Number Of Oxygen Vacancies Research Articles

The effect of Ar plasma bombardment upon physical property of tungsten oxide thin film in inverted top-emitting organic light-emitting diodes

This study examined the mechanism of performance degradation induced by the plasma sputtering process for the formation of the ITO top anode in inverted top-emitting organic light-emitting diodes (ITOLEDs) with WO 3 thin film as the hole injection layer (HIL) and the buffer layer. The degradation is mainly caused by the changes in the physical properties of the WO 3 thin film as well as the damages of organic layers, which are caused by the bombardment of energetic particles induced by the plasma sputtering process. The number of oxygen vacancies in the WO 3 thin film is increased with the increase of the bombardment energy of energetic particles such as Ar ions, resulting in the decrease in the work function and optical band gap and the dramatic increase in conductivity. Above all, the increase in the energy potential difference between WO 3 HIL and NPB HTL, which was attributed to the reduced work function of the WO 3 HIL, reduces the efficiency of carrier injection and dominantly affects the device performance. These results show that the plasma damage effect, induced by the sputtering process for ITO deposition, could not be effectively removed, even when the metal oxide thin film is used as the buffer layer in ITOLEDs.

Impact of dopants on the sulfation, desulfation and NO x reduction performance of Ba-based NO x storage-reduction catalysts

The performance of a NO x storage-reduction (NSR) catalyst is strongly dependent on the relative stabilities of nitrates and sulfates on the catalyst surface. This effort studies the effects of introducing 5 mol% La, Ca, and K-dopants into a BaO phase of a model Pt/Ba/Al 2O 3 NSR catalyst. The dopants were chosen with a range of properties to affect the BaO lattice spacing and/or the number of oxygen vacancies. The resulting changes in the storage material, in turn, impact the stability of stored nitrates and sulfates, as measured by NO x conversions and desulfation temperatures. The Ca- and La-doped material shows equivalent or better NO x reduction performance between 200 and 400 °C, while the K-doped NSR catalyst showed significant decreases in performance at 200 °C but maintained the high performance at 300 and 400 °C. Following the performance measurements, the samples are then sulfated to 5.5 mg S/gcat and desulfated to 1000 °C. All NSR catalysts generally show similar desulfation behavior, but in determining the temperature of 20% sulfur removal ( T 20%), it is shown that the Ca + Ba sample has a 25 °C lower T 20% than both the Ba-only and La + Ba samples, while K + Ba is 70 °C higher. Additional Ca-based samples were than prepared at the 10, 20 and 100 mol% levels. The higher Ca-doped materials show similar NO x reduction performance, but the 5% Ca + Ba sample maintains the lowest T 20%. Interestingly, the Ca-only sample has a T 20% that is 60 °C higher than the Ba-only NSR catalyst, which indicates that the introduction of 5% Ca into the Ba-lattice has a synergistic effect in lowering the desulfation temperature.

Ecofriendly synthesis and solar photocatalytic activity of S-doped ZnO

The S-doped ZnO was prepared by new ecofriendly method, which involves simple mechanochemical synthesis followed by thermal decomposition of bisthiourea zinc oxalate (BTZO) powders. The BTZO was characterized by FTIR and TG–DTA analysis while S-doped ZnO crystallite was characterized by XRD, XPS, SEM, EDXS, and photoluminescence (PL) spectra. X-ray diffraction data suggest the single phase wurtzite structure for S-doped ZnO and the incorporation of sulfur expand the lattice constants of ZnO. Room temperature PL spectra show more number of oxygen vacancies in S-doped ZnO as compare to that of pure ZnO. Photocatalytic activity of S-doped ZnO was checked by means of solar photocatalytic degradation (PCD) of resorcinol, using a batch photoreactor. The PCD efficiency of S-doped ZnO was found to be 2 times greater than that of pure ZnO. The inherent relationship between PL intensity and photocatalytic activity of S-doped ZnO was discussed.

