Effect Of Oxygen Nonstoichiometry Research Articles

Effect of oxygen nonstoichiometry on electrical conductivity and oxygen transport parameters of Cu-substituted La0.5Sr0.5Co0.8Fe0.2O3-δ perovskite oxides

Effect of oxygen nonstoichiometry on electrical conductivity and oxygen transport parameters of Cu-substituted La0.5Sr0.5Co0.8Fe0.2O3-δ perovskite oxides

Phase Transformations of Perovskite La0.64(Ba1−xCax)0.36FeO3−δ Investigated by Mechanical Spectroscopy

Herein, perovskite La0.64(Ba1−x Ca x )0.36FeO3−δ () samples are synthesized and investigated by X‐ray diffraction and mechanical spectroscopy. The room‐temperature structure of La0.64Ba0.36FeO3−δ is a mixture of orthorhombic and cubic phases. The structures of calcium‐doped La0.64(Ba1−x Ca x )0.36FeO3−δ are orthorhombic at room temperature. A modulus dip is observed above room temperature in La0.64(Ba1−x Ca x )0.36FeO3−δ () samples. This corresponds to a phase transition from orthorhombic to rhombohedral structure with increasing temperature. The effect of oxygen nonstoichiometry on the room‐temperature structure and phase transition is observed by mechanical spectroscopy.

Effect of oxygen nonstoichiometry on the photoelectrochemical performance of oxide-nanorod based TiO2/Sb2S3 and ZnO/Sb2S3 heterostructured photoanodes

Single crystalline ZnO and TiO2 nanorods are grown on fluorine-doped tin oxide (FTO) substrates by hydrothermal method. The nanorods are annealed under air and reducing conditions to alter the oxygen nonstoichiometry and hence the mid-bandgap defect states. Such an annealing process is shown to impart significant change on the photoelectrochemical (PEC) performance of the photoelectrodes. Large photocurrent densities (J) of 0.78 mA cm−2 are obtained for air annealed (AA) TiO2 nanorods (TNR) compared to hydrogen annealed (HA) TNR (J = 0.36 mA cm−2). ZnO nanorods (ZNR), on the contrary, shows photocurrent density of 0.76 mA cm−2 and 0.36 mA cm−2 for ZNR-HA and ZNR-AA photoanodes, respectively. The contrasting difference in the PEC performance is attributed to the synergetic effect of interfacial impedance with electrolytes and the oxygen nonstoichiometry. Further, to overcome the limitation of light absorption by these materials owing to their wide bandgap, TiO2 and ZnO nanorods are coated with Sb2S3 by chemical bath deposition to form heterostructured TNR-AA/Sb2S3(CBD) and ZNR-HA/Sb2S3(CBD) thin films. Such heterostructures exhibit enhanced photocurrent values of ∼1.39 mA cm−2 and 3.36 mA cm−2 (at 1.6 V versus Ag/AgCl), respectively. The PEC performances of the nanorods are analyzed in terms of the annealing conditions and subsequent introduction of defect states in the bandgap. The present study shows the importance of oxygen defect control at the interface between the oxide and chalcogenide, and its role in the betterment of PEC performance in TiO2/Sb2S3 and ZnO/Sb2S3 heterostructure photoanodes.

Effect of Oxygen Nonstoichiometry on Phase Separation, Structure, and Magnetic Properties of the Complex Oxide NdSr2Mn2O7

Effect of Oxygen Nonstoichiometry on Phase Separation, Structure, and Magnetic Properties of the Complex Oxide NdSr2Mn2O7

Effect of Oxygen Nonstoichiometry on the Magnetic Phase Transitions in Frustrated YBaCo4O7 + x (x = 0, 0.1, 0.2) Cobaltites

The structural and elastic characteristics of YBaCo4O7 + x (x = 0, 0.1, 0.2) cobaltites synthesized by various technologies and having various excess oxygen contents x are experimentally studied. The distortion of the crystal structure in stoichiometric samples is found to remove frustrations and to bring about a longrange magnetic order in the cobalt subsystem, which is accompanied by well-pronounced anomalies in the elastic properties in the temperature range of a magnetic phase transition TN. At a weak deviation from oxygen stoichiometry, the structure distortion disappears, frustrations are retained, and the further development of a long-range magnetic order is hindered. As a result of an absent long-range magnetic order, the anomalies of the elastic characteristics at TN smooth rapidly and disappear. This finding points to the suppression of structural and magnetic transitions in nonstoichiometric samples and to the conservation of only short-range correlations of order parameter. It is found that nonstoichiometric samples can be separated into two phases depending on the ceramic synthesis conditions.

