Polar Nanoregions Research Articles

Boosting ultra-wide temperature dielectric stability of multilayer ceramic capacitor through tailoring the combination types of polar nanoregions

With the rapid development of space exploration and new energy vehicles, it is urgent to build ultra-wide temperature multilayer ceramic capacitors (UWT MLCCs) to match electronic circuits that can withstand harsh environmental conditions. Relaxor ferroelectrics with diffuse phase transition feature are potential dielectrics for the construction of UWT MLCCs. However, how to ensure high dielectric constant together with low dielectric loss in the wide temperature region is still a big challenge. Here, the above difficulties are addressed by tailoring the combination types of polar nanoregions (PNRs) in the (1-x) (0.8Na0.5Bi0.5TiO3-0.2K0.5Bi0.5TiO3)-xNaTaO3 (NBT-KBT-xNT) system. Compared with PNRs types of P4bm + R3c and P4bm + Pbnm, the combination type of P4bm + Pbnm + R3c PNRs in NBT-KBT-0.31NT is the most beneficial to obtain comprehensive excellent dielectric performance because it can balance the relationship between high dielectric constant and temperature stability over a wide temperature region. Further, by optimizing the laminating pressure and co-firing temperature to realize a tight interfacial structure between the dielectric layer and the Pt inner electrode, a record-high dielectric constant (εr = (907% ± 15%)) together with low dielectric loss (tanδ ≤ 0.025) is achieved over an ultra-wide range from −61 °C to 306 °C for NBT-KBT-0.31NT MLCC, demonstrating that tailoring the combination types of PNRs is a powerful strategy in designing UWT MLCC dielectrics.

Ergodic polar cluster state and its dynamics in K and Nb modified BaTiO3

Ferroelectric to relaxor crossover of (KxBa1-x)(NbxTi1-x)O3 [KBNTx]; (x = 0, 0.05, 0.075 and 0.150) system has been investigated by exploring its average and local structure using X-ray diffraction, Raman scattering and dielectric spectroscopy. X-ray diffraction confirmed all compositions' overall cubic (Pm-3m) structure. Dielectric spectroscopy clearly showed ferroelectric to relaxor crossover at x = 0.150. In the Raman spectra of doped compounds, three new modes of chemical origin that are absent in BaTiO3 are observed at frequencies ∼120 cm−1, 830 cm−1 and 850 cm−1 at room temperature. The temperature-dependent Raman scattering revealed the existence of ergodic polar regions by the presence of first-order ferroelectric mode at 302 cm−1 [B1/E(TO3)/E(LO2)], along with two static disorder-related modes 220 and 550 cm−1 for T > Tc in the paraelectric phase. Moreover, Raman studies also elucidate that the decreased size of ergodic polar regions is responsible for relaxor crossover at x = 0.150 composition with the increased broadening of 302 cm−1 modes with an increase of K and Nb concentration. Further, the polar dynamic investigations indicated that the interactions among polar nano regions slow down nano-polar dynamics without freezing or glass transition. Identifying polar regions and their dynamics in the present work will significantly impact the understanding of the tunability of K and Nb-modified BaTiO3 lead-free ferroelectrics.

Modulation of magnetic and dielectric properties by Al3+ substitution in Ca3CoMnO6 ceramics

We report a detailed study of the influence of non-magnetic Al3+ doping on the microstructure, magnetic, and dielectric characteristics Ca3CoMnO6. The introduction of Al3+ leads to the suppression of competing short-range magnetic orders, a gradual disappearance of the spin freezing peak in Ca3CoMn1-xAlxO6 was observed, accompanied by the release of magnetic frustration. Moreover, a weakening of the antiferromagnetic order in Ca3CoMnO6 was attributed to the dilution effect induced by non-magnetic Al3+ within the Co-Mn-Co-Mn spin chains. The dielectric measurements exhibit excellent agreement with the magnetic measurements. The substitution of Mn4+ with Al3+ results in the attenuation of relaxor ferroelectric behavior, accompanied by a decrease in the static freezing temperature Tf and an increase in the activation energy Ea. It indicates that Al3+ substitution could well suppress the formation of polar nanoregions. With introducing Al3+ the magnetodielectric effect of Ca3CoMnO6 is also significantly enhanced. For the x = 0.15 sample, the magnetodielectric effect undergoes a notable variation of approximately 10 % under a magnetic field of H = 4 T.

