Thermoelectric enhancement in triple-doped strontium titanate with multi-scale microstructure

Strontium titanate(SrTiO_(3))is a thermoelectric material with large Seebeck coefficient that has potential applications in high-temperature power generators.To simultaneously achieve a low thermal conductivity and high electrical conductivity,polycrystalline SrTiO_(3)with a multi-scale architecture was designed by the co-doping with lanthanum,cerium,and niobium.High-quality nano-powders were synthesized via a hydrothermal method.Nano-inclusions and a nano/micro-sized second phase precipitated during sintering to form mosaic crystal-like and epitaxial-like structures,which decreased the thermal conductivity.Substituting trivalent Ce and/or La with divalent Sr and substituting pentavalent Nb with tetravalent Ti enhanced the electrical conductivity without decreasing the Seebeck coefficient.By optimizing the dopant type and ratio,a low thermal conductivity of 2.77 W·m^(-1)·K^(-1)and high PF of 1.1 mW·m^(-1)·K^(-2)at 1000 K were obtained in the sample co-doped with 5-mol%La,5-mol%Ce,and 5-mol%Nb,which induced a large ZT of 0.38 at 1000 K.

Aeromagnetic Compensation Algorithm Based on Levenberg-Marquard Neural Network

The magnetic compensation of aeromagnetic survey is an important calibration work,which has a great impact on the accuracy of measurement.In an aeromagnetic survey flight,measurement data consists of diurnal variation,aircraft maneuver interference field,and geomagnetic field.In this paper,appropriate physical features and the modular feedforward neural network(MFNN)with Levenberg-Marquard(LM)back propagation algorithm are adopted to supervised learn fluctuation of measuring signals and separate the interference magnetic field from the measurement data.LM algorithm is a kind of least square estimation algorithm of nonlinear parameters.It iteratively calculates the jacobian matrix of error performance and the adjustment value of gradient with the regularization method.LM algorithm’s computing efficiency is high and fitting error is very low.The fitting performance and the compensation accuracy of LM-MFNN algorithm are proved to be much better than those of TOLLES-LAWSON(T-L)model with the linear least square(LS)solution by fitting experiments with five different aeromagnetic surveys’data.

Transient liquid-phase to guide multiphase evolution in reactive-hotpressed ZrB_(2)-SiC-ZrC ceramics

In reactive-hot-pressed ZrB_(2)-SiC-ZrC ceramics,ZrO_(2) was found to replace ZrC phase,hence leading to confusion in designing ultra-high-temperature ceramics(UHTCs).We employ high-precision X-ray diffraction and electron microscopies to reassess the phase behavior during entire reaction and densification and to reveal the evolution of multiphase relationship at different stages before reaching the final ZrB2-SiC-ZrO_(2) composition.Frozen from transient liquid-phase,bulk glassy phase of 15 vol% was found to be constituted of Zr-Si-B-C-O with stable Zr:O ratio,which starts as early as in the intermediate stage to suppress ZrC in favor of SiC nucleation.Inhomogeneity in phase relations and microstructures results from variation in local transient liquid-phase to develop SiC phase in various modes and rates.As inferred from the earlier report of phase formation,competing reactions for ZrC and ZrB_(2) phases in the initial stage below 1000℃ were mediated via Zr-O-B-C liquid phase.Such liquid phase was moderated by stable B-O components,as initiated from surface oxides of starting powders.This picture under a continuous mother liquid phase can unify the reactions and sintering into a collective meltingenucleationegrowth process,which enables and guides the evolution of multiphase relationship through several stages to reach final densification at relatively low temperature with the help of residual oxides.

Transition-layer of coreerim structures andβ→a transformation in SiC ceramics

Similar to Si_(3)N_(4)ceramics,β→a phase transformation in SiC ceramics plays a key role in tailoring the microstructures thus optimizing related properties.SiC microstructures are dominated with the core erim structures by AlN-solution,and by EBSD analysis,a-lamellae were revealed as stacking-faults(SF)and twin-boundaries(TB)in b-grains,co-existing with the coreerim structures asα/β→α’/β’transformation by sintering.The structural transformation can proceed much further by gas-pressuresintering than hot-pressing with only RE2O3 agents,while the latter retain a high-density of SF/TB in the metastable b-SiC grains.By high-angle secondary-electron imaging,nanoscale transition-layer(TL)was observed as an inter-phase to fully separate the core and rim,which is created by a transitory equilibrium in the solutionereprecipitation process.The enrichment of AlN or RE in TL demonstrates their segregation to core surface until reaching the super-saturation and before the growth of rims.With higher AlN or RE solution and after sintering,a shear stress can develop from TL contour to drive the expansion of SF/TB in Martensitic transition,especially under an external isotropic pressure.The combinations ofβ→a transformation,coreerim structures and viscous liquid-phase enable the comprehensive assessment of sintering-microstructure-property-performance relationship of SiC ceramics,as demonstrated for their creep behaviors and fracture toughness.

