Phase transition behavior of Pb(Hf,Sn, Ti,Nb)O3 ceramics at morphotropic phase boundary

The phase transition and dielectric properties of Pb_0.988(Hf_0.945Sn_xTi_0.03-xNb_0.025)O₃ ceramics (0 ≤ x ≤ 0.03, correspondingly abbreviated as H1, H2, H3, and H4) at the morphotropic phase boundary were systematically investigated. X-ray diffraction results and P-E hysteresis loops show that the dominate orthorhombic antiferroelectric phase and a small amount of the tetragonal FE phase coexist in Pb_0.988(Hf_0.945Sn_xTi_0.03-xNb_0.025)O₃ ceramics. As the Sn content increases, the antiferroelectricity is significantly enhanced, accompanied with an increased Curie temperature and sharply reduced peak dielectric constant. H1 and H2 experience an irreversible field-induced AFE-FE phase transition at the ambient temperature, and the transition from a metastable FE phase to the original AFE phase is observed in H2 when heated to 60°C. H3 and H4 experience an invertible AFE-FE phase transition, along with an enhanced forward phase switching field E_F. Moreover a decreased backward phase switching field E_A for H4 is detected as the electric field increases due to the AFE/FE coexistence. These results reveal the unique phase transition characteristics of AFE materials near the phase boundary, which is helpful for better understanding of AFE/FE materials.     

Antiferroelectric‐ferroelectric phase transition in lead‐free AgNbO3 ceramics for energy storage applications

The high‐energy storage density reported in lead‐free AgNbO₃ ceramics makes it a fascinating material for energy storage applications. The phase transition process of AgNbO₃ ceramics plays an important role in its properties and dominates the temperature and electric field dependent behavior. In this work, the phase transition behavior of AgNbO₃ ceramics was investigated by polarization hysteresis and dielectric tunability measurements. It is revealed that the ferrielectric (FIE) phase at room temperature possesses both ferroelectric (FE)‐like and antiferroelectric (AFE)‐like dielectric responses prior to the critical AFE‐FE transition point. A recoverable energy storage density of 2 J/cm³ was achieved at 150 kV/cm due to the AFE‐FE transition. Based on a modified Laudau phenomenological theory, the stabilities among the AFE, FE and FIE phases are discussed, laying a foundation for further optimization of the dielectric properties of AgNbO₃.     

Systematical investigation on energy-storage behavior of PLZST antiferroelectric ceramics by composition optimizing

Featured with high polarization and large electric field-induced phase transition, PbZrO₃-based antiferroelectric (AFE) materials are regarded as prospective candidates for energy-storage applications. However, systematical studies on PbZrO₃-based materials are insufficient because of their complex chemical compositions and various phase structures. In this work, (Pb_0.94La_0.04)(Zr_1-x-ySn_xTi_y)O₃ (abbreviated as PLZST, 0 ≤ x ≤ 0.5, 0.01 ≤ y ≤ 0.1) AFE system was selected and the energy-storage behavior was regulated. It is found that low Ti content benefits to obtain satisfactory electric breakdown strength, realizing high energy-storage density. With Sn content increasing, the electric hysteresis decreases gradually, which is beneficial to improve energy conversion efficiency. As a result, a large recoverable energy-storage density of 9.6 J/cm³ and a high energy conversion efficiency of 90.2% were achieved in (Pb_0.94La_0.04)(Zr_0.49Sn_0.5Ti_0.01)O₃ ceramic. This work reveals energy-storage behavior of PLZST AFE materials systematically, providing reference for performance tailoring and new material designing in energy-storage applications.     