High-entropic relaxor ferroelectric perovskites ceramics with A-site modification for energy storage applications

With the growing concept of developing smart cities, the demand for evolving eco-benign and efficient energy storage applications with extraordinary performance has risen significantly. To overcome such high demands, configurationally complex composites/alloys are engineered by populating the single lattice site of perovskite materials deliberately with distinct cations to create highly entropic form of materials. Herein, two high entropy ceramics (Ba0.2Na0.2Ca0.2Sm0.2Bi0.2)TiO3 (BNCSBT) and (Ba0.2Na0.2Mg0.2La0.2Bi0.2)TiO3 (BNMLBT) are deliberately engineered to analyze their structural, ferroelectric and dielectric capacitive performance. XRD analysis, tolerance factor and Rietveld refinement of measured XRD patterns of the ceramics have confirmed the Cubic symmetry with Pm3‾m space group. Both BNCSBT and BNMLBT ceramics have demonstrated the maximum polarization (Pmax) of 26.3 μC/cm2 and 28. 02 μC/cm2, recoverable energy density (Wrec) of 1.0715 J/cm3 and 1.1225 J/cm3 and energy conversion efficiency (ƞ) of 81.42% and 80.12% respectively. Moreover, the temperature dependent dielectric analysis of BNCSBT and BNMLBT ceramics has presented the wide transition temperature effect due to the creation of polar nano-regions, confirming the relaxor ferroelectric behavior with diffusion coefficient values of 1.8312 and 1.8021 respectively. Such engineered high-entropic ceramics with excellent relaxor ferroelectric and dielectric capacitive performances even at the high temperature (120 °C) are phenomenal for temperature dependent energy storage applications.

Achieved excellent energy storage properties and ultrahigh power density of Ba0.85Ca0.15Zr0.1Ti0.9O3 lead-free ceramics modified by Bi(Mg0.5Hf0.5)O3

Herein, novel binary systems of (1-x)Ba0.85Ca0.15Zr0.1Ti0.9O3-xBi(Mg0.5Hf0.5)O3 ((1-x)BCZT-xBMH, x = 0.00 ∼ 0.30) were fabricated based on a collaborative optimization strategy of compositional modulation and nano-domain. All the samples have a pure perovskite structure with a compact microstructure devoid of pores. Interestingly, an excellent recoverable energy density (Wrec ∼ 3.29 J/cm3) and high efficiency (η ∼ 90%) were achieved in 0.75BCZT-0.25BMH ceramics under 305 kV/cm. The improved energy storage performances (ESP) could be attributed to the fact that the introduction of Bi(Mg0.5Hf0.5)O3 increases the band gap, decreases the leakage current and grain size, in particular, frustrates the long range ferroelectric order, leading to the formation of the polar nanoregions (PNRs). Moreover, an ultrahigh power density (∼133.76 MW/cm3), an ultrafast discharge time (∼98 ns), an high frequency stability (1–103 Hz), fatigue resistance (×104 cycles), and good temperature stability (20–120 °C) can be concurrently realized in the optimized ceramics. These results demonstrate that the environmentally friendly 0.75BCZT-0.25BMH lead-free ceramics are a potential candidate for dielectric energy storage devices.

Antiferroelectric-like BiFeO3-SrTiO3 based ceramics with high breakdown strength and energy-storage density