Effects of Elevated CO_2 on Growth, Carbon Assimilation, Photosynthate Accumulation and Related Enzymes in Rice Leaves during Sink-Source Transition

To study the effects of growing rice (Oryza sativa L.) leaves under the treatment of the short-term elevated CO2 during the period of sink-source transition, several physiological processes such as dynamic changes in photosynthesis, photosynthate accumulation, enzyme activities (sucrose phosphate synthase (SPS), and sucrose synthase (SS)), and their specific gene (sps1 and RSus1) expressions in both mature and developing leaf were measured. Rice seedlings with fully expanded sixth leaf (marked as the source leaf, L6) were kept in elevated (700 μmol/mol) and ambient (350 mol/L) CO2 until the 7th leaf (marked as the sink leaf, L7) fully expanded. The results demonstrated that elevated CO2 significantly increased the rate of leaf elongation and biomass accumulation of L7 during the treatment without affecting the growth of L6. However, in both developing and mature leaves, net photosynthetic assimilation rate (A), all kinds of photosynthate contents such as starch, sucrose and hexose, activities of SPS and SS and transcript levels of sps1 and RSus1 were significantly increased under elevated CO2 condition. Results suggested that the elevated CO2 had facilitated photosynthate assimilation, and increased photosynthate supplies from the source leaf to the sink leaf, which accelerated the growth and sink-source transition in new developing sink leaves. The mechanisms of SPS regulation by the elevated CO2 was also discussed.

氮掺杂黑色二氧化钛用于高性能超级电容器

对于储能系统,同时实现高能量密度和高功率密度仍是一个巨大的挑战.电化学超级电容器通过表面吸附或表面氧化还原反应实现储能,是解决上述问题的潜在方法之一.本论文报道了一种新型高氮掺杂(9.29 at.%)黑色二氧化钛(TiO2-x:N)超级电容器电极材料.该材料具有独特的微观结构,由高导电的非晶壳层和一个纳米晶核组成.在酸性电解液中,该材料可以通过氮参与的氧化还原反应(TiO2-xNy+z H++ze■-TiO2-xNyHz)可逆地与质子结合实现能量的高效快速储存,实现极高的比电容(2 mV s-1扫速下容量高达750 F g-1,1 A g-1电流密度下容量可达707 F g-1)、高倍率特性(极高电流密度20 A g-1时容量仍可达503 F g-1)和长时间循环下的高稳定性.作为一种新型超级电容器电极材料,氮掺杂黑色二氧化钛或将引领金属氧化物型超级电容器的复兴.

Effect of mechanical alloying on sinterability and phase evolution in pressure-less sintered TiB_(2)-TiC ceramics

Phase relation and microstructure evolution in the pressure-less sintered TiB_(2)‒TiC ceramics preceded with mechanical alloying were systematically studied by a combination of SEM analysis.WC debris from milling balls promotes sintering by dissolving into the TiC phase to achieve dense microstructures at 1600℃.Variation of W solution in TiC grains exposes two types of core-rim structures,with no or more W in dark and white cores respectively but with common medium W in both rims.Diminishing whitecores reveal an exchange reaction between WC and TiC via mechanical alloying to form the Ti_(1-z)W_(z)C phase prior to sintering.The dark-cores inherit from the as-milled TiC power to further enable the reprecipitation of rims from a mixed liquid-phase,which facilitated also the anisotropic growth of TiB_(2) grains.The dark-cores grow persistently in the second-step at 2000℃ enabled by this liquid-phase,which coarsens the TiB2 grains too.With more alloyed phase,sintering was insufficient at 1500℃ with only the surface fluidity from the primary powders,and the second-step sintering increased the fluidity in the liquid-phase to fully densify the binary microstructure.Re-distribution of the alloyed W by two-step sintering rationalizes the evolution process of the binary microstructures and leads to better understanding of the mechanical behaviors.

