Structural origin of size effect on piezoelectric performance of Pb(Zr,Ti)O3

Grain size effect plays a vital role in piezoelectric performance from both scientific and technological view. However, the underlying structural mechanism related to grain size is still unclear. In the present study, the structural mechanism of grain size effect on piezoelectric performance has been revealed in the prototype Pb(Zr,Ti)O₃ system by using in-situ synchrotron X-ray diffraction. The miniaturization of grain size tends to favor the appearance of higher symmetric tetragonal phase, while a single monoclinic phase is determined in the coarse-grained ceramics. The direct structural evidence reveals that both tetragonal and monoclinic phases in the fine-grained ceramics are less sensitive to the electric field, corresponding to the inferior piezoelectric performance, while the single monoclinic phase in the coarse-grained ceramics is more active to be driven by the electric field, generating good piezoelectric behavior. Both domain switching ability and lattice strain are suppressed with decreasing grain size, which directly leads to the deterioration in piezoelectric performance. The current results will benefit the structural understanding of the size effect of piezoelectric and other related systems.     

Effects of addition of Pb(Y1/2Nb1/2)O3 (PYN) on microstructure and piezoelectric properties of Pb(Zr0.53Ti0.47)O3

Pure and Pb(Y_1/2Nb_1/2)O₃ (PYN)-doped Pb(Zr_0.53Ti_0.47)O₃ have been characterized. The samples were prepared by conventional mixed-oxide ceramic technology. PYN dopant was added to PZT at content levels ranging from 1 to 2.5 mol%. The microstructures of the samples were examined using SEM and TEM. The average grain size was observed to decrease as the dopant content increased. Herringbone-like and wedge-shaped domain patterns were observed in all the samples. The piezoelectric properties of PZT were greatly improved by the addition of PYN. The highest piezoelectric constant d₃₁ was nearly twice that of pure PZT.     

Pb(Zr0.53Ti0.47)O3陶瓷超细粉体制备及分散研究

用化学共沉淀法合成了陶瓷Pb(Zr0.53Ti0.47)O3超细粉体,以聚乙二醇(PEG)为分散剂对所得粉体进行分散。通过X衍射、扫描电镜分析,研究了合成条件和煅烧温度对PZT粉体性能的影响。结果表明,随着煅烧温度的升高,PZT超细粉晶化度提高,一次晶粒尺寸增加,而二次粒子尺寸却减小。当分散剂分子量为10000,用量为1%时,得到分散良好的超细粉体。测定了用合成的粉体烧结的PZT陶瓷的压电性能。     

Softening-hardening transition of electrical properties for Fe3+-doped (Pb0.94Sr0.05La0.01)(Zr0.53Ti0.47)O3 piezoelectric ceramics

Fe³⁺-doped (Pb_0.94Sr_0.05La_0.01)(Zr_0.53Ti_0.47)O₃ (PSL(ZT)_1-x-Fe_x) piezoelectric ceramics were prepared by the solid-state reaction method and with a variation of the Fe³⁺ content. When the Fe³⁺ content was less than 0.010, the ceramics exhibited the features of soft piezoelectric ceramics with a large remnant polarization (P_r) of 35.7 μC/cm², a large bipolar strain of 0.22% and a high piezoelectric coefficient (d₃₃) of 412 pC/N. The number of oxygen vacancies increased and the domain walls were pinned by the defect diploes with a further increase of the Fe³⁺ content. Meanwhile, the PSL(ZT)_1-x-Fe_x ceramics showed typical hard behavior and the mechanical quality factor Q_m was as high as 500. The softening-hardening transition of electrical properties was also systematically analyzed by adjusting the oxygen vacancies, the space charges and the difference between the unipolar strain and the value of d₃₃×E.     

