Simultaneous enhancement of energy storage performance and thermal stability of NaNbO_(3)-based ceramics via multi-scale modulation

More and more attention is being paid to the environmental friendliness of the dielectric capacitors,which have a rapid charging and discharging speed and steady operation.However,the low recoverable energy storage density(W_(rec))limits the practical application of dielectric capacitors in solid-state energy storage devices.In this paper,(1-x)(0.92NaNbO_(3)-0.08Bi(Mg_(0.5)Ti_(0.5)O_(3))-xSrTiO_(3))(x=0.05,0.10,0.15,0.20)energy storage ceramics were fabricated based on various strategies such as nanodomain engineering,component and grain size optimization.Thus excellent energy storage performance(W_(rec)~6.0 J/cm^(3),η~81.0%)was obtained in NN-BMT-0.15ST.SrTiO_(3)could enhance the internal disorder,improve the relaxation properties and increase the breakdown field strength of ceramics.Signifi-cantly domain relaxor behavior,as evidenced by Vogel-Fulcher(V-F)model,provides strong evidence for restraining early polarization saturation.In addition,Pulse charge/discharge tests have illustrated that the sample has excellent and stable charge/discharge performance(CD~1,068.9 A/cm^(2),PD~96.1 MW/cm^(3),t0.9 z 0.99 ms)It is concluded that there is a huge prospect of NN-BMT-0.15ST ceramics as a kind of pulsed-power-storing electronics.

UltrahighQ Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)microwave dielectric ceramics for temperature-stable millimeter-wave dielectric resonator antennas

Microwave dielectric ceramics should be improved to advance mobile communication technologies further.In this study,we prepared Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)ceramics with nonstoichiometric Sr^(2+)ratios based on our previously reported SrY_(2)O_(4) microwave dielectric ceramic,which has a low dielectric constant and an ultrahigh quality factor(Q value).The ceramic exhibited a 33.6% higher Q-by-frequency(Q×f)value(Q≈12,500)at x=0.02 than SrY_(2)O_(4).All Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)ceramics exhibited pure phase structures,although variations in crystal-plane spacings were observed.The ceramics are mainly composed of Sr-O,Y1-O,and Y_(2)-O octahedra,with the temperature coefficient of the resonant frequency(τ_(f))of the ceramic increasing with Y_(2)-O octahedral distortion.The ceramic comprises uniform grains with a homogeneous elemental distribution,clear grain boundaries,and no obvious cavities at x=0.02.The Sr_(1+x)Y_(2)O_(4+x)(x=0-0.04)ceramics exhibited good microwave dielectric properties,with optimal performance observed at x=0.02(dielectric constant(εr)=15.41,Q×f=112,375 GHz,and τ_(f)=-17.44 ppm/℃).The τ_(f) value was reduced to meet the temperaturestability requirements of 5G/6G communication systems by adding CaTiO_(3),with Sr_(1.02)Y_(2)O_(4.02)+2wt% CaTiO_(3) exhibiting ε_(r)=16.14,Q×f=51,004 GHz,andτf=0 ppm/℃.A dielectric resonator antenna prepared using Sr_(1.02)Y_(2)O_(4.02)+2wt%CaTiO_(3) exhibited a central frequency of 26.6 GHz,with a corresponding gain and efficiency of 3.66 dBi and 83.14%,respectively.Consequently,Sr_(1.02)Y_(2)O_(4).02-based dielectric resonator antennas are suitable for use in 5G millimeter-wave band(24.5-27.5 GHz)applications.

Sintering behavior,phase composition,microstructure,and dielectric characteristics of garnet-type Ca_(3)Fe_(2)Ge_(3)O_(12) microwave ceramics

This paper describes the solid-state production of a unique yellowish-grey microwave dielectric ceramic,Ca_(3)Fe_(2)Ge_(3)O_(12)(CFG).Rietveld refinement demonstrated that CFG corresponds to a cubic system(space group 230:Ia 3 d).The relative density of the ceramic initially increased and then decreased with the sintering temperature,reaching a maximum of 96.92%at 1330℃.According to scanning electron mi-croscopy and energy-dispersive spectroscopy results,the CFG ceramic grains are spherical and consistent in size;furthermore,they have distinct grain boundaries and a uniform distribution of the four con-stituent elements.The CFG ceramic has a superior crystal structure and a high crystallinity,according to transmission electron microscopy.Raman spectroscopy revealed that the Q×f value of the ceramic and the full width at half maximum of the Raman peak are negatively correlated.The ceramic possesses the best overall dielectric characteristics after sintering at 1330℃for 4 h:ε_(r)=10.31,Q×f=82636 GHz,andτ_(f)=-45.66×10^(-6)℃^(-1),showing that it is a promising candidate for use in mobile devices.

