Resistive switching in highly disordered thin oxide films

Ionic and electronic transport in functional oxide materials is of great relevance for applications in the fields of energy and data storage, e.g. solid oxide fuel cells (oxygen ion conductivity), oxygen permeation membranes (ambipolar diffusion of oxygen), or data storage materials (electronic and/or ionic conductivity). In this contribution, our recent work on highly non-stoichiometric, amorphous thin film oxides will be discussed. In amorphous solids structural disorder can lead to an insulator–metal transition due to Anderson localization, i.e. the electronic states below the mobility edge are localized. If the Fermi energy passes through the mobility edge, the material changes from an electronic insulator to a metal. In addition, large deviations from the ideal stoichiometry of an oxide, that is, high defect concentrations, provide a high concentration of electronic defects (self-doping). We will consider examples of highly disordered oxides that were prepared by pulsed laser deposition and sputtering as well and discuss their electronic conductivities and their application in resistive memory devices

Reversible water uptake and release of pseudo-cubic type La0.7Sr0.3Mn1- xNixO3 at intermediate temperatures

Solid oxide fuel cells (SOFCs) based on oxide-ion conducting electrolytes possess several attractive advantages such as high energy conversion, low pollutant emission and fuel flexibility. However, SOFCs suffer from the high operating temperatures 800-1000 °C; such high temperature operations result in the increase of costs and lessened lifetimes of materials. Hence, there exists a strong demand to decrease the working temperature into intermediate temperature (IT) region below 600 °C. Proton conducting ceramic fuel cells (PCFCs) is a kind of promising IT-fuel cells operating at around 400-600 °C because of lower activation energies of proton conductivity than oxide-ion conductivity. Recently Choi et al [1] reported that PCFC with BaZr0.4Ce0.4Y0.1Yb0.1O3 electrolyte exceeds 500 mW cm-2 at 500 °C, however, the performance still lags far behind the predicted values that is over 1.0 W cm-2 at 500°C. There are two major challenges, one is big ohm resistance of Zr-rich Ba(Zr, Ce, Y)O3 (BZCY) electrolyte, and the other one is lack of highly efficient cathode specially designed for PCFCs [2]. Since most of the cobaltite base cathodes are oxide-ion conductors, the mismatch of main ionic carriers between cathode and electrolytes limits the efficient cathodic reaction area into cathode-electrolyte-gas triple boundaries. Hence, it is motivated to develop cathode catalysts which exhibit sufficient proton conductivity in order to extend the efficient reaction zone and thus reduce cathode overpotentials and finally increase reaction efficiency. The protonic defects are incorporated into oxides via hydration reaction, whereas, many oxides do not have enough large hydration enthalpy [3-5] and thus, the reaction is less-pronounced at elevated temperatures. Please click Additional Files below to see the full abstract

