Desired Stoichiometry Research Articles

Ball-Milled (Cu-Ni-Fe + Fe2O3) Composite as Inert Anode for Aluminum Electrolysis

A (Cu-Ni-Fe + Fe2O3) composite was prepared by ball milling and evaluated as an oxygen-evolving anode for aluminum electrolysis. The material was prepared by first milling elemental Cu, Ni and Fe powders to form a Cu(Ni,Fe) solid solution. Then, the milling operation was resumed for different periods of time (from 30 min to 4 h) in presence of a fixed amount of nanosized Fe2O3 particles to achieve the desired stoichiometry (Cu65Ni20Fe15)98.6O1.4. After 4 h of milling, Fe2O3 precipitates are found to be homogeneously dispersed in the Cu-Ni-Fe matrix. The powder was then heated at 1000°C and pressed to form an electrode for evaluation in low-temperature (700°C) KF-AlF3 electrolyte at an anode current density of 0.5 A cm−2 for 20 h. The cell voltage was stable at ca. 4.5 V and the Cu, Fe and Ni contamination of the produced Al and electrolyte were quite low, resulting in an estimated anode erosion rate of 1.2 cm year−1. This good corrosion resistance is attributed to the formation of a protective NiFe2O4-rich layer on the electrode during Al electrolysis, which is likely to be favored by the presence of the finely dispersed Fe2O3 precipitates acting as nucleation sites for the formation of NiFe2O4.

Suppression of Precipitates in the La2-xSrxCuO4 Films Grown on LaSrAlO4 Substrates by Introducing Homoepitaxial Layer

We have investigated impacts of a LaSrAlO4 (LSAO) homoepitaxial layer (HL) on the quality of La2-xSrxCuO4 (LSCO) films grown on single crystal LSAO (001) substrates by pulsed laser deposition. Introduction of the LSAO HL significantly suppressed the segregation of impurity phases in the LSCO films especially in a higher Sr-doping range (x > 0.20), leading to the improvement of the surface morphology. The suppression of impurity phases also enables us to obtain the desired stoichiometry of the LSCO films, which show the superconducting dome in the x-temperature phase diagram very similar to that of bulk samples.

Oxygen stoichiometry control of nanometric oxide compounds: The case of titanium ferrites

Three techniques have been coupled with an original device, based on H 2/H 2O equilibrium, controlling oxygen partial pressure: XRD, TGA and DC conductivity in order to characterize very reactive compounds such as nanometric powders. From XRD, both the structure and the oxygen stoichiometry (thanks to their lattice parameter) were investigated in situ. From TGA, it was the oxygen stoichiometry (thanks to mass gain or loss) which was determined. From DC conductivity, it was both the structure and the oxygen stoichiometry (thanks to the activation energy) which were obtained. The advantages were to determine very rapidly and with a small amount of powder the equilibrium conditions ( T, pO 2) necessary to obtain the desired phase and stoichiometry. These methods have been evaluated for nanometric titanium ferrites. Two phenomena have been observed during the reducing process: the precipitation of a rhombohedral phase and a significant grain growth linked together.

EuNiO3 thin films- growth and characterization

We report on the process formation of EuNiO3 thin films on various substrates, studies of optimization conditions for synthesis process and primary investigation. EuNiO3 thin films were deposited by Radio Frequency Magnetron Sputtering in Ar-O atmosphere using a ceramic target with additional nickel pellets. We used Si, NdGaO3 and SrTiO3 substrates. Afterwards samples were annealed in high pressure and temperature in order to achieve a desired oxygen stoichiometry. Thickness of the film was controlled by deposition time and calculated by X-ray Reflectivity. X-ray diffraction measurements revealed that obtained thin films exhibit EuNiO3 phase on the surface still accompanied by Eu2NiO4 and NiO phases in the bulk. Therefore annealing seems to be a very surface sensitive process. That inhomogeneity was confirmed in X-ray photoemission depth profiling studies for EuNiO3/Si (60nm) thin film. Surface contamination with adsorbed oxygen has been observed with grazing angle analysis. Ni2p photoemission line analysis revealed a possible mixed-valence character of Ni electronic state.

