Nonstoichiometric Oxygen Content Research Articles

Investigating the critical transitional temperature increase in graphene oxide doped bulk YBCO

Y1Ba2Cu3O7-δ (YBCO) was doped with thermally stable graphene oxide (TS-GO) and thermally unstable graphene oxide (TU-GO) in the following %wt. concentrations: 0.1, 0.5 and 0.7. TS-GO and TU-GO was characterized using RAMAN, fourier transform infrared spectroscopy (FTIR) and energy-dispersive X-ray spectroscopy (EDX). The critical transition temperature (TCmid) increased in all TU-GO and TS-GO doped samples. The highest TCmid of 101 K was that of the 0.7 %wt. TU-GO doped sample. The increase in TCmid was greater for the samples doped with TU-GO. Non-stoichiometric oxygen content (δ) was seen to increase with an increase in doping concentration of both TS-GO and TU-GO. X-ray diffraction (XRD) analysis was carried out to determine the lattice parameters and phase characterization of the TU-GO and TS-GO doped samples. Lattice parameters show an increase in the copper oxide (CuO2) planar area with TCmid for TS-GO and TU-GO doping. To determine strain effects, the Williamson Hall method was used to determine the lattice strain (ɛ). The ɛ was seen to decrease for both TS-GO and TU-GO doped samples. The formation of magnetic manganese oxide nanoparticles in TS-GO and TU-GO doped samples was observed, and resulted from impurities found in the graphene oxide (GO) dopant material. The magnetic particles were extracted magnetically and characterized using EDX. YBCO was doped with trimanganese tetraoxide (Mn3O4) and manganese dioxide (MnO2) in a 0.1 and 0.2 %wt. concentration. The TCmid is seen to increase to 94 K and 104 K respectively for 0.1 %wt. MnO2 and Mn3O4 doped samples. The 0.2 %wt. doped Mn3O4 sample resulted in a decrease in TCmid. Magnetic susceptibility measurements confirmed a superconducting phase changes. The increase in TCmid above YBCO’s Tc = 93 K, correlates to the presence of manganese nano-impurities. This increase is hypothezied to be related to an increase in surface area of YBCO’s 2D copper oxide (CuO2) plane structure with GO doping.

Electrochemical determination of glucose in blood serum and sweat samples by the strontium doped Co3O4

• The conventional synthesis routes were investigated for the preparation of Sr doped Co 3 O 4 (Sr-Co 3 O 4 ). • The successful incorporation of Sr in Co 3 O 4 lattice was found for hydrothermal method. • The occupation of Sr in octahedral sites increases the non-stoichiometric oxygen in the Co 3 O 4 lattices. • These defected electronic structures were inspected against the electrocatalytic activity of glucose oxidation. • The Sr-Co 3 O 4 is applied in real-time monitoring of glucose in blood serum and sweat samples which received good recoveries. This work reports the noninvasive electrochemical determination of glucose by strontium doped cobaltic cobalt oxide nanostructures (Sr-Co 3 O 4 ). The Sr-Co 3 O 4 is prepared by three conventional methods namely hydrothermal, magnetic stirring, and ultrasound. Among all, the hydrothermal method effectively incorporated the Sr in the Co 3 O 4 lattice. The Sr percentage and Co oxidation states were investigated by x-ray photoelectron spectroscopy. The Sr has a more ionic radius than cobalt, therefore, it is occupied in the octahedral site. As a result, the non-stoichiometric oxygen content was increased in the Co 3 O 4 lattices, which are the main contributor to the electrochemical determination of glucose. The results revealed that hydrothermally synthesized Sr-Co 3 O 4 (HSC) exhibited improved electrocatalytic activity such as low peak potential (0.55 V) and high current (116 µA) towards glucose oxidation than the other electrocatalysts. The HSC/GCE revealed a good sensitivity (9.01 ± 0.15 µA mM −1 cm −2 ) and low LoD (31 ± 3 nM). Also, high selectivity was observed towards glucose detection in the presence of co-interfering species. Moreover, the Sr-Co 3 O 4 is applied in real-time monitoring of glucose in blood serum and sweat samples which received good recoveries.

