A series of the samples La_(1-x)(Sr_(1-y)Na_y)_xMnO_3(y=0.0,0.2,0.4,0.6,0.8,1.0) were prepared by the solid-state reaction method.Magnetoresistance enhancement and temperature stability of magnetoresistance in the sys...A series of the samples La_(1-x)(Sr_(1-y)Na_y)_xMnO_3(y=0.0,0.2,0.4,0.6,0.8,1.0) were prepared by the solid-state reaction method.Magnetoresistance enhancement and temperature stability of magnetoresistance in the system La_(1-x)(Sr_(1-y)Na_y)_xMnO_3 with unchanged Mn^(3+)/Mn^(4+) ratio through the doping of both monovalent and divalent elements at A site were studied through the measurements of X-ray diffraction(XRD) patterns,resistivity-temperature(ρ-T) curves and magnetoresistance-temperature(MR-T) curves.The results indicate that with the increase of Na doping amount,the peak value of MR increases,and it increases from 12.4% for y=0.2 to 50.6% for y=1.0 in the magnetic field B=0.8 T;ρ-T curves exhibit the double-peak phenomenon,which comes from the competition between the resistivity of surface phase and that of body phase;for the sample of y=0.8,MR increases slowly from 8.3% to 9.4% in the temperature range from 259 to 179 K,and MR is so stable in such a wide temperature range,which provides reference for the research on the temperature stability of MR.展开更多
The novel nitride-based luminescent materials have received much attention since the end of the last century. In this paper, the commercial Eu2＋-activated nitride red phosphors, Sr1.95Si5N8：Eu0.05, Sr1.85Si5N8：Eu0....The novel nitride-based luminescent materials have received much attention since the end of the last century. In this paper, the commercial Eu2＋-activated nitride red phosphors, Sr1.95Si5N8：Eu0.05, Sr1.85Si5N8：Eu0.15 and Ca0.99AlSiN3：Eu0.01 phosphors were an-nealed at different temperatures （beyond 300 oC） to investigate the dependence of their luminescence performance and structure vari-ability on the temperature. By photoluminescence spectra, X-ray diffraction （XRD） and thermogravimetry-differential scanning calo-rimetry （TG-DSC） analysis, the high temperature stability of the hosts and activator of the three samples were disclosed. With the an-nealing temperature increasing, the activator Eu2＋ions were firstly oxidized and then host in Sr1.95Si5N8：Eu0.05 and Sr1.85Si5N8：Eu0.15, but for Ca0.99AlSiN3：Eu0.01, only the oxidation of the host could be observed, which would lead to the luminescence degradation and even failure of these phosphors. The activator Eu2＋ions were much more stable in CaAlSiN3：Eu than Sr2Si5N8：Eu due to their crystal surroundings, and its concentration also influenced the temperature stability of Sr2Si5N8：Eu.展开更多
In this work,a novel high entropy perovskite oxide(1-x)(Na_(0.2)Bi_(0.2)Ba_(0.2)Sr_(0.2)Ca_(0.2))TiO_(3-x)NaNbO_(3)(abbrevi-ated as(1-x)NBBSCT-x NN,x=0,0.05,0.1,0.15,and 0.2)was designed to improve temperature dielect...In this work,a novel high entropy perovskite oxide(1-x)(Na_(0.2)Bi_(0.2)Ba_(0.2)Sr_(0.2)Ca_(0.2))TiO_(3-x)NaNbO_(3)(abbrevi-ated as(1-x)NBBSCT-x NN,x=0,0.05,0.1,0.15,and 0.2)was designed to improve temperature dielectric stability and energy storage performance by combining relaxor and antiferroelectric characteristics.The optimal composition of x=0.2 exhibits a high energy storage density of 3.51 J/cm^(3),together with wide temperature stable stability(■<15%,-70 to 110℃),excellent frequency stability(W rec andηvary by only±2.1%and±5.2%within the range of 1-600 Hz)and fast discharge rate(t_(0.9)=55.2 ns).This is mainly due to the enhancement of relaxation behavior and increase of E b caused by the decrease of grain size.These results offer a new strategy for designing high entropy ceramic materials of high performance in the future.展开更多
The oxidation resistance behavior of SmCo(2:17)-type high-temperature magnets modified with Ni-Cr two-layer coating was studied. The study depicts the mass gain kinetics and magnetic properties of uncoated and NiCr-mo...The oxidation resistance behavior of SmCo(2:17)-type high-temperature magnets modified with Ni-Cr two-layer coating was studied. The study depicts the mass gain kinetics and magnetic properties of uncoated and NiCr-modified magnets oxidized at high temperature(500 ℃) in air for 200 h. The oxidation test results illustrate that the mass gain of uncoated magnet is6.95 mg·cm^(-2) which is more than that(0.08 mg·cm^(-2)) of coated magnet after 200 h. For the magnetic properties concerned, there is a great loss for uncoated magnet, while for coated magnet, magnetic properties do not change much. The study of uncoated magnet through X-ray diffraction(XRD) and electron probe microanalysis(EPMA) shows that the invasion of oxygen at high temperature leads to the loss of magnetic properties by changing the microstructure of magnet.展开更多
The flourishing development of emerging electromechanical applications has stimulated an urgent demand for ferroelectric ceramics with high piezoelectric properties and broad temperature usage range.However,it remains...The flourishing development of emerging electromechanical applications has stimulated an urgent demand for ferroelectric ceramics with high piezoelectric properties and broad temperature usage range.However,it remains a challenge to simultaneously obtain good piezoelectricity and reliable temperature stability in lead zirconate titanate(PZT)-based piezoelectric ceramics.To solve this issue,a synergetic strategy was proposed to introduce lead vacancies through niobium doping and construct morphotropic phase boundary(MPB).In this work,Pb_(0.905)Ba_(0.085)(V Pb″)_(0.01)[(Zr_(x)Ti_(1-x))_(0.98)Nb_(0.02)]O_(3)(PBZTN-x)material system was designed.Good comprehensive properties(d_(33)=864 pC/N,k_(p)=84%,T_(C)=201℃)and excellent temperature stability(less than 10%variation of electrical properties from 20℃ to 160℃)were obtained in PBZTN-0.540 ceramics.Good piezoelectricity can be attributed to high extrinsic contribution(domain wall motion)induced by Pb^(2+)vacancies and the existence of nano-domains emerged at MPB,while excellent temperature stability is mainly attributed to the minimized local stress in the lattice and the stable domain structure.展开更多
Polycrystalline samples of Lal-x（Srl-yAgy）x MnO3 （y = 0.0, 0.2, 0.4, 0.6, 1.0） were prepared by the solid-state reaction method. The temperature stability of magnetoresistance and magnetoresistance enhancement in ...Polycrystalline samples of Lal-x（Srl-yAgy）x MnO3 （y = 0.0, 0.2, 0.4, 0.6, 1.0） were prepared by the solid-state reaction method. The temperature stability of magnetoresistance and magnetoresistance enhancement in Lal_x（Srl_yAgy）~MnO3 system with both univalent and bivalent elements doped at A site and with unchanged value of Mn~＋/Mn4＋ ratio were explored through the measurements of X-ray diffraction patterns, magnetiza- tion-temperature （M-T） curves, resistivity-temperature （p-T） curves and magnetoresistance-temperature （MR-T） curves. The results are as follows： there are two peaks in the p-T curves of the samples with Ag doping, one is caused by resistance change during the paramagnetism- ferromagnetism transition, and the other is from boundary- dependent scattering of conduction electrons on the boundaries of grains. The peak value of MR increases with increasing Ag doping content, and it increases from 8.2 % for y ---- 0.2 to 29.6 % for y ---- 1.0 under the magnetic field of B = 0.8 T; MR remains a constant of 12 % in the temperature range of 218-168 K for the sample with y = 1.0, and the temperature stability of MR is in favor of the practical application of MR.展开更多
