Moderate Fields, Maximum Potential: Achieving High Records with Temperature‑Stable Energy Storage in Lead‑Free BNT‑Based Ceramics

The increasing awareness of environmental concerns has prompted a surge in the exploration of leadfree,high-power ceramic capacitors.Ongoing efforts to develop leadfree dielectric ceramics with exceptional energystorage performance(ESP)have predominantly relied on multicomponent composite strategies,often accomplished under ultrahigh electric fields.However,this approach poses challenges in insulation and system downsizing due to the necessary working voltage under such conditions.Despite extensive study,bulk ceramics of(Bi_(0.5)Na_(0.5))TiO_(3)(BNT),a prominent lead-free dielectric ceramic family,have seldom achieved a recoverable energy-storage(ES)density(Wrec)exceeding 7 J cm^(−3).This study introduces a novel approach to attain ceramic capacitors with high ESP under moderate electric fields by regulating permittivity based on a linear dielectric model,enhancing insulation quality,and engineering domain structures through chemical formula optimization.The incorporation of SrTiO_(3)(ST)into the BNT matrix is revealed to reduce the dielectric constant,while the addition of Bi(Mg_(2/3)Nb_(1/3))O_(3)(BMN)aids in maintaining polarization.Additionally,the study elucidates the methodology to achieve high ESP at moderate electric fields ranging from 300 to 500 kV cm^(−1).In our optimized composition,0.5(Bi_(0.5)Na_(0.4)K_(0.1))TiO_(3)–0.5(2/3ST-1/3BMN)(B-0.5SB)ceramics,we achieved a Wrec of 7.19 J cm^(−3) with an efficiency of 93.8%at 460 kV cm^(−1).Impressively,the B-0.5SB ceramics exhibit remarkable thermal stability between 30 and 140℃ under 365 kV cm^(−1),maintaining a Wrec exceeding 5 J cm^(−3).This study not only establishes the B-0.5SB ceramics as promising candidates for ES materials but also demonstrates the feasibility of optimizing ESP by modifying the dielectric constant under specific electric field conditions.Simultaneously,it provides valuable insights for the future design of ceramic capacitors with high ESP under constraints of limited electric field.

Fabrication and Performances of 1-3-2 Piezoelectric Ceramic/Polymer Composite

A novel 1-3-2 piezoelectric composite has been developed,which consists of piezoelectric ceramic plate and 1-3 piezoelectric composite.The composite was fabricated by dicing PZT ceramic along mutual perpendicular two directions and then filling epoxy into grooves.The piezoelectric and electromechanical properties of the novel composite were determined. The results show a coefficient d_ (33) of 405pC/N,a vibration displacement of 113.5pm,an acoustic impendence of 13.3 Mraly, a bandwidth of 12kHz and a thickness electromechanical coupling coefficient of 0.56.

All-dielectric metamaterial frequency selective surface

Frequency selective surface(FSS)has been extensively studied due to its potential applications in radomes,antenna reflectors,high-impedance surfaces and absorbers.Recently,a new principle of designing FSS has been proposed and mainly studied in two levels.In the level of materials,dielectric materials instead of metallic patterns are capable of achieving more functional performance in FSS design.Moreover,FSSs made of dielectric materials can be used in different extreme environments,depending on their electrical,thermal or mechanical properties.In the level of design principle,the theory of metamaterial can be used to design FSS in a convenient and concise way.In this review paper,we provide a brief summary about the recent progress in all-dielectric metamaterial frequency selective surface(ADM-FSS).The basic principle of designing ADM-FSS is summarized.As significant tools,Mie theory and dielectric resonator(DR)theory are given which illustrate clearly how they are used in the FSS design.Then,several design cases including dielectric particle-based ADM-FSS and dielectric network-based ADM-FSS are introduced and reviewed.After a discussion of these two types of ADM-FSSs,we reviewed the existing fabrication techniques that are used in building the experiment samples.Finally,issues and challenges regarding the rapid fabrication techniques and further development aspects are discussed.

Ultra-slim electrostrains with superior temperature-stability in leadfree sodium niobate-based ferroelectric perovskite

Large electrostrains with high temperature stability and low hysteresis are essential for applications in high-precision actuator devices.However,achieving simultaneously all three of the aforementioned features in ferroelectric ceramics remains a considerable challenge.In this work,we firstly report a high unipolar electrostrain(0.12%at 60 kV/cm)in(1ex)NaNbO_(3)-x[(Ba0.85Ca0.15)(Zr_(0.1)Ti_(0.9))O_(3)](NN-xBCZT)ferroelectric polycrystalline ceramics with excellent thermal stability(variation less than 10%in the temperature range of 30-160℃)and ultra-low hysteresis(<6%).Secondly,the high-field electrostrain response is dominated by the intrinsic electrostrictive effect,which may account for more than 80%of the electrostrain.Furthermore,due to the thermal stability of the polarization in the pure tetragonal phase,the large electrostrain demonstrates extraordinarily high stability from room temperature to 140℃.Finally,in-situ piezoelectric force microscopy reveals ultra-highly stable domain structures,which also guarantee the thermal stability of the electrostrain in(NN-xBCZT ferroelectrics ceramics.This study not only clarifies the origin of thermally stable electrostrain in NN-xBCZT ferroelectric perovskite in terms of electrostrictive effect,but also provides ideas for developing applicable ferroelectric ceramic materials used in actuator devices with excellent thermal stability.