Development of MgMnO3-δ as an oxygen carrier material for chemical looping combustion

Chemical looping combustion (CLC) is attracting attention as a promising technology for carbon dioxide separation. Oxygen carrier materials are the most important factor in determining the efficiency of CLC. In this paper, we present MgMnO3-δ with a defect cubic spinel structure as an oxygen carrier material with high efficiency, low cost, and stable properties. MgMnO3-δ has a non-stoichiometric oxygen content of MgMnO2.68. The reduced composition of MgMnO3-δ in H2, CO, or CH4 is a complete solid solution of (Mg,Mn)O. The redox reaction from MgMnO3-δ to (Mg,Mn)O is reversible and stable. Interestingly, MgMnO3-δ also shows a chemical looping oxygen uncoupling (CLOU) phenomenon and is reduced to MgMn2O4 and MgO in N2 at 900 °C. The oxygen transfer capacities of MgMnO3-δ under 15% H2/N2, 15% CO/CO2, 15% CH4/N2, and 15% CH4/CO2 are 8.34, 8.56, 8.42, and 8.74 wt%, respectively, at 900 °C. The oxygen transfer capacity was well maintained during the 5th redox cycle. No phase or structure changes or agglomeration occurred as the redox cycle number increased. Moreover, MgMnO3-δ has a high tolerance to carbon deposition when used in CO or CH4 fuels.

A study of nonstoichiometric oxides in the Ln-Ni-O (Ln=La, Pr, Nd) system

The non-stoichiometric compositions Ln2-xNiO4-3x/2+d (Ln=La, Pr, Nd, 0£x£0,4) were obtained using coprecipitation method from nitrates solutions by K2CO3 followed by calcination of the obtained blend at 950°С. According to X-ray phase analysis compositions in the range La2NiO4.17 – La1.6NiO3.63 are monophase and crystallize in tetragonal symmetry K2NiF4, space group I4/mmm. Nd2-xNiO4-y and Pr2-xNiO4-y in the range 0£x£0,2 are monophase and have orthorombic and monoclinic(correspodingly) distorted K2NiF4 structure. Samples with 0,2<x£0,4 are polyphase and contain Ln2NiO4 (Ln=Pr, Nd), NiO and rare earth oxides. Electrical conductivity of obtained samples have semiconducting behavior and it is strong depended to nonstoichiometric oxygen content.

ZnO nanowire arrays synthesized on ZnO and GaN films for photovoltaic and light-emitting devices

The wide bandgap, one-dimensional zinc oxide (ZnO) nanowires (NWs) and their heterostructures with other materials provide excellent pathways for efficient photovoltaic (PV) and light-emitting devices. ZnO NWs sensitized with quantum dots (QDs) provide high-surface area and tunable bandgap absorbers with a directional path for carriers in advanced PV devices, while ZnO heterojunctions with other p-type wide bandgap materials lead to light-emitting diodes (LEDs) with better emission and waveguiding properties compared with the homojunction counterparts. Synthesis of the structures with the desired morphology is a key to device applications. In this work, ZnO NW arrays were synthesized using hydrothermal method on ZnO and GaN thin films. Highly crystalline, upright, and ordered arrays of ZnO NWs in the 50 to 250-nm diameter range and 1 μm in length were obtained. The morphology and optical properties of the NWs were studied. Energy dispersive x-ray spectroscopy (EDX) analysis revealed nonstoichiometric oxygen content in the grown ZnO NWs. Photoluminescence (PL) studies depicted the presence of oxygen vacancy and interstitial zinc defects in the grown ZnO NWs, underlining the potential for LEDs. Further, hydrophobically ligated CdSe/ZnS QDs were successfully incorporated to the NW arrays. PL analysis indicated the injection of electrons from photoexcited QDs to the NWs, showing the potential for quantum dot-sensitized solar cells.

