Anomalous Oxidation States in Multilayers for Fuel Cell Applications

Significant recent interest has been directed towards the relationship between interfaces and reports of enhanced ionic conductivity. To gain a greater understanding of the effects of hetero‐interfaces on ionic conductivity, advanced analytical techniques including electron microscopy (TEM/STEM), electron energy loss spectroscopy (EELS), and secondary ion mass spectrometry (SIMS) are used to characterize CeO₂/Ce_0.85Sm_0.15O₂ multilayer thin films grown by pulsed laser deposition. High quality growth is observed, but ionic conductivity measured by impedance spectroscopy and ¹⁸O tracer experiments is consistent with bulk materials. EELS analysis reveals the unusual situation of layers containing only Ce(IV) adjacent to layers containing both Ce(III) and Ce(IV). Post oxygen annealing induced oxygen diffusion and mixed oxidation states in both layers, but only in the vicinity of low angle grain boundaries perpendicular to the layers. The implications of the anomalous behavior of the Ce oxidation states on the design of novel electrolytes for solid oxide fuel cells is discussed.     

Chemistry of electron doped Ln2−xCexCuO4 superconductors

The electron doped Ln_2−xCe_xCuO₄ (Ln=lanthanide) oxides have intergrowth structures consisting of superconductively active CuO₂ sheets alternating with inactive (Ln, Ce)₂O₂ fluorite layers along the c-axis. Stabilization of such intergrowth structures requires bond length matching across the intergrowth interface. The bond length matching criterion causes a monotonic decrease in the Ce solubility limit from x=0.24 to x=0.15 as the size of Ln³⁺ decreased from Ln=La_0.5Nd_0.5 to Ln=Gd. Annealing in N₂ atm of Ln_2−xCe_xCuO₄ at temperatures above 900°C creates oxygen vacancies and the number of vacancies decreases with increasing Ce content. The value of x at which a semiconductor to superconductor transition occurs in Ln_2−xCe_xCuO₄ increases with decreasing size of Ln³⁺ due to an increasing Madelung energy caused by a decreasing Cu−O bond length.     

Ce和Ni共掺杂BiFeO3薄膜的光学和铁磁性能

利用溶胶-凝胶工艺在石英衬底上制备了镍铈共掺杂铁酸铋Bi_(0.9)Ce_(0.1)Fe_(1-x)Ni_xO_3(xBCFNO,x=0,0.03,0.05,0.07)薄膜.X-射线衍射(XRD)测试表明所有样品的晶体结构都为四方钙钛矿铁酸铋BiFeO_3结构.由于Ce和Ni共掺杂,XRD显示,峰位置发生偏移.主峰(012/110)峰值在Ni含量x=0.05时峰值最大.扫描电子显微镜(SEM)测试也显示x=0.05时晶粒最大,结晶度最好.光学透射测试显示xBCFNO薄膜x=0.03时的光学禁带宽度最小,为2.14 eV.铁磁测试结果表明镍铈共掺杂可以进一步提高铁酸铋的室温铁磁性.     

Superconducting and structural characteristics of YBa2Cu3O7−x thin films on si(001) substrates with YSZ buffer layers

We have prepared high quality c-axis oriented superconducting YBa₂Cu₃O_7−x thin films on Si(001) substrates covered with YSZ = (ZrO₂ + 10 at.% Y₂O₃) layers by an in situ high pressure (3–5 mbar) oxygen d.c./r.f. sputtering process at substrate temperatures of about 750°C. The films were characterized by X-ray diffraction, transmission electron microscopy (TEM) and electron scanning (SEM) techniques. A superconducting transition temperature T_c(R− 0) = 89 K was determined by resistivity and susceptibility measurements. Cross sectional TEM analysis showed a sharp interface between YSZ and Si; however an inter diffusion zone was observed between YSZ and YBa₂Cu₃O_7−x layers.     