In order to analyze the influence of the addition of yttrium and manganese on the soot combustion performance and high temperature stability of CeO_(2) catalyst,a series of Y/Mn-modified CeO_(2) catalysts were prepare...In order to analyze the influence of the addition of yttrium and manganese on the soot combustion performance and high temperature stability of CeO_(2) catalyst,a series of Y/Mn-modified CeO_(2) catalysts were prepared.The effects of structural properties,textural properties,oxygen vacancies,Ce^(3+),surface adsorbed oxygen species,reduction properties and desorption properties of oxygen species on the activity were analyzed by various characterization methods.The results of the activity test show that the addition of manganese is beneficial to enhancement of the activity,while the addition of yttrium increases the amount of reactive oxygen species,but decreases the activity.After aging at 700℃,the activity of the CeMn catalyst decreases most sharply,while the catalytic activity of the CeY catalyst can be maintained to a certain extent.Interestingly,the addition of yttrium and manganese at the same time can stabilize the activity.The fundamental reason is that yttrium and manganese move to the surface of the solid solution after aging,which increases the reduction performance of the catalyst,thus contributing to the increase of activity.Although the activity of CeYMn catalyst decreases after aging at 800℃,it is still higher than that of other catalysts aged at 700℃.展开更多
In this study, finite element analysis based on an Ansoft Maxwell software was used to reveal the temperature stability of a magnet ring and the equivalent structural periodic permanent-magnet（PPM） focusing system. ...In this study, finite element analysis based on an Ansoft Maxwell software was used to reveal the temperature stability of a magnet ring and the equivalent structural periodic permanent-magnet（PPM） focusing system. It is found that with the temperature increasing, the decrease rate of magnetic induction peak（Bz）maxof single magnet ring is greater than that of remanence Brof magnet in the range from room temperature to 200 °C, however,the PPM focusing system do have the same temperature characteristics of permanent-magnet materials. It indicates that the magnetic temperature properties of the PPM system can be effectively controlled by adjusting the temperature properties of the magnets. Moreover, the higher permeability of the magnets indicates the less Hcb, giving rise to lower magnetic induction peak （Bz）′max： Finally, it should be noted that the magnetic orientation deviation angle θ（／15°） of permanent magnets has little effect on the focusing magnetic field of the PPM system at different temperatures and the temperature stability. The obtained results are beneficial to the design and selection of permanent magnets for PPM focusing system.展开更多
The temperature stability of supercapacitor（SC） is largely determined by the properties of the electrolyte.Hydrogel electrolytes（HGE）, due to their hydrophilic polymer skeleton, show different temperature stabilit...The temperature stability of supercapacitor（SC） is largely determined by the properties of the electrolyte.Hydrogel electrolytes（HGE）, due to their hydrophilic polymer skeleton, show different temperature stability to that of liquid aqueous electrolytes. In this study, symmetric activated carbon（AC） SCs had been assembled with in situ electrodeposited poly（vinyl alcohol） potassium borate（PVAPB） HGE. The electrochemical performance of the SCs was systematically studied at different temperatures. Results show that the conductivity of PVAPB HGE is comparable with that of liquid aqueous electrolytes at different temperatures. The operating temperature range of PVAPB HGE SCs is -5–60°C, while those of the 1 mol/L Na2SO4SCs and the 0.9 mol/L KClSCs are 20–80°C and 20–40°C, respectively. The specific capacitance of PVAPB HGE SC is higher than those of SCs using liquid aqueous electrolytes at any temperature. The excellent temperature stability of PVAPB HGE makes it possible to build stable aqueous SCs in the wider temperature range.展开更多
High temperature self-propagating synthesis （SHS） process is very rapid, the reaction process becomes un-controlled after the SHS reaction is ignited. So the initial reaction conditions will have great effects on ph...High temperature self-propagating synthesis （SHS） process is very rapid, the reaction process becomes un-controlled after the SHS reaction is ignited. So the initial reaction conditions will have great effects on phase compositions and microstructures of reaction products. In this paper, the effects of the proportioning amount of Mg on the yield ratio and particle sizes of CeB6 were studied. The SHS reaction products and leached products were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results indicated that the SHS products consisted of MgO, CeB6 and little Mg3B206. The single CeB6 phase was contained after the SHS reaction products were leached. The purity of CeB6 was higher than 99.0 mass%, and the minimum particle sizes of CeB6 were within 30-70 nm. When the propor- tioning amount of Mg was 25% more than the theoretic amount, the yield of CeB6 was 68.68%. The antioxidant ability of CeB6 was rather stronger, which was oxidized step by step, and the initial oxidation temperature was 750 ℃ which indicated that it had good high temperature stability. The apparent activation energies of oxidation reactions of CeB6 were 200.09 and 312.10 kJ/mol, respectively, and reaction orders were 0.69 and 0.40, respectively.展开更多
Temperature stability and toughness of magnets are very important properties especially for application in motor. In this paper, it is found that temperature stability and toughness of magnets are improved when Fe is ...Temperature stability and toughness of magnets are very important properties especially for application in motor. In this paper, it is found that temperature stability and toughness of magnets are improved when Fe is substituted with Co and heavy rare earth is substituted for Nd in part and suitable rich B grain-boundary phase is added. In addition, heavy rare earth substitution decreases the remanence temperature coefficient greatly, but has a little effect on Curie temperature of the magnets, which is beneficial to Nd-Fe-B magnets for the application in motor.展开更多
The coupling efficiency of hollow-core fiber changes with temperature,which leads to the decrease of the finesse(F)of fiber resonator and limits the performance of the resonant fiber optic gyroscope(R-FOG)system.Negat...The coupling efficiency of hollow-core fiber changes with temperature,which leads to the decrease of the finesse(F)of fiber resonator and limits the performance of the resonant fiber optic gyroscope(R-FOG)system.Negative-curvature antiresonant fiber(ARF)can maintain single-mode characteristics under the condition of large mode field diameter,achieve efficient and stable fiber coupling,and significantly improve the consistency of the F of the spatial coupling resonator in variable temperature environment.A new type of ARF with a mode field diameter(MFD)of 25μm is used to fabricate a fiber resonator with a length of 5.14 m.In the range of 25℃-75℃,the average F is 31.45.The ARF resonator is used to construct an R-FOG system that shows long-term bias stability(3600 s)of3.1°/h at room temperature,4.6°/h at 75℃.To our knowledge,this is the best reported index of hollow-core fiber resonator and R-FOG system within the temperature variation range of 50℃ test.展开更多