Stress Effects on Stabilizing Antiferroelectric Phase in Multilayer Ceramics

Controllable phase transformation between antiferroelectric (AFE) and ferroelectric (FE) states suggests multifunctional properties valuable for many device applications. Compared to AFE bulk ceramics with large voltage required for driving electric field‐induced phase transition, implementation of structures comprising multiple thin AFE ceramic layers can realize applications by reducing the switching operation voltage in the feasible range. Here, it is found that a compressive residual stress is developed in multilayer (Pb_0.97,La_0.02)(Zr_0.66,Sn_x,Ti_0.34?x)O₃ (PLZST) ceramic co‐fired with multiple Pd/Ag electrode layers, and the compressive residual stress can stabilize AFE phase. AFE phase forms in the PLZST multilayer ceramic with composition corresponding to FE in the bulk materials. Thermodynamic analysis based on free energy of FE and AFE phases well explains the FE to AFE phase transformation observed in the multilayer ceramic under the compressive stress. The findings exhibit a new strategy to tune structure and functional properties of multilayer ceramics through stress engineering for achieving device applications.     

Structure evolution and electric-field-induced reversible transition in perovskite Na(Nb1−xTax)O3 ceramics

Na(Nb_1−xTa_x)O₃ binary solid-solution ceramics with high quality were fabricated by conventional solid-state sintering routes for improving the electric(E)-field-induced irreversible polarization and transition behaviors of NaNbO₃. The studied results confirm that this binary solid-solution ceramics exhibit orthorhombic Pbcm space group companying with reduced unit-cell volume at x ≤ 0.4, and orthorhombic Pbnm space group at x = 0.5. As the Ta⁵⁺ content increases in the binary solid-solutions, the E-field-induced irreversible antiferroelectric → ferroelectric (AFE → FE) transition becomes reversible at x ≥ 0.2, giving rise to double-polarization hysteresis; the key E-fields triggering both irreversible and reversible transitions (E_F) increase in general. In particular, the E-field-induced FE phase at x = 0.15 is unstable upon unloading E-field to zero, which can return to AFE phase with time lapse. At x = 0.5, the Curie temperature (T_C) of AFE shifts to below room temperature, but E-field-induced reversible transition is still observed, which results in a nonlinear polarization with the lowest hysteresis and contributes to the largest energy-storage density. This transition is not due to the AFE ↔ FE transition but rather to the order ↔ disorder behavior of polar clusters or/and nanoregions within nonpolar Pbnm structure matrix.     

Re-entrant ferroelectric relaxor phenomena in the (1 − x)[Bi1/2(Na1/2K1/2)1/2TiO3]-xPbZrO3 system

The solid solution (1 − x)[Bi_1/2(Na_1/2K_1/2)_1/2TiO₃]-xPbZrO₃, (0.00 ≤ x ≤ 0.12) was investigated to examine the phase equilibria, dielectric and electromechanical properties. The composition corresponding to x = 0.00 exhibits tetragonal symmetry with the expected classical ferroelectric (FE) behavior. The system exhibited FE to relaxor crossover with the addition of lead zirconate at the composition x = 0.05. This is indicated by typical relaxor characteristics such as a transition to the global pseudocubic phase, a constriction in the FE hysteresis loop, and a sudden decrease in the negative strain accompanied by an increase in maximum strain. Most notably, with a further increase in x (>0.05), there is evidence for a return to a FE phase that exhibits classical FE characteristics. The combined results demonstrate that there exists a narrow FE-relaxor boundary near x = 0.05, where FE and relaxor phases coexist. At the critical composition, enhancement in the piezoelectric properties, including an increase in the effective (350 pm/V) was observed. This transition in the electromechanical properties is consistent with changes observed in the phase equilibria for this solid solution. The crystal structure transitions from tetragonal symmetry for x = 0.00, to pseudocubic symmetry for the relaxor compositions (x = 0.05), and finally to a lower symmetry perovskite phase for the re-entrant FE phase (x> 0.05). This composition-induced transition from FE to relaxor to a re-entrant FE state in the (1 − x)[Bi_1/2(Na_1/2K_1/2)_1/2TiO₃]-xPbZrO₃ system is unusual among relaxor FE systems and thus is of great scientific and technological interest.     