Effect of oxygen nonstoichiometry on kinetics of oxygen exchange and diffusion in lanthanum-strontium manganites

Effect of oxygen nonstoichiometry on kinetics of oxygen exchange and diffusion in lanthanum-strontium manganites

Effect of oxygen nonstoichiometry on kinetics of oxygen exchange and diffusion in lanthanum-strontium cobaltites

The method of isotopic exchange was used to study the kinetics of oxygen exchange and diffusion in complex oxides of La1 − x Sr x Co1 − y Fe y O3 − δ (x = 0.0, y = 0.0; x = 0.6, y = 0.2, 0.4). The rates of oxygen interfacial exchange and its diffusion coefficient were determined for LaCoO3 − δ at the pressure of 5 torr in the temperature range of 600–850°C and at the temperature of 700°C in the pressure range of 1–70 torr. The contributions of the three exchange types were calculated. The order of the dependence of the interfacial exchange rate on the oxygen pressure was 0.51 ± 0.01. In the case of La0.4Sr0.6Co1 − y Fe y O3 − δ (y = 0.2, 0.4) in the temperature range of 600–900°C at the oxygen pressure of 10 torr, the oxygen exchange rates and diffusion coefficients were determined in the material bulk and in the subsurface region; contributions of the three types of exchange were calculated. The paper considers the mechanism of oxygen exchange and diffusion as compared to nonstoichiometry in the oxygen sublattice of the La1 − x Sr x Co1 − y Fe y O3 − δ oxides.

Effect of oxygen nonstoichiometry on electrical conduction property of BaBiO 3−δ

In order to clarify the effect of oxide ion vacancy on electronic structure of BaBiO 3− δ , electrical conduction property at high temperature under various oxygen partial pressures, P(O 2), was investigated. At 775 °C, in dependence of electrical conductivity on log P(O 2) three phases were observed, showing agreement with oxygen nonstoichiometry data measured with thermogravimetry. Under log P(O 2) higher than −1.75, n-type semiconducting property was observed which could be attributed to charge density wave originating from two kinds of Bi sites in crystal structure. In log P(O 2) region between −1.75 and −2.45, electrical conductivity almost independent of log P(O 2) was observed. This suggested semi-metallic electronic structure with itinerant electron which could originate from single Bi site in BaBiO 3− δ with ideal perovskite structure clarified by neutron diffraction. Below log P(O 2) of −2.45, abrupt decrease of electrical conductivity was observed, suggesting localization of electron in Bi orbital, which could also be speculated from low symmetry around Bi site in BaBiO 2.5.

Effect of oxygen nonstoichiometry on photo-electrochemical properties of TiO 2− x

Polycrystalline TiO 2− x pellets were equilibrated at 1220–1420 K in a flow of Ar + 7 vol.% H 2 gas mixture. The resulting deviation x from stoichiometric composition of titanium dioxide was determined gravimetrically. X-ray diffractometry revealed coexistence of rutile with Ti n O 2 n−1 Magnéli phases. Optical reflectance and photocurrent spectroscopies served as experimental methods of the band gap determination. Polycrystalline TiO 2− x were used as photoanodes in a photoelectrochemical cell. The photocurrent response to the applied voltage was studied. It was found that TiO 2− x with x ca. 0.006 exhibited the best photoelectrochemical performance.

Structural and electrical properties of low pressure metalorganic chemical vapor deposition grown Eu2O3 films on Si(100)

Structural and electrical properties of Eu2O3 films grown on Si(100) in 500–600°C temperature range by low pressure metalorganic chemical vapor deposition are reported. As-grown films also possess the impurity Eu1−xO phase, which has been removed upon annealing in O2 ambient. Film’s morphology comprises uniform spherical mounds (40–60nm). Electrical properties of the films, as examined by capacitance-voltage measurements, exhibit fixed oxide charges in the range of −1.5×1011to−6.0×1010cm−2 and dielectric constant in the range of 8–23. Annealing has resulted in drastic improvement of their electrical properties. Effect of oxygen nonstoichiometry on the film’s property is briefly discussed.

The Effect of Defect Disorder on the Electronic Structure of Rutile TiO<sub>2-x</sub>

The purpose of this work is to study the effect of bulk point defects on the electronic structure of rutile TiO2. The paper is focused on the effect of oxygen nonstoichiometry in the form of oxygen vacancies, Ti interstitials and Ti vacancies and related defect disorder on the band gap width and on the local energy levels inside the band gap. Ab initio density functional theory is used to calculate the formation energies of such intrinsic defects and to detect the positions of these defect induced energy levels in order to visualize the tendency of forming local mid-gap bands. Apart from the formation energy of the Ti vacancies (where experimental data do not exist) our calculated results of the defect formation energies are in fair agreement with the experimental results and the defect energy levels consistently support the experimental observations. The calculated results indicate that the exact position of defect energy levels depends on the estimated band gap and also the charge state of the point defects of TiO2.

Effect of oxygen nonstoichiometry on structural and magnetic properties of [formula omitted

The influence of oxygen content on the structural and magnetic properties of the layered Co-based perovskites PrBaCo 2 O 5 + δ ( 0.16 < δ < 0.80 ) was investigated by means of both X-ray diffraction and bulk magnetic measurements. An antiferromagnetic state is found for δ < 0.35 compounds. For the samples with an oxygen stoichiometry δ = 0.5 , a strong competition between ferro- and antiferromagnetic states exists in a narrow temperature range 180 < T < 250 K . For δ ∈ [0.35–0.7], the temperature and field dependencies of the magnetization measurements point toward the appearance of a cluster-glass, in which oxygen-rich and oxygen-poor clusters coexist. The long-range ferromagnetic order, observed for larger oxygen contents ( δ > 0.7 ), could thus be arising from the percolation of oxygen-rich ferromagnetic clusters.

