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As a typical lead-free antiferroelectric material, silver niobate has attracted much attention in recent years due to its excellent performance in energy storage. In this work, based on a spherical aberration–corrected STEM-high angle annular dark field technique, the sites of each cation column of pure silver niobate and Ta-doped silver niobate were quantitatively obtained. Besides conventional antiferroelectric displacements along the ±[1−10]c directions, B-site ions were found to also deviate along ±[001]c directions and form many local off-centering nanoregions, which may induce weak ferroelectricity, just like polar nanoregions in relaxed ferroelectrics. Such results will further increase our understanding of silver niobate in the microscopic view and may help explain some unsolved questions. [ABSTRACT FROM AUTHOR]

The development of electronic materials for storing electrical energy is a thriving research field, where the materials used in batteries, supercapacitors, and dielectric capacitors have attracted extensive interest in last decades. The dielectric capacitors showing unique characteristics such as high power density and large charge/discharge rate have been actively studied, where the antiferroelectrics demonstrate great potentials for dielectric energy storage applications by storing and releasing energy upon a reversible electric-field induced antiferroelectric- ferroelectric phase transition. Recently, lead-free antiferroelectric AgNbO3 has emerged as a promising candidate to substitute conventional lead-based antiferroelectrics (such as PbZrO3) in energy storage applications. The phase transition dynamics of AgNbO3 is driven by a complex sequence of oxygen octahedron tilting orders in addition to cation displacement, which can be effectively engineered by a doping strategy. In this article, we present a succinct overview of the phase transition mechanisms in AgNbO3-based ceramics and describe how the phase transition characteristics are affected by the dopants. By exploring the composition related average structure and local structural evolutions, we provide a view toward the goal of establishing a link between the phase transition and physical properties tailored for dielectric energy storage applications. The development of electronic materials for storing electrical energy is a thriving research field, where the materials used in batteries, supercapacitors, and dielectric capacitors have attracted extensive interest in last decades. The dielectric capacitors showing unique characteristics such as high power density and large charge/discharge rate have been actively studied, where the antiferroelectrics demonstrate great potentials for dielectric energy storage applications by storing and releasing energy upon a reversible electric-field induced antiferroelectric- ferroelectric phase transition. Recently, lead-free antiferroelectric AgNbO3 has emerged as a promising candidate to substitute conventional lead-based antiferroelectrics (such as PbZrO3) in energy storage applications. The phase transition dynamics of AgNbO3 is driven by a complex sequence of oxygen octahedron tilting orders in addition to cation displacement, which can be effectively engineered by a doping strategy. In this article, we present a succinct overview of the phase transition mechanisms in AgNbO3-based ceramics and describe how the phase transition characteristics are affected by the dopants. By exploring the composition related average structure and local structural evolutions, we provide a view toward the goal of establishing a link between the phase transition and physical properties tailored for dielectric energy storage applications. [ABSTRACT FROM AUTHOR]

Rare-earth element-doped BiFeO3 has an ultrahigh piezoelectric response near the morphotropic phase boundary (MPB), making it a promising substitute for toxic lead-based piezoelectric materials. As a ferroelectric–antiferroelectric MPB, its microscopic mechanism, especially the contribution of each phase to the piezoelectric performance, is still unclear. In this work, the origin of the giant piezoelectric response of Sm-doped BiFeO3 thin films was studied by combining nanoscale in situ electric field experiments and atomic-resolution electron microscopy. Two independent reversible phase transitions were found under an external electric field: a phase transition between the polar and nonpolar phases and a phase transition between the polar and antipolar phases. Calculations indicated that the enhancement of the piezoelectric response at the MPB originated from these two reversible phase transitions, which were realized via the nucleation of the nanoscale new phase and the motion of the phase boundary under the external electric field. The above results provide deeper insight into the mechanism of the electromechanical response near the ferroelectric–antiferroelectric MPB in rare-earth element-doped BiFeO3 thin films. [ABSTRACT FROM AUTHOR]

The leakage current of BiFeO3 thin films can be reduced by Sm or Ti doping, and their codoping effect is significant. X-ray photoelectron spectroscopy revealed that the reduction in the leakage current can be ascribed to decreased Fe2+ ions and oxygen vacancies. The leakage mechanisms of pristine and doped BiFeO3 films were studied by analyzing their leakage current characteristics through curve fitting. It was found that Ti could stabilize the trapped carriers, while Sm might decrease the trap energy and contrarily benefit the excitation of the trapped carriers, which explains the greater effect of Ti in reducing the leakage current than that of Sm. The piezoelectric properties of Sm/Ti-codoped BiFe0.9Ti0.1O3 (BFO) films were comparable to those of pristine BFO owing to the enhanced electric breakdown despite their reduced remanent polarization. [ABSTRACT FROM AUTHOR]

We describe the design, fabrication, and testing of a spectroscopic refractometer that employs plasmonic interferometry to measure the optical dielectric functions of materials in the visible range. The proposed device, dubbed a plasmonic refractometer, consists of an array of slit-groove plasmonic interferometers etched in a ~300 nm-thick metal film (silver or gold) with arm lengths varying in steps of 25 nm up to ~8 lm. The nano-groove in each interferometer is able to generate propagating surface plasmon polaritons efficiently in a broad wavelength range, without requiring prism- or grating-coupling configurations. An integrated microfluidic channel ensures uniform delivery of dielectric materials in liquid phase. Spectrally resolved plasmonic interferograms are generated by measuring light transmission spectra through the slit of each slit-groove plasmonic interferometer and plotting the normalized intensity as a function of arm length (0.26-8.16 μm) and incident wavelength (400-800 nm) for various combinations of metal/dielectric materials. Fits of the plasmonic interferograms with a surface plasmon interference model allow determination of the refractive index dispersion of a broad class of dielectric materials, over a wide range of wavelengths and dielectric constants. As proof of concept, we extract and report the dielectric functions of representative materials, such as silver, gold, water, methanol, and ethanol. [ABSTRACT FROM AUTHOR]

