Ta Metal Research Articles

Activity and Durability of Mn Binary Oxide-Based Electrocatalyst for an Alternative Anode

Compared with alkaline water electrolysis (AWE), proton exchange membrane water electrolysis (PEMWE) has several advantages such as high current density, compact system and high purity of hydrogen gas. However, a conventional anode of PEMWE utilizes precious metal oxide such as iridium oxide (IrO2) with high cost and low resources. Recently, it has been reported that the performance of low-loading IrO2 anodes deteriorates due to the potential fluctuations simulated variable renewable energies [1-2]. Thus, it is required to develop a low-cost catalyst with high durability against the potential fluctuations. We have focused on the tantalum oxide-based electrocatalyst because of its low cost and high chemical stability in acid. In this study, we have investigated on the catalytic activity and durability of Mn added Ta oxide-based thin film (Mn-TaOx) for the alternative anode of PEMWE. For the purpose of improvement of durability, Mn-TaOx coated with ZrO2 fabricated by the Atomic Layer Deposition (ALD) was also prepared to evaluate the durability of potential cycling.A Ti rod was used as the substrate, and Mn-TaOx was prepared by RF magnetron sputtering deposition. Mn disk was used as the sputtering target, and the Ta plate was placed on the Mn target to prepare Mn-TaOx. Mn addition was fixed at 50 at%, and it was controlled by the area ratio considering sputtering rate of Mn and Ta metal. Partial pressure of Ar and O2 gas were kept constant at 0.23 Pa for 20 min during the sputtering. The substrate heating temperature was constant at 673 K during the sputtering. The prepared Mn-TaOx electrode was coated with ZrO2 fabricated by ALD (ZrO2 coating Mn-TaOx). The thickness of coating ZrO2 was varied in the range of 0.5 to 2.0 nm. All electrochemical measurements such as oxygen evolution reaction (OER) was used by conventional three electrode cell in 1 M H2SO4 at 303 K. In addition, electrochemical impedance spectroscopy (EIS) was also performed to estimate several factors such as charge transfer resistance (R ct), film resistance (R film) and so on. The protocol of potential cycling as a durability test was set the potential in the range of 1.5 to 2.0 V with 50 mV s-1 for 10000 cycles, and the slow scan voltammetry was conducted every 2000 cycle in the range of 1.2 to 2.0 V with 5 mV s-1 to compare the OER activity before and after test.The OER current of ZrO2 coating Mn-TaOx was smaller than that of Mn-TaOx without coating (Mn50-TaOx (0 nm)). In particular, the OER current of Mn-TaOx coated with 2 nm of ZrO2 (“2 nm”) was greatly decreased because the film thickness of ZrO2 is too thick so that it has low electric conductivity. Furthermore, the APD-ZrO2 covered on the surface, and it is also hard to react with reactant at active site. From results of EIS, the R ct and R film of “2 nm” increased. On the other hand, the OER current of Mn-TaOx coated with 1 nm of ZrO2 (“1 nm”) did not drastically decrease compared to Mn-TaOx and it was suggested that “1 nm” relatively maintained its activity.Figure 1 shows the geometric current density (i geo) at 2.0 V of ALD-ZrO2 coated on Mn-TaOx after potential cycling. The i geo at 2.0 V of Mn-TaOx without coating also shows in Fig. 1. The i geo of Mn50-TaOx (0 nm) was decreased about half value after 2000 cycles of durability test, but that of Mn-TaOx coated with ZrO2 did not decrease significantly even after 2000 cycles of potential cycling. In particular, the i geo of “1 nm” was the highest current after the 2000 cycles of potential cycling in this study, and the degradation didn’t observe in this cycle range. According to the results from XPS spectrum, a small amount of ZrO2 was detected on the surface of “1 nm” after the potential cycling. The redox peak of Mn(Ⅲ)/(Ⅳ) [3] observed at the ALD-ZrO2 coated on Mn-TaOx was also detected after the potential cycling, so that the Mn species as an active site of Mn-TaOx for the OER was still remained. Therefore, the reason why the “1 nm” was relatively stable is that the amounts of both active and protect site have maintained during the durability test.AcknowledgementThis work is partially supported by Suzuki Foundation.References(1) Ayers, Curr. Opin. Electrochem., 18, 9 (2019).(2) M. Alia, and G. C. Anderson, J. Electrochem. Soc., 166, F282 (2019).(3) Morita, C. Iwakura, and H. Tamura, Electrochim. Acta, 24, 357 (1979). Figure 1