Investigation of lead-free BiFeO_(3)–BaTiO_(3)piezoelectric ceramics through precise composition control

BiFeO_(3)-BaTiO_(3)is a promising lead-free piezoelectric ceramic,exhibiting high Curie temperature and superior electrochemical characteristics.In this work,e_(1-x)TBiFeO_(3)-xBaTiO_(3)(BF-xBT,x=0.26,0.28,0.30,0.32,0.34,0.36)ceramics were fabricated using the conventional solid-state reaction method through precise composition control.Multiple characterization techniques,including X-ray powder diffraction(XRD),scanning electron microscope(SEM),and electrical property testing systems,were applied to systematically examine the crystallographic structure,microstructure,as well as the dielectric,ferroelectric and piezoelectric properties of the BF-xBT ceramics.The XRD results confirm that all compositions exhibit a typical perovskite structure,transitioning from a single rhombohedral phase to a rhombohedral-cubic phase mixture as the BT content increases.SEM shows apparent core-shell microstructures in the ceramics.Notably,the results demonstrated that the BF-0.30BT ceramic exhibits the maximum piezoelectric constant(d_(33))-217 pC/N,while the BF-0.34BT ceramic displays the maximum converse piezoelectric constant(d_(33)^(*))-323 pm/V,which highlights the suitability of BF-BT ceramics for high-performance piezoelectric applications.

Entropy regulation in LaNbO_(4)-based fergusonite to implement high-temperature phase transition and promising dielectric properties

High-entropy effect is a novel design strategy to optimize properties and explore novel materials.In this work,(La_(1/5)Nd_(1/5)Sm_(1/5)Ho_(1/5)Y_(1/5))NbO_(4)(5RNO)high-entropy microwave dielectric ceramics were successfully prepared in the sintering temperature(S.T.)range of 1210–1290℃via a solid-phase reaction route,and medium-entropy(La_(1/3)Nd_(1/3)Sm_(1/3))NbO_(4) and(La_(1/4)Nd_(1/4)Sm_(1/4)Ho_(1/4))NbO_(4)(3RNO and 4RNO)ceramics were compared.The effects of the entropy(S)on crystal structure,phase transition,and dielectric performance were evaluated.The entropy increase yields a significant increase in a phase transition temperature(from monoclinic fergusonite to tetragonal scheelite structure).Optimal microwave dielectric properties were achieved in the high-entropy ceramics(5RNO)at the sintering temperature of 1270℃for 4 h with a relative density of 98.2%and microwave dielectric properties of dielectric permittirity(ε_(r))=19.48,quality factor(Q×f)=47,770 GHz,and resonant frequency temperature coefficient(τ_(f))=–13.50 ppm/℃.This work opens an avenue for the exploration of novel microwave dielectric material and property optimization via entropy engineering.

Dielectric temperature stability and energy storage performance of NBT-based lead-free ceramics for Y9P capacitors

In this work,novel(1−x)(0.75Na_(0.5)Bi_(0.5)TiO_(3))-0.25Sr(Zr_(0.2)Sn_(0.2)Hf_(0.2)Ti_(0.2)Nb_(0.2))O_(3)-xNaNbO_(3)(NBT-SZSHTN-xNN,x=0.1,0.15,0.2,0.25)ceramics were fabricated.The influence of co-doping of NN and high entropy perovskite oxide(SZSHTN)on the phase structure,microstructure and dielectric properties of NBT-based lead-free ceramics was investigated.Dense microstructure with a grain size of~5μm is observed.When x=0.25,a wide dielectric temperature stable range of−35.4-224.3℃ with a low temperature coefficient of capacitance of<10%is achieved,fulfilling the industry standard of Y9P specification.Furthermore,excellent energy storage performance with recoverable energy density of 2.4 J/cm^(3),discharge efficiency of 71%,power density of 25.495 MW/cm^(3) and discharge rate<200 ns are simultaneously obtained,which shows great potential for high temperature capacitor applications.

