A-site Vacancies Research Articles

High Temperature-Insensitive Electrostrain Obtained in (K, Na)NbO3-Based Lead-Free Piezoceramics.

Over the last decades, notable progress is achieved in (K, Na)NbO3 (KNN)-based lead-free piezoceramics. However, more studies are conducted to increase its piezoelectric charge coefficient (d33). For actuator applications, piezoceramics need high electric-field induced strain under low electric fields while maintaining exceptional temperature stability across a wide temperature range. In this study, this work developes Li/Sb-codoped KNN (LKNNS) ceramics with high electrostrain by defect engineering and domain engineering. A remarkable strain of 0.43%, along with a giant d33* value of 2177 pm V-1, is attained in the LKNNS ceramic at 20 kV cm-1. The ceramic exhibits a minimal performance decrease of less than 15% over a temperature range from room temperature to 150 °C. The exceptional strain is attributed to the presence of A-site vacancy-oxygen vacancy ( ) defect dipoles and the increase in nano-domains. The hierarchical domain configuration and defect dipoles impede the switched domains from reverting to their original state as temperature increases, furthermore, the elongated dipole moments of caused by rising temperatures compensate for strain reduction results in exceptional temperature stability. This study provides a model for designing piezoelectric materials with exceptional overall performance under low electric fields and across a wide temperature range.

The phase composition, dielectric, and energy storage performance of A-site vacancy modulated BaTiO3 ceramics with Bi(In1/2(Li0.5Ta0.5)1/2)O3 modification

The (1-x)Ba0.94Ce0.04TiO3-xBi(In1/2(Li0.5Ta0.5)1/2)O3 (BCT-BILT) relaxor ferroelectric ceramic system was explored based on the A-site vacancy design and defect dipole engineering. The impacts of different doping concentrations on the phase composition, dielectric and energy storage performance of the BCT-BILT ceramics were studied and discussed in detail. The pure BCT and 0.95BCT-0.05BILT samples exhibited a mixed crystal structure of tetragonal (T) and pseudo-cubic (PC) phase, while the BCT-BILT samples with x > 0.05 possessed a cubic (C) phase, accompanied by the secondary phases of BaBi2Ta2O9 and BaTa2O6. With an increase in the BILT doping concentration, the surface morphologies of the ceramics were continuously modulated, and the dielectric loss had been reduced to 0.001 at 1 kHz, which was beneficial to improve the energy storage properties. Compared to the pure BCT, the breakdown field strength was significantly enhanced owing to the formation of Aurivillius phase BaBi2Ta2O9 and the increased dielectric relaxation. Ultimately, the highest energy storage density of Wrec = 0.7 J/cm3 and high energy conversion efficiency of η = 95 % was realized at the composition of x = 0.05 under a small electric field of 130 kV/cm. Furthermore, the good temperature stability with the ΔWrec/Wrec30°C < 9 % and Δη/η30°C < 6.5 % was acquired for the samples with x = 0.20–0.30 in the temperature range of 30–120 °C, owing to the synergistic roles of the defect dipoles, impurities BaBi2Ta2O9, and polar nanoregions (PNRs). The 0.95BCT-0.05BILT ceramic obtains discharge energy density Wdis of 0.35 J/cm3 and fast discharge speed t0.9 of 312 ns at 60 kV/cm, current density CD of 255.4 A/cm2 and power density PD of 10.2 MW/cm3 at 80 kV/cm. This work is of guiding significance for designing and optimizing energy storage performance of lead-free relaxors from the perspective of defect building and engineering.

A Single Model for the Thermodynamics and Kinetics of Metal Exsolution from Perovskite Oxides.

