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.

Superior piezoelectric performance with high operating temperature in bismuth ferrite-based ternary ceramics

Due to the thermal depolarization effect,adequate piezoelectric performance with high operating temperature is regarded to be challenging to accomplish concurrently in piezoceramics for applications in specific piezoelectric devices.In this work,we synthesized(0.8−x)BiFeO_(3)-x PbTi_(3)-0.2Ba(Zr_(0.25)Ti_(0.75))O_(3)(abbreviated as BFO-x PT-BZT)ternary solid solutions with 0.15≤x≤0.30 by conventional solid-state reaction method.The MPB composition with a coexisting state of rhombohedral-tetragonal phases exhibits enhanced electromechanical properties,including Curie temperature of 380℃,large-signal equivalent piezoelectric coefficient d^(∗)_(33)of 395 pm V^(-1),small-signal piezoelectric coefficient d_(33)of 302 pC N^(-1),and electromechanical coupling factor k_(p)of 50.2%,which is comparable to commercial PZT-5A ceramics,indicating potential in high-temperature applications.Furthermore,in-situ X-ray diffraction(XRD)and piezoelectric force microscopic(PFM)techniques demonstrate that multiphase coexistence and complex nanodomains promote piezoelectric response via synergism.The x=0.24 composition exhibits the highest in-situ d_(33)of 577 pC N^(-1)and good temperature stability in 30−280℃,indicating that BZT-modified BFO-PT ceramics are promising candidates for high-temperature piezoelectric devices.

Creation of periodical domain structure by local polarization reversal in planar waveguide produced by soft proton exchange in LiNbO_(3)

The paper presents the results of an experimental study of the local polarization reversal and creation of domains by a biased tip of scanning probe microscope(SPM)in lithium niobate single crystals of congruent composition with a surface layer modified by soft proton exchange(SPE).The depth dependence of Ht ions concentration in the SPE-modified layer measured by confocal Raman microscopy demonstrates a sufficient composition gradient.The creation of isolated domains and stripe domain structures has been done by two switching modes:(1)point switching by field application in separated points and(2)line scanning switching by motion of the biased tip being in contact with the sample surface.For point switching for pulse durations less than 10 s,the logarithmic dependence of the domain diameter on the pulse duration was observed.The change of the dependence to a linear one for pulse duration above 10 s has been attributed to the transition from the stochastic step generation at the domain wall to the deterministic one at the domain vertexes.The periodical structure of stripe domains was created in SPE CLN planar waveguides by scanning at elevated temperature.The revealed switching regime suppresses electrostatic interaction of neighboring domains and leads to a significant improvement of the domain structure regularity.The creation of the stable periodical domain structure with submicron periods in SPE CLN planar waveguides was demonstrated.

Ferroelectric-to-relaxor transition and ultrahigh electrostrictive effect in Sm^(3+)-doped Pb(Mg_(1/3)Nb_(2/3))O_(3)-PbTiO_(3)ferroelectrics ceramics

Rare-earth Sm^(3+)-doped Pb(Mg_(1/3)Nb_(2/3))O_(3)-0.25PbTiO_(3)(PMN-0.25PT)ferroelectric ceramics with doping amounts between 0%-3%were developed via a conventional solid-state method.The doping effect of Sm^(3+)ions on the PMN-0.25PT matrix was systematically investigated on the basis of the phase structure,temperature-dependent dielectric,ferroelectric,and electrotechnical properties.Due to the disruption of long-range ferroelectric order,the addition of Sm^(3+)ions effectively lowers the Tm(temperature corresponding to maximum permittivity)of the samples,leading to enhanced relaxor ferroelectric(RFE)characteristic and superior electric field-induced strain(electrostrain)properties at room temperature.Intriguingly,a considerable large-signal equivalent piezoelectric coefficient d∗_(33)of 2376 pm/V and a very small hysteresis were attained in the PMN-0.25PT component doped with 2.5 mol.%Sm^(3+).The findings of piezoelectric force microscopy indicate that the addition of Sm^(3+)increases the local structural heterogeneity of the PMN-0.25PT matrix and that the enhanced electromechanical performance is due to the dynamic behavior of polar nanoregions.Importantly,strong temperature-dependent electrostrain and electrostrictive coefficient Q33 are observed in the critical region around Tm in all Sm^(3+)-modified PMN-0.25PT ceramic samples studied.This work elucidates the phase transition behavior of Sm^(3+)-doped PMN-0.25PT and reveals a critical region where electrostrictive properties can be greatly improved due to a strong temperature-dependent characteristic.

Self-assembled domain structures:From micro-to nanoscale

The recent achievements in studying the self-assembled evolution of micro-and nanoscale domain structures in uniaxial single crystalline ferroelectrics lithium niobate and lithium tantalate have been reviewed.The results obtained by visualization of static domain patterns and kinetics of the domain structure by different methods from common optical microscopy to more sophisticated scanning probe microscopy,scanning electron microscopy and confocal Raman microscopy,have been discussed.The kinetic approach based on various nucleation processes similar to the first-order phase transition was used for explanation of the domain structure evolution scenarios.The main mechanisms of self-assembling for nonequilibrium switching conditions caused by screening ineffectiveness including correlated nucleation,domain growth anisotropy,and domain–domain interaction have been considered.The formation of variety of self-assembled domain patterns such as fractal-type,finger and web structures,broad domain boundaries,and dendrites have been revealed at each of all five stages of domain structure evolution during polarization reversal.The possible applications of self-assembling for micro-and nanodomain engineering were reviewed briefly.The review covers mostly the results published by our research group.