Robust resistivity against electrical cycling at not only ambient conditions but also enhanced temperatures is an essential requirement for high-end actuator applications. In this study, the temperature and electric field dependence of unipolar fatigue behaviors of CaZrO3-modfied (K, Na)NbO3 lead-free piezoceramics were investigated. The space charge accumulation during unipolar cycling is responsible for the build-up of internal bias field, the dynamics of which with respect to temperature and driving field can be described using a model based on Maxwell-Wagner relaxation process. Besides, clamping of domain walls can be inferred by comparing the large and small signal permittivity. Most intriguingly, the unipolar strain exhibits a fatigue-free behavior even at elevated temperatures, rendering the material exceptionally suitable for actuator applications. [ABSTRACT FROM AUTHOR]

The mechanical properties, electronic structure and thermodynamic properties of the Mo2XB2 and MoX2B4 (X=Fe, Co, Ni) ternary borides were calculated by first-principles methods. The elastic constants show that these ternary borides are mechanically stable. Formation enthalpy of Mo2XB2 and MoX2B4 (X=Fe, Co, Ni) ternary borides are at the range of -118.09 kJ/mol to -40.14 kJ/mol. The electronic structures and chemical bonding characteristics are analyzed by the density of states. Mo2FeB2 has the largest shear and Young's modulus because of its strong chemical bonding, and the values are 204.3 GPa and 500.3GPa, respectively. MoCo2B4 shows the lowest degree of anisotropy due to the lack of strong direction in the bonding. The Debye temperature of MoFe2B4 is the largest among the six phases, which means that MoFe2B4 possesses the best thermal conductivity. Enthalpy shows an approximately linear function of the temperature above 300K. The entropy of these compounds increase rapidly when the temperature is below 450 K. The Gibbs free energy decreases with the increase in temperature. MoCo2B4 has the lowest Gibbs free energy, which indicates the strongest formation ability in Mo2XB2 and MoX2B4 (X=Fe, Co, Ni) ternary borides. [ABSTRACT FROM AUTHOR]

A transportable fountain clock with high reliability is important for high-precision time-frequency measurements. Because of its relatively small cold atoms' collision frequency shift and ease of attaining high quantum state preparation efficiency, the rubidium atomic fountain clock has an indicated higher stability and reliability. This paper reports the design and operation of a transportable rubidium atomic fountain clock developed by the Shanghai Institute of Optical and Fine Mechanics, Chinese Academy of Science. After being transported more than 1000 km from Shanghai to the Changping Campus of the National Institute of Metrology, China, the optical platform and other hardware of the fountain clock did not need to be adjusted. The rubidium fountain clock maintained a stability of 4.0 × 10−13τ1/2, reaching 5.0 × 10−16 at 300 000 s. After transportation, the rubidium fountain clock and a cesium fountain clock (NIM5) were operated together against the reference frequency of a hydrogen maser. In three separate operating periods, over a total of nearly three months, the average frequency repeatability of the rubidium fountain was less than 3.8 × 10−15. [ABSTRACT FROM AUTHOR]

Electrical poling is indispensable for endowing isotropic ferroelectric polycrystals with a net macroscopic polarization and hence piezoelectricity. However, little attention has been paid to the optimization of poling conditions in (K, Na)NbO3-based ceramics with a polymorphic phase transition. This study investigated the electrical properties of CaZrO3-modified (K, Na, Li)(Nb, Ta)O3 lead-free piezoceramics as a function of the poling temperature. Peak piezoelectric coefficient d33 of 352 ± 7 pC/N and planar electromechanical coupling factor kp of 0.47 were obtained at the optimized poling temperature of 120 °C, which crosses the polymorphic phase transition regime. In-depth analysis of the asymmetric polarization hysteresis loops and bipolar strain curves uncovered striking analogy between electrical poling and unipolar cycling in the current system, which is attributed to a competition between domain reorientation and space charge accumulation. [ABSTRACT FROM AUTHOR]

We report on temperature dependence of local electromechanical properties of lead-free (K,Na)NbO3-based ceramics that macroscopically manifests a large temperature-insensitive strain. Piezoresponse force microscopy reveals the particular role of the orthorhombic-tetragonal phase transition, where a reconstruction of the domain structure occurs and local piezoelectric response shows a peak value. A good quantitative agreement between temperature dependences of the local and previously reported macroscopic small-signal piezoelectric coefficients is observed. An influence of the polymorphic phase transition on polarization switching kinetics was revealed. [ABSTRACT FROM AUTHOR]

The effect of uniaxial compressive stress on the crystal structure of a 6 mol. % Li-doped (K,Na)NbO3 (LKNN6a) ceramic was investigated using in situ synchrotron X-ray diffraction, revealing the stress-induced relative change in monoclinic Pm and tetragonal P4mm phases. As such, stress-induced phase transformations, in addition to the lattice deformation and domain switching, are the contributing factors for the observed macroscopic mechanical behavior of LKNN6a. The in situ stress-dependent diffraction data also demonstrates a method to mechanically modulate the polymorphic phase transition temperature (TPPT) to a higher temperature, as observed by the temperature-dependent permittivity measurements under a constant bias stress. The external uniaxial compressive stress increases the stability of the lower symmetry monoclinic phase, shifting TPPT to a higher temperature by 60 °C for the maximum uniaxial compressive stress of 300 MPa in the studied composition. Importantly, the stress-induced stabilization of the room-temperature ferroelectric phase can be useful to optimize the phase transition region, as well as increase the temperature stability of lead-free KNN. [ABSTRACT FROM AUTHOR]

