Structure‐property relationships in BiScO3–PbTiO3–PbMg1/3Nb2/3O3 ceramics near the morphotropic phase boundary

The phase structure, dielectric, ferroelectric, and piezoelectric properties of (1?2x)BiScO₃–xPbTiO₃–xPbMg_1/3Nb_2/3O₃ ceramics (x = 0.30‐0.46) were studied. It was found that an increase in x leads to a structural phase transition between the rhombohedral and tetragonal phase via an intermediate monoclinic phase and to a crossover from the nonergodic relaxor state to the ferroelectric one. It was proposed that at x > 0.42 the phase transition changes from second to first order. The assumption about the existence of a tricritical point on the phase diagram at x ≈ 0.42 with the enhanced dielectric response has been made. The observed structure‐property relationships of the studied solid solutions are discussed. It is shown that the solid solutions with x = 0.42 are characterized by the high piezoelectric parameters (d₃₃ = 509 pC/N, d₃₁ = ?178 pC/N, d_h = 153 pC/N), which makes possible their applications in sonar equipment.     

Structural and Electrical Characteristics of (1−x)Pb(Lu1/2Nb1/2)O3–xPbTiO3 Ceramics with Low PbTiO3

A solid solution of (1?x)Pb(Lu_1/2Nb_1/2)O₃–xPbTiO₃ with composition of 0.01 ≤ x ≤ 0.08 have been prepared successfully. XRD analysis indicates the crystal structure adopts an orthorhombic (O) phase in 0.01 ≤ x ≤ 0.06 interval and becomes the coexistence of O and rhombohedral (R) phase at x = 0.07, then turns into R phase mostly at x = 0.08. In addition, two sets of superlattice reflections due to B‐site ordering and antiparallel cation displacement are distinguished by XRD and the superstructures which arise from antiparallel cation displacement disappear gradually with the increasing x. The grain size increases gradually with the increasing x, and then becomes the bimodal microstructure at x ≥ 0.06 due to the coexistence of O and R phase. The dielectric spectra exhibit Curie temperature decreases from 248°C to 147°C with increasing x from 0.01 to 0.08. As 0.01 ≤ x ≤ 0.04, the samples display typical double hysteresis loops, suggesting antiferroelectric nature, then turn into ferroelectric gradually at x = 0.05. Finally, it exhibit typical ferroelectric hysteresis loops in 0.06 ≤ x ≤ 0.08 interval.     

Dielectric and ferroelectric properties of lanthanum‐modified lead zirconate stannate titanate (42/40/18) ceramics

The effect of lanthanum (La) content on the phase transformation of Pb_1?3x/2La_x(Zr_0.42Sn_0.40Ti_0.18)O₃ (PLZST 100x/42/40/18, 0 ≤ x ≤ 0.06) ceramics was investigated by the dielectric and ferroelectric properties. The base composition PLZST 0/42/40/18 located in the ferroelectric (FE) rhombohedral phase region. As x increased, the compositions showed successively FE and antiferroelectric (AFE) state at room temperature, and their peak temperatures (T_max) decreased gradually in line as T_max = 162.21‐1507x. Evidence was presented that there were two dielectric anomalies in PLZST 2/42/40/18, which were corresponding to the FE‐AFE and AFE‐paraelectric (PE) phase transformations, respectively. With increasing the dc bias fields, the two phases merged into one. PLZST 3/42/40/18 showed AFE characteristics with the first loop outside of the second loop and there was only one dielectric inflection. The critical lanthanum content occurred at x = 0.03 from the dielectric temperature spectra and hysteresis loops. Furthermore increase in La above 0.03, these compositions showed typical antiferroelectric behaviors with double hysteresis loops. The stored energy properties of the three compositions (PLZST 4/42/40/18, 5/42/40/18 and 6/42/40/18) displayed different temperature dependencies from room temperature to 140°C (over their respective T_max). Comparing the above results with previous investigations on PLZSTs, some questions were discussed.     