Exsolution has emerged as an outstanding route for producing oxide-supported metal nanoparticles. For ABO3-perovskite oxides, various late transition-metal cations can be substituted into the lattice under oxidizing conditions and exsolved as metal nanoparticles after reduction. A consistent and comprehensive description of the point-defect thermodynamics and kinetics of this phenomenon is lacking, however. Herein, supported by hybrid density-functional-theory calculations, we propose a single model that explains diverse experimental observations, such as why substituent transition-metal cations (but not host cations) exsolve from perovskite oxides upon reduction; why different substituent transition-metal cations exsolve under different conditions; why the metal nanoparticles are embedded in the surface; why exsolution occurs surprisingly rapidly at relatively low temperatures; and why the reincorporation of exsolved species involves far longer times and much higher temperatures. Our model's foundation is that the substituent transition-metal cations are reduced to neutral species within the perovskite lattice as the Fermi level is shifted upward within the bandgap upon sample reduction. The calculations also indicate unconventional influences of oxygen vacancies and A-site vacancies. Our model thus provides a fundamental basis for improving existing, and creating new, exsolution-generated catalysts.

Defect Control of Donor Doping on Dielectric Ceramics to Improve the Colossal Permittivity and Temperature Stability

As the demand for miniaturization of electronic devices increases, ceramics with an ABO3 structure require further improvement of the dielectric constant with high permittivity. In the present work, Ba1−1.5xBixTiO3 (BB100xT, x = 0.0025, 0.005, 0.0075, 0.01) ceramics were prepared via a solid-state reaction process. The effect of Bi doping on dielectric properties of lead-free relaxor ferroelectric BaTiO3-based ceramics was studied. The results showed that both colossal permittivity (37,174) and a temperature stability of TCC ≤ ±15% (−27–141 °C) were achieved in BB100xT ceramics at x = 0.5%. The A-site donor doping produces A-site vacancies, a larger space for Ti4+, and fluctuation of the component, which is partially responsible for the high permittivity and responsible for the temperature stability. Meanwhile, the contribution of defect dipoles, and IBLC and SBLC effects to polarization leads to the colossal permittivity. The formation of a liquid phase during sintering promotes mass transfer when the doping content is higher than 0.5%. This work benefits the exploration of novel multilayer ceramic capacitors with colossal permittivity and temperature stability via defect engineering.

Improvement of energy storage properties of NN-based ceramics by high-entropy strategy and A-site cation vacancies

High-entropy dielectric capacitors have recently drawn increasing attention in the field of energy storage. In this study, NiO has been incorporated into [(Na0.7Bi0.1)0.8Sm0.02Ca0.02Sr0.02Ba0.02]Nb0.8Sb0.1Ta0.1O3-based ceramics. We applied the concept of high-entropy design to introduce cation vacancies at the A-site, enhancing conformational entropy. This approach led to the successful preparation of a novel type of energy-storage ceramics with an ABO3 perovskite structure, denoted as (1-x)NBSCSBNST-xNiO (x = 0, 0.02, 0.04, & 0.06). We conducted a systematic study of the microstructural, dielectric, and ferroelectric characteristics, along with an exploration of the influence of the high-entropy strategy on their performance. The ΔSconfig increases with NiO doping, and the Eb of the NBSCSBNST-0.02Ni sample exhibits a significant increase to 730 kV/cm from 550 kV/cm of NBSCSBNSTN. This enhancement is accompanied by a recoverable energy density (Wrec) of 4.43 J/cm3 and an efficiency (η) of 75.9 %. As the content of NiO increases from x = 0 to x = 0.06, the phase transition diffusion behavior strengthens. Additionally, the permittivity (εr) spectrum becomes more uniform, and the activation energy of the prepared ceramic samples increases from 1.03 eV to 1.76 eV. This effect suppresses the emergence of localized electric branching, eventually improving the breakdown strength of NBSCSBNST-xNi ceramic materials. The obtained results indicate that the concept of high-entropy design to introduce cation vacancies at the A-site is an efficient approach to improve the energy storage characteristics of lead-free dielectric capacitors.

Defect dipole stretching enables ultrahigh electrostrain.