Thermogravimetric study of metal–organic precursors and their suitability for hybrid molecular beam epitaxy

Although metal–organic (MO) precursors are widely used in technologically relevant deposition techniques, reports on their temperature-dependent evaporation and decomposition behaviors are scarce. Here, MO precursors of the metals Ti, V, Al, Hf, Zr, Ge, Ta, and Pt were subjected to thermogravimetric analysis to experimentally determine their vapor pressure curves and to gain insight into their temperature-dependent decomposition kinetics. Benzoic acid was used as a calibration standard and vapor pressure curves were extracted from thermogravimetric measurements using the Langmuir equation. The obtained data is used to discuss the suitability of these MO precursors in chemical vapor deposition-based thin film growth approaches in general, and hybrid molecular beam epitaxy in particular. All MOs, except for Ta- and one Ti-based MOs, were deemed suitable for gas inlet systems. The Ta-based MO demonstrated suitability for an effusion cell, while all MOs showed compatibility with cracker usage.Graphical

Detection of decomposed gases in SF6 surge arrester contaminated conditions in ultra-high voltage transmission lines based on Ta-doped defective h-BN nanosheet: A DFT study

SF6 surge arrester on ultra-high voltage transmission lines plays a critical role in the entire power transmission system. They not only protect electrical equipment from the dangers of high transient over voltages, but also bear the responsibility of maintaining the safety and stability of the transmission lines. Detecting the decomposed gases under polluted conditions inside SF6 surge arresters is of paramount importance. In this paper, based on extensive investigations and the application of density functional theory and 2D materials, we conducted a study on the detection of decomposed gases (HF, H2S, SOF2) in SF6 surge arresters for ultra-high voltage transmission lines under polluted conditions using Ta-doped defective h-BN nanosheets gas sensor. Revealing the adsorption and sensing mechanisms of these target gases on h-BN sensors through band structure, density of states, projected density of states, and differential charge density analysis. The results showed that Ta metal particle modification significantly improves the electronic activity of defective h-BN, substantially reducing the band gap values from 4.560 eV to 0.153 eV and 0.912 eV in the B atom and N atom defective oping systems. Meanwhile, Ta-doped defective h-BN exhibits strong selectivity and sensitivity to three decomposition components, with the adsorption capability ranking as SOF2 > H2S > HF, all of which are physical chemisorption types. Furthermore, in terms of various adsorption parameters, defective h-BN’s adsorption ability far surpasses other materials, offering broad prospects for practical applications. The results of this work contribute to the development and application of Ta-doped defective h-BN sensors for the detection of decomposed gases inside SF6 surge arresters under polluted conditions.

Current-Induced Magnetization Switching in Light-Metal-Oxide/Ferromagnetic-Metal Bilayers via Orbital Rashba Effect.

The orbital angular momentum (OAM) generation as well as its associated orbital torque is currently a matter of great interest in spin-orbitronics and is receiving increasing attention. In particular, recent theoretical work predicts that the oxidized light metal Cu can serve as an efficient OAM generator through its surface orbital Rashba effect. Here, for the first time, the crucial current-induced magnetic-field-free in-plane magnetization reversal is experimentally demonstrated in CoFeB/CuOx bilayers without any heavy elements. We show that the critical current density can be comparable to that of strong spin-orbit coupling systems with heavy metals (Pt and Ta) and that the magnetization reversal mechanism is governed by coherent rotation in the grains through the second-harmonic and magneto-optical Kerr effect measurements. Our results indicate that light metal oxides can play an equally important role as heavy metals in magnetization reversal, broadening the choice of materials for engineering spintronic devices.