Compositional modulation in In(x)Ga(1-x)N: TEM and X-ray studies

Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) have been used to study compositional modulation in In(x)Ga(1-x) N layers grown with compositions close to miscibility gap. The samples (0.34 < x < 0.8) were deposited by molecular beam epitaxy using either a 200 nm thick AlN or GaN buffer layer grown on a sapphire substrate. Periodic compositional modulation leads to extra electron diffraction spots and satellite reflections in XRD in the theta-2theta coupled geometry. The ordering period delta measured along c-axis was about delta = 45 A for x = 0.5 and delta = 66 A for x = 0.78 for samples grown on AlN buffer layer. TEM and XRD determinations of delta were in good agreement. Compositional modulation was not observed for the sample with x = 0.34 grown on a GaN buffer layer. Larger values of delta were observed for layers with higher In content and for those having larger mismatch with the underlying AlN buffer layer. The possibility that the roughness of the AlN growth surface promotes strong In segregation on particular crystallographic planes leading to compositional modulation is considered.     

MoO3掺杂Ba0.98Bi0.02(Ti0.9Zr0.1)O3陶瓷的介电性能研究

采用固相反应法制备了Ba<,0.98>Bi<,0.02>(Ti<,0.9>Zr<,0.1>)<,1-x>Mo<,x>O<,3>(x=0,0.01,0.03,0.05)陶瓷,研究了MoO<,3>掺杂对Ba<,0.98>Bi<,0.02>(Ti<,0.9>Zr<,0.1>)O<,3>陶瓷的相结构、表面形貌和介电性能的影响....     

A new method for preparing plan-view TEM specimen of multilayered films using focused ion beam

A new method is proposed for preparing plan-view specimens of a CeO(2)/Gd(2)Zr(2)O(7) multilayer on a metal substrate using focused ion beam milling. In the plan-view specimen, a membrane from the surface region of the CeO(2) to the Gd(2)Zr(2)O(7) layer was thinned to electron transparence so that the entire span of the multilayer can be observed in a single sample. The in-plane alignments of the CeO(2) layer and the Gd(2)Zr(2)O(7) layer were analysed using selected-area diffraction patterns (SADPs). The boundaries between the CeO(2) grains were also examined using SADPs.     

Tunable properties of cadmium substituted ZnS nanocrystals

Tailored Zn_1−xCd_xS (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles, synthesized by co-precipitation method under ultrasonic irradiation, were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), UV–Vis and photoluminescence (PL) spectroscopy measurements. According to the XRD results, substitution of Zn²⁺ by Cd²⁺ ion leads to an increase in the lattice parameters and the average size of zinc blended nanoparticles are in the range of 3–4 nm. Transmission electron microscopy image revealed the formation of nano-sized particles with dimension of 5 nm confirming that the samples are quantum dots. The shift observed in the absorption edges by increasing Cd²⁺ ion substitution is ascribed by the alloying effect but the enhancement of band gap energy compared to that of the corresponding bulk value is attributed to the nanometric grain size and quantum confinement effects. The position and intensity of PL emission peaks are tuned with Cd²⁺/Zn²⁺ ion content.     

Synthesis and characterization of cerium–silver co-doped zinc oxide as a novel sunlight-driven photocatalyst for effective degradation of Reactive Red 120 dye

Cerium–silver (Ce–Ag) co-doped ZnO was synthesized by precipitation–decomposition and tested for the degradation of Reactive Red 120 dye under natural sun light irradiation. Three weight percent Ce co-doped Ag–ZnO was found to be most efficient. Hence, this catalyst (3 wt% Ce–Ag–ZnO) has been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). XRD and XPS reveal the presence of metallic Ag and tetravalent Ce. Ag and Ce shift the absorption of ZnO to entire visible region. It was found that the Ce–Ag–ZnO exhibited higher degradation efficiency when compared to Ag-ZnO, Ce–ZnO, prepared ZnO, Commercial ZnO, TiO₂, and TiO₂-P25 at neutral pH (=7). Quantum yields of all processes were calculated and compared. Higher activity of Ce–Ag–ZnO in natural sunlight may be due to higher visible light absorption of Ce–Ag–ZnO when compared to native ZnO. The influences of operational parameters such as the amount of photocatalyst, dye concentration, initial pH on photo mineralization of RR 120 have been analyzed. The mineralization of RR 120 dye was confirmed by chemical oxygen demand (COD) measurements. A dual mechanism has been proposed for efficient degradation of RR 120 dye by Ce–Ag–ZnO under solar light at neutral pH. This photocatalyst was found to be reusable up to four runs.     