Piezoelectric actuators have been extensively utilized as micro-displacement devices because of their advantages of large output displacement, high sensitivity, and immunity to electromagnetic interference. Here, we propose a straightforward approach to design <110>-oriented defect dipoles by introducing A-site vacancies and oxygen vacancies in (K0.48Na0.52)0.99NbO2.995 ceramics. As a result, we achieve ultrahigh electrostrains of 0.7% at 20 kV cm-1 (with an effective piezoelectric strain coefficient d33* = 3500 pm V-1), outperforming the performance of existing piezoelectric ceramics at the same driving field. The exceptional electrostrain is primarily attributed to the large stretching of defect dipoles when subjected to an applied electric field, a phenomenon that has been experimentally confirmed. Moreover, the strong interaction between these defect dipoles and <110> spontaneous polarizations plays a critical role in minimizing hysteresis and ensuring excellent fatigue resistance. Our findings present a practical and effective strategy for developing high-performance piezoelectric materials tailored for advanced actuator applications.

Bi compensation and poling process to enhance piezoelectric properties of BiFeO3-BaTiO3 lead-free piezoceramics

BiFeO3-BaTiO3 (BF-BT) ceramics are an excellent choice for high-temperature lead-free piezoelectric ceramic due to their high Curie temperature and good piezoelectric properties, but the volatilization of Bi leads to the formation of A-site cationic vacancies and oxygen vacancies, culminating in heightened leakage currents and detrimental effects on piezoelectric properties. In this study, a chemical composition of 0.70Bi(1+x)Fe0·97Al0·03O3-0.30BaTiO3 ceramics, abbreviated as B1+xFA-BT, where 0 ≤ x ≤ 0.05, were synthesized, with special attention on the effects of Bi compensation and poling process on their insulation and piezoelectric properties. Due to the coexistence of R-PC phases and low leakage current, B1+xFA-BT ceramics exhibit excellent piezoelectric properties and high Curie temperature, among which the B1.02FA-BT ceramic boasts optimal overall properties: d33 = 196 pC N−1, TC = 480 °C, kp = 34%, θmax = 49.5° and Qm = 32, under optimal poling parameters Ep = 50 kV cm−1 and Tp = 100 °C. The poling process is directly linked to the reorientation of domains, the redistribution of positive/negative space charge and the aggregation or injection of holes, which is achieved by tuning the poling field and temperature in a ceramic with optimal integrated piezoelectric properties. The poling process of BF-BT ceramics is significantly influenced by their leakage characteristics, which can have a significant impact on their overall performance. Optimizing electrical poling conditions and minimizing leakage current is crucial to achieving favorable piezoelectric properties in BF-BT ceramics with R-PC coexisting structures.

A Theoretical Study of Oxygen Anion Diffusion through the A-Site Deficient SrTiO3 Lattice Structure: A Machine Learning Approach.

The performance of strontium titanate-based perovskite materials, widely employed as electrode materials for reversible solid oxide cells, is directly characterized by their efficiency and their ability to facilitate the diffusion of generated oxygen ions. A technique frequently employed for enhancing oxygen ion diffusivity involves artificially generating A-site vacancies in these structures. In this study, the molecular-level mechanism of oxygen ion diffusion for a range of A-site deficient structures is extensively investigated using combined molecular dynamics simulations and machine learning-based technique. The analysis of molecular simulation trajectories yields diffusion parameters for the bulk system. Additionally, clustering analysis of time-overlapped locations of oxygen ions provides a spatial distribution of oxygen ion dislocations. Concurrently, tracking the motion of individual oxygen ions elucidates the contribution of each ion to the overall ionic conductance. Overall, the systematic generation of A-site deficiency is found to significantly influence oxygen ion dislocations, thereby impacting the performance of these materials in terms of oxide ion conduction.

Strain Regulation of Mixed-Halide Perovskites Enables High-Performance Wide-Bandgap Photovoltaics.

Wide-bandgap mixed-halogen perovskite materials are widely used as top cells in tandem solar cells. However, serious open-circuit voltage (Voc ) loss restricts the power conversion efficiency (PCE) of wide-bandgap perovskite solar cells (PSCs). Herein, it is shown that the resulting methylammonium vacancies induce lattice distortion in methylammonium chloride-assisted perovskite film, resulting in an inhomogeneous halogen distribution and low Voc . Thus, a lattice strain regulation strategy is reported to fabricate high-performance wide-bandgap PSCs. Rubidium (Rb) cations are introduced to fill the A-site vacancy caused by the methylammonium volatilization, which alleviates shrinkage strain of the perovskite crystal. The reduced lattice distortion and increased halide ion migration barrier result in a homogeneous mixed-halide perovskite film. Due to improved carrier transport and suppressed nonradiative recombination, the Rb-treated wide-bandgap PSC (1.68eV) achieves an excellent PCE of 21.72%, accompanied by a high Voc of 1.22V. The resulting device maintains more than 90% of its initial PCE after 1500h under 1-sun illumination conditions.