The Grain Size Influence on the E1' Centre Observed in Quartz of Atmospheric Deposition at Two Japanese Cities: A Preliminary Study

The Grain Size Influence on the E1' Centre Observed in Quartz of Atmospheric Deposition at Two Japanese Cities: A Preliminary Study The grain size influence on the number of oxygen vacancies in quartz was investigated by ESR in atmospheric deposition collected at two Japanese cities, Fukuoka and Akita, in 1969 and 1971. The finer grain size fraction shows the highest value of concentration of oxygen vacancies, most closely resembling dust originating in the Taklamakan desert. Month to month and year to year variation of the dependence was also observed which could possibly be attributed to the variation of the mixture ratio of at least two dust sources in China, A conclusive statement can not be made at this stage.

Dielectric and Ferroelectric Properties of (Cr,Nb)-Doped Lead Zirconate Titanate Ceramics

The 3 mol% Nb2O5 doped Pb(Zr0.52Ti0.48)O3 with addition of 1-3 mol% Cr2O3 prepared via the solid-state reaction technique have been investigated. The XRD shows that a sample is primarily in both tetragonal and rhombohedral phases coexist and the amount of rhombohedral phase decreases that is due to the donor (Nb) dopant reduces the number of oxygen vacancies and leads to a lower amount of rhombohedral phase. The maximum dielectric constant tend to decrease with increasing Cr doping concentration from 0.1 to 1 mol%. Further increase in Cr concentration, the maximum dielectric constant increase dramatically. The hysteresis loop measurements, the electrical coercivity and the remnant polarization do not show a systematic trend at low concentration of Cr doping. It is possibly due to the partial solubility of Cr doping. The observations clearly indicate the hardening behavior at higher concentration because of more solubility of Cr.

Evaluation of oxide ion diffusivity in YAG ceramics

Transparent yttrium aluminium garnet (YAG) polycrystal can be used as a host material for a solid state laser. In the present study, the authors prepared completely transparent YAG ceramics from active powder. The optical and mechanical properties of YAG ceramics are very sensitive to point defects. In order to examine the relationship between these properties and point defects, it is first necessary to characterise the defects. The authors report the effect of doping on oxygen diffusivity in several YAG ceramics, doped with various elements. Although Nd doping slightly increases the oxygen diffusion coefficient and the number of oxygen vacancies increases with increasing Nd concentration in as sintered materials, the variation of the oxygen diffusion coefficient in well annealed samples is small. These results suggest that the oxygen vacancies exist in non-equilibrium. However, grain boundary diffusivity was not influenced by preannealing before the oxygen diffusion experiments. The oxygen defect structure in transparent YAG ceramics is also discussed.

SrCo0.95Sb0.05O3−δ as Cathode Material for High Power Density Solid Oxide Fuel Cells

