PZT ‘composite’ ferroelectric thick films

Thick-films of lead zirconate titanate ceramic have been fabricated at low-temperature using a modified sol-gel/ceramic powder technology termed the composite technique. In this process, a ferroelectric powder is suspended in an organometallic solution of the same composition, which is deposited either on metallic or platinised silicon substrates using spin-coating. Dielectric properties have been improved from values around 450–680 by incorporating a novel Cu₂O/PbO liquid-phase sintering aid. Rheology studies were carried out to monitor ageing of both the organometallic solution and composite suspension. Over a trial period of 41 days, the organometallic solution was shown to remain stable. Tests further indicated solution stability down to −20°C. Such low temperatures may be experienced during transportation in large-scale manufacturing. By modelling such thick films as 0–3 composites, it is known that electric properties are enhanced with greater powder:solution ratio. This necessary greater loading has been achieved by adjusting the pH of the organometallic solution, allowing the zeta-potential developed on suspended particles to be increased. This considerably lowers the viscosity of the composite suspension and hence allows much greater powder loading. In this way, loadings of up to 2.5 g/ml have been achieved. Optimum permittivities and losses in sintered films of up to 680 and 0.01 have been measured on films 16 μm thick, with associated spontaneous polarisation of 19.8 μC/cm² with 1.6 V/μm applied.     

Self-polarized ferroelectric PVDF homopolymer ultra-thin films derived from Langmuir–Blodgett deposition

It was found that Langmuir–Blodgett (LB) deposition process led to the direct formation of ferroelectric β phase in poly(vinylidene fluoride) (PVDF) homopolymer ultra-thin films, in which the molecular chains were parallel to the substrates and the dipoles were aligned perpendicular to the substrates. Theoretical analysis and experimental results further showed that the mechanism of forming the β phase and the dipole orientation were attributed to the hydrogen bonds formed between the PVDF molecules and water through the LB deposition. A large local effective piezoelectric coefficient (d_zz) of ?49.4 pm/V was observed in the self-polarized PVDF LB film.     

A phenomenological potential and ferroelectric properties of BaTiO3–CaTiO3 solid solution

A modified phenomenological potential was constructed for BaTiO₃-CaTiO₃ solid solution single crystal based on the Landau–Devonshire theory. The Ba_1−xCa_xTiO₃ solid solution phase diagram of temperature vs concentration (T-x) is obtained and shown to perfectly agree with experimental observations. Sustained Curie temperature can be obtained by the increase of Ca concentration x, while the transition temperatures from tetragonal to orthorhombic phase, and further to rhombohedral phase decrease with increasing Ca content. In this work, spontaneous polarization and dielectric constant dependence on concentration are studied and the relationship between hydrostatic pressure and transition temperatures is established to pave the way for the generation of temperature-concentration-pressure phase diagram.     

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.     

Multiscale study of ferroelectric–relaxor crossover in BaSnxTi1−xO3 ceramics

A systematic study of BaSn_xTi_1−xO₃ solid solutions (x = 0–0.20) by a combined field-induced dielectric and ferroelectric analysis with Raman and PFM investigations was realized, in order to obtain new insights concerning the composition-induced modification of the structural phase transitions and ferroelectric–relaxor crossover induced by the increase of Sn addition. The ceramics prepared via solid state reaction and sintering at 1400 °C/4 h showed average tetragonal symmetry for x ≤ 0.15 and cubic for x = 0.20. However, the dielectric and Raman analysis demonstrated that x = 0.05 and x = 0.15 are characterized by a coexistence of phases, which enhances their macroscopic properties (polarization for x = 0.05 and permittivity for x = 0.15). The domain structure shows a gradual modification when increasing Sn addition. No detectable domain structure has been found for x ≥ 0.15. All the compositions show local d₃₃(V) hysteresis loops at room temperature.     