Passivating A-Site and X-Site Vacancies Simultaneously via N-Heterocyclic Amines for Efficient Cs2AgBiBr6 Solar Cells.

To address the toxicity and stability issues of traditional lead halide perovskite solar cells (PSCs), the development of lead-free PSCs, such as Cs2AgBiBr6 solar cells, is of great significance. However, due to the low defect formation energy of Cs2AgBiBr6, a large number of vacancies, including A-site vacancies and X-site vacancies, form during the fabrication process of the Cs2AgBiBr6 film, which seriously damage the performance of the devices. The traditional phenylethylammonium (PEA) cation, mainly focusing on passivating A-site vacancies, is incapable of reducing X-site vacancies and so results in a limited performance improvement in Cs2AgBiBr6 solar cells. Herein, inspired by the capability of the Lewis base to coordinate with metal cations, a series of N-heterocyclic amines are introduced to serve as a dual-site passivator, reducing A-site and X-site vacancies at the same time. The highest power conversion efficiency of modified Cs2AgBiBr6 solar cells has been increased 36% from 1.10 to 1.50%. Further investigation reveals that the higher electron density of additives would lead to a stronger interaction with metal cations like Ag+ and Bi3+, thus reducing more X-site defects and improving carrier dynamics. Our work provides a strategy for passivating perovskite with various kinds of defects and reveals the connection between the coordination capability of additives and device performance enhancement, which could be instructive in improving the performance of lead-free PSCs.

Selective reactivity-assisted sacrificial additive coating for surface passivation of wide bandgap perovskite solar cells with cesium tetrafluoroborate

A novel method, named “selective reactivity-assisted sacrificial additive coating”, allowed the BF4− from the sacrificial additive to react selectively with the Cs+ from the perovskite, forming CsBF4 to passivate the A-site vacancy on the surface.

Intolerance of Ruddlesden-Popper La2NiO4±δ Structure to a-Site Cation Deficiency

Mixed ionic-electronic conductors derived from Ruddlesden-Popper Ln2NiO4+δ (Ln = La, Pr, Nd) attract significant attention as oxygen electrode materials for solid oxide fuel and electrolysis cells. However, literature data on the impact of A-site deficiency on the phase relationships and functional properties of Ln2NiO4+δ-based phases are contradictory. While some works report an accommodation of A-site vacancies up to x = 0.15 in La2-x NiO4±δ, others indicate difficulties in the synthesis of single-phase La2-x NiO4+δ even for low x values. The present work explores the impact of the nominal A-site deficiency on the phase composition and electrical transport properties of La2-x NiO4±δ ceramics.Ceramics with the nominal composition La2-x NiO4±δ (x = 0, 0.02, 0.05, 0.10) were synthesized by the glycine-nitrate technique and sintered at 1350-1450°C. While XRD analysis suggested the formation of single-phase materials with orthorhombic K2NiF4-type structure, the lattice parameters remained independent of composition within the experimental uncertainty. Neutron diffraction studies of x = 0 and 0.05 samples revealed that the lattice parameters, La:Ni atomic ratio (2:1) and oxygen sites occupancy remain identical for both samples, while the presence of impurity NiO phase (0.4 wt.%) was detected for La1.95NiO4±δ. SEM/EDS inspection of ceramic samples confirmed the presence of nickel-rich inclusions for x ≥ 0.02, which could not be eliminated by increasing the temperature and time of sintering. The volume fraction of inclusions increased with x. The experimental observations are supported by the atomistic simulations showing that the coexistence of cation-stoichiometric La2NiO4+δ with nickel-rich La4Ni3O10 or NiO is more favorable compared to cation-deficient La1.95NiO4±δ. Molecular dynamics simulations of La1.95NiO4±δ lattice demonstrated that the introduction of La vacancies leads formation of instability zone in the rock-salt-type layer and destabilization of the crystal lattice. The intolerance of La2NiO4+δ lattice to A-site vacancies and coexistence of La2NiO4+δ with traces of Ni-rich secondary phase in the samples with the nominal composition La2-x NiO4±δ results in an insignificant variation of electrical transport properties with x. Acknowledgements This work was developed within the scope of the project CARBOSTEAM (POCI-01-0145-FEDER-032295) funded by FEDER through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI) and by national funds through FCT/MCTES, and the project CICECO-Aveiro Institute of Materials (UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020) financed by national funds through the FCT/MCTES (PIDDAC). A.B. acknowledges the PhD scholarship by the FCT (grant SFRH/BD/150704/2020). This work was partially supported by the National Science Centre, Poland, grant UMO-2020/37/B/ST8/02097.