Hydrogen Production via Chemical Looping Redox Cycles Using Atomic Layer Deposition-Synthesized Iron Oxide and Cobalt Ferrites

Iron oxide (γ-Fe2O3) and cobalt ferrite (CoxFe3−xO4) thin films were synthesized via atomic layer deposition (ALD) on high surface-area (50 m2 g−1) m-ZrO2 supports. The oxide films were grown by sequentially depositing iron oxide and cobalt oxide, adjusting the number of iron oxide to cobalt oxide cycles to achieve a desired stoichiometry. High resolution transmission electron microscopy and X-ray diffraction indicate that the films are crystalline and have a thickness of ∼2.5 nm. Raman spectroscopy was used to confirm the predominance of the spinel phase in the case of cobalt ferrite. Films were chemically reduced at 600 °C using mixtures of H2, CO, and CO2. The evolution of oxide phases as a function of time during this reduction was observed using in situ X-ray diffraction, showing that γ-Fe2O3 are reduced only to FeO, while CoxFe3−xO4 are reduced all the way to a Co/Fe alloy. Subsequent water splitting measurements in a stagnation flow reactor yielded peak H2 rates exceeding virtually all of those rep...

Generalized selectivity description for polymeric ion-selective electrodes based on the phase boundary potential model

A generalized description of the response behavior of potentiometric polymer membrane ion-selective electrodes is presented on the basis of ion-exchange equilibrium considerations at the sample–membrane interface. This paper includes and extends on previously reported theoretical advances in a more compact yet more comprehensive form. Specifically, the phase boundary potential model is used to derive the origin of the Nernstian response behavior in a single expression, which is valid for a membrane containing any charge type and complex stoichiometry of ionophore and ion-exchanger. This forms the basis for a generalized expression of the selectivity coefficient, which may be used for the selectivity optimization of ion-selective membranes containing electrically charged and neutral ionophores of any desired stoichiometry. It is shown to reduce to expressions published previously for specialized cases, and may be effectively applied to problems relevant in modern potentiometry. The treatment is extended to mixed ion solutions, offering a comprehensive yet formally compact derivation of the response behavior of ion-selective electrodes to a mixture of ions of any desired charge. It is compared to predictions by the less accurate Nicolsky–Eisenman equation. The influence of ion fluxes or any form of electrochemical excitation is not considered here, but may be readily incorporated if an ion-exchange equilibrium at the interface may be assumed in these cases.

Pulsed laser deposited Y-doped BaZrO 3 thin films for high temperature humidity sensors

Pulsed laser deposited (PLD) Y-doped BaZrO 3 thin films (BaZr 1- x Y x O 3- y/2 , x = 0.2, y > 0), were investigated as to their viability for reliable humidity microsensors with long-term stability at high operating temperatures ( T > 500 °C) as required for in situ point of source emissions control as used in power plant combustion processes. Defect chemistry based models and initial experimental results in recent humidity sensor literature [1,2]. indicate that bulk Y-doped BaZrO 3 could be suitable for use in highly selective, high temperature compatible humidity sensors. In order to accomplish faster response and leverage low cost batch microfabrication technologies we have developed thin film deposition processes, characterized layer properties, fabricated and tested high temperature humidity micro sensors using these thin films. Previously published results on sputtering Y-doped BaZrO 3 thin films have confirmed the principle validity of our approach [3]. However, the difficulty in controlling the stoichiometry of the films and their electrical properties as well as mud flat cracking of the films occurring either at films thicker than 400 nm or at annealing temperature above 800 °C have rendered sputtering a difficult process for the fabrication of reproducible and reliable thin film high temperature humidity microsensors, leading to the evaluation of PLD as alternative deposition method for these films. X-ray Photoelectron Spectroscopy (XPS) data was collected from as deposited samples at the sample surface as well as after 4 min of Ar + etching. PLD samples were close to the desired stoichiometry. X-ray diffraction (XRD) spectra from all as deposited BaZrO 3:Y films show that the material is polycrystalline when deposited at substrate temperatures of 800 °C. AFM results revealed that PLD samples have a particle size between 32 nm and 72 nm and root mean square (RMS) roughness between 0.2 nm and 1.2 nm. The film conductivity increases as a function of temperature (from 200 °C to 650 °C) and upon exposure to a humid atmosphere, supporting our hypothesis of a proton conduction based conduction and sensing mechanism. Humidity measurements are presented for 200–500 nm thick films from 500 °C to 650 °C at vapor pressures of between 0.05 and 0.5 atm, with 0.03–2% error in repeatability and 1.2–15.7% error in hysteresis during cycling for over 2 h. Sensitivities of up to 7.5 atm −1 for 200 nm thick PLD samples at 0.058 atm partial pressure of water were measured.