Mass and Charge Transport Properties of Al Doped La2NiO4+δ

Mixed oxide-ion and electron conducting ceramic material La2NiO4+ d(LNO) have been reported to exhibit impressive oxide ion and p-type electronic conductivity, and high catalytic activity which make them an excellent component of some electrochemical devices such as fuel cell cathode, oxygen permeation membrane. The hyperstoichiometric LNO oxides show high oxygen diffusion coefficient and high oxygen ion conductivity, which are attributes of their crystal structure.The extent of oxygen nonstoichiometry significantly affects the electrochemical properties of LNO systems. The nonstoichiometric oxygen content may be varied by aliovalent doping or by substituting the host cation with smaller size cations[1,2]. The conduction mechanism in LNO-based system has been explained on the basis of both, the band conduction by delocalized electrons and polaron-hopping by localized electrons[3,4].The objective of this work is to study the effect of a donor cation (Al3+) on oxygen nonstoichiometry and resultant thermodynamic properties of LNO system. In this work we have prepared a non-transition metal cation Al3+-doped LNO system, La2Ni0.95Al0.05O4.025+ d, and presented an equilibrium defect model for this system. The variation of oxygen nonstoichiometry was measured by coulometric titration and the absolute value of oxygen nonstoichiometry was calculated from thermogravimetric analysis. Various thermodynamic quantities for LNAO were calculated from the experimental data and were compared with those for LNO in our previous work.Fig.1 shows pO2 dependence of oxygen nonstoichiometry at different temperature. As can be seen, the values of δ increased with decreasing temperature and with increasing pO2. The inset of Fig. 1 shows the relationship of log δ vs. log pO2, as can be seen, at isothermal condition the dependence of δ on the pO2exponent (m) is slightly less than 1/6. It is clear from the above observation that the oxygen exponent decreases with increasing oxygen activity, suggesting a positive deviation of the LNAO system from the ideal solution behavior[4].The best estimated values of Nv obtained from fitting the Eq. (1) with fitting parameters Kox, Kf, and Nv to the δ vs. log(pO2) data in Fig.(1). The density of states of the valence band varies from 1.87x1020 to 2.55x1020 in 800-1000 oC range. And , the effective mass mh *of holes is 1.02 - 1.21 times the rest mass mo. This indicates the occurrence of band-like conduction and allows the effect of conduction by a small degree of polaron hopping to be ignored. The behavior of holes starts deviates from that of ideal solution at a very low δ value and rh • increases with the increasing δ and reaches to ~7 at rh •≈0.08 and T=900°C. The calculation of excess partial molar quantities showed that incorporation of interstitial oxygen is less favorable in La2Ni0.95Al0.05O4.025 + δ in comparison to La2NiO4 + δ. Reference Nakamura T, Yashiro K, Sato K, Mizusaki, J. Solid State Ionics, 180, 368 (2009).Naumovich EN, Patrakeev MV, Kharton VV, Yaremchenko AA, Logvinovich DI, Marques FMB. Solid State Sciences, 7,1353 (2005).H. S. Kim, and H. I. Yoo, Solid State Ionics, 232, 129 (2013).H. S. Kim, and H. I. Yoo, Phys. Chem. Chem. Phys., 12, 4704 (2010).

Assessment of perovskite-type La0.8Sr0.2ScxMn1−xO3–δ oxides as anodes for intermediate-temperature solid oxide fuel cells using hydrocarbon fuels

Composites formed by the infiltration of 40wt% La0.8Sr0.2ScxMn1−xO3–δ (LSSM) oxides (x=0.1, 0.2, 0.3) into 65% porous yttria-stabilized zirconia (YSZ) are investigated as anode materials for intermediate-temperature solid oxide fuel cells for hydrocarbon oxidation. The oxygen non-stoichiometry and electrical conductivity of each LSSM–YSZ composite are determined by coulometric titration. As the concentration of Sc increases, the composites show higher phase stability and the electrical conductivity of LSSM is significantly affected by the Sc doping, the non-stoichiometric oxygen content, and oxygen partial pressure (p(O2)). To achieve better electrochemical performance, it is necessary to add ceria-supported palladium catalyst for operation with humidified CH4. Anode polarization resistance increases with Sc doping due to a decrease in electrical conductivity. An electrolyte-supported cell with a LSSM–YSZ composite anode delivers peak power densities of 395 and 340mWcm−2 at 923K in humidified (3% H2O) H2 and CH4, respectively, at a flow rate of 20mLmin−1.