Recently, several creative processing techniques yielded thermoelectrics with reduced thermal conductivity and, thereby, an enhanced figure or merit. These were based on engineered complex microstructures with attendant dislocation structures. In this study, we implement highly controlled mesoscopic dislocation structures into the model thermoelectric SrTiO3 in order to quantify phonon scattering at dislocations. Both single crystals and polycrystalline material have been furnished with enhanced dislocation densities increased by a factor of 150–300 by plastic deformation. Thermal conductivity was measured using laser flash analysis between room temperature and 325 °C. Etch pit techniques and ultra-high voltage electron microscopy afford quantification of dislocation density. Experimental results were compared to predictions by the Debye-Callaway model. The latter revealed that dislocation densities of 1015 m−2 would be necessary for the reduction of thermal conductivity of SrTiO3 in the investigated temperature range, which could not be realized using the plastic deformation mechanism applied. [ABSTRACT FROM AUTHOR]

Domain-wall dynamics under strong, super-coercive electric fields in polycrystalline bismuth ferrite (BiFeO3) are not well established due to the experimental difficulties in processing high phase purity perovskite with low electrical conductivity. Overcoming these difficulties, here we present x-ray diffraction measurements carried out in situ during electrical poling with a trapezoidal electric-field to investigate the domain wall dynamics and lattice strain in this material. It is observed that during field ramping, microscopic strains, i.e., non-180° domain texture and lattice strain, increase simultaneously. During DC field dwell, however, a lattice strain decrease occurs over time, accompanied by an increase in the non-180° domain texture. This inverse time-dependent trend of microscopic strain mechanisms is speculated to be due to mobile charged defects residing in domain wall regions. The configuration of these charged point defects may also play a role in the observed post-poling relaxations of non-180° domain texture and macroscopic piezoelectric coefficients on removal of the field. Since conducting domain walls have been recently identified in a number of ferroelectrics, these results should significantly impact the understanding of strain mechanisms not only in BiFeO3 but on a broader range of ferroelectric materials. [ABSTRACT FROM AUTHOR]

We present a theoretical analysis of liquid viscosity sensors using ZnO and AlN thin film bulk acoustic wave resonators (FBARs) with tilted polar c-axis orientations. Besides the thickness longitudinal mode, the tilted c-axis orientation induces thickness shear mode in the resonator, which allows resonators operated in liquid medium without significant damping for sensory application. The equation for predicting electric impedance of shear mode film bulk acoustic wave resonators (FBARs) with a viscous liquid loading was derived from the basic piezoelectric constitutive equations. The viscosity sensitivity of shear mode ZnO and AlN resonators was achieved by calculation of resonant frequency shift due to viscous liquid loading. In the simulation, it is assumed that all the resonators have 2 μm thickness and 300 μm×300 μm electrode area; three different liquids (water, acetone, and olive oil) were chosen as the liquid loadings; and different tilt c-axis angles for both ZnO FBARs and AlN FBARs have been examined. It was found that the sensitivities of shear mode resonators to the three liquid loading are very close, and do not change much with the c-axis tilt angle with a value rang from 0.91e-3 to 0.97e-3 (kg m-3 Pa·S)-0.5 for ZnO FBARs and from 1.12e-3 to 1.13 e-3 (kg m-3 Pa·S)-0.5 for AlN FBARs. When the resonator's mechanical quality factor (Q) is changed from 50 to 10 000, viscosity sensitivities are almost same. However, Q has a great effect on resonator impedance; and if Q is too low or the viscosity of the liquid is high, the maximum phase angle of the resonator will be less than 0, which makes excitation of the oscillation difficult if an oscillator circuit is used for sensor measurement. The results can be used for design and application of ZnO or AlN FBARs to monitor liquid viscosity. [ABSTRACT FROM AUTHOR]

Microscale 1-3-type-like magnetoelectric (ME) composites with ferromagnetic microstrips laterally embedded in a piezoelectric ceramic substrate were fabricated by a dice-and-insert method. Mechanically sliced microstrips of Li/Ta-modified (K,Na)NbO3 lead-free ceramics and CoFe2O4 ceramics were used as the piezoelectric and piezomagnetic phases, respectively, which were inserted into each other and bonded together by epoxy. The ME properties of such 1-3-type-like composites with piezoelectric substrates were verified. The maximum ME coefficient was found to vary with the strip size, substrate thickness, and thickness of epoxy bonding layers. A maximum value of 48 mV/(cm·Oe) was achieved. In addition, a special anisotropy was obtained in the present lateral 1-3 type ceramic composites and made it have potential applications in detecting magnetic field directions. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric xLiNbO3–(1-x)(K0.52Na0.58)NbO3 (LKNN) (x=0, 0.04, 0.06, and 0.08) thin films on Pt/Ti/SiO2/Si(100) substrates were prepared by a sol-gel method. The effects of the Li substitution content on the crystal structure, microstructure, and electrical properties of LKNN films were investigated. The Li substitution leads to a remarkable improvement in the piezoelectric properties of the films. The LKNN film with an optimized Li substitution of x=0.06 showed a high local effective piezoelectric coefficient d33* of 192 pm/V, which is comparable to the piezoelectric performance of Pb(Zr,Ti)O3 films. An enhanced ferroelectricity was also obtained in the x=0.06 LKNN film, with a remnant polarization of 9.7 μC/cm2 and a coercive field of 36.5 kV/cm. Furthermore, an in-depth analysis of the leakage current characteristics of the LKNN films was also conducted in this study. [ABSTRACT FROM AUTHOR]