Electrodeposition of High-Tc Superconducting Bi-Sr-Ca-CuO Nanostructures

We report on the reproducible growth of superconducting (Bi1-xPbx)2Sr2CuO6+δ and (Bi1-xPbx)2Sr2Ca2Cu3O10+δ nanostructures, which has been a major difficulty in the electrochemical deposition of thin films of BSCCO. The precursors of superconducting Bi(Pb)-Sr-Ca-CuO were electrodeposited in an electrolytic bath prepared from the nitrate salts of the constituent metals in an organic solvent, dimethylsulfoxide (DMSO). The superconductor was electrodeposited in the form of nanotubes and nanowires. The as-deposited samples were given a controlled oxidative thermal treatment in air. The influence of deposition potential, annealing temperature and pH was studied and optimized to get the desired stoichiometry, 2201 and 2223 phase of superconducting Bi(Pb)-Sr-Ca-CuO. A novel three-step electrodeposition scheme was implemented to control the elemental stoichiometry specifically, the oxygen stoichiometry in the sample. Characterization of the electrodeposited and annealed nanostructures was done using XRD, EDS, SEM and PPMS. A plausible theoretical interpretation is given to explain the purpose behind the electrodepositing nanostructures.

Robotic Hierarchical Mixing for the Production of Combinatorial Libraries of Proteins and Small Molecules

We present a method to automatically plan a robotic process to mix individual combinations of reactants in individual reaction vessels (vials or wells in a multiwell plate), mixing any number of reactants in any desired stoichiometry, and ordering the mixing steps according to an arbitrarily complex treelike assembly protocol. This process enables the combinatorial generation of complete or partial product libraries in individual reaction vessels from intermediates formed in the presence of different sets of reactants. It can produce either libraries of chimeric genes constructed by ligation of fragments from different parent genes or libraries of chemical compounds constructed by convergent synthesis. Given concentrations of the input reactants and desired amounts or volumes of the products, our algorithm, RoboMix, computes the required reactant volumes and the resulting product concentrations, along with volumes and concentrations for all intermediate combinations. It outputs a sequence of robotic liquid transfer steps that ensures that each combination is correctly mixed even when individualized stoichiometries are employed and with any fractional yield for a product. It can also account for waste in robotic liquid handling and residual volume needed to ensure accurate aspiration. We demonstrate the effectiveness of the method in a test mixing dyes with different UV-vis absorption spectra, verifying the desired combinations spectroscopically.