About the Effectivity of the Priming Water Channel in the Pool-and-Weir-Fishway

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

Manganese oxide base electrocatalysts for proton-conducting ceramic cells

There has been a strong interest in clean and renewable energy sources due to finite fossil fuel sources, increasing oil prices and environmental concerns. Hydrogen is regarded as the leading candidate fuel, because it releases only H2O during combustion and it is compatible to use in high efficiency fuel system. Steam reforming of hydrocarbon gas is currently the main way to produce hydrogen but still relies on fossil fuel consumption. On the contrary, water electrolysis using electric power generated by renewable energy is attracted as sustainable hydrogen production method. Especially, steam electrolysis using solid electrolyte cells is promising for efficient hydrogen production because high-temperature heat partly offers the energy for water electrolysis, leading favorable kinetics and thermodynamics. Hence, it is motivated to investigate on solid oxide electrolysis cell (SOEC) using proton-conducting ceramics to achieve highly efficient conversion from electrical power into chemical fuel gas directly. However, sufficient performance has not be achieved yet in the current system because large overpotential is needed for oxygen evolution reaction at anode owing to the relatively slow kinetics and the limited active zone in the anode/electrolyte interfaces due to the mismatch of ionic carries, Accordingly, it is a great challenge to develop high performance oxygen electrode with efficient electrocatalytic ability for 4 electron transfer oxygen evolution reaction. Recently, it is reported that high valence state metal oxide reveal superior electrocatalytic activity for water oxidation s because the energy levels between the occupied metal orbital and the O 2p orbital are very close, causing a strong hybridization and facilitating o-o bond formation. Herein, we examined electrocatalytic performance of high valence state Mn(V) oxide Ba3(MnO4)2 as an anode for SOEC This oxide has been reported to be very stable at elevated temperatures in oxidative conditions. Proton-conducting BaZr0.4Ce0.4Y0.2O3-δ (BZCY) was used as proton conducting electrolyte. Bulk electrolyte cell were constructed with a BZCY disc which were prepared by solid state reactive sintering (SSRS) method. The electrolyte precursor powder was prepared by mixing proper amount of BaCO3, CeO2, ZrO2, and Y2O3 according to the desired stoichiometry with the addition of 1.0wt.% NiO as a sintering aid. This mixture was ball-milled for 48 h and uniaxially pressed under 20 MPa for 1 min and then cold-isostatic-pressed under 100 MPa for 1 min. Finally, green pellets were calcined at 1500°C for 10 h so as to obtain dense electrolyte disc (2 mmd, 9 mmf)Pt paste was applied at one side of the surface as a cathode. LSCF or LSCF/Ba3(MnO4)2 mixed ink were screen-printed at the other side of the surface as anode materials. Samples are evaluated by XRD and XAS. The electrochemical impedance spectroscopy and I-V measurements were carried out to evaluate the SOEC properties. Two kinds of anode materials were examined in this research, namely, the cell-1: Pt | BZCY | LSCF and cell-2: Ba3(MnO4)2/LSCF mixed anode cell. The cell-2 showed superior steam electrolytic performance compared to cell-1. The current density of steam electrolysis of cell-2 was 145 mA cm-2 meanwhile cell-1 was 145 mA cm-2 in bias voltage of 1.5 V at 600°C. Impedance spectroscopy was conducted to evaluate the anodic polarization resistance. LSCF anode gives 6 Ω cm2, however, the Ba3(MnO4)2/LSCF composite anode gives 3 Ω cm2. Furthermore, the spectral features were completely different between both. The spectrum of LSCF anode had three semi-circles: high frequency arc (10x-10y Hz), middle frequency arc (10zz-10zy Hz) and low frequency arc (10zz-10zy Hz). On the other hand, Ba3(MnO4)2/LSCF involves only two semi-circles: high frequency arc (10x-10y Hz) and low frequency arc (10zz-10zy Hz). These results indicate Ba3(MnO4)2 changes the reaction pathway of water oxidation electrode/solid electrolyte interface. .The oxygen evolution rate was measured by gas chromatography when electrolysis was performed at a constant current density of 100 mA, 200 mA, and 300 mA. The flax of oxygen from anode side is corresponded to that of calculated from the current density, indicating that the faradaic efficiency was almost 100%. XRD pattern of the sample after electrolysis showed that there were no secondary phases, indicating stability of Ba3(MnO4)2 is enough to use in SOEC anodic condition. The above results suggest the Ba3(MnO4)2 is promising for OER electrocatalysts for SOEC

Glenohumeral joint motion after subscapularis tendon repair: an analysis of cadaver shoulder models

BACKGROUND: As for the surgical treatment of the rotator cuff tears, the subscapularis tendon tears have recently received much attention for the mini-open or arthroscopic repair. The results of surgical repair for the subscapularis tendon tear are satisfactory, but the range of external rotation is reported to be restricted after the repair. The purpose of this study was to evaluate the range of glenohumeral joint motion after repairs of various sizes of subscapularis tendon tears. METHODS: Using eight fresh frozen human cadaveric shoulders (mean age at death, 81.5 years), three sizes of subscapularis tendon tear (small, medium, and large) were made and then repaired. With the scapula fixed to the wooden jig, the end-range of glenohumeral motion was measured with passive movement applied through 1.0-Nm torque in the directions of scapular elevation, flexion, abduction, extension, horizontal abduction, and horizontal adduction. The passive end-ranges of external and internal rotation in various positions with rotational torque of 1.0 Nm were also measured. Differences in the ranges among the three type tears were analyzed. RESULTS: As tear size increased, range of glenohumeral motion in horizontal abduction after repair decreased gradually and was significantly decreased with the large size tear (P < 0.01). The end-range of external rotation decreased progressively with increasing tear size in every glenohumeral position. The prominent decrease in external rotation (around 40° reduction from intact shoulders) was observed in shoulders after repair of large size tear at 30° to 60° of scapular elevation and abduction. CONCLUSIONS: As the size of the subscapularis tendon tear increased, the passive ranges of horizontal abduction and external rotation of the glenohumeral joint after repair decreased significantly. In shoulders with a subscapularis tendon tear, it is necessary to consider the reduction of external rotation depending on tear size

