Fabrication and Thermally Sensitive Properties of VO_x Thin Films by Sol-Gel Method

For the high temperature coefficient of resistivity (TCR) of VO_x thin films,the preparation process including the heat-treating and the application of seed layer,has been investigated.When the films were prepared without a seed layer, heated in air for 2 h,and then in N_2 for 2 h at 470℃,the TCR of about 1.07% K^(-1) (3.75% K^(-1) at 45℃～65℃) was gained.The R_(20℃)/R_(100℃) was about 28.75,while the R_(20℃)/R_(100℃) of the thin films prepared on a seed layer was 5.5.The X-ray diffraction (XRD) showed that better heating conditions led to less phase compositions and higher V_2O_5 diffraction peak,which led to higher TCR.The experiment results showed that the optimum heating condition was at 470℃for 4 h.

Enhancing energy storage efficiency in lead-free dielectric ceramics through relaxor and lattice strain engineering

Dielectric capacitors with high power density and fast charge-discharge speed play an essential role in the development of pulsed power systems.The increased demands for miniaturization and practicality of pulsed power equipment also necessitate the development of dielectric materials that possess high energy density while maintaining ultrahigh efficiency(η).In particular,ultrahigh efficiency signifies minimal energy loss,which is essential for practical applications but challenging to effectively mitigate.Here,we demonstrate a strategy of incorporating heterovalent elements into Ba(Zr_(0.1)Ti_(0.9))O_(3),which contributes to achieving relaxor ferroelectric ceramics and reducing lattice strain,thereby improving the comprehensive energy storage performance.Finally,optimal energy storage performance is attained in 0.85Ba(Zr_(0.1)Ti_(0.9))O_(3)-0.15Bi(Zn_(2/3)Ta_(1/3))O_(3)(BZT-0.15BiZnTa),with an ultrahighηof 97.37%at 440 kV/cm(an advanced level in the lead-free ceramics)and an excellent recoverable energy storage density(Wrec)of 3.74 J/cm^(3).Notably,the BZT-0.15BiZnTa ceramics also exhibit exceptional temperature stability,maintaining fluctuations in Wrec within∼10%andηconsistently exceeding 90% across the wide temperature range of−55℃ to 160℃,and under a high electric field of 250 kV/cm.All these features demonstrate that the relaxor and lattice strain engineering strategies have been successful in achieving high-performance lead-free ceramics,paving the way for designing high-efficiency dielectric capacitors with a wide temperature range.

Regulating local electric field to optimize the energy storage performance of antiferroelectric ceramics via a composite strategy

Electrostatic energy storage technology based on dielectrics is the basis of advanced electronics and high-power electrical systems.High polarization(P)and high electric breakdown strength(Eb)are the key parameters for dielectric materials to achieve superior energy storage performance.In this work,a composite strategy based on antiferroelectric dielectrics(AFEs)has been proposed to improve the energy storage performance.Here,AlN is selected as the second phase for the(Pb_(0.915)Ba_(0.04)La_(0.03))(Zr_(0.65)Sn_(0.3)Ti_(0.05))O_(3)(PBLZST)AFEs,which is embedded in the grain boundaries to construct insulating networks and regulate the local electric field,improving the Eb.Meanwhile,it is emphasized that AFEs have the AFE–FE and FE–AFE phase transitions,and the increase of the phase transition electric fields can further improve the recoverable energy density(Wrec).As a result,the Eb increases from 180 to 290 kV·cm−1 with a simultaneous increase of the phase transition electric fields,magnifying the Wrec to~144%of the pristine PBLZST.The mechanism for enhanced Eb and the phase transition electric fields is revealed by the finite element simulation method.Moreover,the PBLZST:1.0 wt%AlN composite ceramics exhibit favorable temperature stability,frequency stability,and charge–discharge ability,making the composite ceramics a promising candidate for energy storage applications.

Integrated sensor based on acoustics-electricity-mechanics coupling effect for wireless passive gas detection

Integrated sensor combines multiple sensor functions into a single unit,which has the advantages of miniaturization and better application potential.However,limited by the sensing platforms of the sensor and the selectivity of the sensitive film,there are still challenges to realize multi-component gas detection in one unit.Herein,a principle integration method is proposed to achieve the multi-component gas detection based on the acoustics-electricity-mechanics coupling effect.The electrical and mechanical properties of the Bi_(2)S_(3)nanobelts materials in different atmospheres indicate the possibility of realizing the principle integration.At the same time,the surface acoustic wave(SAW)sensor as a multivariable physical transducer can sense both electrical and mechanical properties.Upon exposure to 10 ppm NO_(2),NH_(3),and their mixtures,the integrated SAW gas sensor shows a 4.5 kHz positive frequency shift(acoustoelectric effect),an 11 kHz negative frequency shift(mechanics effects),and a reduced 4 kHz negative frequency shift(acoustics-electricity-mechanics coupling effect),respectively.Moreover,we realize wireless passive detection of NO_(2)and NH_(3)based on the SAW sensor.Our work provides valuable insights that can serve as a guide to the design and fabrication of single sensors offering multi-component gas detection via different gas sensing mechanisms.