Experimental and first-principles DFT studies of electronic,optical and magnetic properties of cerium–manganese codoped zinc oxide nanostructures

Syntheses, structural, optical and magnetic characterizations of codoped ZnO nanoparticles have been reported. Nanoparticles of Zn_1−2xCe_xMn_xO (x=0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) were synthesized using a microwave-assisted combustion method. Structural, optical and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and a vibrating sample magnetometer (VSM). The observed shift in XRD peak position, change in peak intensity, cell parameters, volume and stress confirmed the substitution of cerium-manganese (Ce–Mn) dopants within ZnO lattice. The synthesized nanoparticles show different microstructure without changing the parent hexagonal wurtzite structure of zinc oxide (ZnO). The average crystallites size was decreased from 43 to 21 nm. Energy dispersive X-ray spectra confirmed the presence of Ce and Mn in ZnO system and the weight percentage was nearly equal to their nominal stoichiometry. DRS analysis showed a decrease in the energy gap with increasing dopants content. The observed luminescence in the green, violet and blue regions strongly depends on the nature of the doping elements and their concentration owing to the formation of different oxygen vacancy, zinc interstitial, and surface morphology. Our results demonstrate that Mn ions doping concentration play an important role in the observed room temperature ferromagnetism (RTFM) of Ce–Mn codoped ZnO nanoparticles. First- principles calculation results indicate that Ce governs the stability, while Mn adjusts the magnetic characteristics in codoped ZnO.     

Structural Determination and Imaging of Charge Ordering and Oxygen Vacancies of the Multifunctional Oxides REBaMn2O6‐χ (RE = Gd,Tb)

Charge ordering and oxygen vacancy ordering are revealed in REBaMn₂O_6‐δ (RE = Gd, Tb) oxides with perovskite‐related structures. Electron diffraction and transmission electron microscopy results indicate a modulation of the crystal structure. The average oxidation state of Mn and the oxygen stoichiometry are determined by means of electron energy‐loss spectroscopy, giving a REBaMn₂O_5.75 general formula. A 1:3 Mn⁴⁺:Mn³⁺ charge ordering model is confirmed by neutron powder diffraction, and oxygen vacancies‐Mn³⁺ association is suggested by pair distribution function analysis. Direct imaging of the oxygen sublattice is obtained by phase image reconstruction. Location of the oxygen vacancies in the anion sublattice is achieved by analysis of the intensity of the averaged phase image. Both ionic conduction and multiferroic behavior are predicted from the crystal structures of these oxides.     

Ca[(Li_(1/3)Nb_(2/3))_(0.95)Zr_(0.15-x)Ti_x]O_(3+δ)陶瓷的微波介电性能

研究了Zr和Ti复合取代Ca[(Li1/3Nb2/3)0.95Zr0.15-xTix]O3+δ(0≤x≤0.15,CLNZT)陶瓷B位对其晶体结构及微波介电性能的影响,并分析了谐振频率温度系数τf随容忍因子t的变化关系。当0≤x≤0.15时,CLNZT陶瓷为单一斜方钙钛矿相,随x的增加,τf由–9.4×10–6/℃变为–15.8×10–6/℃,而品质因数与谐振频率乘积Q·f值先增大,x=0.10时又开始下降。当x=0.10时,陶瓷具有较好的微波介电性能:εr为32.8,Q·f值为1.66×104GHz,τf为–13.6×10–6/℃。     