Aluminide diffusion coatings for improving the pesting behavior of refractory metals

Refractory metal based alloys show great potential as structural materials for high-temperature applications due to their high melting points, but they are prone to catastrophic oxidation at around ▪. The effectiveness of aluminium diffusion coatings on the oxidation resistance of pure molybdenum, niobium, tantalum, and tungsten was investigated. Homogeneous diffusion layers of Al-rich intermetallic phases were formed on all four refractory metals after pack cementation. Thermodynamic calculations and experimental assessments (e.g., of the activator) determined the most suitable conditions for the pack cementations. Subsequent thermogravimetric analysis of the uncoated and coated samples at ▪ and ▪ for up to ▪ in dry synthetic air was used to determine the protective effect of the coatings and investigate the underlying oxidation mechanisms. Optical and electron microscopy, EPMA, XRD and Raman spectroscopy were used to investigate the diffusion layers and the oxide scales. For two refractory metals (Mo and Ta) the aluminization resulted in an improved oxidation behavior and a substantially decreased oxide growth rate compared to uncoated substrates.

Obtaining and application of high-pure tantalum and ruthenium

The results of systematic research on the complex refining of refractory metals Ta and Ru, and some applications of these are represented. Methods of electron beam melting, zone recrystallization and zone recrystallization in combination with electrotransport in high vacuum were mainly used for the refining of these metals. Refining of tantalum and ruthenium based on the use of complementary physical methods and use high vacuum technology, achieves the high degrees of purification and obtaining metals in its pure form: Ta – 99,999 wt.%; Ru > 99.99 wt.%.

Synergistic effect on silicon surface under low energy he ion irradiation at elevated temperatures

One of the major challenges in nuclear fusion, nanolithography, and various industries is the effect of low energy ion irradiation on the surface morphology of materials. For example, the effect of low energy irradiation on plasma-facing materials' lifetime in fusion reactors, the effect on the optical systems in nanolithography laser produced plasma devices, and the effect on mass production of effective and flexible anti-reflecting coatings in photovoltaic (PV) industry. Silicon and carbides in particular, showed interest in nuclear fusion as potential wall materials, as in mirror designs for nanolithography devices, and as coatings in PV system components. Recently innovative novel Si nanostructures such as nanocones (NCs) demonstrated great feasibility in several areas including the next generation PV cells, batteries, supercapacitors, nano-optoelectronics, photonics, and energy storage devices. Their unique electronic properties and significantly higher absorption over a wide broadband range, offer paramount potential in various fields including microelectronics, optoelectronics, photonics, photovoltaics, biology, sensors, templet for selective growth (on nanostructured substrates), fast electronic devices, and even in high- density data storage. We tailor Si NCs using simultaneous low energy helium (He) ion irradiation on planar Si (111) and (100) and Ta metal masks. In a series of successive experiments, three key parameters, temperature, flux, and presence of Ta metal impurity, were tuned to study the progression of nanostructure development, as well as the effect of these nanostructures on key material properties. Before performing He ion sputtering experiments, 100 eV Ar+ ion irradiations, for 10 min duration, were also performed in-situ in each case for removing any preexisting SiO2 form planer Si substrates. Clear and distinctive progressions of NC development were found during the tuning of each parameter. During the temperature dependent studies, we clearly observed a sequential progression from thicker and less dense cones (773 K) to finer and more densely packed NCs (1073 K). On the other hand, during the case of flux dependent studies, it was found that increasing flux increases the size of the NCs, with low flux resulting in sparsely placed nanodots, and high fluxes resulting in large conglomerates. Finally, the effect of Ta impurity shows an increased propensity for NCs development. In addition, using optical-reflectivity studies we clearly observed a significant reduction (from ∼65 to almost zero) in optical reflectivity.

Critical metals distribution in the late Triassic–early Jurassic Nasr-Abad bauxite deposit, Irano–Himalayan karst bauxite belt, NW Iran

In the late Triassic–early Jurassic Nasr-Abad deposit, bauxite ores are bauxitic iron ore and Fe-rich bauxite, grading into bauxite and clayey bauxite upward the succession. The ores mainly consist of a mineral assemblage of diaspore, hematite, kaolinite, and rutile. Conservative elemental ratios of provenance, such as Eu/Eu*, Sm/Nd, and Nb/Ta, suggest a derivation from a mafic protolith, although, in some cases, the Eu/Eu* ratio indicates a felsic protolith, probably derived from Precambrian rock units. R-mode factor analysis indicates that most of the variance of the dataset is explained by a factor related to climatic and redox paleo-environmental conditions. This factor, which controls some critical metals, such as Co, V, and LREE, accounts for the competition between SiO2 and the Fe2O3 + P2O5 pool. The second factor is related to the accumulation of Al and Ti (oxyhydr)oxides, and low-solubility critical metals, such as Ga, Nb, Hf, and Ta, during late stages of bauxitization under dry conditions. The Nasr-Abad bauxite ores are remarkably enriched in critical metals Ti, Nb, Ta, V, and Co with respect to the average Upper Continental Crust. Among these, Ti, Nb, and Ta are particularly enriched in the uppermost Al-rich bauxite and clayey bauxite ores, whereas V and Co are particularly enriched in the bauxitic iron ores.