Realizing simultaneously excellent energy storage and discharge properties in AgNbO_(3)based antiferroelectric ceramics via La^(3t)and Ta^(5+)co-substitution strategy

AgNbO_(3)based antiferroelectric(AFE)ceramics have large maximum polarization and low remanent polarization,and thus are important candidates for fabricating dielectric capacitors.However,their energy storage performances have been still large difference with those of lead-based AFEs because of their room-temperature ferrielectric(FIE)behavior.In this study,novel La^(3+)and Ta^(5+)co-substituted AgNbO_(3)ceramics are designed and developed.The introduction of La^(3+)and Ta^(5+)decreases the tolerance factor,reduces the polarizability of B-site cations and increases local structure heterogeneity of AgNbO_(3),which enhance AFE phase stability and refine polarization-electric field(PeE)loops.Besides,adding La^(3+)and Ta^(5+)into AgNbO_(3)ceramics causes the decrease of the grain sizes and the increase of the band gap,which contribute to increased Eb.As a consequence,a high recoverable energy density of 6.79 J/cm3 and large efficiency of 82.1%,which exceed those of many recently reported AgNbO_(3)based ceramics in terms of overall energy storage properties,are obtained in(Ag0.88La0.04)(Nb0.96Ta0.04)O_(3)ceramics.Furthermore,the discharge properties of the ceramic with discharge time of 16 ns and power density of 145.03 MW/cm3 outperform those of many lead-free dielectric ceramics.

Point-defect-driven flattened polar phonon bands in fluorite ferroelectrics

The scale-free ferroelectric polarization of fluorite MO_(2)(M=Hf,Zr)due to flat polar phonon bands are promising for nonvolatile memories.Defects are also widely introduced to improve the emergent ferroelectricity.However,their roles are still not fully understood at the atomic-level.Here,we report a significant effect of point-defect-driven flattening of polar phonon bands with more polar modes and polarization contribution in doped MO_(2).The polar phonon bands in La-doped MO_(2)(M=Hf,Zr)can be significantly flattened,compared with pure ones.However,the lower energy barrier with larger polarization of VO-only doped MO_(2) compared with La-doped cases suggest that VO and local lattice distortion should be balanced for high-performance fluorite ferroelectricity.The work is believed to bridge the relation between point defects and the generally enhanced induced ferroelectricity in fluorite ferroelectrics at the atomic-level and inspire their further property optimization via defect-engineering.

High electrocaloric effect in barium titanate-sodium niobate ceramics with core-shell grain assembly

Electrocaloric effect(ECE)is promising in realizing solid-state cooling as an alternative to the conventional refrigeration with environmentally harmful coolant and low efficiency.High ECE in lead-free ferroelectric ceramics is highly desirable for the EC cooling.In this work,different from the researches that tune the ECE by conventional compositional design or external stress engineering,we fabricated the(1-x)BaTiO_(3)-xNaNbO_(3)(BTO-xNN)lead-free ceramics with a core-shell grain structure arising from the inhomogeneous stoichiometry of element distribution,leading to the internal compressing stress in the grains.It is interesting that the phase transition behavior,including the phase transition temperature and the diffusion property,is regulated by the core-shell grain structure induced internal stress,which can be capitalized on for the favorable ECE.Cooperated with 0.02 NN,a high ECE,e.g.adiabatic temperature change(ΔT)of 3.6 K and isothermal entropy change(ΔS)of 4.5 J kg^(-1) K^(-1),is attained in the BTO ceramic.As the internal stress further increases with more NN,the BTO-0.06NN exhibits an extremely stable ECE with a variety rate below ±4% in a wide temperature range from 300 K to 360 K.This work provides a novel approach to explore pronounced ECE in lead-free ferroelectrics for eco-friendly refrigeration.

Field-driven merging of polarizations and enhanced electrocaloric effect in BaTiO_(3)-based lead-free ceramics

Solid-state cooling technology based on electrocaloric effect(ECE)has been advanced as an alternative to replace the vapour-compression approach to overcome the releasing of the global warming gases.However,the development in high ECE materials is still a challenge.In this work,polarization merging strategy was proposed to achieve a large ECE in xBa(Sn_(0.07)Ti_(0.93))O_(3)–(1−x)Ba(Hf_(0.1)Ti_(0.9))O_(3) ferroelectric ceramics,where x=0,0.2,0.4,0.6,0.8,and 1.Ba(Sn_(0.07)Ti_(0.93))O_(3) with an orthorhombic phase and Ba(Hf_(0.1)Ti_(0.9))O_(3) with a rhombohedral phase at room temperature were prepared beforehand as precursors,and phase-coexisted xBSnT–(1−x)BHfT ceramics were formed via a solid-state reaction approach.Phase coexisting structures were confirmed using the X-ray diffraction.The merged polarization was confirmed by the dielectric and ferroelectric properties.Optimal ECEs were obtained for 0.2BSnT–0.8BHfT ceramics,i.e.,adiabatic temperature change DT=2.16±0.08 K at 80℃and 5 MV/m,and DT=3.35±0.09 K at 80℃and 7 MV/m.