Domain wall-grain boundary interactions in polycrystalline Pb(Zr0.7Ti0.3)O3 piezoceramics

Interactions between grain boundaries and domain walls were extensively studied in ferroelectric films and bicrystals. This knowledge, however, has not been transferred to polycrystalline ceramics, in which the grain size represents a powerful tool to tailor the electromechanical and dielectric response. Here, we relate changes in dielectric and electromechanical properties of a bulk polycrystalline Pb(Zr_0.7Ti_0.3)O₃ to domain wall interactions with grain boundaries. Samples with grain sizes in the range of 3.9–10.4 μm were prepared and their microstructure, crystal structure, and dielectric/electromechanical properties were investigated. A decreasing grain size was accompanied by a reduction in large-signal electromechanical properties and an increase in small-signal relative permittivity. High-energy diffraction analysis revealed increasing microstrains upon decreasing the grain size, while piezoresponse force microscopy indicated an increased local coercive voltage near grain boundaries. The changes in properties were thus related to strained material volume close to the grain boundaries exhibiting reduced domain wall dynamics.     

Effect of pore size and porosity on piezoelectric and acoustic properties of Pb(Zr0.53Ti0.47)O3 ceramics

We studied the effect of porosity and pore morphology on the functional properties of Pb(Zr_0.53Ti_0.47)O₃ (PZT) ceramics for application in high frequency ultrasound transducers. By sintering a powder mixture of PZT and polymethylmetacrylate spherical particles (1.5 and 10?μm) at 1080°C, we prepared ceramics with ～30% porosity with interconnected micrometer sized pores and with predominantly ～8?μm spherical pores. The acoustic impedance was ～15?MRa for both samples, which was lower than for the dense PZT. The attenuation coefficient α (at 2.25?MHz) was higher for ceramics with ～8?μm pores (0.96?dB?mm^??1?MHz^??1), in comparison to the ceramic with smaller pores (0.56?dB?mm^??1?MHz^??1). The high α value enables the miniaturisation of the transducer, which is crucial for medical imaging probes. The dielectric and piezoelectric coefficients, polarisation, and strain response decreased with increased porosity and decreased pore/grain size. We suggest a possible role of pore/grain size on the switching behaviour.     

Effects of LiF addition on microstructure and dielectric properties of CaCu3Ti4O12 ceramics

The effects of small amounts of lithium fluoride sintering aid on the microstructure and dielectric properties of CaCu₃Ti₄O₁₂ (CCTO) ceramics were investigated. CCTO polycrystalline ceramics with 0.5 and 1.0 mol% LiF, and without additive were prepared by solid state synthesis. Good densification (>90% of the theoretical density) was obtained for all prepared materials. Specimens without the sintering aid and sintered at 1090 °C exhibit secondary phases as an outcome of the decomposition reaction. The mean grain size is controlled by the amount of LiF in specimens containing the additive. Impedance spectroscopy measurements on CaCu₃Ti₄O₁₂ ceramics evidence the electrically heterogeneous nature of this material consisting of semiconductor grains along with insulating grain boundaries. The activation energy for grain boundary conduction is lower for specimens prepared with the additive, and the electric permittivity reached 53,000 for 0.5 mol% LiF containing CCTO.     

Effect of Samarium substitution on dielectric properties of (Pb)(Zr, Ti, Fe, Nb)O3 type ceramic system

The influence of Samarium substitution on the dielectric properties of modified PZT composition with representative formula [Pb_1−xSm_xZr_0.588Ti_0.392Fe_0.01Nb_0.01O₃] system is reported. Samarium (Sm) was varied from 0 to 0.01/FU in the present system in a step of 0.0025. The samples were prepared by the traditional solid state reaction process. XRD analysis showed all the samples to be single phase with tetragonal structure. Dielectric properties were studied in detail as a function of frequency and temperature (from room temperature (RT) 30 to 400 °C). All compositions show phase transition and the transition temperature (T_C) is found to decrease with increase in Sm substitution. Room temperature dielectric constant shows an increasing trend while loss improves with Sm doping.     