All-dielectric metamaterial frequency selective surface based on spatialarrangement ceramic resonators

In this paper,we demonstrate a method of designing all-dielectric metamaterial frequency selective surface(FSS)with ceramic resonators in spatial arrangement.Compared with the traditional way,spatial arrangement provides a flexible way to handle the permutation and combination of different ceramic resonators.With this method,the resonance response can be adjusted easily to achieve pass/stop band effects.As an example,a stop band spatial arrangement all-dielectric metamaterial FSS is designed.Its working band is in 11.65–12.23 GHz.By adjusting permittivity and geometrical parameters of ceramic resonators,we can easily modulate the resonances,band pass or band stop characteristic,as well as the working band.

Polarization insensitive metamaterial absorber based on E-shaped all-dielectric structure

In this paper,we designed a metamaterial absorber performed in microwave frequency band.This absorber is composed of E-shaped dielectrics which are arranged along different directions.The E-shaped all-dielectric structure is made of microwave ceramics with high permittivity and low loss.Within about 1 GHz frequency band,more than 86%absorption efficiency was observed for this metamaterial absorber.This absorber is polarization insensitive and is stable for incident angles.It is figured out that the polarization insensitive absorption is caused by the nearly located varied resonant modes which are excited by the E-shaped all-dielectric resonators with the same size but in the different direction.The E-shaped dielectric absorber contains intensive resonant points.Our research work paves a way for designing all-dielectric absorber.

Na/K RATIOS DEPENDENCE OF PIEZOELECTRIC AND FERROELECTRIC PROPERTIES IN(K_(1-x)Na_(x))TNbO_(3)LEAD-FREE CERAMICS

In order to clarify the Na/K ratios dependence of piezoelectric properties,(K_(1-x)Na_(x))TNbO_(3)cer-amics were prepared by conventional solid-state sintering at a=0.4-0.6 with a smaller com-positional interval(0.02 mol).The results demonstrate that the Na/K ratios have obvious effecton piezoelectric and ferroelectric properties of(K_(1-x)Na_(x))NbO_(3)ceramics.Piezoelectric and fer-roelectric properties show the maximum(d_(33)147 pc/N,k_(p)=0.40,and P_(r)=24μC/cm^(2))at=0.54,which is not consistent with conventional viewpoint.The reasons should be attributedto the existence of a phase boundary at a=0.54 mol,which is similar to the morphotropic phaseboundary in Pb(Zr,Ti)O_(3)ceramics.

Editorial-Energy storagematerials

We are glad to introduce the special issue(SI)of the Journal of Advanced Dielectrics(JAD),containing a collection of peer-reviewed papers on energy storage materials.Research on energy storage materials,one of the most extensively investi-gated materials,has grown rapidly over the past decade and has attracted great attention from physicists,chemists,materials and electronic scientists and engineers.Many research activities in this field have triggered the emergence of next generation energy storage devices,including supercapacitors,batteries and high-power pulse capacitors,demonstrating the potential for novel properties and technological innovations.This SI includes 10 feature articles,contributed by reputable research groups in Chinese universities and research institutes,and are reviewed strictly through peer review procedure,providing a comprehensive coverage on the current research status of energy storage materials and related phenomena.This SI was organized by Assoc.Prof.Hongliang Du and Assoc.Prof.Li Jin.

A transmit/reflect switchable frequency selective surface based on all dielectric metamaterials

In this paper,we propose a novel transmit/reflect switchable frequency selective surface(FSS)in millimeter wave band based on the effective medium theory under quasi-static limit,which is designed with square-hole elements cut from continuum dielectric plates.The building elements of the surface are composed of all dielectric metamaterial rather than metal material.With proper structural design and parameters tuning,the resonance frequencies can be tuned appropriately.The frequency response of the surface can be switched from that of a reflecting structure to a transmitting one by rotating the surface 90°,which means under different incident polarizations.The reflective response can be realized due to the effect of electric and magnetic resonances.Theoretical analysis shows that the reflective response arises from impedance mismatching by electric and magnetic resonances.And the transmitting response is the left-handed passband,arises from the coupling of the electric and magnetic resonances.In addition,effective electromagnetic parameters and the dynamic induced field distributions are analyzed to explain the mechanism of the responses.The method can also be used to design switchable all-dielectric FSS with continuum structures in other frequencies.