Sputter growth and magnetic properties of exchange-biased La1/4Ca3/4MnO3–La2/3Sr1/3MnO3 epitaxial bilayers

We have grown La1/4Ca3/4MnO3–La2/3Sr1/3MnO3 (LCMO–LSMO) thin films by reactive facing target radio frequency sputtering on SrTiO3(001) substrates. After 1 bar oxygen annealing at 800 °C, the films have the desired oxygen stoichiometry and perovskite structure. Transport properties of single LCMO films reveal the charge order (CO) transition between 100 and 180 K depending on the LCMO layer thickness while LSMO films have a Curie temperature greater than 330 K. Kerr effect measurements show evidence of an increase of the LSMO coercive field HC from ∼50 Oe at room temperature up to 110 Oe at 40 K and a significant decrease in the squareness of the hysteresis loop. This effect is accompanied by a slight shift of the hysteresis loop HE due to exchange bias between the antiferromagnetic charge ordered LCMO layer and the LSMO ferromagnet which reaches 20 Oe at 40 K. Both the onset of HE and the drop in squareness are observed to be close to the charge order transition of a similar LCMO single layer and are assumed to be related to the CO transition.

Superhard, conductive coatings for atomic force microscopy cantilevers

Boron carbide thin films were grown by mass selected ion beam deposition using low energy B11+ and C12+ ions at room temperature. The amorphous films exhibit any desired stoichiometry controlled by the ion charge ratio B+/C+. Films with a stoichiometry of B4C showed the optimal combination of a high mechanical strength and a low electrical resistivity for the coating of atomic force microscopy (AFM) silicon cantilevers. The properties of such AFM tips were evaluated and simultaneous topography and Kelvin mode AFM measurements with high lateral resolution were performed on the systems (i) Au nanoparticles on a p-WS2 surface and (ii) conducting/superconducting YBa2Cu3O7−x.

Synthesis and Crystal Structure of Sr2ScBiO6

A new complex oxide Sr2ScBiO6 was synthesized by a solid state reaction in air. The compound is stable up to 1150°C and acquires the desired oxygen stoichiometry at 850°C. The crystal structure was determined using powder X-ray diffraction, electron diffraction, and high-resolution electron microscopy. Sr2ScBiO6 has a perovskite-derived pseudocubic face-centered unit cell (a=8.1816(3) Å) and a rock-salt ordering of Sc3+ and Bi5+ over the B positions. Electron microscopy investigation reveals that the real structure is of the La2NiRuO6 type, monoclinic with cell parameters a≈b=aper√2≈5.785 Å, c=2aper≈8.182 Å, and P21/n space group. The structure can be described by an a+b−b− system of the BO6 octahedral tilting. The presence of numerous twin domains is a characteristic feature of this compound.

X-ray photoelectron spectroscopy study on the composition and structure of BaTiO 3 thin films deposited on silicon

X-ray photoelectron spectroscopy (XPS) spectral analysis showed that Ba ions in BaTiO 3 thin films prepared by the sol–gel technique consist of one phase corresponding to one electronic state, which we call the β-phase. This phase became stronger at the same depth with increasing annealing temperature. With our preparation conditions, we can prepare BaTiO 3 thin films with Ba electronic states as in bulk BaTiO 3. During Ar + sputtering, a mixture of the different oxidation states Ti +2, Ti +3, Ti +4 of titanium are present as established by XPS. The concentration of Ti +3 increases with increasing annealing temperature. For thin films annealed at 675°C the atomic concentration of Ti +3 is of the order of that of Ti +4. The binding energy of the oxygen O 1s main peak increases with increasing number of sputter cycles. Oxygen atoms terminating the oxide surface are bound differently from subsurface oxygen atoms. Outer-layer oxygen atoms are less negatively charged than in the normal oxide state. X-ray diffraction patterns and XPS analysis of the annealed films show that films annealed at 600°C for 2 h have high crystallinity, the desired stoichiometry, and less Ti +3 defects.

Characterization of optical UV filters using Rutherford backscattering spectroscopy

Rutherford backscattering spectroscopy (RBS) has been used during the development of multilayer thin film optical filters, especially designed for the fluorescence detector of the Pierre AUGER Project. Depth profiles of the heavy components have been measured directly, while reliable results for the light components could also be extracted indirectly. Relative thickness and density of the individual layers and deviations from the desired thickness and stoichiometry have been deduced. The findings of the RBS method have been compared and discussed with results obtained by other characterization techniques.