Realizing high low-electric-field energy storage performance in AgNbO_(3) ceramics by introducing relaxor behaviour

Both sustainable development in environment and safety of high-power systems require to develop a novel lead-free dielectric capacitor with high energy density(Wrec)at low applied electric field.In this work,a remarkably high Wrec of 2.9 J/cm^(3) accompanying with energy storage efficiency of 56% was achieved in Ag_(0.9)Sr_(0.05)NbO_(3) ceramic at a low applied electric field of 190 kV/cm,by improving antiferroelectricity and introducing relaxor behaviour.The improved anti-ferroelectric stability was attributed to the decreased tolerance factor and average electronegativity difference,while the relaxor behaviour was associated with the increased disordered local structure by Sr-doping.Moreover,the Ag_(0.9)Sr_(0.05)NbO_(3) ceramics also exhibited outstanding temperature stability in energy density with small variation less than 5% over 20-140℃.The results indicate that the Ag_(0.9)Sr_(0.05)NbO_(3) ceramic is a promising candidate for low-electric-field driving capacitors.

Realizing enhanced energy storage and hardness performances in 0.90NaNbO_(3)-0.10Bi(Zn_(0.5)Sn_(0.5))O_(3)ceramics

Ceramic dielectric capacitors have a broad scope of application in pulsed power supply devices.Relaxor behavior has manifested decent energy storage capabilities in dielectric materials due to its fast polarization response.In addition,an ultrahigh energy storage density can also be achieved in NaNbO_(3)(NN)-based ceramics by combining antiferroelectric and relaxor characteristics.Most of the existing reports about lead-free dielectric ceramics,nevertheless,still lack the relevant research about domain evolution and relaxor behavior.Therefore,a novel lead-free solid solution,(1-x)NaNbO_(3)-xBi(Zn_(0.5)Sn_(0.5))O_(3)(abbreviated as xBZS,x=0.05,0.10,0.15,and 0.20)was designed to analyze the domain evolution and relaxor behavior.Domain evolutions in xBZS ceramics confirmed the contribution of the relaxor behavior to their decent energy storage characteristics caused by the fast polarization rotation according to the low energy barrier of polar nanoregions(PNRs).Consequently,a high energy storage density of 3.14 J/cm^(3)and energy efficiency of 83.30%are simultaneously available with 0.10 BZS ceramics,together with stable energy storage properties over a large temperature range(20-100℃)and a wide frequency range(1-200 Hz).Additionally,for practical applications,the 0.10 BZS ceramics display a high discharge energy storage density(W_(dis)≈1.05 J/cm^(3)),fast discharge rate(t_(0.9)≈60.60 ns),and high hardness(H≈5.49 GPa).This study offers significant insights on the mechanisms of high performance lead-free ceramic energy storage materials.

Phase evolution, microstructure, electric properties of (Ba1–xBi0.67xNa0.33x)(Ti1–xBi0.33xSn0.67x)O3 ceramics

(Ba1–xBi0.67xNa0.33x)(Ti1–xBi0.33xSn0.67x)O3(abbreviated as BBNTBS,0.02≤x≤0.12)ceramics were fabricated via a traditional solid state reaction method.The phase transition of BBNTBS from tetragonal to pseudo cubic is demonstrated by XRD and Raman spectra.The BBNTBS(x=0.1)ceramics have decent properties with a highεr(~2250),smallΔε/ε25℃ values of±15%over a wide temperature range from–58 to 171℃,and low tanδ≤0.02 from 10 to 200℃.The basic mechanisms of conduction and relaxation processes in the high temperature region were thermal activation,and oxygen vacancies might be the ionic charge transport carriers.Meanwhile,BBNTBS(x=0.1)exhibited decent energy storage density(Jd=0.58 J/cm3)and excellent thermal stability(the variation of Jd is less than 3% in the temperature range of 25–120℃),which could be a potential candidate for high energy density capacitors.