Understanding the Role of Underlying Substrates on Hydrogen Evolution Reaction (HER) Catalytic Activity of Atomically Dispersed Pt Atoms

Electrochemical water splitting is an environmentally friendly way of producing hydrogen, but this process requires highly efficient catalysts. Platinum (Pt) is known the best catalyst for hydrogen evolution reaction (HER) in acidic media, but the scarcity and high cost of Pt limits its applicability in widespread technologies. In this work, we have uncovered the role of underlying substrate on the HER activity of atomically dispersed Pt atoms. A DC magnetron sputtering technique has been utilized to deposit transition metal (Cu, Mo, W, Ti and Ta) thin films as underlying substrates for atomically dispersed and extremely low loading of Pt (< 1.5 at%). As synthesized samples were characterized as electrocatalysts for the HER in both alkali and acidic media. In combination of standard electrochemical experiments (e.g., CV), the differential electrochemical mass spectrometry (DEMS) results show that despite low loading of Pt, the prepared catalysts produce hydrogen at a rate comparable with that of a pristine Pt. Based on the XPS study, the excellent performance is attributed to the modified electronic properties of the Pt atoms due to interaction with underlying substrates. Additionally, the performance of the Pt atoms is significantly governed by the physical properties of underlying substances. Our catalysts also displayed good stability for HER activity and found to be stable after 1000 cycles of continuous operation.

Shed light on new growth pattern in rapid solidified Ta metal: MD simulation, DFT calculation and CALYPSO search

Aiming at the micro-structures of rapid solidified Ta system under cooling rate of 1×1010 K/s, the lowest-energy and meta-stable geometric structure of Tan (n = 19–30) clusters are systematically investigated via MD simulation, DFT calculation and CALYPSO search. It is revealed that the ground-state geometric structure of free Ta clusters plays a significant role in determining its solidified atomic structures and evolution laws in the early stage of nucleation. We explained why the hexagonal close packed (hcp) atomic clusters (Ta22) dominate the solid state of Ta when cooled at a rate of 1 × 1010 K/s. And found that the coexistence of slightly distorted icosahedral (Ta13) and hcp clusters (Ta22) at 300 K is due to the high energy stability of free Ta26–C2v (B) cluster. The larger size of Ta clusters with a perfect closed-shell geometric structure plays a key role in energetic effects, as demonstrated by their thermodynamic stability in terms of binding energy. Additionally, electronic structure stability is achieved when there are fewer electrons on the Fermi level (N(EF)), resulting in Ta atomic clusters that exhibit higher energetic stability and lower chemical activity. Our analysis of the interaction between different atoms in Ta clusters revealed that stronger electronic interactions of central(c)-central(c) and central(c)-shell(s) atoms contribute to the higher energy and chemical stability. Finally, we provide insights into understanding the growth patterns of nucleation in liquid metals through an examination of geometric and electronic structures of free Ta cluster.

A DFT study to investigate the physical, electrical, optical properties and thermodynamic functions of boron nanoclusters (MxB2n0; x=1,2, n=3,4,5)

First Principle DFT calculations employing the B3LYP/LanL2DZ/SDD level of theory were used to analyze the various characteristics of boron nanoclusters (B6, B8, and B10). These pure structures were further doped with four transition metals (Ta, Ti, Tc, and V) to examine the enhancement of the pure structures' structural, electrical, and optical features. To study structural stability, we have estimated cohesion energy and imaginary frequencies. Cohesion energies were entirely negative, with a range of −3.37 eV to −8.07 eV, and most constructions had no imaginary frequencies, indicating their structural occurrences. The calculated adsorption energy suggests that the order of stability of the pristine boron nanoclusters is B10>B8>B6, and TcB10 and Tc2B10 are the more stable structures. Mulliken charge, DOS, HOMO-LUMO, and the HOMO-LUMO gap have all been examined in-depth to provide insight into electrical characteristics. UV–Vis and CD measurements show the doped boron nanoclusters have excellent optical properties. Aside from calculating thermodynamic functions, we have also calculated the global DFT parameters, which give us a deep quantum mechanical understanding of the optimized structure for further research and applications in the field of science and technology.

