In this work, three kinds of ultrathin tremella-like MnO2 have been simply synthesized by decomposing KMnO4 under mild hydrothermal conditions. When applied as electrode materials, they all exhibited excellent electrochemical performance. The as- prepared MnO2 samples were characterized by means of XRD, SEM, TEM and XPS. Additionally, the relationship of the crystalline nature with the electrochemical performance was investigated. Among the three samples, the product with the poorest crystallinity had the highest capacitance of 220 Fig at a current density of 0.1 A/g. It is thought that the ultrathin MnO2 nanostructures can serve as promising electrode materials for supercapacitors.
Xiangcang RENChuanjin TIANSa LIYucheng ZHAOChang-An WANG
The oxides with perovskite structure possess abundant physical properties, such as magnetism, dielectricity, photoelectricity, ferroelectricity, etc. The oxygen ions in the perovskite unit cell constitute an octahedral distribution. The deformation or tilting of the special oxygen octahedra structure leads to new performances or properties change. Here, we give a review of the relationship between magnetic and electrical behaviors and oxygen octahedral tilting in several typical perovskite oxides. An understanding of how to tune these properties by controlling the tilting during the sample growth can more effectively guide the design of new structures for high performance and inspiring their potential applications.
A uniaxial magnetic anisotropy Co film was grown on a single-crystal Ba Ti O3(BTO) substrate. The strain yielded by the voltage-induced ferroelastic domain switching in the BTO substrate was recorded by atomic force microscope and modulated the magnetism of the Co film. The manipulation of the magnetism of the Co film is experimentally demonstrated by voltage dependence of magnetic hysteresis loops measured via magneto-optic Kerr effect.
Surface-modified BaTiO_(3)of 230 nm average grain size were synthesized by coating BaTiO_(3)particles with 3 wt.%Al2O_(3)and 1 wt.%SiO2.Ceramic films of different thicknesses were prepared via tape casting and laminating processes followed by two-steps sintering method.After sintering,the average grain size of Surface-modified BaTiO_(3)ceramic slightly increased to 275 nm,and great enhancement of AC breakdown strength(BDS)from 184 kV/cm to 665 kV/cm was obtained as the thickness of ceramic films decreased from 63μm to 12μm,resulting in improvement of discharge energy density from 1.14 J/cm3to 4.06 J/cm3.Because of their low-cost,easily fabrication,lead-free,improved AC BDS and discharge energy density,surface-modified BaTiO_(3)ceramic films appeared promising for applications in multilayer energy storage capacitors.
BiFeO_(3),a room-temperature multiferroic material,has recently been increasingly applied as a potential lead-free piezoelectric material due to its large piezoelectricity achieved by doping.In this work,12%Smdoped BiFeO_(3)epitaxial thin films were fabricated on Nb-doped SrTiO_(3)(001)single crystal substrates via sol-gel method.The epitaxy was verified by reciprocal space mapping(RSM)and transmission electron microscope(TEM).The TEM results indicated the coexistence of R3c and Pbam phases in the film.The domains and piezoelectric properties from room temperature to 200℃were characterized by piezoresponse force microscopy(PFM).Domains became active from 110℃to 170℃,and domain configurations changed obviously.A partially fading piezoresponse indicated the emergence of antiferroelectric Pbam.The in-situ domain analysis suggested that the phase transition was accompanied by domain wall motion.Switching spectroscopy PFM(SS-PFM)was further conducted to investigate the piezoresponse during the phase transition.Anomalous responses were found in both ON and OFF states at 170℃,and the film exhibits typical antiferroelectric behavior at 200℃,implying that the completion of phase transition and structure turned to the Pbam phase.This work revealed the origin of the high piezoresponse of Sm-doped BiFeO_(3)thin films at the morphotropic phase boundary(MPB).
Zhen ZhouWei SunZhenyu LiaoShuai NingJing ZhuJing-Feng Li
Multilayer ceramic capacitors(MLCCs)for energy storage applications require a large discharge energy density and high discharge/charge efficiency under high electric fields.Here,0.87BaTiO3--0.13Bi(Zn23(Nbog8sTao.1s)u3)O3(BTBZNT)MLCCs with double active dielectric layers were fabricated,and the effects of inner electrode and sintering method on the energy storage properties of BTBZNT MLCCs were investigated.By using the pure Pt as inner electrode instead of Ago.6Pdo4 aloys,an alternating current(AC)breakdown strength(BDS)enhancement from 1047 to 1500 kV/cm was achieved.By investigating the leakage current behavior of BTBZNT MLCCs,the Pt inner electrode and two-step sintering method(TSS)were confirmed to enhance the Schottky barrier and minimize the leakage current density.With relatively high permitivity,dielectric sublinearity,and ultra-high BDS,the Pt TSS BTBZNT MLCCs exhibited a surprisingly discharge energy density(Udis)of 14.08 J/cm2.Moreover,under an operating electric field of 400 kV/cm,the MLCCs also exhibited thermal stability with Udis variation<±8%over a wide temperature (t) range from-50 to 175℃ and cycling reliability with Uais reduction<0.3%after 3000 charge-discharge cycles.These remarkable performances make Pt TSS BTBZNT MLCCs promising for energy storage applications.
Hongxian WANGPeiyao ZHAOLingling CHENLongtu LIXiaohui WANG
Voltage-modified magneto-optical Kerr effect(MOKE) is widely used to describe the converse magnetoelectric(ME) effect in the ferroelectric/ferromagnetic(FE/FM) heterostructures. However, the applied voltage can possibly give rise to electro-optical effect of the FE layer, which would also affect the Kerr signals in the MOKE system. Here, we used an AC voltage to modulate the magnetization in the Ni/Pb(Zr0.52Ti0.48)O3(PZT) heterostructures with different pre-polarization states of the PZT layers to investigate the complexity of the Kerr signals. The results suggested that the voltage control of Kerr signal contained several origins; however, the straininduced ME effect dominated in the ME effect in the heterostructures.
Layered porous ceramic used for polymer-infiltrated-ceramic-network materials(PICNs) may be a promising candidate for dental restoration.The effect of sintering temperature of ceramic green bodies on mechanical and optical properties of PICNs is unclear.The purpose was to fabricate PICNs and evaluate their mechanical and optical properties.Polymer-infiltrated layered silicates for dental restorative materials were prepared via infiltrating polymerizable monomers into partially sintered porous silicates and thermo-curing.Bending samples for flexural strength and fracture toughness were fabricated(sample numbers of n=15).Vickers hardness and elastic modulus were measured via nano-indentation(n=10).One-way ANOVA and Weibull statistics were used for statistical analysis.Optical property was characterized by spectral reflectance.Brittleness index was used to characterize the machinability of the materials.Microstructures and phase structures were investigated using scanning electron microscopy(SEM) and X-ray diffractometer(XRD),respectively.Flexural strength of polymer-infiltrated layered silicates varied from 91.29 to 155.19 MPa,fracture toughness ranged from 1.186 to 1.782 MPa·m^1/2,Vickers hardness ranged from 1.165 to 9.596 GPa,and elastic modulus ranged from 25.35 to 100.50 GPa.The formed glass phases at 1200 and 1300℃ showed influences on corresponding optical property,which could be observed from spectral reflectance.A kind of PICNs was fabricated by infiltrating polymerizable monomers into layered porous ceramic networks.Sintering temperature could have dramatic effects on the mechanical and optical properties of porous ceramics and PICNs.These kinds of materials possess similar properties to that of natural tooth and could be used for dental restoration.
Ben-Cang CuiJing LiYuan-Hua LinYang ShenMing LiXu-Liang DengCe-Wen Nan