The title compound has been selected from the SrCo1−xSbxO3−δ series for its enhanced electronic conductivity, as high as 500 S cm−1 at 400 °C, and tested in a single cell as a cathode material for solid oxide fuel cells (SOFC). The characterization of this oxide included X-ray (XRD) and “in situ” temperature-dependent neutron powder diffraction (NPD) experiments, thermal analysis, and impedance spectroscopy. In the test cell, the electrodes were supported on a 300 μm thick pellet of the electrolyte La0.8Sr0.2Ga0.83Mg0.17O3−δ (LSGM) with Sr2MgMoO6 as the anode and SrCo0.95Sb0.05O3-δ as the cathode. The test cells gave a maximum power density of 0.511 and 0.618 W/cm2 for temperatures of 800 and 850 °C, respectively, with pure H2 as fuel and air as oxidant. In the 100−700 °C range, SrCo0.95Sb0.05O3−δ adopts a tetragonal superstructure of perovskite with a = a0, c=2a0 (a0 ≈ 3.9 Å) defined in the P4/mmm space group containing two inequivalent Co positions. Sb atoms are randomly distributed at Co2 positions, whereas Co1 sites do not apparently contain Sb. Flattened and elongated (Co,Sb)O6 octahedra alternate along the c axis sharing corners in a three-dimensional array (3C-like structure). This material experiences a phase transition from the tetragonal superstructure to a simple cubic perovskite between 700 and 850 °C, probably associated with the endothermic peak observed at 816 °C in the DTA curve. This phase transition is related to the disordering of oxygen vacancies from the three available positions in the tetragonal structure to a single oxygen site in the cubic unit cell with an average thermal factor and occupancy. This structure is stable up to 930 °C; at this temperature the oxygen stoichiometry is 2.46(4). The good performance of this material as a cathode is related to its mixed electronic-ionic conduction (MIEC) properties, which can be correlated to the investigated structural features: the Co3+/Co4+ redox energy at the top of the O 2p bands accounts for the excellent electronic conductivity, which is favored by the corner-linked perovskite network. The considerable number of oxygen vacancies, with the oxygen atoms showing high displacement factors (4−6 Å2 in the 700−850 °C range), suggests a significant ionic mobility. Additionally, this cathode material exhibits an extremely low electrode polarization resistance, below 0.1 Ω cm2 in the 750−800 °C range. The thermal expansion is compatible with the electrolyte and the nonreconstructive tetragonal-to-cubic transition does not involve an abrupt change in unit-cell volume, which increases smoothly over the entire temperature interval up to 930 °C.

In situ Observation of the Fatigue-Free Piezoelectric Microcantilever by Two-Dimensional X-ray Diffraction

A (111)Pt/(001)cLaNiO3/(001)(100)Pb(Zr0.44Ti0.56)O3/(001)cLaNiO3/(111)Pt/TiO2/SiO2/(001)Si heterostructured piezoelectric microcantilever demonstrated a high fatigue endurance over 1×1010 switching cycles and a large transverse piezoelectric constant (d31) of about -140 pm/V. The fatigue endurance was improved by suppressing the increase in the number of oxygen vacancies in Pb(Zr0.44Ti0.56)O3 film using LaNiO3 oxide layers as top and bottom electrodes. The origin of the large d31 was a reversible 90°-domain rotation from a- to c-domains, which was confirmed by an in situ two-dimensional X-ray diffraction (XRD2) technique with a 100 µmφ incidence X-ray and a highly sensitive two-dimensional detector under an applied voltage. The XRD2 technique demonstrated the feasibility of superior piezoelectric devices with a large piezoelectric displacement and a high reliability for repetitive operation.

Modification of a shell model for the study of the radiation effects in BaTiO3

In order to study the radiation effects in BaTiO3 ferroelectric crystal, a previously developed shell model is modified. The modifications include adding the ZBL universal potentials at short distances and distance-dependent spring constants for core–shell interactions. The phase transition sequences in BaTiO3 were correctly reproduced using molecular dynamics simulations with this modified shell model. Also, the calculated Frenkel pair formation energies agree well with results obtained by first principles calculations, which suggests that this model is suitable for the simulation of the radiation effects in BaTiO3. The dependence of polarization on the number of oxygen vacancies was also studied.

Raman spectra and room-temperature ferromagnetism of hydrogenated Zn0.95Mn0.05O nanopowders

Two additional vibration modes at 250 and 529 cm−1 were observed in hydrogenated Zn0.98Mn0.05O nanopowders. The number of oxygen vacancies was increased by hydrogenation, which induced the mode at 250 cm−1. The additional vibration mode at 529 cm−1 was due to the increase of the number of subsititutional Mn atoms occupying Zn sites, which resulted that some new lattice defects were introduced or intrinsic host-lattice defects became activated/intensified. The room-temperature ferromagnetism was observed in the hydrogenated Zn0.98Mn0.05O nanopowders prepared at high temperature (T=700 °C), which originated from the lattice defects such as oxygen vacancies and Zn interstitials.