水热法制备CoxMn1-xFe2O4纳米磁性粉体及磁性研究

用水热法成功合成了CoxMn1-xFe2O4纳米磁性颗粒粉体。样品物相用X射线衍射仪表征,形貌通过透射电镜(TEM)观测。CoxMn1-xFe2O4纳米粉体的平均尺寸和晶格常数从XRD计算得到,CoxMn1-xFe2O4纳米颗粒的晶格常数随着Co2+含量的增加而变小。所得样品的磁性用振动样品磁强计(VSM)测试,结果表明,所制备的CoxMn1-xFe2O4粉体在室温下的铁磁性、饱和磁化强度和矫顽力随着Co2+含量的增加而变大。     

(Ca1-xBax)[(Li1/3Nb2/3)0.95Zr0.15)]O3+δ陶瓷微波介电特性

研究了A位Ba2+取代对(Ca1-xBax)[(Li1/3Nb2/3)0.95Zr0.15]O3+δ (0≤x≤0.2,CBLNZ)陶瓷的微观结构及微波介电特性的影响.当0≤x≤0.025时,体系为单一钙钛矿相,随Ba2+含量的增加,谐振频率温度系数(τf)由-9.4×10-6/℃增加到18×10-6/℃,而品质因数(Q)先增大;当x=0.025时,开始下降.用键价理论分析了谐振频率温度系数随B位键价的变化关系.当x(Ba2+)=2.5%时,陶瓷微波介电性能最佳,即介电常数εr=34.3,品质因数与频率的乘积Q·f =13 400 GHz,τf =-2.1×10-6/℃.     

Structural and optical properties of hexagonal MgxZn1−xO thin films

High-quality epitaxial magnesium zinc oxide (Mg_xZn_1-xO) alloy thin films were grown on sapphire (α-Al₂O₃ (0001)) substrates using pulsed laser deposition. The structural and optical properties of these hexagonal films were determined using transmission electron microscopy (TEM), x-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), absorption, and photoluminescence measurements. XRD and TEM data reveal that magnesium zinc oxide alloy films, grown by domain matching epitaxy, exhibited the following relationships: MgZnO[0001] ∥ α-Al₂O₃ [0001] and MgZnO[01 0] ∥ α-Al₂O₃ [2 0]. RBS data demonstrate that a maximum magnesium content of x=0.34 can be obtained in hexagonal Zn_xMg_1-xO thin films. This value is significantly higher than the thermodynamic limitation of x=0.04. The absorption spectra of magnesium zinc oxide alloy films obtained at room temperature demonstrate significant excitonic behavior. The exciton binding energies have been extracted from the absorption data. Values of the exciton bandgap as a function of magnesium content were determined by fitting the bandgap energies using polynomial fitting. The Zn_xMg_1−xO alloy thin films demonstrate bright room-temperature luminescence and significant excitonic behavior. A shift in the excitonic emission peak as a function of magnesium content was observed.     

Preparation,Structure, and Electrochemical Properties of Reduced Graphene Sheet Films

This paper describes the preparation, characterization, and electrochemical properties of reduced graphene sheet films (rGSFs), investigating especially their electrochemical behavior for several redox systems and electrocatalytic properties towards oxygen and some small molecules. The reduced graphene sheets (rGSs) are produced in high yield by a soft chemistry route involving graphite oxidation, ultrasonic exfoliation, and chemical reduction. Transmission electron microscopy (TEM), X‐ray diffraction (XRD), scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy clearly demonstrate that graphene was successfully synthesized and modified at the surface of a glassy carbon electrode. Several redox species, such as Ru(NH₃)₆^3+/2+, Fe(CN)₆^3?/4?, Fe^3+/2+ and dopamine, are used to probe the electrochemical properties of these graphene films by using the cyclic voltammetry method. The rGSFs demonstrate fast electron‐transfer (ET) kinetics and possess excellent electrocatalytic activity toward oxygen reduction and certain biomolecules. In our opinion, this microstructural and electrochemical information can serve as an important benchmark for graphene‐based electrode performances.     