Electrical conductivity, Seebeck coefficient, and defect structure of oxygen nonstoichiometric Nd 2− xSr xNiO 4+ δ

To elucidate the electronic state and the conduction mechanism of Nd 2NiO 4+ δ series oxides at high temperatures, the electrical conductivity, Seebeck coefficient, and nonstoichiometric oxygen content of Nd 2− x Sr x NiO 4+ δ ( x = 0, 0.2, 0.4) were measured as a function of the Sr content, temperature, and oxygen partial pressure. The hole mobility is estimated from the electrical conductivity and the hole concentration which is defect chemically determined. The mobility slightly decreases as temperature increases as in metals at high temperatures. The relationships between the Seebeck coefficient, electrical conductivity, and hole concentration can be explained by Mott's equation, which expresses the Seebeck coefficient for metals. Semi-quantitative analyses strongly indicate that the electron or hole is itinerant in Nd 2− x Sr x NiO 4+ δ , and the conduction mechanism is metal-like band conduction at high temperatures. Based on the experimental results, schematics for energy level and band structure are proposed. At high temperatures, free holes in the σ x2− y2 band composed of d x2− y2 orbitals contribute to metallic conduction.

Electrical Conductivity and Thermoelectric Power of La2-xSrxNiO4+δ

Electrical conductivity, Seebeck coefficient, and nonstoichiometric oxygen content of La2-xSrxNiO4+δ (x = 0, 0.2, 0.4) were measured as a function of Sr content, temperature, and oxygen partial pressure. At above around 873 K, mobility of hole decrease as temperature increase. The temperature dependence of hole mobility indicate large polaron conduction. The relationship between Seebeck coefficient and electrical conductivity is explained by metal like band conduction model. The behavior of electrical conductivity and Seebeck coefficient strongly suggests that electron (hole) is itinerant in La2-xSrxNiO4+δ at high temperatures.

Electronic state of oxygen nonstoichiometric La2−xSrxNiO4+δ at high temperatures

In order to elucidate the electronic state and the conduction mechanism of La(2-x)Sr(x)NiO(4+delta) at high temperatures, electrical conductivity, Seebeck coefficient, and nonstoichiometric oxygen content of La(2-x)Sr(x)NiO(4+delta) (x = 0, 0.2, 0.4) were measured as a function of Sr content, temperature, and oxygen partial pressure. The hole mobility is estimated from the electrical conductivity and oxygen content. The mobility decreases slightly as temperature increases, like metals at high temperatures. The relationships between Seebeck coefficient and electrical conductivity, and Seebeck coefficient and hole concentration can be explained by the metallic conduction model. Semi-quantitative analyses strongly indicate that electrons (holes) are itinerant in La(2-x)Sr(x)NiO(4+delta) and the conduction mechanism of La(2-x)Sr(x)NiO(4+delta) is metal-like band conduction at high temperatures. Based on the experimental results and discussions, a schematic of the energy levels and band structure is proposed. At high temperatures, metallic conduction is induced by a free hole in the sigma(x2-y2) band composed of a d(x2-y2) orbital.

Electrochemical Behaviors of Mixed Conducting Oxide Anodes for Solid Oxide Fuel Cell

To clarify guidelines for a high-performance mixed conducting oxide anode, electrochemical behaviors of mixed conducting oxide anodes were studied on the oxides, , , , , , , and . The hydrogen oxidation on the oxide anodes is studied by ac impedance and steady-state polarization measurements. In the ac impedance measurements, a slow relaxation process of the order of was observed with the -based and anodes. The corresponding pseudocapacitances are . These pseudocapacitances are identified as the chemical capacitance due to the variation of the nonstoichiometric oxygen content of the electrode material. At the same electrode potential, the -based anodes showed a far higher steady-state current than the - and the -based anodes. The extension of the reaction zone beyond the three phase boundary is estimated from our experimental results. The reaction zone of the anode extends from the three-phase boundary to the electrode/gas interface. To estimate what determines the electrode performance of the oxide anodes, the effect of the material property and the electrode microstructure was studied. The effect of the material property is much larger than that of the electrode microstructure. High ionic conductivity and catalytic activity with a certain level of electronic conductivity is required for a high-performance oxide anode.