Leakage current mechanism and effect of oxygen vacancy on the leakage current of Bi 5Nb 3O 15 films

The effect of oxygen partial pressure (OPP) on the leakage current density of Bi 5Nb 3O 15 (B 5N 3) films grown on Pt electrodes was investigated. The leakage current density was very high for the film grown under a low OPP of 1.7 mTorr, but was significantly reduced by the subsequent annealing under a high oxygen pressure or for the film grown under high OPP of 5.1 mTorr. The variation of the leakage current density with OPP was explained by the number of oxygen vacancies, which produced electron trap sites at the interface between the Pt electrode and the B 5N 3 film. Schottky emission was postulated as the leakage current mechanism of the B 5N 3 films. The barrier height between the Pt electrode and the B 5N 3 film grown under a high OPP of 5.1 mTorr was approximately 1.55 eV, but decreased to 0.81 eV for the film grown under a low OPP of 1.7 mTorr due to the presence of the oxygen vacancy.

Room temperature optical and magnetic properties of polyvinylpyrrolidone capped ZnO nanoparticles

Defect induced room temperature ferromagnetic properties of polyvinylpyrrolidone (PVP) capped nanocrystalline ZnO samples have been studied. Crystal phase and the lattice parameter of the synthesized nanocrystalline samples have been determined from X-ray diffraction spectra (XRD) and high-resolution transmission electron micrographs (HR-TEM). Room temperature photoluminescence (PL) spectrum for the bare ZnO sample shows a strong band at ~ 379 nm and another band at ~ 525 nm. The PL spectra also revealed that the number of oxygen vacancies in the uncapped sample is more than the PVP capped sample. Both sample exhibit ferromagnetic property at room temperature when annealed at 500 °C for 3 h, due to the formation of adequate oxygen vacancy related defects. The saturation magnetization for the annealed PVP capped sample is found to be larger compared to that for the uncapped sample.

Effects of Oxygen Annealing on Dielectric Properties of LuFeCuO4

We investigated the effect of oxygen annealing on dielectric properties of LuFeCuO4 mainly by dielectric measurements and transmission electron microscopy experiments. It was found that the leakage current density decreases with high-pressure oxygen annealing and the size of nanodomains with orientational polarization increases, which is characterized by the short-range ordering of Fe3+ and Cu2+ ions on a triangular lattice. In addition, the absolute value of relative permittivity ε' decreases with oxygen annealing and ε' exhibits a broad peak in the temperature window between room temperature and 550 K, which is similar to that observed in relaxor ferroelectric materials. The present experimental results suggest that the number of oxygen vacancies has a crucial effect on dielectric properties of LuFeCuO4.

Raman Spectroscopy Study of Oxygen Vacancies in PbTiO3 Thin Films Generated Heat-Treated in Hydrogen Atmosphere

Raman spectroscopy is utilized to study the evaluation of vacancies in PbTiO3 thin films subjected to hydrogen atmosphere heat treatment. The B1 mode consisted of only oxygen ion vibration was shifted to lower frequency with increasing heat treatment temperature. It was considered that the oxygen ions were lacking from PbTiO3, and that oxygen vacancies were generated. It was found that the frequency of the B1 mode is proportional to oxygen ion content. Pb ions were also lacking in the PbTiO3 thin films with oxygen ions and the number of oxygen vacancies was larger than that of Pb ions. We suggest that the Raman spectroscopy is a suitable tool for the evaluation of oxygen vacancies in PbTiO3 thin films.