Ba2+掺杂对CaCu3Ti4O12陶瓷结构与电性能的影响

采用传统固相法制备了Ca1-xBaxCu3Ti4O12(x=0, 0.005, 0.010, 0.020, 0.030, 0.040, 0.050, 0100,摩尔分数) 陶瓷。用X线衍射仪、扫描电子显微镜、介电温谱测试系统及阻抗测试仪研究了Ba2+掺杂量的变化对Ca1-xBaxCu3Ti4O12陶瓷的相结构、微观形貌及电性能影响。研究结果表明,随着Ba2+掺杂量的增加,陶瓷试样产生了第二相CuO,同时Ba2+掺杂使CaCu3Ti4O12的晶格常数增大。Ca1-xBaxCu3Ti4O12陶瓷的晶粒尺寸随Ba2+掺杂量的增加而减小,气孔率随之降低。掺杂适量的Ba2+可有效降低CaCu3Ti4O12陶瓷的介电损耗,也可降低相对介电常数随温度的变化率。一定量的Ba2+掺杂还能增加CaCu3Ti4O12的晶界电阻。     

The role of oxidizing agents in the structural and morphological properties of CeO2 nanoparticles

Cerium oxide (CeO₂) nanoparticles with good crystallinity and smooth surface are prepared by chemical precipitation method with different bases (NH₃, NaOH and KOH) using cerium nitrate as a source material. The effect of precipitating agents on the growth of cerium oxide nanoparticles are investigated by Photoluminescence (PL), X-ray diffraction (XRD), Fourier transform-infra red spectroscopy (FTIR), thermo gravimetric–differential thermal analysis (TG-DTA), Scanning electron microscope (SEM), Transmission electron microscope (TEM), and X-ray Photoelectron Spectroscopy (XPS). Cubic fluorite crystallites are detected by XRD pattern with preferred orientation along (1 1 1) direction. PL spectra revealed the presence of a strong and broad emission band at425 nm due to the blue shift in the visible region. The broad band below 700 cm⁻¹ is due to the envelope of the phonon band of metal oxide (Ce–O) network as revealed by the IR spectra. The TG-DTA curves revealed that the total weight loss of the samples is 19.67% when the samples are heated upto 800 °C. SEM images exhibits weakly agglomerated spheroid crystallites are obtained with the typical size in the range 10–50 nm. TEM images display that the particles are nearly spherical and square in shape with diameter 8–12 nm. XPS spectrum confirms the existence of Ce⁴⁺ oxidation states in CeO₂samples.     

PNiTa-PZT三元系压电陶瓷性能

采用传统陶瓷工艺制备了0.02Pb(Ni1/3Ta2/3)O3+0.98Pb(ZrxTi1–x)O3(x=0.50~0.55,PNiTa-PZT)三元系压电陶瓷,研究了n(Zr)/n(Ti)变化对陶瓷性能的影响。结果表明:随其比值的变化,陶瓷样品均为钙钛矿结构,且对陶瓷显微结构影响不大;当n(Zr)/n(Ti)为52/48时,陶瓷具有较优的压电、介电性能:kp为0.583,d33为266pC/N,tC为394℃,tanδ为0.0055,ε3T3/ε0为1297。其中tC比目前文献报道的PZT基压电材料高30~50℃,有望在高温压电陶瓷领域获得应用。     

Li-Zr共掺杂对Bi_2(Zn_(1/3)Nb_(2/3))_2O_7陶瓷介电性能的影响

采用固相反应法制备了(Bi1.975Li0.025)(Zn2/3Nb4/3–xZrx)O7陶瓷,研究了当Li+替代量一定时,Zr4+掺杂对陶瓷相结构和介电性能的影响。结果表明,当替代量0相似文献