Effect of MnO2 on the microstructure and electrical properties of 0.83Pb(Zr0.5Ti0.5)O3-0.11Pb(Zn1/3Nb2/3)O3-0.06Pb(Ni1/3Nb2/3)O3 piezoelectric ceramics

A sample of 0.83Pb(Zr_0.5Ti_0.5)O₃-0.11Pb(Zn_1/3Nb_2/3)O₃-0.06Pb(Ni_1/3Nb_2/3)O₃ (PZNNT) to which MnO₂ was added, with a high mechanical quality factor (Q_m) and a good transduction coefficient (d₃₃×g₃₃), were systematically investigated. Based on the SEM analysis there existed two kinds of “secondary phases”, Rich Ti and Rich Zn phases, which arose due to the B-site substation of PZNNT-based ceramics by manganese ions. One phase was due to the Mn³⁺ replacing the Ti⁴⁺ to create oxygen vacancies and induce the hardening effect. Another phase was due to the Mn²⁺ replacing the Zn-site to stabilize the perovskite phase. When the addition of MnO₂ reached the solubility limit of 1.5 mol% in the PZNNT-based ceramics, the sample showed optimal electrical properties (Q_m=357, d₃₃×g₃₃=9859 × 10⁻¹⁵ m²/N, k_p=0.56), which suggested its potential application for piezoelectric energy harvesting in larger field excitation environments.     

Grain size engineered (Ba,Sr)(Zr,Ti)O3 ceramics with excellent energy storage properties for high-voltage pulsed capacitors

The macroscopic physical properties of functional ceramics are strongly affected by grain morphology, almost resulting from the sintering process. For a given ceramic material, it has been experimentally confirmed that the enhancement of dielectric breakdown strength E_b can largely increase energy storage density (W). An effective method to increase E_b of ceramic materials is the control of grain morphology. Herein, the (Ba_0.95Sr_0.05)(Zr_0.2Ti_0.8)O₃ ceramics have been intensively investigated by different sintering techniques to improve grain morphology. Compared with single-step sintering, two-step sintering can sharply inhibit grain growth and make size distribution uniform, which is conducive to the increase in the E_b. A competitive energy storage capacity can be achieved with a high W_ch of 3.78 J/cm³, a high W_di of 3.50 J/cm³, and a high η of 92.6% by two-step sintering due to large E_b of 350 kV/cm, accompanied with good thermal stability till to 160 °C and good fatigue characteristics up to 10⁵ cycles, indicating that two-step sintering is an effective strategy of engineering grain morphology.     

Grain size tailoring and enhanced energy storage properties of two-step sintered Nd3+-doped AgNbO3

AgNbO₃ as a lead-free antiferroelectric material, has received widespread attention in recent years due to its promising application in the aspects of energy storage devices. However, the high remnant polarization and low breakdown strength limits its energy storage properties. In this work, Nd³⁺-doped AgNbO₃ (Ag_1−3xNd_xNbO₃, x=0−0.015) ceramics were prepared and a two-step sintering method was employed. The introduction of Nd³⁺ leads to the enhanced stability of the antiferroelectric phase, refined grain size and increased resistivity. Furthermore, by adjusting the pre-heating temperature in the two-step sintering, the homogeneity of microstructure is improved and the resistance of pre-heated samples increases by one order of magnitude compared with normally sintered samples, leading to the enhanced breakdown strength. Ag_0.97Nd_0.01NbO₃ pre-heated at 1100 °C for 2 h exhibits promising energy storage properties, with a recoverable energy storage density of 3.2 J/cm³ and energy efficiency of 52 % under an applied electric field of 210 kV/cm.     

Microstructures,piezoelectric properties and energy harvesting performance of undoped (K0.5Na0.5)NbO3 lead-free ceramics fabricated via two-step sintering

Piezoelectric energy harvesters have become increasingly popular in the field of green energy because of the ability to convert low-frequency environmental vibrations into usable electricity. To fabricate high-performance energy harvesters, the key requirements are piezoelectric ceramics with a small grain size, of near-full density, the intended stoichiometric ratio and a high transduction coefficient. In this work, the effects of two-step sintering on the sinterability, microstructure, piezoelectric properties and energy harvesting performance of (K_0.5Na_0.5)NbO₃ were systematically investigated. Compared with conventional single-step sintering, two-step sintering samples were of higher density, increasing from 91 % to 95 % of theoretical, reduced mean grain size, down from 17 μm to 7.5 μm, and decreased evaporation of the alkali metals. This translated into an improved piezoelectric performance (d₃₃ ∼122 pC/N, k_p ∼36 % and Q_m ∼76), a higher transduction coefficient and energy conversion efficiency as well as a higher open-circuit voltage and power density. This demonstrates the potential of two-step sintering as a high through-put sintering technique for moderate-performance, pure KNN ceramics.     