Energy storage performance of BiFeO3–SrTiO3–BaTiO3 relaxor ferroelectric ceramics

Dielectric capacitors reveal great potential in the application of high power and/or pulsed power electronic devices owing to their ultrafast charge–discharge rate and ultrahigh power density. Among various dielectric capacitors, the environment-friendly lead-free dielectric ceramics have drawn extensive investigations in recent years. Nevertheless, the relatively small recoverable energy storage density (W_rec) is still an obstacle for their application. Herein, the (0.55−x)BiFeO₃–0.45SrTiO₃–xBaTiO₃ ternary ceramics with 0.1 wt% MnO₂ were prepared by the solid-state reaction, and achieved enhanced relaxor behavior as well as breakdown strength E_b. As a result, the x = 0.12 ceramic exhibited superior comprehensive energy storage performance of large E_b (50.4 kV/mm), ultrahigh W_rec (7.3 J/cm³), high efficiency η (86.3%), relatively fast charge–discharge speed (t_0.9 = 6.1 μs) and outstanding reliability under different frequency, fatigue, and temperature, indicating that the BiFeO₃-based relaxor ferroelectric ceramics are prospective alternatives for electrostatic energy storage.     

Phase formation,dielectric and ferroelectric properties of CaxBa1−xNb2O6 ceramics

Lead-free Ca_xBa_1?xNb₂O₆ (CBN, 0.20≤x≤0.35) ceramics were prepared by the conventional solid state method. Effects of Ca content on the phase formation, microstructure, dielectric and ferroelectric properties for the prepared CBN ceramics were systematically studied. XRD results showed that pure CBN phase with tungsten bronze structure could be obtained from the solid solutions of BaNb₂O₆ and CaNb₂O₆ in all ceramics. Higher Ca contents favored the occurrence of grains with anisometric morphology, but no abnormal grain growth could be found in all compositions. With the increase of x, Curie temperature T_c shifted downward, whereas the maximum dielectric constant ε_m increased initially and then decreased. All the ceramics showed an intermediate relaxor-like behavior between normal and ideal relaxor ferroelectrics according to the modified Curie–Weiss law. Normal ferroelectric hysteresis loops were observed in all compositions. Both remnant polarization P_r and coercive field E_c increased initially and then decreased with the increase of x. The ceramics with homogeneous microstructure, high density and better properties were obtained at x=0.28 with ε_m=2998, T_c=234 °C, P_r=3.98 μC cm^?2 and E_c=14.03 kV cm^?1.     

Optical modulation and magnetic transition in PbTi1−xPdxO3−δ ferroelectric thin films

The PbTi_1−xPd_xO_3−δ (xPTPO) thin films prepared by chemical solution deposition have been investigated by means of structural characterizations, optical and magnetic measurements. X-ray diffraction patterns show that all the films have a pseudotetragonal perovskite structure, but also exhibit a lattice dilatation behavior and increased internal strain as the x increases. A possible mechanism for strain-induced structural evolution is discussed. Raman scattering further corroborates this change in average structure, where the characteristic variation of phonon modes, indirectly reveal the incorporation of Pd²⁺ ions into host lattice. Transmittance spectra analysis indicates that Pd doping has a key effect on the energy band structure. The optical bandgap of xPTPO films decreases significantly with increasing Pd content, expressed by (3.5–9.0x) eV (0≤x≤0.09). Also, magnetic switching driven by doping has been confirmed in the films, which is attributed to the competition between ferromagnetic and paramagnetic/antiferromagnetic components.     