Giant electromechanical strain response in lead‐free SrTiO3‐doped (Bi0.5Na0.5TiO3–BaTiO3)–LiNbO3 piezoelectric ceramics

Lead‐free 0.985[(0.94?x)Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–xSrTiO₃]–0.015LiNbO₃ [(BNT–BT–xST)–LN, x=0‐0.05] piezoelectric ceramics were prepared using a conventional solid‐state reaction method. It was found that the long‐range ferroelectric order in the unmodified (BNT–BT)–LN ceramic was disrupted and transformed into the ergodic relaxor phase with the ST substitution, which was well demonstrated by the dramatic decrease in remnant polarization (P_r), coercive field (E_c), negative strain (S_neg) and piezoelectric coefficient (d₃₃). However, the degradation of the ferroelectric and piezoelectric properties was accompanied by a significant increase in the usable strain response. The critical composition (BNT–BT–0.03ST)–LN exhibited a maximum unipolar strain of ~0.44% and corresponding normalized strain, S_max/E_max of ~880 pm/V under a moderate field of 50 kV/cm at room temperature. This giant strain was associated with the coexistence of the ferroelectric and ergodic relaxor phases, which should be mainly attributed to the reversible electric‐field‐induced transition between the ergodic relaxor and ferroelectric phases. Furthermore, the large field‐induced strain showed relatively good temperature stability; the S_max/E_max was as high as ~490 pm/V even at 120°C. These findings indicated that the (BNT–BT–xST)–LN system would be a suitable environmental‐friendly candidate for actuator applications.     

Thermal stability and electric‐field‐induced strain behaviors for PIN‐PSN‐PT piezoelectric ceramics

Pb (In_1/2Nb_1/2) O₃‐Pb (Sc_1/2Nb_1/2) O₃‐PbTiO₃ (PIN‐PSN‐PT) ternary ceramics with compositions near morphotropic phase boundary (MPB) were fabricated by solid‐state‐sintering process. Dielectric and piezoelectric properties of xPIN‐yPSN‐zPT (x = 0.19, 0.23 and z = 0.365, 0.385) ceramics were investigated as a function of temperature, showing high T_r‐t and T_c on the order of 160 ~ 200°C and 280 ~ 290°C, respectively. The xPIN‐yPSN‐0.365PT (x = 0.19 and 0.23) ceramics do not depolarize at the temperature up to 200°C, showing a better thermal stability when compared to the state‐of‐the‐art relaxor‐PbTiO₃ systems. A slight variation (<9%) of k_p, k_t, and k₃₃ was observed in the temperature range of 25°C‐160°C for xPIN‐yPSN‐0.385PT (x = 0.19 and 0.23) ceramics. Rayleigh analysis was employed to quantify the contribution of domain wall motion to piezoelectric response, where the domain wall contribution was found to increase with composition approaching MPB for PIN‐PSN‐PT system.     

Pressure-driven phase transition and energy conversion in ferroelectrics: Principles,materials, and applications

The pressure-driven explosive energy-conversion (EEC) effect of ferroelectric (FE) materials has been extensively studied in scientific research and high-tech applications owing to its high pulse-power output capability. The fundamental principle of this effect is pressure-driven phase transition and depolarization in FE materials, accompanied by discharging behavior from the charge release upon pressure loading. Pb(Zr,Ti)O₃ has been an excellent example of a materials exhibiting these properties. However, recent investigations have been focused on developing other lead-based or lead-free materials with a higher energy-storage ability and better temperature stability. In this article, we review the recent progress achieved in the past decades on different types of lead-based and lead-free ceramics, single crystals, and multilayer films, based on their unique pressure-driven phase transition and energy-conversion properties. Their pulse power discharging performance under actual shock-wave compression is also summarized, followed by a detailed discussion of the failure mechanism under shock-wave compression. Finally, several issues and perspectives are proposed for future investigation in this area. All these not only assist in the design of new materials for high-performance EEC but are also helpful for the practical application of these promising materials in pulse-power technologies.     