Herein, an outstanding excellent energy storage performance (ESP) (Wrec∼4.4 J/cm3; η∼72%; ΔP = 38.1 μC/cm2) was obtained in environmentally friendly 0.52BiFeO3-0.4SrTiO3-0.08NaNbO3 lead-free ceramic. First, the addition of NaNbO3 (NN) lead to composition and charge disorder of A- and B- sites, generating random electric field that induce the emergence of small-sized polar nano-regions (PNRs) to enhance ΔP (Pmax-Pr). Rietveld refinement analysis showed that introducing NN reduces the content of polar R3c phase from 81.8% to 24.4%, and the non-polar Pm3m phase increased. When x ≥ 0.08, the antiferroelectric-like double P-E loops were acquired due to field-induced phase transition, and further lower Pr and Ec were obtained. Then, the introduction of NN greatly improved the breakdown strength of BFO-STO ceramics. That is, enhances electrical homogeneity, increases energy gap (Eg) and refines grain size (from 1.05 to 0.75 µm). Through domain engineering, antiferroelectric-like design and other multi-factors to achieve the optimization of ESP, providing a feasible strategy for lead-free pulse energy storage capacitors. Additionally, the good temperature (20–120 °C) and frequency (1–100 Hz) stability acquired to less than 15% in favor of practical applications.

The unexpected diffuse phase transition in relaxor-PbTiO3 ferroelectrics via acceptor modification

The diffuse phase transition (DPT) and domain structure are essential to the functional properties of relaxor ferroelectrics and are extremely sensitive to the ion doping. The utilization of acceptor doping has been observed to be an effective method in enhancing the high-power properties of relaxor ferroelectric materials. The present study aims to examine the acceptor-doped DPT and domain structure in single crystals of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3. An unexpected physical phenomenon was identified in which Mn-doping increased dielectric diffusion and lowered domain size while suppressing dielectric relaxation. Traceability investigations suggest that Mn-doping inhibited the growth of polar nanoregions by enhancing random electric fields, which increases dielectric diffusion while decreasing the domain size. Meanwhile, Mn doping redistributes the relaxation time function, which results in a reduction in dielectric relaxation. The current research deepens the understanding of the physical basis of DPT and can be applied to the development of high-performance piezoelectric materials.

An ultrahigh energy storage efficiency and recoverable density in Bi0.5Na0.5TiO3 with the modification of Sr0.85La0.1TiO3via viscous polymer process

Currently, the development of dielectric ceramic capacitors is restricted by the contradiction between high efficiency and high recoverable density. Therefore, a novel strategy was designed to achieve a superior balance between them. Firstly, introducing Sr0.85La0.1TiO3 can enhance the content of the weak polar phase (P4bm) to become the main component, which can optimize the relaxor behaviour and improve efficiency. Then, the electric breakdown strength was effectively enhanced by grain refinement and viscous polymer processing. Finally, a high recoverable energy density of ∼5.3 J/cm3 and an excellent efficiency of ∼92.2% were attained in 0.9Bi0.5Na0.5TiO3-0.1Na0.8Sr0.1NbO3 ceramic with the addition of 0.35Sr0.85La0.1TiO3 after viscous polymer processing. The piezoelectric force microscope had been applied to prove the high activity of the polar nanoregions and finite element analysis was adopted to explain the reasons for the enhancing electric breakdown strength. In addition, this ceramic exhibits good temperature and frequency stability, and a fast discharging rate of 0.11 μs, making it a potential candidate for the actual application.

Reversible evolution of ferroelectric-antiferroelectric phase transition in lanthanum-modified NaNbO3-based ceramics

Sodium niobate (NN) lead-free perovskites have been concentrated on due to high performance and abundant phase structure. The complex structure evolution has become a hot topic of research for this kind of materials. In this work, antiferroelectric phase is recovered by introducing La3+ dopant from modified ferroelectric states, indicating reversible composition-induced antiferroelectric-ferroelectric (AFE-FE) phase transition in NN-based ceramics. Significantly, change tendency of decreasing first and then increasing appears for phase transition temperature with increasing La3+, which is different from general phenomenon for ions dopant. Antiferroelectric orthorhombic (Pbma) is induced from ferroelectric tetragonal (P4mm) with a transient state of paraelectric cubic (Pm3m) via enhancing La3+. Further, substitution on A-site and A/B-sites are revealed with low and high content of La3+, respectively, accompanied by decreased first and then increased oxygen vacancy. Moreover, obviously deteriorated piezoelectric response is observed along with poor domain switching due to the vanishing ferroelectric domain for FE-PE-AFE phase transition. Meanwhile, weak strain, piezoelectric and dielectric properties are observed for antiferroelectric phase with antiparallel dipoles, while enhanced strain and dielectric permittivity are gained around ferroelectric-paraelectric coexistence or paraelectric region originating from electric field-induced ferroelectric state from polar nanoregions. Thus, this work demonstrated an abnormal phase transition in NN-based ceramics, promoting the understanding of antiferroelectrics.