Metastable Ferroelectric Phase Induced by Electric Field in xPb(Zn1/3Nb2/3)O3–(1–x)Pb(Zr0.95Ti0.05)O3 Ceramics

A xPb(Zn_1/3Nb_2/3)O₃–(1–x)Pb(Zr_0.95Ti_0.05)O₃ (xPZN–(1–x) PZT) system close to antiferroelectric–ferroelectric (AFE–FE) morphotropic phase boundary has been prepared and investigated. The XRD results reveal PZN addition induces a phase transition from the orthorhombic (AFE) to rhombohedral (FE) phase through a phase coexistence region (AFE+FE). The polarization–electric field (P–E) measurements indicate that the AFE phase can be induced into a metastable FE (FE_m) phase. And the FE_m can recover to AFE around a critical temperature indicated by temperature‐dependent P–E loops. A composition‐temperature phase diagram was generalized within a certain range of PZN content in which an AFE–FE phase boundary connecting orthorhombic antiferroelectric to rhombohedral ferroelectric phase zones is formed near room temperature.     

Effect of lanthanum content on the conduction behaviors and relaxation processes of lead lanthanum zirconate titanate antiferroelectric ceramics

(Pb_1-xLa_x) (Zr_0.92Ti_0.08)_1-x/4O₃ (PLZT x/92/8, x = 3, 5 and 7 at%) ceramics with compositions near the antiferroelectric (AFE)-ferroelectric (FE) phase boundary were fabricated by a solid-state reaction method. The effect of lanthanum content on the conduction behaviors and relaxation processes has been investigated. It was verified that the main phase with orthorhombic structure was formed in all compositions. The increase of lanthanum substitution resulted in an enhancement of diffuse phase transition. Impedance analysis suggested that the ac conductivity decreased with increasing lanthanum content. Moreover, thermally stimulated depolarization current study was utilized to establish the correlation between defect structures and relaxation processes. It showed three peaks with distinct characteristics, which originated from dipole orientation, oxygen vacancy migration and phase transition respectively. The oxygen vacancy-related defects induced by lanthanum doping were mainly responsible for the variation of conduction behaviors and relaxation processes.     

New Antiferroelectric Solid Solution of Pb(Mg1/2W1/2)O3–Pb(Zn1/2W1/2)O3 as Dielectric Ceramics

A new solid solution of (1?x)Pb(Mg_1/2W_1/2)O₃–xPb(Zn_1/2W_1/2)O₃ has been prepared in the form of ceramics by solid‐state reaction with composition x up to 30%. It is found that with the substitution of Zn²⁺ for Mg²⁺ on the B site of the of complex perovskite structure the antiferroelectric (AFE) Curie temperature T_C of PMW increases from 40°C (x = 0) to 67°C (x = 30%), indicating an enhancement of antiferroelectric order, whereas, at the same time, the phase transition becomes more diffuse due to a higher degree of chemical inhomogeneity. X‐ray diffraction analysis indicates that the crystal structure adopts an orthorhombic space group (Pmcn) with a decrease in lattice parameter a, but an increase in b and c as the Zn²⁺ concentration increases. The low dielectric constant (~ 10²), low dielectric loss (tanδ ≈ 10^?3), linear‐field‐induced polarization, and significantly high breakdown field (~ 125 kV/cm) at room temperature make this family of dielectric materials a promising candidate for ceramic insulators.     

High-energy density of Pb0.97La0.02(Zr0.50Sn0.45Ti0.05)O3 antiferroelectric ceramics prepared by sol-gel method with low-cost dibutyltin oxide

Lead lanthanum zirconate stannate titanate (PbLa(ZrSnTi)O₃) antiferroelectric (AFE) ceramics are widely used in dielectric capacitors due to their superior energy-storage capacity. Generally, these ceramics can be synthesized by solid-state reaction and sol-gel methods. Ceramics prepared using the sol-gel method have a purer phase than those prepared using the solid-state reaction method because the sol-gel method can avoid the segregation of Sn. However, because the commonly used raw material tin acetate is very expensive, the preparation of PbLa(ZrSnTi)O₃ AFE ceramics via the sol-gel method is not cost-effective, which prevents the use of sol-gel method for manufacturing PbLa(ZrSnTi)O₃ in a large scale. In this work, low-cost dibutyltin oxide instead of expensive tin acetate is used to synthesize Pb_0.97La_0.02(Zr_0.50Sn_0.45Ti_0.05)O₃ (PLZST) nanopowders, and single-phase powders with a perovskite structure and average grain size of 200 nm are obtained at a calcination temperature of 580°C. In addition, dense PLZST AFE ceramics with a pure perovskite structure are obtained by sintering the PLZST nanopowders at temperatures as low as 1100°C. The sintered PLZST ceramics exhibit a room-temperature recoverable energy-storage density as high as 1.93 J/cm³ with an efficiency of 75%, which varies only slightly in the temperature range of 20-120°C. The high energy-storage density (>1.9 J/cm³) over a wide temperature range illustrates that the sol-gel-derived PLZST ceramics with low-cost dibutyltin oxide are quite promising for manufacturing pulse power capacitors.     