Effect of oxygen nonstoichiometry on structural and magnetic properties of Ho 0.1Sr 0.9CoO 3− x perovskites (0.15⩽ x⩽0.49)

Results of neutron diffraction and bulk magnetic measurements on powder samples Ho 0.1Sr 0.9CoO 3− x as a function of oxygen deficiency 0.15< x<0.49 are given. It is found that the oxygen non-stoichiometry affects the crystal and magnetic structures as well as the value of the magnetic moment, and strongly modifies the magnetic ordering temperatures.

Divalent manganese in reduced LaMnO 3− δ—effect of oxygen nonstoichiometry on structural and magnetic properties

By means of topotactic low temperature reactions in a narrow temperature window, trivalent manganese in the LaMnO 3 perovskite is partly reduced to divalent, i.e., LaMnO 3− δ . Presently, phase relations, crystal structure and magnetic properties are described for metastable samples with nominal composition LaMnO 3− δ (0.00⩽ δ<0.25). A Jahn–Teller deformed orthorhombic structure ( Pnma) prevails for 0.00⩽ δ⩽0.08. A two phase region separates it from a second solid solution region with regular GdFeO 3-type orthorhombic structure, 0.20⩽ δ<0.25. The crystal structure of LaMnO 2.80 was determined by combined refinements of high-resolution powder synchrotron X-ray and neutron diffraction data; space group Pnma, a=555.23(1), b=797.16(2), c=557.41(1) at 298 K. The cooperative Jahn–Teller distortion is lost when the average manganese valence is outside 3.00±0.15. For 0.00⩽ δ⩽0.20 antiferromagnetic order occurs below T N≈140 K. For LaMnO 2.80 the A x -type antiferromagnetically ordered moment is μ Ax =1.5(2) μ B at 8 K. The low value is probably a result of spin frustrations as earlier seen for oxidized LaMnO 3.08 with the same crystal structure. The present study of extending the valence range of normal perovskites into the mixed Mn II/Mn III regime opens for novel studies of manganites of interest for CMR purposes.

Effect of Oxygen Non-Stoichiometry on La1−xAxMnO3±δ Cathode at Electrode Polarized State

Effect of Oxygen Non-Stoichiometry on La1−xAxMnO3±δ Cathode at Electrode Polarized State

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.

Effect of Oxygen Non-Stoichiometry on Electrode Activity of La1−xAxMnO3±δ Cathode

Effect of Oxygen Non-Stoichiometry on Electrode Activity of La1−xAxMnO3±δ Cathode

Structure and superconducting properties of Bi2Ba2−xMxCuO6+δ

The effect of oxygen nonstoichiometry and barium cation substitution on the structure and superconducting properties of Bi2Ba2−xMxCuO6 +δ(M = Sr, Ru, Rh, Pd, In, Sb or Pb;xchanged from 0 to 0.2) were studied. The cation-substituted samples annealed in oxygen flow contain a superconducting phase withTcinitnear 95 K.

The effect of oxygen nonstoichiometry on the properties and structure of the low Tc phase in BrSrCaCuO superconductor

The properties and structure of the low Tc phase in BrSrCaCuO superconductors was greatly affected by the oxygen content, which was varied by annealing specimens in various atmospheres. The Tc of low Tc phase increased up to 100 K by annealing in nitrogen. Annealing in nitrogen caused the reversible weight loss of about 0.2% and the increase in the c-axis by 0.01 nm. The variation of microstructure was examined by TEM. The average period of modulation in Bi-O layer was found to be unvaried (2.7 nm) but the detailed local structure seemed to be disordered by oxygen evolution.

Laser ablated bismuth cuprate thin films preparation and effect of oxygen nonstoichiometry upon superconductivity

Thin films of Bi2Sr2CaCu2O8 and (Bi, Pb)2Sr2Ca2Cu3O10 have been prepared on monocrystalline (100) MgO substrates, using a laser ablation method with post annealing treatment. The influence of substrate temperature and oxygen pressure during deposition were investigated. SEM observations, EDS analysis, electric and magnetic measurements have been used to characterize the films. Superconducting “2212” films, with Tc(R = 0) at 80–83 K and Jc (50 K) up to 5 × 105 A/cm2, have been currently achieved, while Pb-doped “2223” films exhibit Tc as high as 110 K with Jc = 5 × 104 A/cm2 at 77 K. The effect of annealing at low temperature (350°C) in an argon flow has been studied for the 2212 phase, it shows the influence of the oxygen non-stoichiometry, i.e. of the hole carrier density upon Tc's which can be measured up to 89 K (zero resistance).