Enhanced pyroelectric properties in (Bi0.5Na0.5)TiO3–BiAlO3–NaNbO3 ternary system lead‐free ceramics

High pyroelectric performance and good thermal stability of pyroelectric materials are desirable for the application of infrared thermal detectors. In this work, enhanced pyroelectric properties were achieved in a new ternary (1?x)(0.98(Bi_0.5Na_0.5)(Ti_0.995Mn_0.005)O₃–0.02BiAlO₃)–xNaNbO₃ (BNT–BA–xNN) lead‐free ceramics. The effect of NN addition on the microstructure, phase transition, ferroelectric, and pyroelectric properties of BNT–BA–xNN ceramics were investigated. It was found that the average grain size decreased as x increased to 0.03, whereas increased with further NN addition. The pyroelectric coefficient p at room temperature (RT) was significantly increased from 3.87 × 10^?8Ccm^?2K^?1 at x = 0 to 8.45 × 10^?8Ccm^?2K^?1 at x = 0.03. The figures of merit (FOMs), F_i, F_v and F_d, were also enhanced with addition of NN. Because of high p (7.48 × 10^?8Ccm^?2K^?1) as well as relatively low dielectric permittivity (~370) and low dielectric loss (~0.011), the optimal FOMs at RT were obtained at x = 0.02 with F_i = 2.66 × 10^?10 m/V, F_v = 8.07 × 10^?2 m²/C, and F_d = 4.22 × 10^?5 Pa^?1/2, which are superior to other reported lead‐free ceramics. Furthermore, the compositions with x ≤ 0.03 exhibited excellent temperature stability in a wide temperature range from 20 to 80°C because of high depolarization temperature (≥110°C). Those results unveil the potential of BNT–BA–xNN ceramics for infrared detector applications.     

NaNbO3‐BaTiO3‐NaSbO3 lead and potassium‐free ceramics with thermally stable small‐signal piezoelectric properties

A new lead‐potassium‐free ceramic of (0.9‐x)NaNbO₃‐0.1BaTiO₃‐xNaSbO₃ (NN‐BT‐xNS) was successfully prepared via a solid‐state reaction method. The microstructure, phase structure, dielectric, ferroelectric, and piezoelectric properties were investigated as a function of NS content. The substitution of NS for NN was found to dramatically change the grain morphology from cube‐like grains typical for alkaline niobate‐based ceramics to conventional sphere‐like grains especially for Pb‐based perovskite ceramics. A normal to relaxor ferroelectric phase transformation was accompanied by a tetragonal (T) to rhombohedral (R) phase transition. A composition‐temperature phase diagram demonstrated a vertical morphotropic phase boundary between T and R phases in the composition range of x=0.03‐0.04, where optimum electrical properties of d₃₃=252 pC/N, k_p=36%, Q_m=168, =2063, and T_c=109°C were obtained in the x=0.035 ceramic sintered at 1260°C. Particularly, excellent temperature insensitivity of small‐signal piezoelectric properties suggested large application potentials in various actuators and sensors in comparison with other typical lead‐free materials.     

Structural phase transition and electrical properties of Sr2+ substituted porous PMN‐PZT ceramics

In this study, Sr²⁺ modified porous PMN‐PZT ceramics with one‐dimensional pore channels were produced by the ionotropic gelation process of alginate/PMN‐PZT suspensions. The ion‐exchange method was employed during the fabrication procedure to adjust the content of SrO addition. With the SrO addition increasing from 1.653 wt.% to 2.957 wt.%, the structural phase of porous PMN‐PZT ceramics transformed from rhombohedral (R) to tetragonal (T) perovskite phase. Accordingly, the electromechanical coupling coefficient (k_t) value of porous PMN‐PZT ceramics decreased from 64.7% to 58.7%, while the hydrostatic figure of merit (HFOM) value increased from 1510 to 5547 × 10^?15 m²/N, and acoustic impedance Z value ranged from 4.59 to 7.55 MRayls, which helped for applications in underwater transducers or hydrophones.     

Structure development and dielectric properties of Zn-doped Pb([Mg,Fe],W)O3 perovskite ceramics

Ceramic samples of a pseudo-binary system Pb(Mg_1/2W_1/2)O₃-Pb(Fe_2/3W_1/3)O₃ (PMW-PFW) were prepared by solid-state reaction. In addition, their compositions were modified by 20 mol% Pb(Zn_1/2W_1/2)O₃ (PZW) doping in order to investigate the role of zinc in the perovskite formation and dielectric properties. The perovskite contents were ≥95.1% at the overall composition range, except for a significantly low value of 79.0% at 0.8PFW-0.2PZW. The extension of sintering time for PMW accelerated superstructure formation, resulting in the ordering factor increased up to 0.40 after 12 hours heat treatment. The maximum dielectric constant values increased with increasing PFW fractions. In comparison, the phase transition temperatures decreased sharply (by up to 161°C) at low concentrations of PFW, followed by mild changes (by up to 47°C) afterward. The dielectric constant spectra were analyzed in terms of diffuseness characteristics, which reflected the phase transition modes quite well.     