Nonlinear dielectric response and positive dielectric tunability in antipolar CaTiSiO5

Dielectric tunability has been extensively investigated in ferroelectric materials, which exhibit a negative tunability of dielectric permittivity in an external electric field. In contrast, positive tunability is rare and has been reported only in a few antiferroelectric materials. We present positive (and negative) tunability in the titanite, CaTiSiO₅. The dielectric property of CaTiSiO₅ was measured up to an extraordinarily high electric field of 40 MV/m. A nonlinear polarization field loop with no hysteresis was obtained. The dielectric permittivity of ε_r ~ 25 increases up to ε_r ~ 40 at 20 MV/m and room temperature. Although titanite has an antipolar structure and is expected to be “antiferroelectric,” its dielectric response in high electric fields up to ~40 MV/m differs from that of conventional antiferroelectrics. We demonstrate that the phase-transition temperature and dielectric tunability could be modulated through the chemical substitution of Ca_1−xLa_xTiSi_1−xAl_xO₅, in which the destabilization of the long-range antipolar order is revealed by transmission electron microscopy analysis. These results indicate that the observed dielectric response to an electric field may originate from the unique features of the antipolar and domain structures in CaTiSiO₅.     

Electric field tuning of magnetization in an antiferroelectric-based heterostructure: Example of NMG/PLZST/NMG

A magnetoelectric (ME) heterostructure was fabricated by depositing a Ni-Mn-Ga (NMG) magnetic film on an antiferroelectric (AFE) PLZST—(Pb, La)(Zr, Sn, Ti)O₃—ceramic substrate. Significant and reversible electric field-induced relative magnetization changes (∆M/M₀) were firstly observed in this magnetic/AFE heterostructure, and the ∆M/M₀ vs electric field loops have been found to correspond well with the strain-electric field curve of PLZST ceramic. The maximum ∆M/M₀ variation can reach 15%, indicating an obvious strain-mediated converse magnetoelectric (CME) effect. A maximum CME coefficient of 1.14 × 10^-9 s/m was obtained at the switching electric fields of PLZST. The collected results suggest that AFE materials with a large electric-field-induced phase transition strain could be alternative candidates in ME coupling heterostructures.     

Achieving high energy storage performance of Pb(Lu1/2Nb1/2)O3 antiferroelectric ceramics via equivalent A-site engineering

Manipulating the critical switching field between antiferroelectric (AFE) state and ferroelectric (FE) is an important concept for tuning the energy storage performance of AFEs. As one of the lead-based AFE systems, Pb(Lu_1/2Nb_1/2)O₃ promises high potential in the miniaturization of pulsed power capacitors, but the extremely high critical switching field and low induced saturated polarization demonstrate severe drawbacks with respect to temperature stability and flexibility. Here, A-site Ba²⁺ doping engineering is used to effectively reduce the critical switching field and improve the saturated polarization in Ba_xPb_1-x(Lu_1/2Nb_1/2)O₃ (0.01 ≤ x ≤ 0.08, abbreviated as xBa-PLN) ceramics. We found the AFE-FE phase transition can be occurred at 80ºC with a high energy storage density of 4.03 J/cm³ for Ba_0.06Pb_0.94(Lu_1/2Nb_1/2)O₃ ceramic. Our results show that Ba²⁺ additions destroy the antiparallel structure of AFE phase, and finally reduce the critical switching field, demonstrating a potential alternative to modulate the energy storage performance of AFEs.     