ΔThe effect of co-doping on the yttrium local environment and ionic conductivity of yttria-stabilised zirconia

The effect of co-doping yttria-stabilised zirconia with calcia and scandia has been investigated. Changes in the yttrium ion local environment have been monitored using solid-state magic angle sample spinning 89Y nuclear magnetic resonance. The effect on the low-temperature (below 320 °C) bulk ionic conductivity has been observed using AC impedance spectroscopy. It was found that the number of oxygen vacancies in the nearest-neighbour sites to yttrium ions decreased on co-doping with scandia, correlating with an increase in conductivity, but increased on co-doping with calcia, correlating with a decrease in conductivity. This behaviour can be explained by proposing the trapping of oxygen vacancies in the nearest-neighbour yttrium ion sites so that they no longer contribute to the conduction mechanism.

Optical studies of ZnO thin films grown on O- and H-plasma treated Al 2O 3 substrates by plasma-assisted molecular beam epitaxy

Comparative analysis of the structural and optical properties of ZnO thin films, grown on oxygen (O)- and hydrogen (H)-plasma treated sapphire substrates (denoted by samples O and H, respectively), by plasma-assisted molecular beam epitaxy is reported. We found that sample O has better crystal structure quality as compared to sample H by means of high-resolution X-ray diffraction, atomic force microscopy, and Hall measurements. We observed higher intensity ratio of excitonic emission to deep-level emission, longer radiative recombination lifetime, and lower stimulated emission threshold for sample O compared to sample H. From the results, we conclude that the O-plasma treatment on sapphire substrates may result in a decrease in the number of oxygen vacancies and better lattice matching conditions, thereby leading to an enhancement of the crystal quality and the optical properties of ZnO thin films grown on O-plasma treated sapphire substrates.

Preparation and properties of Ba xSr 1− xCo yFe 1− yO 3− δ cathode material for intermediate temperature solid oxide fuel cells

Ba x Sr 1− x Co y Fe 1− y O 3− δ (BSCF) materials with perovskite structure were synthesized via solid-state reaction. Their structural characteristics, electrical-conduction behavior and cathode performance were investigated. Compared to A-site elements, B-site elements show a wide solid-solution range in BSCF. The electrical-conduction behavior of BSCF obeys the small polaron-hopping mechanism. An increase of Ba or Co content in the BSCF samples results in a decrease of electrical conductivity, which is mainly attributable to the preferential existence of B 3+ rather than B 4+ in Ba- or Co-rich samples. At the same time, this leads to increases in the lattice parameter a and the number of oxygen vacancies. BSCF samples with high Ba content show a high structural stability (high oxygen-loss temperature). Ba 0.6Sr 0.4Co 0.8Fe 0.2O 3− δ and Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ materials present good thermal-cycling stability of the electrical conductivity. Compared with Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ , Ba 0.6Sr 0.4Co 0.8Fe 0.2O 3− δ exhibits a better cathode performance in a Ce 0.8Gd 0.2O 2− δ (GDC)-supported half cell. The cell performance can be improved by introducing a certain amount of GDC electrolyte into the BSCF cathode material.