The poor temperature stability of the BaTiO_(3) ceramic has always been the main problem limiting their application.This situation has been improved but sacrifices the intrinsic polarization,which significantly reduce...The poor temperature stability of the BaTiO_(3) ceramic has always been the main problem limiting their application.This situation has been improved but sacrifices the intrinsic polarization,which significantly reduces the dielectric constant.In this work,the mechanism of multiple polarization was creatively introduced,and the temperature stability and dielectric properties of BaTiO_(3)-based ceramics are simultaneously enhanced.In particular,the Ba_(0.9925)Bi_(0.005)Ti_(0.995)Ca_(0.005)O_(2.995)(BBTC0.5)ceramic sample achieved excellent temperature stability(-14.8%to 8.85%)over an ultra-wide temperature range(-47 to 400℃)and exhibited colossal permittivity(27,125,25℃,1 kHz)and low dielectric loss(0.07,25℃,1 kHz).The dielectric properties,complex impedance spectra combined with XPS results indicate that the defective dipole clusters(Ti^(3+)-V_(O)-Ti^(3+),Bi_(Ba) and Ca″_(Ti)-V_(O))along with surface effects lead to colossal permittivity effect.More importantly,SEM images show the presence of the second phase at grain boundaries,which prevent the carriers within the grains from accumulating at the grain boundaries.As a result,the dielectric loss was reduced and the temperature stability was further extended.This strategy breaks the traditional limitation of single/noncomprehensive enhancement by singlepolarization mechanism,and is of great theoretical and practical significance to promote the research and application of high-performance BaTiO_(3)-based ceramic materials.展开更多
BiFeO_(3)-BaTiO_(3)(BF-BT)ceramics exhibit higher piezoelectric coefficients(d33),Curie temperatures(T_(C)),and temperature stability than other high-temperature lead-free piezoelectric materials.However,despite their...BiFeO_(3)-BaTiO_(3)(BF-BT)ceramics exhibit higher piezoelectric coefficients(d33),Curie temperatures(T_(C)),and temperature stability than other high-temperature lead-free piezoelectric materials.However,despite their crucial role in piezoelectric devices,the mechanical properties of BF-BT ceramics have been underexplored.A thorough evaluation of the mechanical properties of BF-BT is crucial for developing cost-effective and durable lead-free piezoelectric ceramics.Moreover,the specific causes of the high piezoelectric response and excellent temperature stability of BFeBT ceramics remain unclear owing to the instrumental detection threshold,which limits experimental studies to temperatures above 140C and below the degradation temperature of d33.To investigate the intrinsic origins of the high piezoelectricity and temperature stability of BF-BT ceramics and to enhance their mechanical properties,a two-step sintering process is used to fabricate these ceramics(0.25≤x≤0.40).Owing to improvements in grain refinement and reduced Bi3t volatilization,the BFe0.33 BT ceramic exhibits enhanced overall performance,with a modified small punch strength of 155 MPa,Vickers hardness of 5.2 GPa,a d33 of 220 pC/N at room temperature,T_(C)of 466℃,and d33 values exceeding 400 pC/N at 260℃.Phase-field simulations,which address the limitations of device detection thresholds,reveal that with increasing temperature,the domain structure relaxes,and polarization intensity decreases.This indicates that changes in the high-temperature piezoelectric properties can be attributed to domain structure relaxation and the increase in dielectric constant.Overall,BFeBT ceramics exhibit superior piezoelectric performance,mechanical properties,and temperature stability,making them highly suitable for use in high-temperature and demanding environments.展开更多
BaTiO_(3) (BT)-based piezoceramics with large temperature-stable strains and low hysteresis are urgently needed for high-precision actuators because of increasing environmental problems. Here, tetragonal [001]c-textur...BaTiO_(3) (BT)-based piezoceramics with large temperature-stable strains and low hysteresis are urgently needed for high-precision actuators because of increasing environmental problems. Here, tetragonal [001]c-textured (Ba_(0.98)Ca_(0.02))(Ti_(0.96)Sn_(0.04))O_(3) (BCTS) ceramics with a texture degree (F_(001)) of ~98% were obtained via the templated grain growth (TGG) method. A large maximum unipolar strain (S_(max)) of ~0.24% with a low strain hysteresis (Hs) of ~3.8% and an optimized piezoelectric strain coefficient (d_(33)^(*)) of ~1124 pm·V^(−1) are simultaneously achieved in the textured BCTS ceramics. Moreover, the variation in the strain response is less than 20% from room temperature (RT) to 100℃ for the textured ceramics. The underlying mechanism for the optimized strain performance could be attributed to the synergetic effect of the polarization extension and a fine domain structure. This work provides new insight for achieving a balance of multiple strain properties (large strain, low hysteresis, and high-temperature stability) in BT-based ceramics, showing the widespread application prospects of lead-free ceramics in high-precision actuators.展开更多
The semi-transparency to thermal radiation,coupled with low nanoparticle retention and formation of semi-melted particles during plasma spraying,significantly limits the hightemperature application of nanostructured y...The semi-transparency to thermal radiation,coupled with low nanoparticle retention and formation of semi-melted particles during plasma spraying,significantly limits the hightemperature application of nanostructured yttria stabilized zirconia(YSZ)(nYSZ)thermal barrier coatings.To address these challenges,this study introduces an innovative approach that involves coating nanoparticles with carbon films to prevent them from melting and merging during the plasma spraying process.This method substantially increases the nanoparticle content within the coating,and nanopores formed at the nanoparticle surfaces when the carbon film is removed at 800℃.These nanopores,in combination with nanoparticles,enhance thermal radiation scattering,improving the scattering coefficient and thermal radiation blocking capability of the coating.In contrast to that of conventional thermal barrier coatings(TBCs)of YSZ,the simulated temperature of the substrate under service conditions decreases by up to 26.26 K due to decreased radiative heat transfer and by 111.2 K when the thermal conductivity is reduced.Additionally,the scattering coefficients remain stable within the 1-5μm range even after heat treatment at 1300°C for 100 h,as the coarsened nanoparticle size approaches the wavelength of thermal radiation.Thus,nYSZ TBCs with enhanced thermal radiation blocking ability and high temperature stability can be created by this approach for higher temperature applications.展开更多