High energy storage density and power density achieved simultaneously in NaNbO_(3)-based lead-free ceramics via antiferroelectricity enhancement

High-performance lead-free dielectric ceramics with simultaneously high energy storage density and power density are in high demanded for pulse power systems.To realize excellent energy-storage characteristics,a strategy to enhance antiferroelectricity and construct a local random field simultaneously was proposed in this study.Based on the above strategy,a series of(1-x)NaNbO_(3)-xBi(Ni_(1/2)Sn_(1/2))O3[xBNS,x=0.05,0.10,0.15,0.20,and 0.22]solid solutions were designed and fabricated.An ultrahigh energy storage density(Utotal)of 7.35 J/cm^(3),and recoverable energy density(Urec)of 5.00 J/cm^(3) were achieved in the 0.10BNS ceramics.In addition,an adequate stability of energy storage properties at a range of temperatures(20e140℃),frequencies(1e100 Hz),and fatigue test durations(1e1-10^(4) cycles)were realized in 0.10BNS ceramics.0.10BNS ceramics displayed a high current density of 1005 A/cm2,an ultrahigh power density of 100.5 MW/cm^(3,)and an ultrashort discharge time of 46.5 ns?This remarkable performance not only justified our strategy but also confirmed 0.10BNS ceramics as a promising candidate for energy storage.

Phase engineering in NaNbO_(3) antiferroelectrics for high energystorage density

The NaNbO_(3) antiferroelectrics have been considered as a potential candidate for dielectric capacitorsapplications. However, the high-electric-field-unstable antiferroelectric phase resulted in low energystorage density and efficiency. Herein, good energy storage properties were realized in (1-x)NaNbO_(3)- xNaTaO_(3) ceramics, by building a new phase boundary. As a result, a high recoverable energy density(Wrec) of 2.2 J/cm3 and efficiency (h) of 80.1% were achieved in 0.50NaNbO_(3)-0.50NaTaO_(3) ceramic at300 kV/cm. The excellent energy storage performance originates from an antiferroelectric-paraelectricphase boundary with simultaneously high polarization and low hysteresis, by tailoring the ratio ofantiferroelectric and paraelectric phases. Moreover, the 0.50NaNbO_(3)-0.50NaTaO_(3) ceramic also exhibitedgood temperature and frequency stability, together with excellent charge-discharge performance. Theresults pave a good way of designing new NaNbO_(3)-based antiferroelectrics with good energy storageperformance.

Lattice vibrational characteristics,crystal structures and dielectric properties of non-stoichiometric Nd_((1+x))(Mg_(1/2)Sn_(1/2))O_(3) ceramics

Non-stoichiometric Nd_((1+x))(Mg_(1/2)Sn_(1/2))O_(3)(-0.04=x≤0.04,NMS)ceramics were fabricated via a conventional solid-state reaction method.Crystal structures and morphologies were investigated by Xray diffraction(XRD)and scanning electron microscopy(SEM),respectively.The main crystalline phase is monoclinic Nd(Mg_(1/2)Sn_(1/2))O_(3) with a double perovskite structure(P21/n space group)for the NMS system proved by XRD.The sample at x=0.01 has the best crystallinity and evenly distributed crystal grains observed by SEM.The optimum performances(ε_(r)=19.87,Q×f=41840 GHz,f=12.05 GHz)are obtained at x=0.01.Lattice vibrational modes of the Raman spectra were assigned and illustrated,in detail.The dielectric properties obtained by fitting infrared reflectance spectra with the help of four-parameter semi-quantum model are consistent with the calculated values by microscopic polarization and damping coefficients.The reverse translational vibration of the NdeMgO_(6),the F_(5u)^((5)) mode,provides the greatest contribution to the dielectric response.The relationships between crystal structures and dielectric properties were mainly established using lattice vibrational modes as a media.

Enhanced thermal and frequency stability and decent fatigue endurance in lead-free NaNbO_(3) -based ceramics with high energy storage density and efficiency

Lead-free ceramic capacitors have the application prospect in the dielectric pulse power system due to the advantages of large dielectric constant,lower dielectric loss and good temperature stability.Never-theless,most reported dielectric ceramics have limitation of realizing large energy storage density(W_(rec))and high energy storage efficiency(h)simultaneously due to the low breakdown electric field(E_(b)),low maximum polarization and large remanent polarization(P_(r)).These issues above can be settled by raising the bulk resistivity of dielectric ceramics and optimizing domain structure.Therefore,we designed a new system by doping(Bi_(0.5)Na_(0.5))_(0.7)Sr_(0.3)TiO_(3) into 0.9NaNbO_(3)-0.1Bi(Ni_(0.5)Zr_(0.5))O_(3) ceramics,which simulta-neously obtained a higher bulk resistivity by decreasing the grain size and achieved a smaller P_(r) by optimizing domain structure,thus the better E_(b) of 530 kV/cm and W_(rec) of 6.43 J/cm^(3) were achieved,h was improved from 34%to 82%.Besides,the 0.4BNST ceramics show excellent temperature,frequency and fatigue stability under the conditions of 20-180℃,1-100 Hz and 104 cycles,respectively.Mean-while,superior power density(P_(D)=107 MW/cm^(3)),large current density(C_(D)=1070 A/cm^(2))and discharge speed(1.025 m s)were achieved in 0.4BNST ceramic.Finally,the charge-discharge performance displayed good temperature stability in the temperature range of 30℃-180℃.The above results indicated that the ceramics have potential practical value in the field of energy storage capacitor.