Structure,dielectric properties of novel Ba(Zr,Ti)O3 based ceramics for energy storage application

(1-x) Ba(Zr_0.2Ti_0.8)O₃-x Na_0.5Bi_0.5TiO₃ (x = 0, 10, 20 30, 40, 50 mol%) (BZTN) ceramics are prepared by the traditional solid phase method. All BZTN ceramics exhibit a pseudo-cubic BZT based perovskite structure. Both the average grain size and the relaxor ferroelectricity of BZTN ceramics gradually increase with increasing NBT content. The W_rec of 3.22 J/cm³ and η of 91.2% is obtained for the BZTN40 ceramic at 241 kV/cm. BZTN40 ceramic also exhibits good temperature stability from room temperature to 150 °C and frequency stability from 1 Hz to 100 Hz. A P_D of 0.621 J/cm³ and a t_0.9 of 82 ns is obtained for the BZTN40 ceramic at 120 kV/cm. BZTN ceramics show application potential in energy storage and pulse power capacitors.     

Piezoelectric properties of (1-x)BZT-xBCT system for energy harvesting applications

In this study, we investigated (1-x)Ba(Zr_0.2Ti_0.8)O₃–x(Ba_0.7Ca_0.3)TiO₃ lead-free piezoelectric ceramics for energy harvester applications. The (1-x)BZT-xBCT ceramic is a promising lead-free piezoelectric material in the field of piezoelectric energy harvesting. Piezoelectric and energy properties of (1-x)BZT-xBCT ceramics were analyzed to confirm the possibility of using them as energy-harvesting materials. Especially, the vicinity of the phase convergence region was investigated to improve their piezoelectric properties. In the phase convergence region, cubic, rhombohedral, orthorhombic, and tetragonal regions co-exist within the narrow region. Near the phase transition region between the orthorhombic and tetragonal phase, the highest piezoelectric property d₃₃?=?464 pC/N and the highest energy density of 158.5 μJ/cm³ were observed. This output energy density of 158.5 μJ/cm³ is the recorded highest value among lead-free ceramics. We found that the optimal sintering temperature was 1475?°C and the optimal composition was BZT-0.5BCT.     

Microstructure and electric properties of Pr-doped Pb(Zr0.52Ti0.48)O3 ceramics

Improving the piezoelectric activity of lead zirconate titanate (PZT) ceramics is of great importance for practical applications. In this study, the influence of Pr³⁺ doping on the ferroelectric phase composition, microstructure, and electric properties on the A-site of (Pb_1-1.5xPr_x)(Zr_0.52Ti_0.48)O₃ is extensively investigated. A dense and fine microstructural sample is obtained with the introduction of Pr³⁺. The results show that the morphotropic phase boundary (MPB) moves to the rhombohedral phase region. The rhombohedral and tetragonal phases exhibit an ideal coexistence in the 4 mol.% Pr³⁺ doped (PPZT4) samples. Lead vacancy and the reduction of the potential energy barrier are considered to be the key mechanisms for donor doping, which is upheld by the Pr³⁺ doping. Combining the I-E hysteresis loops with the P-E hysteresis loops, it becomes apparent that both contribution maximums of the domain switching and residual polarisation are in PPZT4. Moreover, the thermal aging resistance of PZT is improved by doping, and the temperature stability is optimised from 83% in PZT to 96% in PPZT4. Hence, an appropriate amount of Pr³⁺ doping can effectively improve the piezoelectric activity of PZT ceramics in the MPB area and optimise the performance stability of the material under application temperatures.     