Core-rim structure,bi-solubility and a hierarchical phase relationship in hot-pressed ZrB2-SiC-MC ceramics(M=Nb,Hf,Ta,W)

Core-rim structures were identified as a common feature in hot-pressed ZrB2-SiC-MC ceramics(M=Nb,Hf,Ta and W)by a combination of X-ray diffraction,scanning and transmission electron microscopies.Quantitative analyses associate them with the bi-solubility of M in ZrB2 phase,in which transition of solubility across the core/rim boundary is abrupted,signifying their creation via dissolution-reprecipitation process facilitated by transient liquid-phase.The cores were retained from starting powder after surface melting and the rims were grown from the liquid-phase to incorporate more solutes,leaving the residual liquid to turn into ZrC phase with higher solubility of M.We propose g-point scheme in the ZrB2-MB2 diagrams to combine the bi-solubility and the core-rim structures into an intra-phase relationship created by sintering,leading further to a hierarchical phase relationship.The temperature dependence of flexural strength in the ZrB2-SiC-MC ceramics varies with MC additions,which can be respectively strengthened by the strain energy created in the core-rim structures and metal segregation to grain boundaries.

High conductivity polymer electrolyte with comb-like structure via a solvent-free UV-cured method for large-area ambient all-solid-sate lithium batteries

A novel solid polymer electrolyte with comb-like structure is prepared via a solvent-free UV-cured method.The relationship between conductivity and molecular weight is investigated and revealed.The optimal electrolyte presents a considerably high conductivity of 1.44·10^(-4)S·cm^(-1)at 30℃.Meanwhile,it shows excellent compatibility with metallic lithium and wide electrochemical window(>5 V).To investigate the safety and cycling performance,the coin cell and soft package battery are assembled respectively.The LiFePO_(4)/Li coin cells exhibit initial discharge specific capacities of 163.2,147.7,137.3 and 108.7 mA·h·g^(-1)at 0.1,0.2,0.5 and 1C under 60℃,respectively.Notably,when the coin cells work at 30℃,the initial discharge specific capacities at 0.05,0.1,0.2 and 0.5C are 140.5,133.5,107.7 and 55.6 mA·h·g^(-1).Significantly,a 3.5 cm×7 cm solid-state soft pack battery is fabricated and cycling at 30℃.The first discharge capacity reaches to 137.5 mA·h·g^(-1)and the capacity retention is as high as 84.4%after 100 cycles at 0.2C and remain 95.5%after 100 cycles at 0.5C,respectively.These results shows a promising solid polymer electrolyte for solid-state batteries with good cycling and safety performance.

Reactive sintering of dual-phase high-entropy ceramics with superior mechanical properties

1. Introduction The requirements for the performance of materials have become increasingly stringent in recent years, with the rapid development of aerospace, machinery, metallurgy, nuclear energy,chemical industry, and military industry [1,2], and traditional single-phase materials are gradually revealing disadvantages due to the contradiction between demanding service environments and simple material design.

Step distribution of Yb filling fraction during microstructural evolution in skutterudites

To achieve a better material for thermoelectric power generation device, filled skutterudite Yb0.3 Co_4 Sb_(12) samples were fabricated by melting-quenching-annealing-spark plasma sintering(SPS)method. Two sets of samples, before and after SPS, were investigated. In both the two sets of samples,the average grain size of the samples increases monotonously with the increase of annealing time,while Yb filling fraction firstly increases and then decreases. Yb not filling into the skutterudite remains at the grain boundaries in the form of Yb_2 O_3 after SPS, which could be quantified by the spatially difference method of energy dispersive spectra. Step distribution of Yb filling fraction was observed in the samples annealed for 1 h, which was caused by the microstructural evolution from the peritectic phases to the skutterudite phase. The sample annealed for 3 days and SPS sintered possesses the maximum value of Yb filling fraction 0.249 and the maximum ZT value of 1.24 at 850 K. These results are helpful to better understand the microstructural evolution and Yb filling behavior in skutterudite materials.

Initial nucleation of amorphous Si–B–C–N ceramics derived from polymer-precursors