Polar nano-regions originated from local displacive correlations in relaxor-ferroelectric

Polar nano-regions originated from local displacive correlations in relaxor-ferroelectric

Local displacive correlation in the tetragonal relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-0.15PbTiO3

Over the past decades, lead-based relaxor ferroelectrics have served as the model systems to unravel the relationship between electromechanical properties and local structure. Here, by employing pair distribution function analysis and the reverse Monte Carlo method, we investigate the local structural features and their temperature dependence in relaxor ferroelectric Pb(Zn1/3Nb2/3)O3-xPbTiO3 with x = 0.15 (PZN-15PT), which has a tetragonal average structure, but displays frequency dependence at low temperatures. The refined atomic model suggests that ordered polar nanoregions (PNRs) originate from the strong atomic displacive correlation, and their polar directions are the same as the crystallographic symmetry axis. The dipoles in the disordered matrix have weak correlations and can be averaged into a global tetragonal symmetry. These findings establish a detailed picture of the local structure of lead-based relaxor ferroelectrics and provide a deeper insight into the nature of PNRs.

Excellent energy storage performance of Mn-doped SrTiO3-BiFeO3 thin films by microstructure modulation

Dielectric thin film capacitors are expected to be a promising candidate for high-performance energy storage devices due to their high power density, fast charge/discharge speed, and excellent stability. Nevertheless, it remains a challenging endeavor to develop dielectrics with excellent energy storage density comparable to that of commercial batteries. In this work, lead-free 0.8SrTiO3-0.2BiFeO3 (0.8STO-0.2BFO) thin films with coexisting amorphous and nanocrystalline structure were prepared by a sol-gel method. The heat-treatment temperature was adjusted to form polar-nano regions, thereby modulate the breakdown strength and dielectric polarization, and increase the energy storage density. The electric potential, electric field, and current density of the films with different amorphous/crystalline volume fractions were evaluated by the finite element simulation to further verify that the proper crystallization can result in the improved polarization performance and increased breakdown strength of the films, which are beneficial to the enhancement of energy storage performance. Through structural tailoring, the 0.8STO-0.2BFO film annealed at 550 °C demonstrates the optimal energy storage properties with a giant discharge energy storage density of 65 J/cm3 and high efficiency of 75% at room temperature. Simultaneously, a broad temperature stability (20–160 °C), superb operating frequency stability (20 Hz-2 kHz), and excellent fatigue endurance (6.3 ×105) are observed without appreciable degradation of the energy storage performance. The excellent energy storage performance indicates a widespread potential of 0.8STO-0.2BFO films in pulse power applications, such as consumer electronics, microelectronics, and medical devices.

Strong pyroelectric enhancement induced by the evolution of PNRs in paraelectric-phase KTN crystals

KTa1−xNbxO3 crystals exhibit excellent piezoelectric, ferroelectric, and electro-optical properties near the phase transition point, owing to the evolution of polar nanoregions (PNRs). This paper discusses the physical properties of the PNRs in three characteristic temperature ranges and analyzes the dielectric relaxation properties of the crystals. The effects of different heating rates and initial temperatures on the pyroelectric effect are discussed, and the influence of small electric fields on increasing the pyroelectric coefficient is investigated. The polarization characteristics of the crystal were obtained according to the change in the pyroelectric performance, and the influence of different conditions on the dynamic response of the PNRs was analyzed. It is proposed that the evolution of PNRs, induced by external coupling with an internal electric field, significantly affects macroscopic performance.