Olivine-type A_(2)BO_(4)ceramics possess a low permittivity(ε_(r))and low dielectric loss,contributing to a high quality factor(Q×f).However,the large negative temperature coefficient of the resonant frequency(...Olivine-type A_(2)BO_(4)ceramics possess a low permittivity(ε_(r))and low dielectric loss,contributing to a high quality factor(Q×f).However,the large negative temperature coefficient of the resonant frequency(τ_(f))restricts their practical applications.In this work,we prepared a series of CaYGa_(1−x)Al_(x)O_(4)(x=0–1)ceramics with lowε_(r)values via solid-state sintering.By controlling the evolution of orthorhombic olivine to the tetragonal perovskite-like structure(K_(2)NiF_(4))and the ordered regulation of the A-site,an ultralow loss(tanδ=1.38×10^(−4),Q×f=125,530 GHz,and f=17.3 GHz for x=0)and a nearly zero temperature coefficient(τ_(f)=−0.5 ppm/°C for x=0.9)were achieved.The significant changes in the dielectric properties(ε_(r)=8.3–16.2,Q×f=125,530–50,660 GHz,andτ_(f)=−50.9 to 2.9 ppm/°C)of these ceramics are primarily influenced by the characteristics of the second phase,ion polarization,ion order and disorder,and the chemical bonds resulting from structural evolution.Furthermore,a cylindrical dielectric resonator antenna(CDRA)was designed using an ultralow-loss CaYGaO_(4)ceramic,achieving a high gain(5.36–6.15 dBi)and efficiency(>90%)in the bandwidth region(5.065–5.747 GHz),thereby enhancing the efficiency and quality of 5G communications.This work advances the development of control strategies for high-performance dielectric ceramics and dielectric resonator antennas in high-frequency communications.展开更多
Lead-free ceramics with both high piezoelectric response and good temperature stability are urgently demanded for electromechanical conversion devices.Unfortunately,owing to coexistence of poly-morphic phases near roo...Lead-free ceramics with both high piezoelectric response and good temperature stability are urgently demanded for electromechanical conversion devices.Unfortunately,owing to coexistence of poly-morphic phases near room temperature(RT),enhanced piezoelectric properties were usually achieved with occurrence of strong temperature dependence in modified BaTiO_(3)(BT)-based ceramics.In this work,we demonstrate that tailoring grain orientations of tetragonal BT-based ceramics can effectively produce substantially enhanced and thermally stabilized piezoelectric response.Both<001>c-and<111>c-oriented tetragonal(Ba_(0.85)Ca_(0.15))(Zr_(0.05)Ti_(0.95))O_(3)(BCZT)ceramics with texture degrees F>90%were synthesized via templated grain growth.Interestingly,the ceramics textured along the<001>c polar axis show much higher microscopic and macroscopic piezoelectric properties than those with nonpolar<111>c texture,indicating an“extender”ferroelectricity nature.Compared with randomly oriented samples,the<001>c-oriented ceramics exhibit simultaneously~1.6 times higher piezoelectric strain d_(33)^(*)(~760 pm/V),4.4 times higher piezoelectric figure of merit d_(33)×g_(33)(8.8×10^(-12) m^(2)/N),and better temperature stability(strain variation≤5%between RT and 110℃).Such thermally stabilized strain response can be mainly attributed to wide temperature range of tetragonal phase and stable domain structure.This work provides a promising route for further developing lead-free piezoceramics with high and temperature-insensitive performance,which can greatly broaden their application areas.展开更多
Considering the advantages of high Curie temperature and environment-friendly nature of KNN piezoelectric ceramics,the limitation of weak piezoelectric response and their temperature sensitivity to applications is wor...Considering the advantages of high Curie temperature and environment-friendly nature of KNN piezoelectric ceramics,the limitation of weak piezoelectric response and their temperature sensitivity to applications is worth exploring.Herein,the<001>textured(1-x)(K_(0.5)Na_(0.5))(Nb0.96Sb0.04)O3-x(Bi_(0.5)Na_(0.5))HfO_(3)(x=0.01-0.045)lead-free ceramics were synthesized by templated grain-growth method.The high piezoelectric performance(d33 of 474 pC/N and strain of 0.21%)and excellent temperature stability(unipolar strain maintained within 4.3%change between 30℃and 165℃)were simultaneously achieved in the textured KNNS-0.03BNH ceramics.The high piezoelectric performance can be attributed to the summation of the crystallographic anisotropy and phase structure contributions in<001>textured ceramics.The superior temperature stability of piezoelectric properties can be interpreted by the contribution of crystal anisotropy to piezoelectric properties reduces the effect of phase transition on piezoelectric properties deterioration.This study provides an effective strategy for simultaneously achieving high piezoelectric properties and superior temperature stability in KNN-based textured ceramics.展开更多
It is a very difficult work to sinter K_(0.5)Na_(0.5)NbO_(3)(KNN)-based materials with good reduction resistance in strong reducing atmosphere.0.945K_(0.48)Na_(0.52)Nb_(0.96)Ta_(0.04)O_(3)-0.055BaZrO_(3)+0.03ZrO_(2)+y...It is a very difficult work to sinter K_(0.5)Na_(0.5)NbO_(3)(KNN)-based materials with good reduction resistance in strong reducing atmosphere.0.945K_(0.48)Na_(0.52)Nb_(0.96)Ta_(0.04)O_(3)-0.055BaZrO_(3)+0.03ZrO_(2)+y mol%MnO(KNNT-0.055BZ+0.03Zr+yMn)ceramics sintered in reducing atmosphere were prepared successfully by conventional solid-state reaction methods.MnO dopant increases grain size at y=5-8 due to strong lattice distortion and then decreases grain size at y=9 due to much Mn4Nb2O9 accumulated at the grain boundary.MnO dopant as an excellent sintering aid can effectively reduce volatilization of alkali metal by decreasing the sintering temperature(T_(sinter)).Reducing alkali metal volatilization can greatly reduce oxygen vacancies and improve piezoelectric properties.MnO dopant can improve the anti-reduction properties.The KNNT-0.055BZ+0.03Zr+yMn ceramics aty=6-9 show outstanding anti-fatigue of unipolar piezoelectric strain under the synergistic effect of reduced oxygen vacancies due to reduced volatilization and increased grain size.Piezoelectric properties and temperature stability of KNNT-0.055BZ+0.03Zr ceramics sintered in reducing atmosphere are improved simultaneously by MnO dopant.Optimum inverse piezoelectric coefficient(d33)of ceramics at y=8 reaches up to 480 pm/V under low driving electric field E=20 kV/cm at room temperature,and its temperature stability of d33 reaches 158℃.It will be an excellent lead-free material candidate for the preparation of multilayer piezoelectric actuators co-fired with nickel electrode.展开更多
基金supported by the National Natural Foundation of China (No. 19934003)the Natural Science Research Key Program of Anhui Educational Committee (No. KJ2011A259)+2 种基金the Cultivating Base of Anhui Key Laboratory of Spintronics and Nano-materials Research Program(No. 2010YKF01No. 2010YKF04)the Professors’ and Doctors’ Research Startup Foundation of Suzhou University (Nos. 2011jb01 and 2011jb02)
文摘A series of the samples La_(1-x)(Sr_(1-y)Na_y)_xMnO_3(y=0.0,0.2,0.4,0.6,0.8,1.0) were prepared by the solid-state reaction method.Magnetoresistance enhancement and temperature stability of magnetoresistance in the system La_(1-x)(Sr_(1-y)Na_y)_xMnO_3 with unchanged Mn^(3+)/Mn^(4+) ratio through the doping of both monovalent and divalent elements at A site were studied through the measurements of X-ray diffraction(XRD) patterns,resistivity-temperature(ρ-T) curves and magnetoresistance-temperature(MR-T) curves.The results indicate that with the increase of Na doping amount,the peak value of MR increases,and it increases from 12.4% for y=0.2 to 50.6% for y=1.0 in the magnetic field B=0.8 T;ρ-T curves exhibit the double-peak phenomenon,which comes from the competition between the resistivity of surface phase and that of body phase;for the sample of y=0.8,MR increases slowly from 8.3% to 9.4% in the temperature range from 259 to 179 K,and MR is so stable in such a wide temperature range,which provides reference for the research on the temperature stability of MR.