Dielectric properties and related ferroelectric domain configurations in multiferroic BiFeO3–BaTiO3 solid solutions

Dielectric properties and ferroelectric domain configurations of multiferroic xBaTiO₃–(1 ? x)BiFeO₃ (x = 0.10–0.33) solid solutions synthesized by conventional solid-state reaction, were reported. A structural transition from rhombohedral to pseudo-cubic structures appeared around x = 0.33, and the formation of impurity phase of Bi₂Fe₄O₉ was effectively depressed by doping BaTiO₃. Dielectric constants of xBaTiO₃–(1 ? x)BiFeO₃ solid solutions decreased with increasing the frequency, and the degree of decrease was related to the doping content of BaTiO₃. Transmission electron microscopy images revealed that the ferroelectric domain configurations in the multiferroic BiFeO₃–BaTiO₃ solid solutions with rhombohedral symmetry, exhibited a wavy character whereas a predominant intricate domain structure with fluctuating mottled contrast was observed in the multiferroic BiFeO₃–BaTiO₃ solid solution with pseudo-cubic phase structure. The presence of 1/2{1 1 1} superlattice spots in the selected area electron diffraction patterns taken from the multiferroic BiFeO₃–BaTiO₃ solid solutions with rhombohedral symmetry indicated that the ordered regions have a doubled perovskite unit cell.     

Structure–property relations of ferroelectric BaTiO3 ceramics containing nano-sized Si3N4 particulates

Barium titanate/silicon nitride (BaTiO₃/xSi₃N₄) powder (when x = 0, 0.1, 0.5, 1 and 3 wt%) were prepared by solid-state mixed-oxide method and sintered at 1400 °C for 2 h. X-ray diffraction result suggested that tetragonality (c/a) of the BaTiO₃/xSi₃N₄ ceramics increased with increasing content of Si₃N₄. Density and grain size of BaTiO₃/xSi₃N₄ ceramic were found to increase for small addition (i.e. 0.1 and 0.5 wt%) of Si₃N₄ mainly due to the presence of liquid phase during sintering. BaTiO₃ ceramics containing such amount of Si₃N₄ also showed improved dielectric and ferroelectric properties.     

Phase structure and energy storage performance for BiFeO3–BaTiO3 based lead-free ferroelectric ceramics

Recently, BiFeO₃–BaTiO₃ (BF-BT) lead-free ferroelectric ceramics have been widely concerned and deemed as one of the most promising candidates for lead-free energy-storage material because of their high spontaneous polarization and excellent energy storage properties. Herein, a series of Bi_1-zLa_zFeO₃-xBaTiO₃+yMnO₂ (BL_zF-xBT-yMn at 0.45 ≤ x ≤ 0.60 mol, 0.0 ≤ y ≤ 0.4% mol and z = 0 or 0.02 mol) ceramics were prepared to reveal their energy-storage performance. With increasing x, the breakdown strength (BDS) increases, while the maximum polarization (P_max), remanent polarization (P_r), and the difference value between P_max and P_r (ΔP) decrease. Because of the high BDS and ΔP, a large energy storage density W_re = 1.08 J/cm³ is achieved in BF-0.48BT ceramics as the electric field is 130 kV/cm. In addition, with increasing y and z, the increasing BDS and ΔP have been observed. Due to the improvement in BDS and ΔP, an excellent W_re = 1.22 J/cm³ was achieved in Bi_1-zLa_zFeO₃-xBaTiO₃+yMnO₂ ceramics at x = 0.48, y = 0.3% and z = 0.02. This work provides the clue for application of the high-power-energy BF-BT ceramics.     

Clamping of ferroelectric PVDF to enhance the electromechanical performance of a 1–3 PMN-PT/PVDF piezoelectric composite

A group of 1–3 type piezoelectric Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃/polyvinylidene fluoride (PMN-PT/PVDF) composite sheets are prepared using a complex two-step hot-pressing method. Then the molecular structure model of piezoelectric materials and an inverse piezoelectric simulation of the composites are performed to express the horizontal compression, indicating the clamping activity of ferroelectric PVDF on PMN-PT. As such, this composite sheet possesses a high dielectric permittivity (ε_r) of 560 at 100 Hz for its compacted connecting of two phases. After polarization, a very large piezoelectric coefficient (d₃₃) of 1125 pC/N and a considerable electromechanical coupling factor (k_t) of 0.43 is obtained in PMN-PT/PVDF sheet with a proper aspect ratio of 1.4 and a thickness of 2.1 mm, further indicating that promoting effect of PVDF matrix on the strain in Z-direction of PMN-PT. The result shows that ferroelectric PVDF serving as polymer matrix favors the electromechanical coupling effect, and may provide a prospect of the potential application of PMN-PT/PVDF composite in sensor or transistor for matrix ultrasonic probes.     