Nucleation behavior of amorphous Si–B–C–N ceramics derived from boron-modified polyvinylsilazane procusors was systematically investigated by transmission electron microscopy(TEM) combined with spatially-resolved electron energy-loss spectroscopy(EELS) analysis. The ceramics were pyrolyzed at1000℃ followed by further annealing in N2, and SiC nano-crystallites start to emerge at 1200℃ and dominate at 1500℃. Observed by high-angle annular dark-field imaging, bright and dark clusters were revealed as universal nano-structured features in ceramic matrices before and after nucleation, and the growth of cluster size saturated before reaching 5 nm at 1400℃. EELS analysis demonstrated the gradual development of bonding structures successively into SiC, graphetic BNCxand Si3N4 phases, as well as a constant presence of unexpected oxygen in the matrices. Furthermore, EELS profiling revealed the bright SiC clusters and less bright Si3N4-like clusters at 1200–1400℃. Since the amorphous matrix has already phase separated into SiCN and carbon clusters, another phase separation of SiCN into SiC and Si3N4-like clusters might occur by annealing to accompany their nucleation and growth, albeit one crystallized and another remained in amorphous structure. Hinderance of the cluster growth and further crystallization was owing to the formation of BNCxlayers that developed between SiC and Si3N4-like clusters as well as from the excessive oxygen to form the stable SiO2.

Graphene controlled phase evolution in Sr-deficient Sr(Ti, Nb)O_(3) thermoelectric ceramics

Correlated phase and microstructural evolution are systematically investigated by electron microscopies in Sr-deficient Sr(Ti,Nb)O_(3)(STNO)thermoelectric ceramics incorporated with different fraction of reduced graphene oxide(RGO).It is found that while no impurity except for very few Ti_(3)O_(5) precipitates are observed in monolithic STNO,the Nb-enriched rutile TiO_(2) appears in RGO/STNO composites.With increasing RGO content,the amount of precipitates increase at first and then decrease when RGO content becomes high,which can be ascribed to the formation of local Magneli phase.In addition,the energy-dispersive X-ray spectra combined with cathodoluminescence characterization indicates that the variation of Sr deficiency experiences the opposite trend with respect to the precipitates content.These findings clearly reveal the unique reducing effect of RGO on the microstructure of doped SrTiO_(3) with Sr deficiency,which can greatly facilitate the design of perovskite based thermoelectric materials of hierarchical structure.

Correlated evolution of dual-phase microstructures,mutual solubilities and oxygen vacancies in transparent La2-xLuxZr2O7 ceramics

The A2B2O7 series of ternary oxides are derivatives of fluorite structure over a wide range of rA/rB.Competing by two rare-earths the A-site,La2-xLuxZr2O7 ceramics were found transparent only in pore-free microstructures with similar grain sizes of pyrochlore(PY)and defective fluorite(DF)phases.Mutual solubilities of Lu and La in both phases were found by imaging and energy-dispersive spectroscopy analysis in scanning electron microscope.The dual-phase microstructures were developed with liquid-phase resulted from the exothermal reactions,creating a miscibility gap between two structures to moderate their competing grain growth.Change in grain growth behaviors in liquid-phase is described by a nucleation line in La2Zr2O7-Lu2Zr2O7 phase diagram.Variations of solution levels in DF grains and co-existing of dual-phase grain clusters in common orientation were revealed in transparent ceramics by electron backscattered diffraction,resulted by epitaxial relation of two phases promoted by the liquid-phase.Oxygen vacancies and various hole states common in both phases were revealed by characteristic cathodoluminescence peaks.The collective effects of pores,phase and grain boundaries,oxygen vacancies on scattering or absorption of visible light enables to establish a hierarchical microstructure-transparency relationship in such complex oxide ceramics,which could be tailored or further optimized by controllable sintering.

A Quasi-Experimental Study of a Web-Based English Literacy Tool for Grade 3 Students in China

Purpose:This study explores the effectiveness of a A Balanced Reading Approach for Children Always Designed to Achieve Best Results for All(ABRACADABRA;hereinafter,ABRA)-a webbased literacy program designed by Concordia University in Canada-on third-grade students in Nanjing,China.Design/Approach/Methods:Participants comprised 999 students from three treatment schools(N=711)and three control schools(N=288).Three different approaches were used in the treatment schools:namely,a computer laboratory once a week,noontime study after lunch,and single-game instruction(SG)during every English lesson.Interviews were also conducted with teachers,producing qualitative data.Findings:Following 20 weeks of intervention,the overall effect size was 4-0.05.The SG group reflected the smallest effect size(d=-0.52).The noontime study group produced an effect size of 0.39,and the laboratory group an effect size of 0.55.This study conducted interviews with teachers to gain a qualitative understanding of the differential impacts.In doing so,this study found that teachers in the SG group were poorly motivated due to a lack of school support and heavy workload,resulting in passive roles and low ABRA program intensity.Originality/Value:The results of this study indicate that ABRA is an effective means of improving Chinese students*English literacy skills.Results also underscore the need for critical measures to encourage teachers to actively participate in the program.