Study of crystalline size and strain in rare earth doped Cu modified BZT

In three-dimensional cation-oxygen connections, rare earth replacement induces A-site vacancies and deformation, resulting in stochastic local strain with short range coherence. This will modify the electrical and conductive properties of Barium Zirconate Titanate (BZT). Therefore, to make different research on BZT based materials, the study of induced strain and structural modifications due to rare earth doping is necessary. In this context, the current study involves the synthesis of rare earth (Er/Ho) and Cu co-modified Barium Zirconate Titanate (BZT) through a conventional solid state reaction method. The X-ray diffraction (XRD) technique is utilized to gather data for structural analysis such as phase, space group, and lattice parameters for 0.98(BaZr0.05Ti0.95O3)-0.02(CuO:Er2O3) and 0.98(BaZr0.05Ti0.95O3)-0.02(CuO:Ho2O3). Moreover, from the XRD data, the induced strain and crystalline size for differently doped BZT samples have been analysed. In addition to this, Raman spectroscopy is used to authenticate the results obtained from XRD. A successful comparison has been carried out to assess the impact of doping elements and their concentrations on the structural characteristics of the base material BZT.

On the role of cationic defects over the surface reactivity of manganite-based perovskites for low temperature catalytic oxidation of formaldehyde

Defect engineering in catalytic materials is a versatile strategy to fine-tune their performance towards oxidation reactions, and break the related bottlenecks. Herein, a series of La1−xMnO3 perovskite-based materials was designedly synthesized to investigate the effect of cation defects on their physico-chemical properties. Based on extensive characterizations and density function theory (DFT) calculations, it is demonstrated that La-deficiency could orderly induce oxygen vacancies and electronic structure regulation on perovskite, which prominently promotes the catalytic activity towards formaldehyde oxidation. The leading material (La0.6MnO3) could retain high activity for 63 h, either under dry or humid air. In brief, this work unveils the feasibility of modulating the surface reactivity by modifying the electronic structure properties of lanthanum manganite perovskites following simple adjustment of the A-site cationic vacancies, and also highlights A-site deficient perovskite as a potentially efficient catalyst for environmental remediation.

Influence of tetragonal/cubic phase composition on the total ionic conductivity of Li3xLa2/3−xTiO3

Lithium lanthanum titanate (Li3xLa2/3−xTiO3, abbreviated as LLTO, where x = 0.08, 0.1, 0.12, 0.14, 0.16, and 0.167) is prepared using a conventional solid-phase method, and its crystal structure, phase composition, microstructure, and electrical properties are investigated. Experimental results indicate that when the Li content is low (x = 0.8), there exist tetragonal, cubic, and orthogonal phases in LLTO. As the Li content increases (x ≥ 0.1), the orthogonal phase disappears, and there are changes in the phase composition of tetragonal and cubic phases. When the occupancy rates of Li and La are low, the number of A-site vacancies increases, as does the electrical conductivity of LLTO. At room temperature, the ionic conductivity of LLTO increases and then decreases. The Li0.30La0.56TiO3 ceramic electrolyte exhibits the highest total ionic conductivity of 7.22 × 10−5 S/cm, a minimum activation energy of 0.31 eV, and an electrical conductivity of 6.26 × 10−11 S/cm. This paper provides a theoretical basis for subsequent research on solid Li3xLa2/3−xTiO3 electrolytes.