Mn- and Mn/Cu-doped PIN-PMN-PT piezoelectric ceramics for high-power transducers

The effects of acceptor doping with manganese as either MnO₂ or MnNb₂O₆ (MnN) with CuO on the dielectric, ferroelectric, and piezoelectric properties of PIN-PMN-PT ceramics were investigated. The 2% MnNb₂O₆-doped PIN-PMN-PT (6Pb(Mn_1/3Nb_2/3)O₃-25Pb(In_1/2Nb_1/2)O₃-34Pb(Mg_1/3Nb_2/3)O₃-35PbTiO₃) ceramics possessed hard properties such as high coercive field (E_C) of 11.7 kV/cm, low dielectric loss (tan δ) of 0.7%, and high electromechanical quality factor (Q_M) of 1011. These properties were diminished in MnO₂-doped ceramics because of lower oxygen vacancy defect concentration, and exaggerated grain growth resulted in >20 µm grain size. Co-doping with 2 mol% MnNb₂O₆ and 0.5 mol% CuO retained hardened properties such as high E_C of 9.6 kV/cm, low tan δ of 0.6%, and high Q_M of 1029. MnNb₂O₆-doped and MnNb₂O₆ + Cu co-doped ceramics display excellent figures of merit for resonance and off-resonance applications as well as high energy conversion efficiencies which make them promising candidates for high-power transducer elements.     

Submicron crystalline buildup and size‐dependent energy harvesting characteristic in PZN–PZT ternary ferroelectrics

Piezoelectric energy harvester converts low‐frequency vibrational energy in the environment into electrical energy, enabling the purpose of self‐supplying power for low‐energy consumption devices. The key to miniaturizing energy harvester is the buildup of the submicron‐grained ceramic with a high transduction coefficient (d×g), which is still a big challenge from a technical point of view. In this work, the popular ternary system of Pb(Zn_1/3Nb_2/3)O₃–Pb(Zr_0.5Ti_0.5)O₃ (PZN–PZT) has been selected as objective compound, and the submicron‐grained ceramics were prepared by a combination of high‐energy ball milling and pressureless sintering technology. The results revealed that nanocrystalline PZN–PZT powders can be synthesized by one step mechanochemical route without the calcination stage. Using these nanopowders as precursors, dense ceramics with different grain size have been prepared through tailoring the sintering temperature. The study of size‐dependent energy harvesting characteristic evidenced an optimum transduction coefficient of 7980×10^?15 m²/N was obtained for 950°C sintered specimen, which has uniform microstructure with mean grain size of 0.33 μm. In the mode of the cantilever‐type energy harvester constructed by this material, the output power at low frequency of 89 Hz was as high as 69 μW at an acceleration of 10 m/s², showing the suitability for piezoelectric generators harvesting environmental vibrational energy.     

Ferroelectric and magnetic properties in (1−x)BiFeO3–x(0.5CaTiO3–0.5SmFeO3) ceramics

Multiferroic ceramics were prepared and characterized in (1?x)BiFeO₃–x(0.5CaTiO₃–0.5SmFeO₃) system by a standard solid‐state reaction process. The structure evolution was investigated by X‐ray diffraction and Raman spectrum analyses. The refinement results confirmed the different phase assemblages with varying amounts of polar rhombohedral R3c and nonpolar orthorhombic Pbnm as a function of the substitution content. In the compositions range of 0.2≤x≤0.5, polar R3c and nonpolar Pbnm coexisted, which was referred to polar‐to‐nonpolar morphotropic phase boundary (MPB). According to the dielectric and DSC analysis results, the ceramics with x≤0.2 changed to diffused ferroelectric, and the ferroelectric properties were enhanced significantly. Two dielectric relaxations were detected in the temperature range of 200‐300 K and 500‐700 K, respectively. The high‐temperature dielectric relaxation was attributed to the grain‐boundary effects. While the low temperature dielectric relaxation obtained in the samples with x=0.3‐0.5 was related to the charge transfer between Fe²⁺ and Fe³⁺. The magnetic hysteresis loops measured at different temperature indicated the enhanced magnetic properties in the present ceramics, which could be attributed to the suppressed cycloidal spin magnetic structure by Ti ions. In addition, the rare‐earth Sm spin moments might also affect the magnetic properties at relatively lower temperature.     