Pulse energy-storage performance and temperature stability of Bi2O3-added BaTiO3 based ceramics

The temperature stability and temperature stability range of barium titanate-based pulse energy-storage ceramics were modified by Bi2O3 tailoring in (Ba0.98-xLi0.02Bix) (Mg0·04Ti0.96)O3 (x = 0, 0.025, 0.05, 0.075, 0.1) and (Ba1.03-1.5xLi0.02Bix) (Mg0·04Ti0.96)O3 (x = 0.125, 0.15, 0.2, 0.25) ceramics. Excellent pulse energy-storage performances of ceramic films are achieved via the new dual priority strategy of establishing cationic vacancies and forming a liquid phase. The dielectric constant plateau appears due to the cubic phase and space charges. Outstanding temperature stability, frequency stability and antifatigue performance are obtained in the ceramics, and their variations are all less than 15%. The comprehensive energy-storage properties with dual priority parameters of energy-storage density and efficiency of 3.13 J/cm3 and 91.71%, accompanied by an excellent pulse discharge energy density of 2.48 J/cm3, current density of 1313.23 A/cm2 and power density of 195.26 MW/cm3 are gained at x = 0.1. The perfect pulse energy-storage performances as well as ultrahigh stability are correlated with synergistic effects of multiphase coexistence, cubic phase, liquid-phase sintering, grain size, ceramic resistance, space charges and polar nanoregions. The comprehensive parameters indicate that the (Ba0·88Li0·02Bi0.1) (Mg0·04Ti0.96)O3 ceramics have potential application in high precision fields.

Relaxor antiferroelectric-relaxor ferroelectric crossover in NaNbO3-based lead-free ceramics for high-efficiency large-capacitive energy storage

Relaxor ferroic dielectrics have garnered increasing attention in the past decade as promising materials for energy storage. Among them, relaxor antiferroelectrics (AFEs) and relaxor ferroelectrics (FEs) have shown great promise in term of high energy storage density and efficiency, respectively. In this study, a unique phase transition from relaxor AFE to relaxor FE was achieved for the first time by introducing strong-ferroelectricity BaTiO3 into NaNbO3-BiFeO3 system, leading to an evolution from AFE R hierarchical nanodomains to FE polar nanoregions. A novel medium state, consisting of relaxor AFE and relaxor FE, was identified in the crossover of 0.88NaNbO3–0.07BiFeO3–0.05BaTiO3 ceramic, exhibiting a distinctive core-shell grain structure due to the composition segregation. By harnessing the advantages of high energy storage density from relaxor AFE and large efficiency from relaxor FE, the ceramic showcased excellent overall energy storage properties. It achieved a substantial recoverable energy storage density Wrec ∼ 13.1 J/cm3 and an ultrahigh efficiency η ∼ 88.9%. These remarkable values shattered the trade-off relationship typically observed in most dielectric capacitors between Wrec and η. The findings of this study provide valuable insights for the design of ceramic capacitors with enhanced performance, specifically targeting the development of next generation pulse power devices.

On the random temperature model for relaxors

The dependence of the Burns temperature on the parameters of the regions of structural heterogeneity was determined and the freezing temperature of a separate polar nanoregion was estimated within the framework of the phenomenological model of random temperature proposed to describe the properties of ferroelectric relaxors. It is shown that taking into account the temperature dependence of the free energy of the polar region is important for determining the dependence of the relaxation frequency on temperature.

X-ray diffuse scattering and polar nanoregion of a relaxor ferroelectric under electric field

We have measured X-ray diffuse scattering (XDS) of a relaxor ferroelectric 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 single crystal under an electric field along [111] to investigate the electric field response of polar nanoregions (PNRs). Our ellipsoidal PNR model with a polarization along [110] and principal axes along [], [], and [] well reproduced observed three-dimensional XDS intensities around each Bragg reflection under the electric field at 300 K. The dimension of the ellipsoidal PNR is estimated to be 0.6 × 1.8 × 1.2 nm3 along the principal axes. The electric field dependence of XDS strongly couples with the piezoelectric lattice strain and ferroelectric polarization switching. Irreversible changes in XDS intensities observed under the electric field are explained by an antiferroelectric dipolar stabilization of reoriented PNRs.