基金Project supported by the National Natural Science Foundation of China(51102021)the Ministry of Science and Technology of China(2014CB643801,2011AA03A101)the Beijing Nova Program(2012099)
文摘The novel nitride-based luminescent materials have received much attention since the end of the last century. In this paper, the commercial Eu2＋-activated nitride red phosphors, Sr1.95Si5N8：Eu0.05, Sr1.85Si5N8：Eu0.15 and Ca0.99AlSiN3：Eu0.01 phosphors were an-nealed at different temperatures （beyond 300 oC） to investigate the dependence of their luminescence performance and structure vari-ability on the temperature. By photoluminescence spectra, X-ray diffraction （XRD） and thermogravimetry-differential scanning calo-rimetry （TG-DSC） analysis, the high temperature stability of the hosts and activator of the three samples were disclosed. With the an-nealing temperature increasing, the activator Eu2＋ions were firstly oxidized and then host in Sr1.95Si5N8：Eu0.05 and Sr1.85Si5N8：Eu0.15, but for Ca0.99AlSiN3：Eu0.01, only the oxidation of the host could be observed, which would lead to the luminescence degradation and even failure of these phosphors. The activator Eu2＋ions were much more stable in CaAlSiN3：Eu than Sr2Si5N8：Eu due to their crystal surroundings, and its concentration also influenced the temperature stability of Sr2Si5N8：Eu.
基金This work was financially supported by the National Natural Science Foundation of China(No.52172118).
文摘In this work,a novel high entropy perovskite oxide(1-x)(Na_(0.2)Bi_(0.2)Ba_(0.2)Sr_(0.2)Ca_(0.2))TiO_(3-x)NaNbO_(3)(abbrevi-ated as(1-x)NBBSCT-x NN,x=0,0.05,0.1,0.15,and 0.2)was designed to improve temperature dielectric stability and energy storage performance by combining relaxor and antiferroelectric characteristics.The optimal composition of x=0.2 exhibits a high energy storage density of 3.51 J/cm^(3),together with wide temperature stable stability(■<15%,-70 to 110℃),excellent frequency stability(W rec andηvary by only±2.1%and±5.2%within the range of 1-600 Hz)and fast discharge rate(t_(0.9)=55.2 ns).This is mainly due to the enhancement of relaxation behavior and increase of E b caused by the decrease of grain size.These results offer a new strategy for designing high entropy ceramic materials of high performance in the future.
基金financially supported by the National Science Foundation of China(No.51471016)the Natural Science Foundation of Beijing(No.2151002)
文摘The oxidation resistance behavior of SmCo(2:17)-type high-temperature magnets modified with Ni-Cr two-layer coating was studied. The study depicts the mass gain kinetics and magnetic properties of uncoated and NiCr-modified magnets oxidized at high temperature(500 ℃) in air for 200 h. The oxidation test results illustrate that the mass gain of uncoated magnet is6.95 mg·cm^(-2) which is more than that(0.08 mg·cm^(-2)) of coated magnet after 200 h. For the magnetic properties concerned, there is a great loss for uncoated magnet, while for coated magnet, magnetic properties do not change much. The study of uncoated magnet through X-ray diffraction(XRD) and electron probe microanalysis(EPMA) shows that the invasion of oxygen at high temperature leads to the loss of magnetic properties by changing the microstructure of magnet.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.52002252 and 52032007).
文摘The flourishing development of emerging electromechanical applications has stimulated an urgent demand for ferroelectric ceramics with high piezoelectric properties and broad temperature usage range.However,it remains a challenge to simultaneously obtain good piezoelectricity and reliable temperature stability in lead zirconate titanate(PZT)-based piezoelectric ceramics.To solve this issue,a synergetic strategy was proposed to introduce lead vacancies through niobium doping and construct morphotropic phase boundary(MPB).In this work,Pb_(0.905)Ba_(0.085)(V Pb″)_(0.01)[(Zr_(x)Ti_(1-x))_(0.98)Nb_(0.02)]O_(3)(PBZTN-x)material system was designed.Good comprehensive properties(d_(33)=864 pC/N,k_(p)=84%,T_(C)=201℃)and excellent temperature stability(less than 10%variation of electrical properties from 20℃ to 160℃)were obtained in PBZTN-0.540 ceramics.Good piezoelectricity can be attributed to high extrinsic contribution(domain wall motion)induced by Pb^(2+)vacancies and the existence of nano-domains emerged at MPB,while excellent temperature stability is mainly attributed to the minimized local stress in the lattice and the stable domain structure.
基金financially supported by the National Natural Science Foundation of China(NSFC)(No.19934003)the Key Program of Natural Science Foundation of Anhui Province(No.KJ2011A259)+1 种基金the Program of Professors and Doctors'Research Startup Foundation of Suzhou College(Nos.2011jb01 and 2011jb02)the Cultivating Base of Anhui Key Laboratory of Spintronics and Nano-materials Research Program(No.2010YKF04)
文摘Polycrystalline samples of Lal-x（Srl-yAgy）x MnO3 （y = 0.0, 0.2, 0.4, 0.6, 1.0） were prepared by the solid-state reaction method. The temperature stability of magnetoresistance and magnetoresistance enhancement in Lal_x（Srl_yAgy）~MnO3 system with both univalent and bivalent elements doped at A site and with unchanged value of Mn~＋/Mn4＋ ratio were explored through the measurements of X-ray diffraction patterns, magnetiza- tion-temperature （M-T） curves, resistivity-temperature （p-T） curves and magnetoresistance-temperature （MR-T） curves. The results are as follows： there are two peaks in the p-T curves of the samples with Ag doping, one is caused by resistance change during the paramagnetism- ferromagnetism transition, and the other is from boundary- dependent scattering of conduction electrons on the boundaries of grains. The peak value of MR increases with increasing Ag doping content, and it increases from 8.2 % for y ---- 0.2 to 29.6 % for y ---- 1.0 under the magnetic field of B = 0.8 T; MR remains a constant of 12 % in the temperature range of 218-168 K for the sample with y = 1.0, and the temperature stability of MR is in favor of the practical application of MR.