A-site vacancy induced electronic engineering of perovskite for synergistic modulation of redox activity and magnetocaloric effect

Realizing “Power to Syngas” by electrifying chemical reactors via induction heating is one of the key enabling technologies to decarbonize the chemical industry. Nevertheless, developing catalysts for the induction heating process that can simultaneously serve as magnetic susceptors under high-temperature conditions remains challenging. Herein, we formulate a A-site vacancy induced electronic engineering strategy and, accordingly, synthesize a series of LaFe0.5Al0.5O3 perovskite catalysts with different amounts of La vacancies (VLa) (LFAO, 1.5 M-LFAO, and 3 M-LFAO). In this way, we tune both the redox activity and the magnetocaloric effect (MCE) of perovskite and, for the first time, achieve induction heating methane partial oxidation coupled with CO2 splitting for syngas production. Compared with the reported catalysts, the 3 M-LFAO had not only superior syngas and CO yields (101.84 L·kg cat−1/54.96 L kg cat−1) but also a great MCE (875 °C). Spectroscopic investigations and DFT calculations rationalize these observations and demonstrate that the VLa cause a unique Fe4+–O2-–Fe3+ configuration in perovskite, accounting for an upshift of Fe 3d and O 2p band centers and therefore enhancing redox activity and MCE. This work deepens the understanding of the relationship between catalysis and MCE and unlocks the novel guidance to design induction heating chemical processes.

Improvement of piezoelectric properties of epitaxial (K,Na)NbO3 thin films grown on Si substrates

Lead-free epitaxial (K0.47Na0.53)NbO3 (KNN) thin films were fabricated on (001)SrRuO3/Pt/ZrO2/Si substrates by RF magnetron sputtering at 650 °C and were post-annealed at the same 650 °C by a rapid thermal annealing (RTA) process. The crystal structure of epitaxial KNN thin films were changed by RTA, i.e. the lattice parameter c in the out-of-plane direction decreased instead of an increase of the parameter a in the in-plane direction. The displacement–electric field curve of the RTA-annealed KNN thin films was symmetrical and the shift of the polarization reversal field was smaller than in the KNN thin films annealed by a conventional furnace. This means that RTA is effective in compensating for oxygen vacancies as well as suppressing the generation of A-site vacancies at the interface between the thin film and the substrate. The converse piezoelectric coefficient ∣e 31,f ∣ of the epitaxial KNN/Si unimorph cantilever was found to improve by up to 7.7 C m−2 due to the decrease in defect density resulting from RTA.

Thermoelectric enhancement in A-site deficient high-entropy perovskite (Sr0.25Ca0.25La0.25Ba0.25)1-xTiO3±δ ceramics by fine manipulating cation vacancies

SrTiO3-based perovskite structured oxides have attracted much attention as an n-type thermoelectric material over a wide temperature range. An enhancement in performance requires strategies that simultaneously optimize electron and phonon transports. In this work, a series of A-site cation vacancies were introduced into a high-entropy system to fabricate A-site deficient (Sr0.25Ca0.25La0.25Ba0.25)1-xTiO3±δ(0＜x ≤ 0.125) samples which optimize configuration entropy ranges 10.08–11.24 J mol−1K−1 and simultaneously manipulate electronic and phonon transports properties. Most importantly, the direct evidence of positron annihilation and iDPC-STEM results unambiguously confirms these A-site cation vacancies. Consequently, carrier mobility was improved by 16.5 times which significantly contributed to an increase in the electrical conductivity. The low lattice thermal conductivity of 2.54 W m−1K−1 was obtained at 1073 K which was significantly reduced by 21.4% compared to the majority values of SrTiO3-based ceramics. The maximum ZT = 0.24 was attained for the x = 0.100 sample with an enhancement of 27.8% than that of stoichiometric ceramic due to the synergistic effect of higher PF and relatively low κ. This study reveals that in a distorted, high-entropy perovskite structure, multiple band degeneracy is advantageous for enhancing the electrical characteristics due to the delocalized electrons that result from enhanced crystal symmetry. In the meanwhile, anharmonicity and localized phonons inhibited the propagation of transverse phonons resulting in a markedly reduced lattice thermal conductivity. This feasible strategy of defect engineering combined with entropy manipulation demonstrates that it is not necessary to simply pursue a much higher configuration entropy in TE ceramics to optimal ZT values.