산소와 수소 플라즈마로 처리한 사파이어 기판 위에 성장된 ZnO 박막의 구조적.광학적 특성

[ <TEX>$Al_2O_3$</TEX> ]기판을 산소 plasma 또는 수소 plasma로 표면 처리한 후 그 위에 plasma-assisted molecular beam epitaxy 방법으로 성장된 ZnO 박막의 구조적 특성과 광학적 발광 특성을 체계적으로 조사하였다. 제작된 ZnO 박막은 high resolution X-ray diffraction 측정과 atomic force microscope를 사용하여 구조적 특성과 표면 특성을 관찰하였으며, photoluminescence (PL) 측정을 통하여 엑시톤과 관련된 광학적 전이특성을 온도에 따라 조사하였다. free exciton, bound exciton, 그리고 이들의 phonon replica들의 특성을 온도에 따라 분석하였으며, 산소 plasma로 표면 처리한 시료의 PL 세기가 수소 plasma 표면 처리한 시료의 PL 세기보다 상당히 커짐을 관찰하였다. 산소 plasma로 처리된 기판 위에 성장된 ZnO 시료가 수소 plasma로 처리된 경우보다 우수한 구조적 특성과 광학적 특성을 보였는데, 이는 산소 plasma로 표면 처리함으로써 산소 공공(oxygen vacancy)과 같은 결함 구조가 적게 생성되고 좋은 격자 상수 일치를 보여주므로 구조적 특징과 발광 특징이 향상되는 것으로 해석되었다. Structure and optical properties of ZnO epilayers grown on oxygen- and hydrogen-plasma treated sapphire substrates by plasma-assisted molecular beam epitaxy (denoted as samples A and B, respectively) have been investigated by various techniques. The crystal quality and structural properties of the surface for the ZnO epilayers were investigated by high-resolution X-ray diffraction and atomic force microscope. For investigating the optical properties of excitonic transition of ZnO, we carried out photoluminescence experiments as a function of temperature. The free exciton, bound exciton emission and their phonon replicas were investigated as a function of temperature from 10 to 300 K, and the intensity of excitonic PL peak emission from the sample A is found to be higher than that of sample B. From the results, we found that sample A has better crystal structure quality and optical properties as compared to sample B. The number of oxygen vacancies may be decreased in sample A, resulting in an enhancement of the crystal quality and a higher intensity of excitonic emission band as compared to sample B.

Nickel catalysts supported on ZrO 2, Y 2O 3-stabilized ZrO 2 and CaO-stabilized ZrO 2 for the steam reforming of ethanol: Effect of the support and nickel load

Catalysts with various nickel loads were prepared on supports of ZrO 2, ZrO 2–Y 2O 3 and ZrO 2–CaO, characterized by XRD and TPR and tested for activity in ethanol steam reforming. XRD of the supports identified the monoclinic crystalline phase in the ZrO 2 and cubic phases in the ZrO 2–Y 2O 3 and ZrO 2–CaO supports. In the catalysts, the nickel impregnated on the supports was identified as the NiO phase. In the TPR analysis, peaks were observed showing the NiO phase having different interactions with the supports. In the catalytic tests, practically all the catalysts achieved 100% ethanol conversion, H 2 yield was near 70% and the gaseous concentrations of the other co-products varied in accordance with the equilibrium among them, affected principally by the supports. It was observed that when the ZrO 2 was modified with Y 2O 3 and CaO, there were big changes in the CO and CO 2 concentrations, which were attributed to the rise in the number of oxygen vacancies, permitting high-oxygen mobility and affecting the gaseous equilibrium. The liquid products analysis showed a low selectivity to liquid co-products during the reforming reactions.

Low-temperature oxygen plasma treatment of TiO 2 film for enhanced performance of dye-sensitized solar cells

The effects of low-temperature O 2 plasma treatment of a TiO 2 film are studied with the objective of improving the performance of dye-sensitized solar cells (DSSCs). X-ray photoelectron spectra (XPS) reveal that the ratio of titanium dioxide to titanium sub-oxides is increased in the O 2 plasma-treated TiO 2 film, compared with that of the untreated TiO 2 film. This increase suggests that the oxygen vacancies in the film are effectively reduced. The near-edge X-ray absorption fine structure (NEXAFS) spectra results agree with the XPS result. It is proposed that there is a correlation between the shifts of the peaks in the NEXAFS spectra and the adsorption of N719 dye on the TiO 2 particles. A DSSC having an O 2 plasma-treated, 4 μm thick TiO 2 film electrode renders a short-circuit photocurrent of 7.59 mA cm −2, compared with 6.53 mA cm −2 for a reference cell with an untreated TiO 2 electrode of the same thickness. As a result of these changes, the solar-to-electricity conversion efficiency of the O 2 plasma-treated cell is found to be 4.0% as compared with 3.5% for the untreated cell. This improvement in the performance is rationalized on the basis of increased N719 dye adsorption on to the TiO 2, due to the reduction in the number of oxygen vacancies caused by the oxygen plasma treatment.