基金Project supported by the National Natural Science Foundation of China(21962021)the Yunnan Fundamental Research Projects(202001AU070121)+1 种基金the National Natural Science Foundation of China(51908091)the Special Basic Cooperative Research Programs of Yunnan Provincial Undergraduate Universities'Association(202101BA070001-084)。
文摘In order to analyze the influence of the addition of yttrium and manganese on the soot combustion performance and high temperature stability of CeO_(2) catalyst,a series of Y/Mn-modified CeO_(2) catalysts were prepared.The effects of structural properties,textural properties,oxygen vacancies,Ce^(3+),surface adsorbed oxygen species,reduction properties and desorption properties of oxygen species on the activity were analyzed by various characterization methods.The results of the activity test show that the addition of manganese is beneficial to enhancement of the activity,while the addition of yttrium increases the amount of reactive oxygen species,but decreases the activity.After aging at 700℃,the activity of the CeMn catalyst decreases most sharply,while the catalytic activity of the CeY catalyst can be maintained to a certain extent.Interestingly,the addition of yttrium and manganese at the same time can stabilize the activity.The fundamental reason is that yttrium and manganese move to the surface of the solid solution after aging,which increases the reduction performance of the catalyst,thus contributing to the increase of activity.Although the activity of CeYMn catalyst decreases after aging at 800℃,it is still higher than that of other catalysts aged at 700℃.
基金financially supported by the National Natural Science Foundation of China (No. 61001120)
文摘In this study, finite element analysis based on an Ansoft Maxwell software was used to reveal the temperature stability of a magnet ring and the equivalent structural periodic permanent-magnet（PPM） focusing system. It is found that with the temperature increasing, the decrease rate of magnetic induction peak（Bz）maxof single magnet ring is greater than that of remanence Brof magnet in the range from room temperature to 200 °C, however,the PPM focusing system do have the same temperature characteristics of permanent-magnet materials. It indicates that the magnetic temperature properties of the PPM system can be effectively controlled by adjusting the temperature properties of the magnets. Moreover, the higher permeability of the magnets indicates the less Hcb, giving rise to lower magnetic induction peak （Bz）′max： Finally, it should be noted that the magnetic orientation deviation angle θ（／15°） of permanent magnets has little effect on the focusing magnetic field of the PPM system at different temperatures and the temperature stability. The obtained results are beneficial to the design and selection of permanent magnets for PPM focusing system.
文摘The temperature stability of supercapacitor（SC） is largely determined by the properties of the electrolyte.Hydrogel electrolytes（HGE）, due to their hydrophilic polymer skeleton, show different temperature stability to that of liquid aqueous electrolytes. In this study, symmetric activated carbon（AC） SCs had been assembled with in situ electrodeposited poly（vinyl alcohol） potassium borate（PVAPB） HGE. The electrochemical performance of the SCs was systematically studied at different temperatures. Results show that the conductivity of PVAPB HGE is comparable with that of liquid aqueous electrolytes at different temperatures. The operating temperature range of PVAPB HGE SCs is -5–60°C, while those of the 1 mol/L Na2SO4SCs and the 0.9 mol/L KClSCs are 20–80°C and 20–40°C, respectively. The specific capacitance of PVAPB HGE SC is higher than those of SCs using liquid aqueous electrolytes at any temperature. The excellent temperature stability of PVAPB HGE makes it possible to build stable aqueous SCs in the wider temperature range.
基金supported by National Natural Science Foundation of China (51002025)National High Technology Research and Development Program of China(863 Program) (2010AA03A405)National Science and Technology Support Plan of China during the 12th Five-Year Plan (2012BAE01B02)
文摘High temperature self-propagating synthesis （SHS） process is very rapid, the reaction process becomes un-controlled after the SHS reaction is ignited. So the initial reaction conditions will have great effects on phase compositions and microstructures of reaction products. In this paper, the effects of the proportioning amount of Mg on the yield ratio and particle sizes of CeB6 were studied. The SHS reaction products and leached products were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results indicated that the SHS products consisted of MgO, CeB6 and little Mg3B206. The single CeB6 phase was contained after the SHS reaction products were leached. The purity of CeB6 was higher than 99.0 mass%, and the minimum particle sizes of CeB6 were within 30-70 nm. When the propor- tioning amount of Mg was 25% more than the theoretic amount, the yield of CeB6 was 68.68%. The antioxidant ability of CeB6 was rather stronger, which was oxidized step by step, and the initial oxidation temperature was 750 ℃ which indicated that it had good high temperature stability. The apparent activation energies of oxidation reactions of CeB6 were 200.09 and 312.10 kJ/mol, respectively, and reaction orders were 0.69 and 0.40, respectively.
基金This work was financially supported by the National Natural Science Foundation of China (No.50371019) and Beijing Municipal Science & Technology Committee Key Project (No.D0406002000091).
文摘Temperature stability and toughness of magnets are very important properties especially for application in motor. In this paper, it is found that temperature stability and toughness of magnets are improved when Fe is substituted with Co and heavy rare earth is substituted for Nd in part and suitable rich B grain-boundary phase is added. In addition, heavy rare earth substitution decreases the remanence temperature coefficient greatly, but has a little effect on Curie temperature of the magnets, which is beneficial to Nd-Fe-B magnets for the application in motor.
基金supported by the National Natural Science Foundation of China(61973019)。
文摘The coupling efficiency of hollow-core fiber changes with temperature,which leads to the decrease of the finesse(F)of fiber resonator and limits the performance of the resonant fiber optic gyroscope(R-FOG)system.Negative-curvature antiresonant fiber(ARF)can maintain single-mode characteristics under the condition of large mode field diameter,achieve efficient and stable fiber coupling,and significantly improve the consistency of the F of the spatial coupling resonator in variable temperature environment.A new type of ARF with a mode field diameter(MFD)of 25μm is used to fabricate a fiber resonator with a length of 5.14 m.In the range of 25℃-75℃,the average F is 31.45.The ARF resonator is used to construct an R-FOG system that shows long-term bias stability(3600 s)of3.1°/h at room temperature,4.6°/h at 75℃.To our knowledge,this is the best reported index of hollow-core fiber resonator and R-FOG system within the temperature variation range of 50℃ test.