Sintering behaviour and microwave dielectric properties of MgO-2B_(2)O_(3)--xwt%BaCu(B_(2)O_(5))-ywt%H_(3)BO_(3) ceramics

This study investigates the bulk density,sintering behaviour,and microwave dielectric properties of the MgO-2B_(2)O_(3) series ceramics synthesised by solid-state reaction.According to the X-ray diffraction and microstructural analyses,the as-prepared MgO-2B_(2)O_(3) ceramics possess a single-phase structure with a rod-like morphology.The effects of different quantities of H_(3)BO_(3) and BaCu(B_(2)O5)(BCB)on the bulk density,sintering behaviour,and microwave dielectric properties of the MgO-2B_(2)O_(3) ceramics were investigated.Accordingly,the optimal sintering temperature was obtained by adding 30 wt%H_(3)BO_(3) and 8 wt%BCB.We also reduced the sintering temperature to 825°C.Furthermore,the addition of 40 wt%H_(3)BO_(3) and 4 wt%BCB increased the quality factor,permittivity,and temperature coefficient of resonance frequency of MgO-2B_(2)O_(3) to 44,306 GHz(at 15 GHz),5.1,and-32 ppm/℃,respectively.These properties make MgO-2B_(2)O_(3) a viable low-temperature co-fired ceramic with broad applications in microwave dielectrics.

A first-principle study on the electronic properties of substitutionally Cu(Ⅰ,Ⅱ)-doped LiNbO_(3)

The electronic properties of Cu-doped lithium niobate(LiNbO_(3))systems are investigated by first-principles calculations.In this work,we focus on substitutionally Cu→Li-doped LiNbO_(3) system with cuprous and cupric doping,which corresponds to the Li_(5/6)Cu_(1/6)NbO_(3) and Li_(4/6)Cu_(1/6)NbO_(3)[abbreviated as(Li,Cu Ⅰ)NbO_(3) and(Li,Cu Ⅱ)NbO_(3)].The density functional theory(DFT)calculations show that the electronic property of LiNbO_(3) is completely different from(Li,Cu Ⅰ)NbO_(3) and(Li,Cu Ⅱ)NbO_(3).The calculated band structure and density of state(DOS)of(Li,Cu Ⅰ)NbO_(3) show a small band gap of 1.34 eV and the top of valance band(VB)is completely composed of a doping energy level originating from Cu 3d filled orbital.However,the calculated band structure and DOS of(Li,Cu Ⅱ)NbO_(3) show a relatively large band gap of 2.22 eV and the top of VB is mainly composed of Cu 3d unfilled orbital and O 2p orbital.

Giant permittivity and good thermal stability of LiCuNb_(3)O_(9)-Bi(Mg_(0.5)Zr_(0.5))O_(3) solid solutions

(1-x)LiCuNb_(3)O_(9)-Bi(Mg_(0.5)Zr_(0.5))O_(3) ceramics((1-x)LCN-xBMZ)with 0≤x≤0.08 were synthesized by a solid-state reaction method.The phase structure of(1-x)LCN-xBMZ ceramics was characterized by X ray diffraction(XRD),which revealed that the ceranics were distorted cubic perovskite structures.Apparent giant permitivity of 1.98× 10^(4)-1.05× 10^(5) at 100kHz over the measured temperature range(259℃-250℃)was observed in the sintered(1-x)LCN-xBMZ(0≤x≤0.08)ceramics.Especially for the sample of x=0.04,the temperature stability of permitivity was markedly increased(△ε/ε100℃≤±15%),and high relative permitivity(>8.3 × 10^(4))were obtained over a wide temperature range from 100℃ to 250℃at 100 kHz,which indicates that this ceramic is a promising dielectrice material for elevated temperature dielectrics.The giant dielectric property of(1-x)LCN-xBMZ ceramics are profoundly concerned with the Maxwell-Wagner effect.