Dielectric and ferroelectric hysteresis properties of 1–3 lead magnesium niobate–lead titanate ceramic/Portland cement composites

In this work, lead magnesium niobate–lead titanate (PMN–PT) ceramic was cut and filled with Portland cement (PC) to produce 1–3 connectivity PMN–PT/PC composites. Dielectric and ferroelectric hysteresis properties of these composites with PMN–PT ceramic volume content of 60% were investigated. Room temperature dielectric constant (?_r) at 1 kHz of the PMN–PT/PC composite was found to be ≈1500. At higher frequency (20 kHz), the dielectric constant was reduced to the value of ≈1300. Ferroelectric (polarization–electric field) hysteresis loops at 10–90 Hz and varying electric field were measured. The “instantaneous” remnant polarization (P_ir) at 50 Hz and at the electric field of 7 kV/cm of the PMN–PT/PC composite was found to be ≈10 μC/cm². These values of 1–3 composites therefore are promising when compared to previous results of composites at similar conditions.     

Investigation on ferromagnetic and ferroelectric properties of (La,K)-doped BiFeO3–BaTiO3 solid solution

Multiferroic materials of BiFeO₃–BaTiO₃ solid solution have been fabricated in order to improve ferromagnetic and ferroelectric properties. The effects of La (1 mol%) and K (varied from 0.5–5 mol%) doped 0.75BiFeO₃–0.25BaTiO₃ on phase formation, ferromagnetic and ferroelectric properties have been investigated and discussed. The rhombohedral perovskite phase of specimens was characterized by XRD technique. Fracture morphology reveals the grain growth characteristics with increasing K content. (La, K)-doped 0.75BiFeO₃–0.25BaTiO₃ with La=1 mol% and K=3 mol% exhibits the highest remnant polarization and remnant magnetization.     

Reversible ferroelectric phase transition of 1,4-diazabicyclo [2,2,2]octane N,N′-dioxide di(perchlorate)

1,4-Diazabicyclo [2,2,2]octane N,N′-dioxide di(perchlorate), C₆H₁₄N₂O₂^2 +·2ClO₄⁻, was synthesized and separated as colorless block crystals. Differential scanning calorimetry detected that this compound underwent a reversible phase transition at ca. 216 K with a hysteresis of 5.5 K width, which was also confirmed by dielectric measurements. Single crystal X-ray diffraction data suggested that there was a transition from a room temperature phase with the space group of P2₁/c (a = 6.815(7) Å, b = 12.644(13) Å, c = 8.676(9) Å, β = 101.466(15)°, V = 732.7(13) ų, Z = 4) to a low temperature one with a space group of P2₁ (a = 9.892(8) Å, b = 12.559(10) Å, c = 17.401(13) Å, β = 92.065(8)°, V = 2160(3) ų, Z = 2). Crystallographic analysis showed that it belonged to chiral space group P2₁ with ferroelectric behaviors, and a typical ferroelectric feature of electric hysteresis loop was obtained in the low temperature phase. The disorder-order transformation of H₂-Dabcodo^2 + cation and ClO₄⁻ anion as well as the change of hydrogen bonds may drive the phase transition.     