Microscale 1–3-type piezoceramic/epoxy composites using Li/Ta-modified (Na,K)NbO3 (NKN-LT) lead-free piezoelectric ceramics were fabricated via a modified dice-fill method, by which the NKN-LT ceramic rods were miniaturized to a lateral width of 150 μm with an aspect ratio (height/width) higher than 3.5. The piezoelectric properties of the 1–3 composites as a function of ceramic volume fraction were measured and compared with theoretical predictions. In addition to a high electromechanical coupling coefficient (kt∼50%) and low acoustic impedances (Z∼10 Mrayls), the developed composites show a clear single thickness mode with a high resonance frequency over 3.5 MHz. The present Pb-free piezocomposites are suitable for medical imaging devices embedded in the human body. [ABSTRACT FROM AUTHOR]

Anatase titania-coated bismuth ferrite nanocomposites (BiFeO3/TiO2) have been fabricated via a hydrothermal approach combined with a hydrolysis precipitation processing. Analysis of the microstructure and phase composition reveals that a core-shell BiFeO3/TiO2 structure can be formed, which results in a significant redshift in the UV-vis absorption spectra as compared to a simple mechanical mixture of BiFeO3–TiO2 nanopowders. The core-shell structured BiFeO3/TiO2 nanocomposites exhibit higher photocatalytic activity for photodegradation of Congo red under visible-light (λ>400 nm) irradiation, which should be attributed to the enhancement of the quantum efficiency by separating the electrons and holes effectively. The obtained BiFeO3/TiO2 nanocomposites can be used as potential visible-light driven photocatalysts. [ABSTRACT FROM AUTHOR]

Coarse (about 1 μm) and fine (about 100 nm) Bi2Te3 particles were synthesized by mechanical alloying for different times, respectively. Their mixtures at different ratios were consolidated by spark plasma sintering to produce nano-/microstructured composites with the same chemical compositions. The Seebeck coefficient was significantly enhanced by addition of fine particles through the potential barrier scattering. The electrical resistivity increased rapidly when the weight fraction of fine particles exceeded about 60%, probably due to an effect similar to percolation phenomenon. However, the thermal conductivity was reduced almost linearly with increasing fraction of fine particles. Because of the combined effects of the potential barrier scattering, nonlinear change in electrical property and linear change in thermal transport property, a peak value of dimensionless figure of merit (ZT) was achieved for the sample containing 60% fine particles. This study demonstrated the possibility to enhance ZT value by introducing nonuniform microstructures even without changing chemical compositions. [ABSTRACT FROM AUTHOR]

Tetragonal Nb-doped Pb(Zr0.3Ti0.7)O3 (PNZT) films with a lead oxide seeding layer were deposited on the Pt(111)/Ti/SiO2/Si(100) substrates by sol-gel processing. The as-grown PNZT films with thicknesses ranging from about 0.08 to 0.78 μm show highly a-axis preferential orientation, and their ferroelectric and piezoelectric properties improved with increasing film thickness. Due to the combined effects of Nb doping and a-axis texturing as well as reduced substrate constraint, a high d33 constant up to 196 pm/V was obtained for PNZT film at 0.78 μm in addition to a large remnant polarization of 69 μC/cm2. This well a-axis-oriented PNZT films on platinized Si with a high piezoresponse are suitable for the fabrication of microelectromechanical devices. [ABSTRACT FROM AUTHOR]

1–3 connectivity lead zirconic titanate (PZT)/epoxy composite thick films containing fine-scale and high aspect ratio PZT pillars (40 μm sectional width, 40 μm spacing, and 5.5 aspect ratio) were obtained by a modified dice and fill method. The composite thick film works at a high frequency >7 MHz with a clear and uncoupled thickness mode, together with a relatively high electromechanical coupling coefficient (kt=56.4%), low acoustic impedance (Z=7.8 Mrayls), and low mechanical Qm (3.3). High piezoelectric coefficient (d33=332 pC N-1) along with reduced dielectric constant ([variant_greek_epsilon]r=105) endowed the composite films an enhanced piezoelectric voltage coefficient g33 value of 357×10-3 m2/C, which is required to increase the receiving voltage sensitivity. The present piezocomposite thick film with microscale ordered structure is promising for high-frequency ultrasonic transducers. [ABSTRACT FROM AUTHOR]

(Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3 (BNT-BKT) ceramics as a promising candidate for lead-free piezoelectric ceramics were studied with a special emphasis on the compositional dependence of piezoelectric and ferroelectric properties. One mole percent excess Bi was added to compensate for the volatilization of Bi3+ ions during sintering, which was found to be effective in improving the piezoelectric properties of the resultant BNT-BKT ceramics. The piezoelectric, ferroelectric, and dielectric properties of the Bi-compensated BNT-BKT ceramics were investigated and discussed in relation to the morphotropic phase boundary that is close to the composition range of 20–24 mol % BKT. The maximum piezoelectric constant d33 (207 pC/N) and electromechanical coupling factor kp (35%) were obtained at the compositions of 23% and 20%, respectively. [ABSTRACT FROM AUTHOR]