MC Type Phase Structure and Temperature‐Induced MC‐C Transition in the As‐Grown PMN‐0.36PT Single Crystal

The phase structure in the as‐grown PMN‐0.36PT single crystal was studied and the temperature‐induced domain evolution was investigated using a polarized light microscope (PLM). The crystal is identified to be M_C type monoclinic based on the PLM results and tends to transform to cubic (C) phase directly through polarization rotation. The M_C phase is metastable below Curie temperature (T_C), but prone to tetragonal phase upon electric field poling or high‐temperature annealing. We suppose that the formation of the M_C phase structure is associated with the strain gradient originated from Ti⁴⁺ segregation and the special M_C‐C phase transformation style is mediated by the corresponding residual ferroelastic strain stored within the as‐formed domain structure.     

A critical phenomenon of phase transition in hydroxyapatite investigated by thermally stimulated depolarization currents

We observed a critical phenomenon of ferroelectric transition in hydroxyapatite (HAp) through measuring the thermally stimulated depolarization current of polycrystalline monoclinic HAp. Two peaks attributable to hydroxide (OH^?) ion dipole reorientations were observed. The one was very sharp, the other displayed a broad peak ranging from 350 to 550 K. While the broad peak can be attributed to the diffusive reorientation motions of OH^? ion dipoles, the sharp peak, related to the ferroelectric phase transition, implies the presence of ferroelectricity in HAp. The sharp peak was found near 380 K, the phase‐transition temperature from the monoclinic to hexagonal is ascribed to a critical phenomenon caused by the ferroelectric behavior of OH^? ion dipole reorientations.     

Enhanced electrical properties and strong red light‐emitting in Eu3+‐doped Sr1.90Ca0.15Na0.9Nb5O15 ceramics

The luminescent‐ferroelectic materials based on Sr_1.90Ca_0.15Na_0.9Nb₅O₁₅ (SCNN) matrix doping with Eu³⁺ were synthesized by the conventional solid‐state reaction method. The crystal structure, photoluminescence, thermal stability, dielectric, ferroelectric, and piezoelectric behaviors were systematically investigated. XRD results revealed that Eu³⁺ introduction could induce the tungsten bronze phase transition from orthorhombic to tetragonal structures. The dielectric spectra of all specimens showed two broad dielectric anomalies: a high‐temperature ferroelectric phase transition (T_c) and a low‐temperature ferroelastic phase transition (T_s), both of which were suppressed at higher Eu³⁺ concentrations. The enhanced electrical properties were obtained in a proper Eu³⁺ concentration range of 0.03‐0.05. For all SCNN:xEu³⁺ samples, the strong red emission peak at 617 nm originating from the electric dipole transition of ⁵D₀ →⁷F₂ was excited by different light excitations of 395 or 463 nm. Our results demonstrated that Eu³⁺‐doped SCNN materials might have promising potential in advanced multifunctional optoelectronic applications.     

Defect‐driven evolution of piezoelectric and ferroelectric properties in CuSb2O6‐doped K0.5Na0.5NbO3 lead‐free ceramics