Realizing ultrahigh energy-storage density in Ca0.5Sr0.5TiO3-based linear ceramics over broad temperature range

In the realm of energy storage, there is an exigent need for dielectric materials that exhibit high energy storage density (Wrec) and efficiency (η) over wide temperature ranges. Linear dielectrics exhibit superior breakdown strength (Eb) compared to ferroelectrics, yet their utility is restricted by low polarization. Here, an ultrahigh Wrec up to 7.92 J/cm3 and η ≈ 94.3% are realized in (Ca0.5Sr0.5)1-1.5xSmxTiO3 ceramic with ultrafast discharge time (t0.9 = 20 ns) which is one of the best energy storage performances recorded linear ceramics. By employing the charge balance method, the production of oxygen vacancies (VO··) can be prevented, leading to improved insulation. The creation of A-site vacancies serves to enhance the breakdown field strength. Furthermore, the incorporation of Sm3+ effectively limits the thermal activation of oxygen vacancies at elevated temperatures, ultimately resulting in an increase in bulk resistivity. The results also unveil the outstanding stability across a wide range of temperatures (20 °C–140 °C) and frequencies (1 Hz–500 Hz). Consequently, this study provides significant insights into enhancing Eb and attaining high-energy storage capacitors.

Suppression of the ferroelectric phase for (K0.5Na0.5)NbO3 ceramic by A/B-sites disorder for enhancement the energy storage properties and dielectric breakdown strength

In the present study, we propose a new strategy called suppression ferroelectricity of (K0.5Na0.5)NbO3 (KNN) lead-free ceramics for significant enhancement of energy storage properties (ESPs) and dielectric breakdown strength (DBSs). Both of pure KNN and (Na0.6Ag0.1Bi0.1)(Nb0.8Ti0.25)O3 (abbreviate NN-ABT) were synthesized using solid reaction technique. The crystal structure, dielectric and ferroelectric properties of both prepared ceramics were investigated. NN-based ceramics shown ferroelectric to relaxor phase crossover with pseudo-cubic crystal structure at ambient temperature. Present relaxor phase is attributed to substitution of monovalent (K1+) by trivalent (Bi3+) which can cause A-site cation vacancies and charge misfit of KNN lattice. The inhabitation of grain size to sub-micrometer observed by scanning electron microscope and this could be attributed to the lower ionic radius of (Ag1+ = 1.15 Å) and (Bi1+ = 1.38 Å) compared to (K1+ = 1.64 Å) which can suppressed the tolerance factor (τ) from 1.01 for KNN (ideal ferroelectric phase) to τ = 0.85 for NN-ABT . Suppression of the (τ) value can enhanced the degree of the relaxor phase, while inhibition of grain size can improved the DBSs or Eb. Superior enhancement of energy storage properties were achieved in NN-based ceramic due to hybridization between Bi3+ 6 P and O2- 2 P orbitals instead of K1+ 1 S and O2- 2 P orbitals which resulting in increasing the maximum polarization. The results shown that (NN-ABT) is acquired the preeminent of recoverable energy storage density Wrec ∼ 11 J/cm3, energy storage efficiency (ƞ = 89%) at E = 550 kV/cm. Furthermore, the sample shown an excellent thermal and frequency stabilities variation in a wide range of temperature (25–175 °C) and frequency (2–50 Hz). The significant enhancement in energy storage performance of NN-ABT ceramic is attributed to disturb the ferroelectric phase of KNN and forming PNRs of relaxor phase at ambient temperature. Therefore, the present study provides a good guideline for optimizing the ESPs and DBSs of NN-based ceramics to be more applicable for pulsed power and energy storage applications.