CoSb3-xTex(x=0.05-0.3) skutterudite polycrystals with an average grain size of 160 nm were fabricated by mechanical alloying combined with spark plasma sintering. The variation of lattice parameter with Te content indicates that the solution limit of Te was x=0.15, above which the impurity phases of Te, CoTe2, and CoSb2 appeared, and the matrix cracked above 500 °C. All samples behaved as degenerate semiconductors. The forbidden energy gap was estimated to be 0.047 eV from the temperature corresponding to the occurrence of intrinsic excitation, which is in good agreement with Singh’s theoretical calculation (0.05 eV) [D. J. Singh and W. E. Pickett, Phys. Rev. B 50, 11235 (1994)]. The CoSb2.85Te0.15 sample had the highest power factor and the lowest thermal conductivity, resulting in the highest thermoelectric figure of merit, ZT=0.93 at 547 °C. The role of Te substitution in enhancing thermoelectric properties is discussed in relation to the bipolar diffusion mechanism. [ABSTRACT FROM AUTHOR]

Ta-doped Ti1-xTaxCoSb (0≤x≤0.08) half-Heusler compounds were synthesized by melting and annealing process. Their thermoelectric properties were studied in the temperature range of 300–900 K. The Ti1-xTaxCoSb compounds exhibit negative Seebeck coefficients with considerably large absolute values. With increasing Ta substitution, the electrical conductivity was greatly increased, but the thermal conductivity was reduced. Because of the combined effects of increased electrical conductivity and reduced thermal conductivity, the thermoelectric performance of Ti1-xTaxCoSb alloys was apparently improved by doping Ta. The dimensionless figure of merit of 0.3 was obtained for Ti0.92Ta0.08CoSb compound at 900 K. This value is about ten times larger than that of the undoped TiCoSb compound. [ABSTRACT FROM AUTHOR]

A pseudo-1-3-type multiferroic composite consisting of Pb(Zr,Ti)O3 (PZT) rod array (with base) and Terfenol-D/epoxy matrix was prepared by the dice-and-fill technique. Simple series and parallel mixture rules well described the measured dielectric and piezoelectric constants. Large magnetoelectric coefficients were observed in the pseudo-1-3-type composite, e.g., over 300 mV/cm Oe below 40 kHz and over 4500 mV/cm Oe at resonant frequency. The magnetoelectric response strongly depends on the magnetostrictive behavior of the matrix and the volume fraction of PZT rods, which gives us two convenient ways to modify their magnetoelectric response. For this pseudo 1-3-type multiferroic composite, the remarkable magnetoelectric response and well-developed fabrication technique are advantageous for their practical applications in piezoelectric-magnetoelectric multifunctional devices and large bandwidth magnetic sensors. [ABSTRACT FROM AUTHOR]

Two channels of the conductance G exist in cold-pressed powder compacts of CrO2/(CrO2/Cr2O3), where two types of granules have different coercivities. One of the channels is the spin-dependent intergranular tunneling conductance, and the other one is the spin-independent higher-order inelastic hopping conductance. The conductance is mainly related with the spin-dependent tunneling channel at low temperature. A large low field tunneling magnetoresistance (TMR) of 30.4% is achieved in 950 Oe field at 2 K. The reason is the relative orientation of the magnetization that tends to be antiparallel between the two coercivities. Field dependence of the tunneling magnetoresistance shows two better-separated peaks than that of CrO2 powder compact. The results suggest that the introduction of CrO2/Cr2O3 improves low field sensitivity, TMR, and switching characteristics. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate [Pb(ZrxTi1-x)O3, PZT] thin films with various compositions, whose Zr/Ti ratio were varied as 40/60, 48/52, 47/53, and 60/40, were deposited on Pt(111)/Ti/SiO2/Si substrates by sol-gel method. A seeding layer was introduced between the PZT layer and the bottom electrode to control the texture of overlaid PZT thin films. A single perovskite PZT thin film with absolute (100) texture was obtained, when lead oxide was used as the seeding crystal, whereas titanium dioxide resulted in highly [111]-oriented PZT films. The dielectric and ferroelectric properties of PZT films with different preferential orientations were evaluated systemically as a function of composition. The maximums of relative dielectric constant were obtained in the morphotropic phase boundary region for both (100)- and (111)-textured PZT films. The ferroelectric properties also greatly depend on films’ texture and composition. The intrinsic and extrinsic contributions to dielectric and ferroelectric properties were discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Flexoelectricity (coupling between polarization and strain gradients) is a property of all dielectric materials that has been theoretically known for decades, but only relatively recently it has begun to attract experimental attention. As a consequence, there are still entire families of materials whose flexoelectric performance is unknown. Such is the case of antiferroelectrics: materials with an antiparallel but switchable arrangement of dipoles. These materials are expected to be flexoelectrically relevant because it has been hypothesised that flexoelectricity could be linked to the origin of their antiferroelectricity. In this work, we have measured the flexoelectricity of two different antiferroelectrics (PbZrO3 and AgNbO3) as a function of temperature, up to and beyond their Curie temperature. Although their flexocoupling shows a sharp peak at the antiferroelectric phase transition, neither flexoelectricity nor the flexocoupling coefficients are anomalously high, suggesting that it is unlikely that flexoelectricity causes antiferroelectricity. [ABSTRACT FROM AUTHOR]

Locally persistent tetragonal distortion in NaNbO3-BaTiO3 relaxor ferroelectrics was identified at multiple length scales by means of in-situ synchrotron x-ray diffraction, absorption fine structure, and Raman spectra although their average symmetry seemingly evolved from a tetragonal to a cubic-like phase with the increasing BaTiO3 content. Theoretical calculations of Nb-O peaks in the R range of 1–2Å provided a clear evidence that Nb5+ in an NbO6 octahedron should be spontaneously shifted along [001]. The competition between B-site Nb5+ ([001]) and Ti4+ ([111]) spontaneous off-center displacement directions would contribute to the disruption of long-range polar ordering. Raman spectra suggested that A-site Ba2+ and Na+ cations should be located at the center of the cubes in the absence of the polar contribution unlike Pb2+/Bi3+ with lone-pairs. A relatively low field-induced strain in NN-BT relaxors was thus ascribed to the small spontaneous polarization magnitude and the absence of structural phase transition during electric loading. [ABSTRACT FROM AUTHOR]