Synergistic effect of multi-phase and multi-domain structures induced high energy storage performances under low electric fields in Na0.5Bi0.5TiO3-based lead-free ceramics

Lead-free dielectric ceramics with ultrahigh-power density, fatigue properties, and excellent thermal stability are regarded as potential dielectric energy storage materials for the next-generation advanced pulse power capacitors. However, the large energy storage density (Wrec) and high discharging efficiency (η) of dielectric capacitors are generally achieved under ultrahigh electric fields. Developing dielectric capacitors with high energy storage performances under low electric fields is of great significance. Herein, we utilized a synergistic design strategy of multi-phase and multi-domain structures to successfully synthesize the (0.65-x)(Na0.5Bi0.5)TiO3-0.35(Sr0.7Bi0.2)TiO3-xAg0.97Nd0.01Ta0.2Nb0.8O3 ((0.65-x)BNT-0.35SBT-xANTN) ceramics suitable for the low electric field situation. The formed multi-phase coexistence structure of the Rhombohedral (R3c) and Tetragonal (P4bm) phases and the elevated concentration of Bi3+ at A site in BNT-SBT-ANTN ceramics are beneficial to obtain the high maximum polarization (Pmax). Meanwhile, the introduction of ANTN in the BNT-SBT matrix can disrupt the long-range order ferroelectric domain structures and also form the local polar nanoregions (PNRs), leading to the small remnant polarization (Pr) and the improvement of the relaxation behavior. Encouragingly, the optimized 0.63BNT-0.35SBT-0.02ANTN composition exhibits excellent energy storage performances with a large Wrec of 3.61 J/cm3 and relatively high η of 80.6% at a low electric field of 200 kV/cm. In addition, this 0.63BNT-0.35SBT-0.02ANTN sample presents better thermal stability (20–120 ℃) and frequency stability (10–1000 Hz). Moreover, the high charge power density (PD) of 69.42 MW/cm3, the rapid discharge speed rate (τ0.9) of 0.22 μs, and the good fatigue endurance are also achieved in the 0.63BNT-0.35SBT-0.02ANTN sample. This work may provide an effective method for designing dielectric ceramics with remarkable comprehensive energy storage performances at low electric fields to meet the requirements of advanced energy storage capacitors under extreme conditions.

Structural evolution and energy storage properties of Bi(Zn0.5Zr0.5)O3 modified BaTiO3-based relaxation ferroelectric ceramics

A series of (1−x)BaTiO3−xBi(Zn0.5Zr0.5)O3 (x = 0–0.15) ceramics were synthesized using the conventional solid-state method. An ultrahigh recoverable energy storage density of 3.58 J/cm3 and a high energy efficiency of 90% are obtained for 0.85BaTiO3–0.15Bi(Zn0.5Zr0.5)O3 lead-free bulk ceramics under an electric field of 430 kV/cm; the energy storage density is thus enhanced by a factor of a ∼ 895% compared with that of the pure BT ceramics. Furthermore, an excellent temperature stability is obtained, with changes in the energy storage density and efficiency <5% and <0.1%, respectively, over the temperature range of 30 °C – 120 °C. These ergodic relaxor ferroelectric characteristics are attributed to the reduced grain size, the transition from the tetragonal phase to the pseudo-cubic phase, and the transformation of the domain structure from macro domains to polar nanoregions. This work provides a lead-free material for realizing high-temperature capacitors for use in energy storage devices.

Effect of the DC-bias electric field on the phase transition characteristics in PMN ceramics

Relaxor ferroelectrics play an important role for technological applications, mainly for using in the fabrication of actuators, transducers and sensors. Therefore, there has been an increasing interest of the scientific community in the investigation of the physical properties of such system in order to better elucidate the observed intriguing and unsolved phenomena. In this work, relaxor Pb(Mg1/3Nb2/3)O3 (PMN) ceramic system was prepared and the dielectric properties have been studied in details as a function of frequency, temperature and magnitude of the DC-bias electric field. Results reveal that the temperature dependence of the dielectric permittivity can be successfully described in the whole analyzed temperature range (100–400 K) by using a macroscopic statistical model, which describe the dielectric response in relaxor systems with diffuse phase transition (DPT). By using this phenomenological model, the temperature and DC-bias electric field dependences of the dielectric permittivity have been also revisited, from the analysis of the DPT behavior, promoting a careful discussion on the nature of the phase transition in relaxors materials. The calculated sizes of the polar nanoregions (PNRs) suggest the development of a structural disorder in the studied system, which promote the high diffuse ferroelectric transition as the amplitude of the DC-bias electric field increases.