Electric Transport and Oxygen Permeation Properties of Lanthanum Cobaltite Membranes Synthesized by Different Methods

Dense perovskite-structured membranes with desired composition of La0.8Sr0.2Co0.6Fe0.4O3-δ (LSCF) were prepared from powders produced by four different methods. LSCF powders prepared by citrate, solid-state, and spray−pyrolysis methods had compositions close to the desired stoichiometry with a slight difference in cobalt concentration, whereas coprecipitated powders had a large strontium deficiency. The membrane composition was a determining factor that affected the electronic conductivity and therefore oxygen permeability. The membrane with a large strontium deficiency had much lower electronic conductivity and oxygen permeability (ionic conductivity) than the other three membranes with compositions close to the desired stoichiometry. The electronic conductivity of membranes prepared from citrate, solid-state, and spray−pyrolysis methods increases with the cobalt concentration of the membrane. For the three membranes with similar composition, the activation energy of oxygen flux decreases with increasing grain size. Oxygen pressure dependency of oxygen vacancy concentration is also influenced by the membrane microstructure and composition. LSCF membranes with same composition and similar microstructure should have similar electric and oxygen transport properties.

ChemInform Abstract: A Transmission Electron Microscopy Study on the Annealing of YBa2Cu3O7‐δ

Abstractis performed, because the final annealing of the superconductor in an oxygen‐rich atmosphere at temp. between 400 and 600 °C is one of the most critical steps in the preparation of materials with the desired oxygen stoichiometry (δ → 0).

Trichloride Vapour Phase Epitaxial Growth of In1-xGaxAs on InP Using an In/Ga Alloy Source

In this paper, we report on the In1-xGaxAs epitaxial layer growth on InP using a Ga/In alloyed source. Lattice-matched In1-xGaxAs can be grown using an In/Ga alloy for 5–9% at. Ga. The influence of different parameters (source and deposition temperatures, the source stoichiometry and the input AsCl3 mole fraction) on the In stoichiometry has been studied in order to obtain the desired stoichiometry within a certain range.

Deposition of High Tc Superconductor thin Films by Pulsed Laser Ablation

ABSTRACTThin superconducting films of YBa2Cu3O7 and HoBa2Cu3O7 have been obtained by ablating material from high-Tc bulk superconductor ceramics onto a nearby substrate using focused excimer laser radiation. Subsequent annealing in oxygen at elevated temperatures was necessary to achieve the superconducting phase. A range of deposition and annealing conditions was investigated to yield films of the desired stoi chiometry and phase.

X-ray photoelectron spectroscopy of ion beam sputter deposited SiO2, TiO2, and Ta2O5

X-ray photoelectron spectroscopy (XPS) was used to examine the atomic bonding in thin oxide films used in reflection enhancing optical coatings. SiO2 was deposited by ion beam sputtering of quartz; TiO2 and Ta2O5 were deposited by ion beam sputtering of metal targets. In each case, an increased oxygen background pressure was used to achieve the desired stoichiometry. All three types of films are amorphous as measured by TEM and by x-ray diffraction and have an optical absorption below 100 parts per million for half-wave thicknesses at 1.06 μm. Depth profiles have been performed on each of the films and some layered structures. The XPS data for each film as deposited shows a single bonding state and no evidence of suboxides above approximately a 5% level. The O 1s line in SiO2 is broader (2.5 eV) than in evaporated SiO2, and is not altered by the ion bombardment of the depth profiling process. The O ls line broadens, however, by up to 50% at a SiO2/TiO2 interface. Sputter-deposited TiO2 and Ta2O5 show a relatively narrow (1.7 eV) O 1s line. Neither the composition nor the bonding in SiO2 is affected by sputter etching with Ar+ at 3 keV. In TiO2, however, oxygen is preferentially sputtered and suboxides observed in the XPS spectrum. With Ta2O5, oxygen is also diminished, but only Ta2O5 and metallic Ta are seen in the XPS spectra.