Synthesis,structure, and dielectric properties of a new binary antiferroelectric solid solution: (1−x)Pb(Mg1/2W1/2)O3–xPbHfO3

Dielectric ceramics are one of the most important electrical insulators because of their excellent electrical stability and nonconducting properties. In this work, new complex perovskite solid solutions, (1−x)Pb(Mg_1/2W_1/2)O₃–xPbHfO₃ [(1−x) PMW–xPHf] (0.00 ≤ x ≤ 0.04), were successfully synthesized in the form of ceramics by the solid-state reaction method and sintering process. The X-ray diffraction results indicate that a single perovskite phase with antiferroelectric (AFE) orthorhombic Pmcn symmetry is formed for x < 0.04 which corresponds to the PMW-type solid solution (SS-PMW). For the composition x = 0.04, however, a small amount (about 1%) of ferroelectric orthorhombic C2mm phase that arises from the PHf-type solid solution (SS-PHf) was found to coexist with the Pmcn phase (99%). The dielectric measurements show that the AFE-paraelectric phase transition temperature T_C of the (1−x)PMW–xPHf ceramics increases from 38.2°C (x = 0) to 40.1°C (x = 0.03) with the increasing PHf content, indicating a slightly enhanced AFE ordering degree. The studied materials show a relatively low dielectric constant (~10²), a low dielectric loss (~10⁻²), a high breakdown field strength (~140 kV/cm), and a linear electric field dependence of polarization at room temperature, which make them a new candidate for potential applications as ceramic insulators.     

Triple Hysteresis Loops of PLZST Ceramics Related to Coexistence of Ferroelectricity and Antiferroelectricity

The hysteresis behaviors and phase characteristics of Pb_0.97La_0.02(Zr_0.90Sn_0.025Ti_0.075)O₃ (PLZST) ceramics were investigated in this work. A single mini hysteresis loop at 3 kV/mm with the maximum polarization (P_max) of 8.3 μC/cm² and triple hysteresis loops at 6.6 kV/mm were observed, which indicates the coexistence of rhombohedral ferroelectric phase and tetragonal antiferroelectric phase. The X‐ray Diffraction patterns and dielectric temperature spectra both demonstrate this coexistence. Moreover, the hysteresis loops with increasing temperature indicated that a ferroelectric–antiferroelectric phase transition occurred at about 60°C. These phenomena would be useful for understanding the domain evolution during ferroelectric and antiferroelectric phase transition.     

Studies on dielectric relaxation in ceramic multiferroic Gd1−xYxMnO3

Dielectric study over a broadband was carried out from 10 to 70 K on ceramic Gd_1?xY_xMnO₃ (x=0.2, 0.3 and 0.4). For all the compositions, a prominent sharp peak about ~18 K was observed in the temperature dependence of both ε′(T) and ε″(T) at all frequencies, indicating a long‐range ferroelectric (FE) transition. Using Cole‐Cole fit to the permittivity data, the relaxation time τ and the dielectric strength ?ε were estimated. Temperature variation of τ(T) in the Arrhenius representation is found to be nonlinear (non‐Debyean relaxation), with increasing barrier‐activation energy over successive temperature‐windows. Interestingly, for all the compositions, we witness a jump in τ(T) about the ferroelectric transition temperature, concurred by a broad‐maximum in ?ε(T),signifying the critical slow down of relaxations near long‐range FE‐correlations.     

Hierarchical domain structures in (Pb,La)(Zr,Sn, Ti)O3 antiferroelectric ceramics

(Pb, La)(Zr, Sn, Ti)O₃ (PLZST) ceramic is one of the most prospective antiferroelectric (AFE) materials for variety of functional applications including energy storage and converter. Systematic structural investigation of domain structures should be of fundamental importance for understanding the structure-property relationship in AFE ceramics. In this study, the hierarchical domain structures and modulated structures correlated to the compositional variation in (Pb_0.97La_0.02) (Zr_0.50Sn_xTi_0.50-x)O₃ (x = 0.375, 0.45 and 0.50) were observed and investigated in details by transmission electron microscopy. The PLZST ceramics show exclusively incommensurate modulated structures (IMS) whose modulation period changed from 9.37 to 6.15 and to 4.04 with increasing of the x value. The hierarchical domain structures include, in decreasing scales, AFE domains, incommensurate domains and nanodomains. The elementary domains in PLZST ceramics are pinstriped nanodomains which were formed based on IMS configuration but by frequent modulation of IMS periodicity and formation of faults. Nanodomains accumulated and then dissociated into incommensurate domains and AFE domains successively. The presently revealed structural characteristics in antiferroelectric PLZST may stimulate future researches on the evolution of IMS-based hierarchical domains under external physical fields, e.g. thermal or electrical, and their correlation to the physical performance.     