基金supported by the Natural Science Foundation of Hebei province(E2020201021 and E2023201019)Hebei Province Innovation Capability Enhancement Plan Project(22567620H)+2 种基金Industry-University-Research Cooperation Project of Colleges and Universities in Hebei Province(CXZX2025016)Industry-University-Research Cooperation Major Projects of Shijiazhuang City(241130477A)Research Innovation Team of College of Chemistry and Environmental Science of Hebei University(hxkytd2102).
文摘The poor temperature stability of the BaTiO_(3) ceramic has always been the main problem limiting their application.This situation has been improved but sacrifices the intrinsic polarization,which significantly reduces the dielectric constant.In this work,the mechanism of multiple polarization was creatively introduced,and the temperature stability and dielectric properties of BaTiO_(3)-based ceramics are simultaneously enhanced.In particular,the Ba_(0.9925)Bi_(0.005)Ti_(0.995)Ca_(0.005)O_(2.995)(BBTC0.5)ceramic sample achieved excellent temperature stability(-14.8%to 8.85%)over an ultra-wide temperature range(-47 to 400℃)and exhibited colossal permittivity(27,125,25℃,1 kHz)and low dielectric loss(0.07,25℃,1 kHz).The dielectric properties,complex impedance spectra combined with XPS results indicate that the defective dipole clusters(Ti^(3+)-V_(O)-Ti^(3+),Bi_(Ba) and Ca″_(Ti)-V_(O))along with surface effects lead to colossal permittivity effect.More importantly,SEM images show the presence of the second phase at grain boundaries,which prevent the carriers within the grains from accumulating at the grain boundaries.As a result,the dielectric loss was reduced and the temperature stability was further extended.This strategy breaks the traditional limitation of single/noncomprehensive enhancement by singlepolarization mechanism,and is of great theoretical and practical significance to promote the research and application of high-performance BaTiO_(3)-based ceramic materials.
基金supported by the National Natural Science Foundation of China(52072028 and 52032007)the National Key Research and Development Program(2022YFB3807400).
文摘BiFeO_(3)-BaTiO_(3)(BF-BT)ceramics exhibit higher piezoelectric coefficients(d33),Curie temperatures(T_(C)),and temperature stability than other high-temperature lead-free piezoelectric materials.However,despite their crucial role in piezoelectric devices,the mechanical properties of BF-BT ceramics have been underexplored.A thorough evaluation of the mechanical properties of BF-BT is crucial for developing cost-effective and durable lead-free piezoelectric ceramics.Moreover,the specific causes of the high piezoelectric response and excellent temperature stability of BFeBT ceramics remain unclear owing to the instrumental detection threshold,which limits experimental studies to temperatures above 140C and below the degradation temperature of d33.To investigate the intrinsic origins of the high piezoelectricity and temperature stability of BF-BT ceramics and to enhance their mechanical properties,a two-step sintering process is used to fabricate these ceramics(0.25≤x≤0.40).Owing to improvements in grain refinement and reduced Bi3t volatilization,the BFe0.33 BT ceramic exhibits enhanced overall performance,with a modified small punch strength of 155 MPa,Vickers hardness of 5.2 GPa,a d33 of 220 pC/N at room temperature,T_(C)of 466℃,and d33 values exceeding 400 pC/N at 260℃.Phase-field simulations,which address the limitations of device detection thresholds,reveal that with increasing temperature,the domain structure relaxes,and polarization intensity decreases.This indicates that changes in the high-temperature piezoelectric properties can be attributed to domain structure relaxation and the increase in dielectric constant.Overall,BFeBT ceramics exhibit superior piezoelectric performance,mechanical properties,and temperature stability,making them highly suitable for use in high-temperature and demanding environments.
基金supported by the National Natural Science Foundation of China(No.52102132)the Natural Science Foundation of Shandong Province of China(Nos.ZR2024ME201 and ZR2021ME085)+1 种基金the Guangdong Provincial Key Laboratory of Electronic Functional Materials and Devices(No.EFMD2023001M)the Natural Science Foundation of Heilongjiang Province(No.LH2022E049).
文摘BaTiO_(3) (BT)-based piezoceramics with large temperature-stable strains and low hysteresis are urgently needed for high-precision actuators because of increasing environmental problems. Here, tetragonal [001]c-textured (Ba_(0.98)Ca_(0.02))(Ti_(0.96)Sn_(0.04))O_(3) (BCTS) ceramics with a texture degree (F_(001)) of ~98% were obtained via the templated grain growth (TGG) method. A large maximum unipolar strain (S_(max)) of ~0.24% with a low strain hysteresis (Hs) of ~3.8% and an optimized piezoelectric strain coefficient (d_(33)^(*)) of ~1124 pm·V^(−1) are simultaneously achieved in the textured BCTS ceramics. Moreover, the variation in the strain response is less than 20% from room temperature (RT) to 100℃ for the textured ceramics. The underlying mechanism for the optimized strain performance could be attributed to the synergetic effect of the polarization extension and a fine domain structure. This work provides new insight for achieving a balance of multiple strain properties (large strain, low hysteresis, and high-temperature stability) in BT-based ceramics, showing the widespread application prospects of lead-free ceramics in high-precision actuators.
基金supported by the National Science and Technology Major Project(No.J2019-VI-0015-0130)the Shaanxi Provincial Innovative Talent Promotion Plan Youth Science and Technology New Star Project(Talent)(No.2023KJXX-075)the Youth Innovation Team of Shaanxi Universities Project(No.23JP072).
文摘The semi-transparency to thermal radiation,coupled with low nanoparticle retention and formation of semi-melted particles during plasma spraying,significantly limits the hightemperature application of nanostructured yttria stabilized zirconia(YSZ)(nYSZ)thermal barrier coatings.To address these challenges,this study introduces an innovative approach that involves coating nanoparticles with carbon films to prevent them from melting and merging during the plasma spraying process.This method substantially increases the nanoparticle content within the coating,and nanopores formed at the nanoparticle surfaces when the carbon film is removed at 800℃.These nanopores,in combination with nanoparticles,enhance thermal radiation scattering,improving the scattering coefficient and thermal radiation blocking capability of the coating.In contrast to that of conventional thermal barrier coatings(TBCs)of YSZ,the simulated temperature of the substrate under service conditions decreases by up to 26.26 K due to decreased radiative heat transfer and by 111.2 K when the thermal conductivity is reduced.Additionally,the scattering coefficients remain stable within the 1-5μm range even after heat treatment at 1300°C for 100 h,as the coarsened nanoparticle size approaches the wavelength of thermal radiation.Thus,nYSZ TBCs with enhanced thermal radiation blocking ability and high temperature stability can be created by this approach for higher temperature applications.