An insulated poly(sodium 4-styrenseulfonate) (PSS) was used to modify monolayer graphene for anode applications of organic photovoltaics (OPVs). With this PSS interfacial modification layer, the OPVs showed a significant increase of 56.4% in efficiency due to an improved work function and hydrophilic feature of graphene and an enlarged recombination resistance of carriers/excitons. Doping a highly contorted 1,2,5-thiadiazole-fused 12-ring polyaromatic hydrocarbon into the active layer to form ternary blended OPVs further enlarged the recombination resistance of carriers/excitons and improved light absorption of the active layer, with which a high power conversion efficiency of 6.29% was acquired. [ABSTRACT FROM AUTHOR]

The influences of external Lévy noise in CO oxidation on the Ir(111) surfaces are numerically examined. Depending on the control parameters, such as the temperature T and the CO fraction Y in the total reactant input gas flux, the reaction exhibits one or two stable stationary states in the absence of noise. Lévy noise is introduced in the reaction by randomly varying the quality of the influx mixture. We then observe a large variety of different types of behaviors depending on the initial CO fraction Y, in particular, the phenomenon of noise-induced shifts of the steady state in the monostable regime is regarded. We also show how the stationary probability density changes in terms of stochastic bifurcation when Lévy noise is applied in the bistable regime. The results provide a strong evidence for noise-induced transitions. We concentrate on the effects of the stability index a; the skewness parameter β; and the noise intensity D that emphasize the differences with Gaussian fluctuations. [ABSTRACT FROM AUTHOR]

Single-crystal SnSe has been found to exhibit exceptional thermoelectric performance, but the efficiency of polycrystalline samples is still far from satisfactory. In this work, with an intention to effectively suppress heat conduction and minimally affect hole transport, we alloyed p-type polycrystalline SnSe with PbSe. Single-phase Sn1-xPbxSe solid solutions were formed up to x-0.12. The lattice thermal conductivity was reduced from 1.4 to 0.85W m-1 K-1 by 12 at. % PbSe alloying due to strain and mass fluctuations. Interestingly, the Seebeck coefficient and carrier concentration were nearly unchanged by Pb substitution, indicating a constant effective mass and an undisrupted valence band maximum. A peak figure of merit (ZT) of 0.85 at 800K was obtained in the x=0 sample, and relatively high performance was also achieved in solid solutions. A concise model was developed involving multiple carrier scattering mechanisms, capturing the dependence of the mobility on composition and temperature. [ABSTRACT FROM AUTHOR]

An enhanced efficiency organic light-emitting device (OLED) with corrugated nanostructures on a small-molecule organic film has been demonstrated. By patterning the hole transport layer via soft nano-imprinting lithography and coating with Ag, a nanostructured cathode is introduced to enhance the light extraction of the OLED without affecting the flatness and conductivity of the indium-tin-oxide film. Both luminance and current efficiency are improved compared with those of conventional planar devices. The observable improvement in luminance and current efficiency can be ascribed to the surface plasmonic and scattering effects caused by the Ag nanostructures. Moreover, theoretical simulations also demonstrate that the power loss to surface plasmon-polariton modes has been recovered. [ABSTRACT FROM AUTHOR]

The band structure, electronic and optical properties of the perovskite CH3NH3CdxPb1-xI3 are predicted using density functional theory. When Cd content is not over Pb content, the band gap of CH3NH3CdxPb1-xI3 is larger than that of CH3NH3PbI3, and the smallest band gap appears in CH3NH3Cd0.875Pb0.125I3 compound. In the wavelength range of 500-800 nm, the optical absorption coefficients of three kinds of composition CH3NH3CdxPb1-xI3 (x=5,6,7) are much larger than those of CH3NH3PbI3. Compared to CH3NH3PbI3, the absorption coefficients of CH3NH3Cd0.875Pb0.125I3 increase averagely 3.54 times in the visible light spectrum and the latter can absorb much more solar energy in infrared range than the former. The CH3NH3Cd0.875Pb0.125I3 compound is exceptional candidates of photovoltaic materials. [ABSTRACT FROM AUTHOR]

PbSe is an inexpensive alternative for PbTe as a mid-temperature thermoelectric material, but few investigations have been reported about its intrinsic properties despite recent efforts on doping techniques. In this work, pristine PbSe bulk materials were synthesized by a process combining mechanical alloying and spark plasma sintering, which is increasingly used for processing thermoelectric materials, and their electrical and thermal transport properties as well as thermoelectric performance were investigated in a wide temperature range. A maximum ZT ~0.83 was obtained at 673 K in nominal composition PbSe + 3 or 4 at. % Pb, leading to nearly 50% enhancement from reported n-type pristine PbSe, mainly benefitting from the improved electrical performance. Furthermore, the potential thermoelectric efficiency was also improved due to the enhanced low-temperature performance, showing a high average ZT of 0.6 that is even comparable to that of commercial n-type Bi2Te3 materials. [ABSTRACT FROM AUTHOR]