Catalytic activity of graphene-covered non-noble metals governed by proton penetration in electrochemical hydrogen evolution reaction

Hu, K., Ohto, T., Nagata, Y. et al. Catalytic activity of graphene-covered non-noble metals governed by proton penetration in electrochemical hydrogen evolution reaction. Nat Commun 12, 203 (2021). https://doi.org/10.1038/s41467-020-20503-

Intermediate-Temperature, Proton-Conducting Membranes of Hafnium Phosphate and Zirconium Phosphate/Borate/Sulfate

Uniform, defect-free nanofilms ͑around 100 nm thick͒ of hafnium phosphate were prepared via layer-by-layer deposition of precursor solution of metal alkoxides and were shown to give practically useful proton conductivity at 300-400°C as fuel cell electrolyte membrane. Annealing of the deposited precursor film at 500°C gave a lower area specific resistance ͑R AS ͒ than that at 400°C, and this effect was coincident with the formation of the pyrophosphate unit. The best ͑lowest͒ R AS value of less than 0.1 ⍀ cm 2 for hafnium phosphate membrane ͑annealing at 500°C, 291 nm thick, conductivity of 3 ϫ 10 −4 S cm −1 at 320°C͒ was comparable to that of a nanofilm of an yttrium-doped zirconium phosphate. The R AS values of nanofilms of zirconium sulfate and zirconium borate were 2-3 orders higher than that of the corresponding zirconium phosphate. It is clear from these results that nanofilms of various solid acids are promising candidates for the electrolyte membrane of fuel cells operating at the intermediate temperatures of 300-400°C. © 2010 The Electrochemical Society. ͓DOI: 10.1149/1.3432600͔ All rights reserved. Solid acid catalysis has been widely used within the petrochemical industry and is attracting increasing attention due to its environment-friendly feature. 1 Solid acid catalysts are composed of wide-ranging acidic materials including clay minerals, zeolites, metal oxides and sulfides, metal hydroxides, and heteropoly acids. The acid sites may either be Broensted or Lewis type. Being a most popular class of solid acids, zeolites are microporous crystalline solids of aluminosilicate with well-defined cage structures of SiO 2 and Al 2 O 3 units. Such basic atomic connectivity must be maintained in the aluminosilicate compounds regardless if they are crystalline or not. The development of electrolyte membranes that are composed of inexpensive materials and are operable at the intermediate temperatures of 200-400°C is strongly desired to enable the next-generation fuel cell ͑FC͒ technology. The novel electrolyte membrane should show satisfactory material stability, effective proton conduction, efficient redox reaction and the consequent reduction of electrocatalyst loading, improvement in CO tolerance, and manageable heat recovery. 2 In addition, anhydrous proton conduction in the intermediate-temperature regime eliminates the elaborate water management required for Nafion-based polymer electrolyte fuel cells ͑PEFCs͒. The idea of using inorganic solid acid as FC electrolyte membrane was examined in our previous study. 3 Surprisingly, amorphous nanofilms of aluminosilicate in fact contained acid sites that enabled efficient proton conduction across the film. A 70 nm thick amorphous aluminosilicate film gave practically useful proton conductivity at 300-400°C as an electrolyte membrane of an FC. This was a strong indication that the local atomic connection of the zeolite structure that provides acid sites was basically preserved even in the ultrathin amorphous film. Our subsequent study 4 demonstrated that many of the silica-based double oxides gave rise to proton conductivity of different degrees in the form of amorphous nanofilms. The presence of effective acid sites was also shown in phosphate materials. 5 Amorphous nanofilms of zirconium phosphate exhibited a practically useful level of proton conductivity at 300°C. A covalent network of metal and phosphate species provided quite robust nanofilms whose morphology and proton conductivity remained unchanged for hundreds of hours during the electrochemical examination of up to 400°C. These findings suggest an exciting possibility of developing a rich variety of proton-conducting nanofilms, even more so than the case of silica-based double oxides. Uniform amorphous nanofilms may be obtainable from a large combination of metal species and multivalent oxyacids. Therefore, they provide a valuable opportunity to conduct an extensive search for materials that would give superior proton conductivity and robustness. An advantage of the amorphous texture is that the variety of combination is not restricted by the stoichiometry of the two major components. Certain metal phosphates 6 and borates 7 exhibit highly efficient proton conductivities as crystalline compounds. Unfortunately, these compounds, as such, did not produce robust uniform nanofilms probably due to their crystalline nature. Because the basic atomic framework is common, their amorphous counterparts may provide acid sites for proton conduction, if properly prepared. As the first step of materials search, we replaced the zirconium species with hafnium, in the current study, as the two metal species belong to the identical IV family in the periodic table. We assumed that they would form closely related covalent networks. The film formation and proton conductivity of hafnium phosphate were compared with those of zirconium phosphate. As for the multivalent oxyacid, we chose boric acid and sulfuric acid by considering the chemical stability of their metal oxygen bonds, and the electrochemical behavior of their zirconium compounds were compared with those of the previously reported results of zirconium phosphate. Nanofilms of zirconium sulfate and zirconium borate were prepared to examine their proton conductivities in relation to their phosphate counterpart. Experimental Materials.-2-Methoxyethanol ͑reagent grade͒, ethanol ͑reagent grade͒, diphosphorous pentoxide, boric acid, ethylenediamine, and anhydrous zirconium tetra-n-butoxide ͑85-90%͒ were obtained from Kanto Chemical. Hafnium tetra-n-butoxide ͑95%͒ and yttrium methoxyethoxide ͑15-18% in methoxyethanol͒ were obtained from Gelest Inc. Yttrium tetra-n-butoxide and indium tin oxide ͑ITO͒ coated glass substrate ͑30 nm thick ITO layer, 70 ⍀͒ were obtained from Aldrich. Sulfuric acid was bought from Junsei Chemical. Preparation of thin films of metal phosphate/borate/ sulfate.-The ITO substrate ͑2.5 ϫ 4 cm͒ was cleaned by sonication in ethanol for 2 min and then dried by flushing nitrogen gas. A thin film of amorphous hafnium phosphate was deposited in a layerby-layer fashion by the surface sol-gel process. The precursor sol was prepared as follows: 0.496 g of hafnium tetra-n-butoxide was added to 20 mL of 2-methoxyethanol. The mixture was vigorously stirred for 5 min at room temperature. P 2 O 5 ͑0.213 g͒ was added to 30 mL of 2-methoxyethanol and the mixture was sonicated in an c Present address