基金supported by the National Natural Science Foundation of China(No.52462016)the Natural Science Foundation of Guangxi Zhuang Autonomous Region(Nos.2025GXNSFAA069448 and 2023GXNSFBA026076)the Guangxi BaGui Young Scholars Funding and Guangxi Special Appointed Experts Funding.
文摘Olivine-type A_(2)BO_(4)ceramics possess a low permittivity(ε_(r))and low dielectric loss,contributing to a high quality factor(Q×f).However,the large negative temperature coefficient of the resonant frequency(τ_(f))restricts their practical applications.In this work,we prepared a series of CaYGa_(1−x)Al_(x)O_(4)(x=0–1)ceramics with lowε_(r)values via solid-state sintering.By controlling the evolution of orthorhombic olivine to the tetragonal perovskite-like structure(K_(2)NiF_(4))and the ordered regulation of the A-site,an ultralow loss(tanδ=1.38×10^(−4),Q×f=125,530 GHz,and f=17.3 GHz for x=0)and a nearly zero temperature coefficient(τ_(f)=−0.5 ppm/°C for x=0.9)were achieved.The significant changes in the dielectric properties(ε_(r)=8.3–16.2,Q×f=125,530–50,660 GHz,andτ_(f)=−50.9 to 2.9 ppm/°C)of these ceramics are primarily influenced by the characteristics of the second phase,ion polarization,ion order and disorder,and the chemical bonds resulting from structural evolution.Furthermore,a cylindrical dielectric resonator antenna(CDRA)was designed using an ultralow-loss CaYGaO_(4)ceramic,achieving a high gain(5.36–6.15 dBi)and efficiency(>90%)in the bandwidth region(5.065–5.747 GHz),thereby enhancing the efficiency and quality of 5G communications.This work advances the development of control strategies for high-performance dielectric ceramics and dielectric resonator antennas in high-frequency communications.
基金The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China(Grant nos.52072092 and 11572103)the Natural Science Foundation of Heilongjiang Province(Grant no.YQ2019E026).
文摘Lead-free ceramics with both high piezoelectric response and good temperature stability are urgently demanded for electromechanical conversion devices.Unfortunately,owing to coexistence of poly-morphic phases near room temperature(RT),enhanced piezoelectric properties were usually achieved with occurrence of strong temperature dependence in modified BaTiO_(3)(BT)-based ceramics.In this work,we demonstrate that tailoring grain orientations of tetragonal BT-based ceramics can effectively produce substantially enhanced and thermally stabilized piezoelectric response.Both<001>c-and<111>c-oriented tetragonal(Ba_(0.85)Ca_(0.15))(Zr_(0.05)Ti_(0.95))O_(3)(BCZT)ceramics with texture degrees F>90%were synthesized via templated grain growth.Interestingly,the ceramics textured along the<001>c polar axis show much higher microscopic and macroscopic piezoelectric properties than those with nonpolar<111>c texture,indicating an“extender”ferroelectricity nature.Compared with randomly oriented samples,the<001>c-oriented ceramics exhibit simultaneously~1.6 times higher piezoelectric strain d_(33)^(*)(~760 pm/V),4.4 times higher piezoelectric figure of merit d_(33)×g_(33)(8.8×10^(-12) m^(2)/N),and better temperature stability(strain variation≤5%between RT and 110℃).Such thermally stabilized strain response can be mainly attributed to wide temperature range of tetragonal phase and stable domain structure.This work provides a promising route for further developing lead-free piezoceramics with high and temperature-insensitive performance,which can greatly broaden their application areas.
基金supported by the National Natural Science Foundation of China(Grant No.52102132)the Natural Science Foundation of Shandong Province of China(Grant Nos.ZR2020QE043,ZR2020ME031and ZR2020ME033)+1 种基金the Innovation Team of Higher Educational Science and Technology Program of Shandong Province(Grant No.2019KJA025)Research Foundation for the Doctoral Program of Liaocheng University(Grant No.318051932).
文摘Considering the advantages of high Curie temperature and environment-friendly nature of KNN piezoelectric ceramics,the limitation of weak piezoelectric response and their temperature sensitivity to applications is worth exploring.Herein,the<001>textured(1-x)(K_(0.5)Na_(0.5))(Nb0.96Sb0.04)O3-x(Bi_(0.5)Na_(0.5))HfO_(3)(x=0.01-0.045)lead-free ceramics were synthesized by templated grain-growth method.The high piezoelectric performance(d33 of 474 pC/N and strain of 0.21%)and excellent temperature stability(unipolar strain maintained within 4.3%change between 30℃and 165℃)were simultaneously achieved in the textured KNNS-0.03BNH ceramics.The high piezoelectric performance can be attributed to the summation of the crystallographic anisotropy and phase structure contributions in<001>textured ceramics.The superior temperature stability of piezoelectric properties can be interpreted by the contribution of crystal anisotropy to piezoelectric properties reduces the effect of phase transition on piezoelectric properties deterioration.This study provides an effective strategy for simultaneously achieving high piezoelectric properties and superior temperature stability in KNN-based textured ceramics.
基金supported by the National Postdoctoral Program for Innovative Talents(Grant No.BX20190158)National Natural Science Foundation of China(Grant Nos.52032005 and 51672148)the Shuimu Tsinghua Scholar.
文摘It is a very difficult work to sinter K_(0.5)Na_(0.5)NbO_(3)(KNN)-based materials with good reduction resistance in strong reducing atmosphere.0.945K_(0.48)Na_(0.52)Nb_(0.96)Ta_(0.04)O_(3)-0.055BaZrO_(3)+0.03ZrO_(2)+y mol%MnO(KNNT-0.055BZ+0.03Zr+yMn)ceramics sintered in reducing atmosphere were prepared successfully by conventional solid-state reaction methods.MnO dopant increases grain size at y=5-8 due to strong lattice distortion and then decreases grain size at y=9 due to much Mn4Nb2O9 accumulated at the grain boundary.MnO dopant as an excellent sintering aid can effectively reduce volatilization of alkali metal by decreasing the sintering temperature(T_(sinter)).Reducing alkali metal volatilization can greatly reduce oxygen vacancies and improve piezoelectric properties.MnO dopant can improve the anti-reduction properties.The KNNT-0.055BZ+0.03Zr+yMn ceramics aty=6-9 show outstanding anti-fatigue of unipolar piezoelectric strain under the synergistic effect of reduced oxygen vacancies due to reduced volatilization and increased grain size.Piezoelectric properties and temperature stability of KNNT-0.055BZ+0.03Zr ceramics sintered in reducing atmosphere are improved simultaneously by MnO dopant.Optimum inverse piezoelectric coefficient(d33)of ceramics at y=8 reaches up to 480 pm/V under low driving electric field E=20 kV/cm at room temperature,and its temperature stability of d33 reaches 158℃.It will be an excellent lead-free material candidate for the preparation of multilayer piezoelectric actuators co-fired with nickel electrode.