We demonstrated a strategy to realize broadband enhanced absorption in the top-incident inverted organic solar cells (OSCs) by employing an external antenna layer on top of the periodic corrugated metallic anode. Surface-plasmon polaritons (SPPs) are excited on the opposite interfaces of the periodic corrugated metallic anode, which mediate the energy transfer from the antenna layer to the active layer through the anode. The absorption of the OSCs is significantly broadened and enhanced by tuning the SPP resonance to coincide with both the emission of the antenna and the absorption of the active material. The power conversion efficiency exhibits an enhancement of 16% compared to that of the OSCs without the antenna layer. [ABSTRACT FROM AUTHOR]

A multi-functional gold nanorods-mesoporous silica Janus nanoparticles (NPs) were fabricated by a facile and mild strategy. These Janus NPs not only exhibit small shift of the local surface plasmon resonance wavelength but also have high potential for drug loading and low cytotoxicity. More importantly, the Janus nano-composites could efficiently deliver the imaging agents or drugs into liver cancer cells, at the same time the Janus NPs have good effect on photothermal, which indicate that the unique Janus NPs could be a promising candidate of theranostic system for combined photothermo-/chemo-cancer therapy. [ABSTRACT FROM AUTHOR]

Effective and tunable light trapping in organic solar cells (OSCs) has been demonstrated by employing Au-Ag alloy nanoparticles (NPs). A simple vacuum thermal annealing method has been employed to fabricate the Au-Ag alloy NPs with tunable molar ratio, and thereafter tunable localized surface plasmon resonance (LSPR). The incorporation of the alloy NPs with an appropriate molar ratio into the OSCs structures supports amplification of the electric field near the particles surface through LSPR and results in an enhanced light absorption at the absorption wavelength region of the absorber owing to the near field coupling. The short-circuit photocurrent density of the alloy NPs-based OSCs is improved from 7.37 to 8.74mA/cm2 compared to that of control OSCs, and the efficiency of 3.03% is obtained, which corresponds to an enhancement factor of 19%. [ABSTRACT FROM AUTHOR]

The crystal structures, elastic and anisotropic properties of CH3NH3BX3 (B = Sn, Pb; X = Br, I) compounds as solar cell absorber layers are investigated by the first-principles calculations. The type and strength of chemical bond B-X are found to determine the elastic properties. B-X bonds and the organic cations are therefore crucial to the functionalities of such absorbers. The bulk, shear, Young's modulus ranges from 12 to 30 GPa, 3 to 12 GPa, and 15 to 37 GPa, respectively. Moreover, the interaction among organic and inorganic ions would have negligible effect for elastic properties. The B/G and Poisson's ratio show it would have a good ductile ability for extensive deformation as a flexible/stretchable layer on the polymer substrate. The main reason is attributed to the low shear modulus of such perovskites. The anisotropic indices AU, AB AG, A1, A2, and A3 show ABX3 perovskite have very strong anisotropy derived from the elastic constants, chemical bonds, and symmetry. [ABSTRACT FROM AUTHOR]

The bipolar fatigue behavior of (K,Na)NbO3 (KNN)-based lead-free piezoceramics was investigated. A comparative analysis demonstrated that CaZrO3-modified KNN ceramics exhibited highly enhanced bipolar fatigue resistance due to the reduced lattice distortion (c/a ratio) and coexistence of orthorhombic and tetragonal phases. The hypothesis was verified by systematical studies of cycle-dependent large and small signal parameters and micro-morphologies. It was identified that mechanical stress induced microstructure damage beneath the electrodes renders the KNN ceramics to be vulnerable to bipolar cycling; while the mild fatigue behavior for CaZrO3-modified ones mainly originates from a thermally reversible domain wall pinning. [ABSTRACT FROM AUTHOR]

A setup based on dynamic method was developed for fast Seebeck coefficient measurement from room temperature to 473 K. Two T-type thermocouples with a response time of less than 0.1 s were used to measure the dynamic temperatures of the sample. The Cu wires of the two thermocouples served as leads for Seebeck voltage measurement. The dynamic temperature feature of the setup was characterized. Test measurements were conducted with LaCo0.9Cu0.1O3 and LaCo0.85Cu0.15O3 samples with the customized setup, and the results had a difference of ±8.4% compared with the data provided by ZEM-2 (Ulvac-Riko, Japan), which showed that the Seebeck measurement with the customized setup was reliable. In addition, the error on the Seebeck coefficient caused by the dynamic variation of temperature was discussed. The setup described in this paper has the advantage of fast Seebeck coefficient measurement with a measurement speed of about 14-23 Kmin-1. [ABSTRACT FROM AUTHOR]

For further thermoelectric performance enhancement by the nanocomposite effect, a small amount (< 2 vol. %) of 30 nm SiC particles were added into a compositionally optimized AgPbmSbTem+2 thermoelectric alloy fabricated by mechanical alloying and spark plasma sintering. Although the energy filtering effect is not available in the present composite due to the mismatched interface between SiC and the matrix, a small amount of SiC dispersions were revealed to be effective to reduce the thermal conductivity via enhancing phonon scattering. A high figure of merit up to 1.54 at 723K was obtained in the AgPbmSbTem+2 matrix composite containing 1 vol. % SiC nanoparticles. [ABSTRACT FROM AUTHOR]

Crystallographic structure of sol-gel-processed lead-free (K,Na)NbO3 (KNN) epitaxial films on [100]-cut SrTiO3 single-crystalline substrates was investigated for a deeper understanding of its piezoelectric response. Lattice parameter measurement by high-resolution X-ray diffraction and transmission electron microscopy revealed that the orthorhombic KNN films on SrTiO3 (100) surfaces are [010] oriented (b-axis-oriented) rather than commonly identified c-axis orientation. Based on the crystallographic orientation and corresponding ferroelectric domain structure investigated by piezoresponse force microscopy, the superior piezoelectric property along b-axis of epitaxial KNN films than other orientations can be explained. [ABSTRACT FROM AUTHOR]