The Structures, Adsorption Characteristics of La−Rb−Cu−O Perovskite-like Complex Oxides, and Their Catalytic Performances for the Simultaneous Removal of Nitrogen Oxides and Diesel Soot

The nanometric La2-xRbxCuO4-λ (λ stands for nonstoichiometric oxygen content) perovskite-like complex oxide catalysts were prepared by the sol−gel autocombustion method. Their structures and physicochemical properties were examined by chemical analysis, XRD, SEM, EDS, FT-IR, H2-TPR, and MS-NO-TPD, and the catalytic performances for the simultaneous removal of nitrogen oxides and diesel soot particulates were investigated by using temperature-programmed oxidation reactions. XRD and IR results demonstrate that the structures of La2-xRbxCuO4-λ change with the increase in the x value. La2CuO4 possessed a single phase with orthorhombic structure, but the so-called T* phase was formed as x > 0.3 in addition to the orthorhombic phase. A new CuO bond was determined by IR vibration band at 980 cm-1 in the CuO5 of the T* phase. Moreover, the formation of the oxygen vacancy and Cu3+ are also related to the x value, and the oxygen vacancy has an important effect on the catalytic activity for the simultaneous removal ...

Effect of Oxygen Nonstoichiometry on Electrode Activity of La1−xAxMnO3±δ Cathode

Lanthanum manganite, an air electrode material of solid oxide fuel cells, is well known for its complicated nonstoichiometry, which depends upon oxygen partial pressure. This nonstoichiometry is considered to have a relation to electrode activity as it affects oxygen activation and/or oxide ion sink sites, etc. However, its relation to cathode activity has not yet been elucidated, mainly because of the lack of detailed data on oxygen nonstoichiometry. In this paper, we report the relation between oxygen nonstoichiometry and cathode activity based on measurements of the oxygen nonstoichiometry and complex-impedance of the system Ar, with in the range of and temperature at 973-1273 K. When the nonstoichiometric oxygen content, increases, the electrode activity decreases and vice versa. These results suggest that vacant sites of cations and/or O are related to the reaction path of cathode reaction. © 2000 The Electrochemical Society. All rights reserved.

電子材料 電子セラミック部品材料の開発

The aim of this paper is to focus on the development in the field of electronic ceramic materials, such as MnZn ferrites, multilayer ferrite chip components, and base metal electrode multilayer ceramic capacitors. There are many requirements for electronic ceramics, among which the reliability and low loss characteristics are of prime importance. New material technologies for ensuring high performance ferrites and highly reliable multilayer chip components are shown with special reference to the microstructure. For achieving high performance ferrite cores, adequate additives and control of nonstoichiometric oxygen content by firing conditions are quite important. Material technology for multilayer ferrite chip components are described with special reference to the behavior of silver during firing. Also, highly reliable multilayer ceramic capacitors with Ni electrodes have been developed by controlling chemical composition and grain boundary chemistry.

Determination of non-stoichiometric oxygen in YBCO superconductors by coulometric titration

A coulometric titration method has been developed for the determination of non-stoichiometric oxygen in YBCO superconductors, The composition of the supporting electrolyte is 1 mol 1 −1 HCl, 0.02 mol 1 −1 CuSO 4 and 0.17 mol 1 −1 KBr. The powdered sample is introduced in the electrolytic cell containing a known excess of Cu(I), previously electrogenerated by galvanostatic reduction of Cu(II) ions, the sample is dissolved, and the non-reacted Cu(I) is back titrated with electrogenerated Br 2. The method was applied to an analysis of monophase YBa 2Cu 3O 6.5 + δ superconductor. Spectrophotometry without calibration is used as a comparative method. The reproducibility of the results for the non-stoichiometric oxygen content obtained by the suggested method is much better than that of the comparative method. The new method is very suitable for series of analysis.