Anisotropy of the high-power piezoelectric properties of Pb(Zr,Ti)O3

Piezoceramics are widely-used in high-power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three-stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high-power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase. Piezoceramics are widely-used in high-power applications, whereby the material is driven in the vicinity of the resonance frequency with high electric fields. Evaluating material's performance at these conditions requires the consideration of inherent nonlinearity, anisotropy, and differences between individual vibration modes. In this work, the relation between electromechanical properties at large vibration velocity and the utilized vibration mode is investigated for a prototype hard piezoceramic. The nonlinear behavior is determined using a combined three-stage pulse drive method, which enables the analysis of resonant and antiresonant conditions and the calculation of electromechanical parameters. The deviations of coupling coefficients, compliances, and piezoelectric coefficients at high-power drive were found to be strongest for the transverse length vibration mode. Differences in the mechanical quality factors were observed only between the planar and transverse length modes, which were rationalized by the different strain distribution profiles and the contribution of different loss tensor components. In addition, the influence of the measurement configuration was investigated and a correction method is proposed. The differences between vibration modes are further confirmed by heat generation measurements under continuous drive, which revealed that the strongest heat generation appears in the radial mode, while transverse and longitudinal length modes show similar temperature increase.     

Enhancing low-temperature energy harvesting by lead-free ferroelectric Ba(Zr0.1Ti0.9)O3

The energy-harvesting ability of the lead-free ferroelectric Ba(Zr,Ti)O₃ was investigated and greatly enhanced using the Kim novel electrothermodynamic cycle for low-temperature application. Ba(Zr,Ti)O₃ was synthesized with a Zr:Ti ratio of 10:90 (BZT10) by hot-press sintering, which exhibited a mix relaxor-ferroelectric behavior. For power generation using the Kim cycle with low and high temperatures of T_L = 25°C, T_H = 120°C, the most optimized temperature pattern occurred for a heating time of 12.5 s and a cooling time of 22.5 s. Under these conditions, the electric field increased during the novel isodisplacement process, and the displacement variation in the isoelectric step reached the highest value and maximized the BZT10 cycle loop area. Applying these conditions while lowering T_L to 20°C, an energy density N_D = 504 mJ/cm³ was achieved. This value is the highest obtained energy density in a practical test for lead-free ferroelectric bulk material in the BaTiO₃ family.     

Enhanced dielectric loss of Mg doped Ba0.7Sr0.3TiO3 ceramics

The effect of MgO doping on the structural, microstructural and dielectric properties of Ba_0.7Sr_0.3TiO₃ (BST) ceramic from the point of view of its application in microwave tunable devices has been studied. All the samples crystallize into perovskite structure. There is significant reduction in the value of loss factor with the increase in Mg-level, the dielectric constant and tunability are also reduced with the increase in Mg-level. Interestingly, the Fig. of merit of the material is found to be enhanced with increase of Mg-doping. The observed dielectric properties are explained on the basis of defect chemistry involved when Mg is doped in Ba_0.7Sr_0.3TiO₃ ceramics. The effect of dc field on the dielectric constant and the dielectric breakdown strength of the paraelectric phase Mg doped BST ceramic samples are also studied.     

Improved energy storage properties of Sr(Zr0.8Nb0.16)O3-doped Bi0.47Na0.47Ba0.06TiO3 ceramics with excellent temperature/frequency stability

Lead-free perovskite dielectric materials for capacitors have received wide concern in recent years, but their energy storage density and efficiency still cannot meet the growing application demand for practical applications. In this work, we prepared a lead-free relaxor ferroelectric ceramic of (1-x)Bi_0.47Na_0.47Ba_0.06TiO₃-xSr(Zr_0.8Nb_0.16)O₃, which was synthesized via a normal solid-state route. The microstructure, dielectric properties and energy storage behavior of the ceramics were explored. The ceramics can be well sintered and situated in the region where rhombohedral and tetragonal phases coexist. The addition of Sr(Zr_0.8Nb_0.16)O₃ (SZN) significantly extends the dielectric-temperature plateau between T_s and T_m and reduces the remnant polarization P_r, but the large saturation polarization P_s is still maintained. Besides, the doping of SZN enhances the relaxation of the material and increases the dielectric breakdown strength (DBS) from 50 kV/cm (x = 0) to 100 kV/cm (x = 0.04 and 0.06). Therefore, the ceramic with x = 0.06 exhibits a high discharging efficiency (η) of 71.1% and energy density (W) of 1.56 J/cm³ at 100 kV/cm and shows the superior thermal stability with the changes in recoverable energy density (W_rec) and η of less than 10% and 30% at the temperature range of 25–180 °C and the excellent frequency stability with the variations of W_rec and η of less than 1.8% and 1% at the frequency range of 10 Hz–100 Hz.