Thermally Stable BaTiO3‐Bi(Mg2/3Nb1/3)O3 Solid Solution with High Relative Permittivity in a Broad Temperature Usage Range

A combined X‐ray diffraction (XRD), Raman spectra, X‐ray photoelectron spectroscopy, Scanning electron microscopy, and dielectric characterization of (1–x)BaTiO₃?xBi(Mg_2/3Nb_1/3)O₃ ceramic system were investigated for compositions of 0 ≤ x ≤ 0.2. Single‐phase perovskite‐type XRD patterns were observed for all compositions. A systematically structural change from tetragonal to pseudocubic symmetry occurred at 0.04 < x < 0.06, which agrees well with the analysis of Raman spectra. Dielectric measurements indicated that the crossover from a classic ferroelectric to relaxor ferroelectric occurred at x ≥ 0.04. Compared with other compositions, the temperature independence of relative permittivity at T > T_m significantly ameliorated at x = 0.1: near‐stable temperature coefficient of higher relative permittivity (~6800 ± 15%) and the corresponding loss tanδ ≤ 0.09 over a more broader temperature range of 25°C–240°C (1 kHz), which indicates that this ceramic is a promising dielectric material for elevated temperature dielectrics.     

High-performance antiferroelectric ceramics via multistage phase transition

Lead-based antiferroelectric (AFE) ceramics have attracted increasing interest in pulse power systems owing to their high-energy storage and power densities. However, the single AFE–ferroelectric (FE) phase transition in conventional AFE materials usually leads to premature polarization saturation and low breakdown strength, which are disadvantageous to energy storage performance. In this study, high energy storage performance was achieved in Pb_0.94−xLa_0.04Ca_x[Nb_0.02(Zr_0.99Ti_0.01)_0.975]O₃ (PLCNZT) AFE ceramics by constructing electric-field-induced multiple phase transitions. A maximum recoverable energy storage density of 12.15 J/cm³ and a high energy efficiency of 85.4% were obtained for the PLCNZT ceramic with x = 0.03 at 420 kV/cm. These excellent properties are attributed to the AFE–FE Ⅰ-FE Ⅱ multiple phase transitions induced by Ca²⁺ doping, which effectively enhances the breakdown strength. This result indicates that field-induced multiple phase transitions significantly improve the energy storage of AFE materials.     

Morphotropic phase boundary,polymorphic phases and enhanced electrostrain/piezoelectricity in Ag1-xKxNbO3 solid-solution ceramics

Ag_1−xK_xNbO₃(AKNx (x ≤ 0.12) ceramics were prepared to understand the relationship of structure-properties driven by compositions and temperatures. The results suggested that this binary system possessed a morphotropic phase boundary (MPB) consisted of ferrielectric and ferroelectric phases with iso-symmetry at room temperature, in which domains switching together with electric-field-induced irreversible phase transition achieved a much higher electrostrain (S_max = 0.4%) than other compositions. But this MPB was destroyed after poling, leading to inferior piezoelectricity. A phase diagram was drawn after analyzing in situ XRD and dielectric data, where an almost vertical ferrielectric/antiferroelectric ↔ polymorphic ferroelectric MPB line starting from a triple point was proposed. As temperature increased, the piezoelectricity significant enhanced near ferroelectric orthorhombic ↔ monoclinic phase boundary, while the highest piezoelectricity was achieved near the monoclinic ↔ paraelectric phase boundary with d₃₃ = 200 pC/N. The enhanced piezoelectricity is intimately related to the ferroelectric monoclinic possessing Pm symmetry.