Structural,dielectric and ferroelectric properties of Ba1−x(Bi0.5Na0.5)xTiO3 ceramics

Lead free Ba_1?x(Bi_0.5Na_0.5)_xTiO₃ (x=0, 0.02, 0.04, 0.06, 0.08, 0.1) ferroelectric ceramics were synthesized by conventional solid state reaction technique. Sintering was done at 1200 °C for 2 h in air atmosphere. The final products have tetragonal symmetry with decreasing c/a ratio confirmed by X-ray diffraction analysis. The grain size varies between 300 nm to 1000 nm for x=0 to 0.1. With increase in Bi_0.5Na_0.5TiO₃ [BNT] content, the room temperature permittivity decreases whereas the Curie temperature (T_c) increases and its highest value was found to be 155 °C for 10 mol% of BNT addition. The ceramics show stable and low dielectric loss characteristics. The remnant polarization (P_r) and the coercive field (E_c) increases monotonously with increase in BNT content. The highest value of 2P_r (=17 μC/cm²) and 2E_c (=22 Kv/cm) was obtained for x=10 mol% BNT addition.     

High- and low-field dielectric responses and ferroelectric properties of (Bi0.5Na0.5)Zr1−xTixO3 ceramics

Bismuth sodium zirconate titanate (Bi_0.5Na_0.5)Zr_1?xTi_xO₃ with (x=0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) ceramics was fabricated by a conventional sintering technique at 850–1000 °C for 2 h. From X-ray diffraction study, three regions of different phases were observed in the ceramic system; i.e., orthorhombic phase region (0≤x≤0.2), mixed-phase region (0.3≤x≤0.4), and rhombohedral phase region (0.5≤x≤0.6). It was observed that the phase evolution from orthorhombic to rhombohedral symmetry resulted in a noticeable increase of the dielectric properties. The results from the high- and low-field dielectric responses indicated that the dielectric properties of both BNZ and BNZT ceramics were dominantly attributed to the reversible contribution. It was also noticed that grain size showed only partial influence on the increase of low-field dielectric constant in Ti-rich BNZT ceramic.     

Dielectric,energy storage,and charge–discharge properties of Yb-modified Sr0.7Bi0.2TiO3 relaxor ferroelectric ceramic

Dielectric capacitors have been widely studied in advanced electronics systems due to their rapid discharge rate and high-power density. Among them, relaxor ferroelectrics characterized by nanodomains possess broad application prospects as dielectric materials with high energy density and high efficiency. In this paper, the dielectric characteristics, energy storage performance, and charge–discharge behavior of rare-earth Yb-doped Sr_0.7Bi_0.2TiO₃ ceramics are systematically investigated. The Yb-doped SBT ceramics reduced the grain size, improved the insulation and thermal conductivity, and significantly improved the dielectric breakdown strength. Finally, a high recoverable energy density of 2.32 J/cm³ and an excellent energy storage efficiency of 92.2% were obtained at 300 kV/cm. In addition, pulsed charge–discharge tests show that Sr_0.7Bi_0.15Yb_0.05TiO₃ possesses a rapid discharge rate and high-power density with superior thermal stability. Based on these outstanding characteristics, Sr_0.7Bi_0.15Yb_0.05TiO₃ exhibits promising applications in pulsed power systems.     

Phase transition behavior and electrical properties of lead-free (Bi0.5K0.5)TiO3–LiNbO3 relaxor ferroelectric ceramics

(1?x)(Bi_0.5K_0.5)TiO₃–xLiNbO₃ ((1?x)BKT–xLN) lead-free relaxor ferroelectric ceramics were prepared by a conventional solid-state route and their phase transition behavior and the corresponding electrical properties were investigated. A morphotropic phase boundary separating rhombohedral and tetragonal phases was identified in the composition range of 0.015<x<0.03, where the improved electrical properties of piezoelectric constant d₃₃=75 pC/N and electromechanical coupling factor k_p=0.18 were obtained. Moreover, all samples show typical relaxor behavior characterized by the presence of diffuse phase transition and frequency dispersion. It was found that the dielectric relaxation behavior of BKT ceramics can be obviously enhanced with the addition of LN. In addition, the effect of the LN addition on the ferroelectric properties was also investigated by measuring polarization versus electric field hysteresis loops.