For a better understanding of piezoelectricity in epitaxial film systems, epitaxially grown tetragonal Pb(Zr0.3Ti0.7)0.98Nb0.02O3 (PNZT) thin films with three primary crystallographic orientations were studied with a focus on their piezoelectric behaviors and domain configuration. Using piezoresponse force microscopy, the (001)-oriented epitaxial films were found to show superior piezoelectric properties compared with the (110)- and (111)-oriented films. This can be attributed to the structural characteristics of the tetragonal PNZT phase after applying an electrical field. Island-distributed domain shapes were also mapped for all three orientations. [ABSTRACT FROM AUTHOR]

The unipolar fatigue behavior of CaZrO3 and MnO2 co-modified (K,Na,Li)(Nb,Ta)O3 lead-free piezoceramics was investigated systematically. The well-known charge agglomeration model is shown to explain the overall changes observed during unipolar fatigue, such as the development of bias field as well as the anisotropy in bipolar strain hysteresis and field-dependent dielectric permittivity. In addition, it is found that the unipolar strain exhibits only small degradation within 3% at the field amplitude of 2 kV/mm up to 107 cycles. This exceptionally good fatigue resistance is identified due to the presence of additional process, assigned as a 'softening' effect that competes against the usual fatigue effect. [ABSTRACT FROM AUTHOR]

Ultrahigh piezoelectric constant (d33 = 683 pC/N) and converse piezoelectric coefficient (dS/dE = 1257 pm/V) were observed in CuO-doped lead-free (Ba,Ca)(Ti,Sn)O3 ceramics at an optimal composition fabricated by a conventional sintering method at a low temperature 1250 °C. Since all samples showed a pure perovskite structure with coexisting multiphases including cubic, tetragonal, orthorhombic, and rhombohedral phases around two converged triple points, a good compositional stability of high piezoelectricity along with a high d33 and dS/dE over 600 pC/N and 1000 pm/V was achieved within a wide compositional region (1.0 ≤ x ≤ 3.0) regardless of the CuO content (x). [ABSTRACT FROM AUTHOR]

The interaction potentials between electron and atom play an important role in electron- atom scattering. Using three potential models, the absolute differential cross section has been calculated by the second Born approximation theory. Results show that these model potentials are successful in the laser-assisted e-Ar scattering system. The influence of static potential, exchange potential and polarization potential on the absolute differential cross section is also analyzed and discussed. [ABSTRACT FROM AUTHOR]

A full set of elastic and electrical coefficients of (K,Na)NbO3-based lead-free piezoceramics with a nominal composition of Li0.03(K0.48Na0.52)0.97(Nb0.8Ta0.2)O3 (abbreviated as KNNLT) was evaluated by the standard resonance method, and compared to those of K4CuNb8O23 doped (K0.45Na0.55)NbO3 (KNN-KCN) as well as typical Pb(Zr,Ti)O3-based piezoceramics PZT5A. The measurement of intermediate elastic stiffness and compliance coefficients of KNNLT indicated that KNNLT is elastically 'softer' than KNN-KCN but 'harder' than PZT5A. An extremely high piezoelectric stiffness coefficient h33 = 68.8 × 108 V/m was obtained, due to an especially low clamped dielectric constant [variant_greek_epsilon]33S of 361. And a large longitudinal electromechanical coupling factor k33 = 57% was observed in the KNNLT system. Furthermore, the piezoelectric coefficient d33 of KNNLT was characterized via three distinctive methods: the resonance method, the Berlincourt method, and the converse piezoelectric strain measurement; while these three techniques yielded values of 174 pC/N, 195 pC/N, and 308 pm/V, respectively. The difference in d33 values determined by the three methods may be attributed to different measurement frequencies and extrinsic piezoelectric contributions related to domain wall vibration and domain switching. Besides, the piezoelectric performances of KNNLT piezoceramics were found insensitive to frequency but susceptible to temperature and electric field cycling. [ABSTRACT FROM AUTHOR]

To attain a deep understanding of ferroelectric and piezoelectric characteristics of K0.5Na0.5NbO3 as a promising lead-free compound, the ferroelectric and piezoelectric responses of its epitaxially grown films with three primary orientations of [001], [110], and [111] were investigated with an emphasis on the influence of crystallographic orientation. The films were prepared by sol-gel processing using Nb-doped SrTiO3 single-crystalline substrates with various cutting directions. A peak remnant polarization value (Pr) of 17.3 μC/cm2 was obtained along the [110] direction due to the coincidence between the spontaneous polarization and the film orientation, which is significantly higher than 10.5 μC/cm2 in [111]-oriented and 10.1 μC/cm2 in [001]-oriented ones. However, a better piezoelectric response was achieved in the [001]-oriented films with an average local effective piezoelectric coefficient (d33) of 50.5 pm/V, as compared with 45.1 pm/V and 39.7 pm/V in [110]- and [111]-oriented films, respectively. [ABSTRACT FROM AUTHOR]

The dependence of the fluorescence on the excitation beam polarization under two-photon excitation was studied in a 1,4-bis(R-cyano-4-diphenylaminostyryl)-2,5-diphenylbenzene organic crystal. The crystal shows strong response to the polarization, especially when the pump intensity was increased. The polarization plays an important role on the threshold of amplified spontaneous emission (ASE) and the ΔGASE under two-photon excitation (TPE). Moreover, the polarization distribution between the TPE (800 nm) and one-photon excitation (400 nm) are very different. The former generates a cos4 θ distribution, while the later gives rise to cos2 θ distribution in different orientation. [ABSTRACT FROM AUTHOR]