in piezoelectric transformers applications. In this study, it was investigated the temperature stability of PNW–PMN–PZT with CeO₂ additives and the variation of Zr/Ti ratio. Meanwhile, effects of CeO₂ additives and the variation of Zr/Ti ratio on the microstructure and electrical properties of PNW–PMN–PZT were investigated in detail. The results revealed that the optimized temperature stability of Δf_r/f_r25 °C = 0.15%, ΔK_p/K_p25 °C = −0.86% and ΔQ_m/Q_m25 °C = −45.26% could be attained at x = 0.1 wt.% and Zr/Ti = 51/49. Moreover, optimized electrical properties were achieved: K_p = 0.60, Q_m = 1405, d₃₃ = 388 pC/N, ?_r = 2140 and tan δ = 0.0059. The obtained temperature stabilities and electrical properties make this composition a good candidate for high power piezoelectric transformer applications.     

Effect of annealing temperature on ferroelectric electron emission of sol–gel PZT films

In this work, the influence of annealing temperature on the ferroelectric electron emission behaviors of 1.3-μm-thick sol–gel PbZr_0.52Ti_0.48O₃ (PZT) thin film emitters was investigated. The results revealed that the PZT films were crack-free in perovskite structure with columnar-like grains. Increasing annealing temperature led to the growth of the grains with improved ferroelectric and dielectric properties. The remnant polarization increased slightly from 35.3 to 39.6 μC/cm² and the coercive field decreased from the 56.4 to 54.6 kV/cm with increasing annealing temperature from 600 to 700 °C. The PZT film emitters exhibited remarkable ferroelectric electron emission behaviors at the threshold voltage above 95 V. The film annealed at 700 °C showed a relatively lower threshold voltage and higher emission current, which is related to the improved ferroelectric and dielectric properties at higher annealing temperature. The highest emission current achieved in this work was around 25 mA at the trigger voltage of 160 V.     

Unique and contrasting mixed-metal lithium–calcium and lithium–barium hexamethyldisilazide complexes

Addition of lithium hexamethyldisilazide to calcium or barium bis(hexamethyldisilazide) in THF resulted in the synthesis of two unique but very different mixed-metal complexes: X-ray crystallography shows these to be, respectively, the heterobimetallic complex [Ca{N(SiMe₃)₂}₃Li(THF)] (1), containing two calcium–lithium bridging amide ligands and the remarkable co-crystalline compound [Ba{N(SiMe₃)₂}₂(THF)₃][Li₂{N(SiMe₃)₂}₂(THF)₂] (2).     

Synthesis and Characterization of Linear and Tri-Block PLLA–PEG–PLLA Blends

This study was conducted to synthesize poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) triblock copolymer (PEGLA) with different poly(L-lactide) block length, and explore its applicability in a blend with linear poly(L-lactide) (3051D NatureWorks) with the intention of improving heat seal and adhesion properties at extrusion coating on paperboard. Poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) was obtained by ring opening polymerization of L-lactide using poly(ethylene glycol) (molecular weight 6000 g mol^?1) as an initiator and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy. The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology and differential scanning calorimeter. All blends containing 10 wt% of PEGLAs displayed similar zero shear viscosities to neat poly(L-lactide), while blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity. However, all blends displayed higher shear thinning and increased melt elasticity (based on tan δ). No major changes in thermal properties were distinguished from differential scanning calorimetric studies. High molecular weight PEGLAs could be used in extrusion coating with 3051D without problems.