Defect greatly affects the microscopic structure and electrical properties of perovskite piezoelectric ceramics, but the microscopic mechanism of defect‐driven macroscopic properties in the materials is not still completely comprehended. In this work, K_0.5Na_0.5NbO₃+x mol CuSb₂O₆ lead‐free piezoelectric ceramics were fabricated by a solid‐state reaction method and the defect‐driven evolution of piezoelectric and ferroelectric properties was studied. The addition of CuSb₂O₆ induces the formation of dimeric (DC1) and trimeric (DC2) defect dipoles. At low doping concentration of CuSb₂O₆ (0.5‐1.0 mol%), DC1 and DC2 coexist in the ceramics and harden the ceramics, inducing a constricted double P‐E loop and high Q_m of 895 at x=0.01. However, DC2 becomes more dominant in the ceramics with high concentration of CuSb₂O₆ (≥1.5 mol%) and thus leads to softening behavior of piezoelectricity and ferroelectricity as compared to the ceramic with x=0.01, giving a single slanted P‐E loop and relatively low Q_m of 206 at x=0.025. All ceramics exhibit relatively high d₃₃ of 106‐126 pC/N. Our study shows that the piezoelectricity and ferroelectricity of K_0.5Na_0.5NbO₃ ceramics can be tailored by controlling defect structure of the materials.     

Superior ferroelectric properties and enhanced depolarization temperature simultaneously achieved in BNT-based ceramics

Bi_0.5Na_0.5TiO₃-based ceramics with high remnant polarization P_r have shown outstanding potential in the application of high-power ferroelectric transducers. However, low depolarization temperature T_d is an obstacle for their application. Here, a composition design strategy was proposed to simultaneously improve the T_d and P_r in BNT-based materials. Ultrahigh P_r of 40.56 µC/cm² and relative high T_d of 184°C were synergistically achieved in (Bi_0.5Na_0.5)(Ti_0.995Mn_0.005)O₃ (BNMT) ceramics by adding 1.0 mol% BiGaO₃ (BG), which is superior to other reported lead-free systems. The excellent ferroelectric properties were attributed to strengthen ferroelectric order as evidenced by increased rhombohedral distortion. Meanwhile, the enhanced depolarization temperature, increasing from 168°C for x = 0% to 184°C for x = 1.0%, can be ascribed to the suppression of the thermal-induced ferroelectric-relaxor phase transition by adding BG. Those results enable the BNMT-BG systems ceramics to be an attractive candidate for application in high-power supplies.     

Investigation of MnO2‐doped (Ba,Ca)TiO3 lead‐free ceramics for high power piezoelectric applications

x% mol MnO₂‐doped Ba_0.925Ca_0.075TiO₃ ceramics (abbreviated as BCT‐Mnx, x=0‐1.5) were synthesized by conventional solid‐state reaction method. The effects of MnO₂ addition and (Ba+Ca)/Ti mole ratio (A/B ratio) on the microstructure and electrical properties of the ceramics were investigated. The internal bias filed E_i was determined from the asymmetrical polarization hysteresis loops and found to increase with the doping concentration of MnO₂. High mechanical quality factors (Q_m>1200) and low dielectric loss (tanδ<0.5%) were found in the BCT‐Mn0.75 and BCT‐Mn1.0 ceramics with E_i>3 kV/cm, meanwhile, the piezoelectric and electromechanical properties were found to decrease compared with the pure BCT, exhibiting a typical characteristic of “hard” behavior. Of particular interest is that the microstructure of BCT‐Mn0.75 ceramics could be controlled by changing the A/B ratio, where enhanced piezoelectric coefficient d₃₃ on the order of 190 pC/N was obtained in the BCT‐Mn0.75 ceramics with A/B=1.01 due to its fine‐grained microstructure, with yet high Q_m, being on the order of 1000. The high d₃₃ and Q_m in MnO₂‐doped BCT ceramics make it a promising candidate for high power piezoelectric applications.     

Effects of phase transition on discharge properties of PLZST antiferroelectric ceramics

The effects of electric field‐induced phase transition on discharge properties of Pb_0.94La_0.04[(Zr_0.52Sn_0.48)_0.84Ti_0.16]O₃ antiferroelectric (AFE) ceramics were investigated. Due to the forward phase transition, high polarization and energy density are achieved. The backward phase transition results in nonlinear increase of current in underdamped circuit. The stored charge (14.2 μC under 40 kV/cm at 22°C) can be released completely in very short duration due to the low remanent polarization. With increasing temperature, the polarization and releasable energy decline. However, the current amplitude reaches maximum at 40°C, which is attributed to the backward phase transition. The maximum current and power density are as high as 143.8 A/cm² and 2.4 MW/cm³, which indicates the potential of the ceramics for pulsed capacitors.