Equivalency of the quality of sublethal lesions after photons and high-linear energy transfer ion beams

The quality of the sublethal damage (SLD) after irradiation with high–linear energy transfer (LET) ion beams was investigated with low-LET photons. Chinese hamster V79 cells and human squamous carcinoma SAS cells were first exposed to a priming dose of different ion beams at different LETs at the Heavy Ion Medical Accelerator in the Chiba facility. The cells were kept at room temperature and then exposed to a secondary test dose of X-rays. Based on the repair kinetics study, the surviving fraction of cells quickly increased with the repair time, and reached a plateau in 2–3 h, even when cells had received priming monoenergetic high-LET beams or spread-out Bragg peak beams as well as X-ray irradiation. The shapes of the cell survival curves from the secondary test X-rays, after repair of the damage caused by the high-LET irradiation, were similar to those obtained from cells exposed to primary X-rays only. Complete SLD repairs were observed, even when the LET of the primary ion beams was very high. These results suggest that the SLD caused by high-LET irradiation was repaired well, and likewise, the damage caused by the X-rays. In cells where the ion beam had made a direct hit in the core region in an ion track, lethal damage to the domain was produced, resulting in cell death. On the other hand, in domains that had received a glancing hit in the low-LET penumbra region, the SLD produced was completely repaired

Effect of Nutrient Inputs on Water Quality Change and Phytoplankton Growth in Atsumi Bay

Eutrophication in an estuary occurs as an effect of the enrichment of nutrient inputs from rivers. This condition has become one of the most common environmental issues experienced around the globe and especially in Japan. Atsumi Bay is a eutrophic coastal area in Japan. The objective of this research was to analyze the influences of nutrient inputs from the Umeda River into Atsumi Bay on pre- and post-rainfall water quality conditions. This study was conducted from July to October 2010. The results showed a decrease of surface salinity after rainfall indicating that huge freshwater inputs had overlaid the surface layer of Atsumi Bay rather than the bottom layer. Moreover, post-rainfall conditions showed an increase of chlorophyll a as an effect of phytoplankton growth, followed by an increase of particulate nutrients. On the other hand, dissolved nutrients decreased due to uptake by phytoplankton and dilution by freshwater