Rare-metal Be–Nb–Ta mineralisation by pegmatite remelting: Insights from Dakalasu deposit in the Chinese Altai orogenic belt

The rare metals Li, Be, Cs, Nb and Ta are mainly extracted from pegmatite deposits that may have formed through extensive fractional crystallisation or local partial melting of crustal rocks. There are a large number of rare-metal pegmatites that formed through crustal melting in the Chinese Altai, but what controls rare-metal enrichment remains enigmatic. Here, a new columbite UPb age of pegmatite mineralisation (247 ± 1 Ma) that is distinct from the ages of surrounding biotite granites (290–270 Ma) in the Dakalasu Be–Nb–Ta deposit in the Altai is reported. Zircon from the border zone with a medium to coarse-grained graphic texture of pegmatite yields two age groups: 290–270 Ma and 249 ± 7 Ma, corresponding to the age of biotite granite and the mineralisation age of pegmatite, respectively. The consistent age of the older group and biotite granite (290–270 Ma) and the elevated εHf(t) ratios and lower Nb/Ta ratios of pegmatite suggest that pegmatite is the end member of biotite granite after fractional crystallisation. The similar age of the younger group and mineralisation, the myrmekitic texture and albite trace elements of pegmatite imply pegmatite remelting and mineralisation occurred at ∼250 Ma. Our modelling agrees with geochronology, petrology and geochemistry that Be–Nb–Ta pegmatite mineralisation requires two melting events. The first step with anatexis of metasedimentary rocks generated biotite granitic melts whose extensive fractional crystallisation generated pegmatite with preliminary Be–Nb–Ta enrichment. The second step with pegmatite remelting (<5% degree) generated the significant enrichments of Be, Nb and Ta, which are sufficient for beryl and columbite crystallisation. The Be–Nb–Ta mineralisation mechanism through pegmatite remelting is likely common in orogenic belts with high-grade metamorphism and, therefore, should be considered in future explorations.

Catalytic upgrading of bio-oil model mixtures in the presence of microporous HZSM-5 and γ-Al2O3 based Ni, Ta and Zr catalysts

Bio-fuel production from bio-oil was investigated in the presence of microporous HZSM-5 and Al2O3 (MA) based catalysts. This study focused on the catalytic upgrading of a model bio-oil compound with ethanol for bio-fuel production. The model compound containing hydroxypropanol/furfural/formic acid: 4/6.5/5 by volume was used as a bio-oil mixture. Activity tests were performed under atmospheric pressure with a volumetric feed ratio of 30/70 bio-oil mixture/ethanol using a 0.5 g catalyst. In the reaction studies performed on the commercial microporous HZSM-5 catalyst, the optimum co-cracking temperature was determined as 400 °C. Mesoporous γ-Al2O3 support was synthesized by the evaporation-induced self-assembly (EISA) synthesis method, and Ni, Ta, and Zr metals were incorporated into the structure of the catalyst by the impregnation method to improve the surface acidity. The synthesized catalysts were characterized by X-ray diffraction (XRD), X-ray absorption near edge spectroscopy (XANES), N2 adsorption–desorption, scanning electron microscopy energy dispersive spectroscopy (SEM/EDS), X-ray fluorescence (XRF), Fourier-transformed infrared spectroscopy (FTIR), pyridine adsorbed diffuse reflectance FTIR spectroscopy (DRIFTS), and thermogravimetric/differential thermal analysis (TGA-DTA). Monometallic and pure alumina catalysts indicated an ordered mesoporous structure with surface area values 106–389 m2/g. Lewis and Brønsted acid sites associated with mild acidity were observed in the DRIFTS results of the 10 wt% Zr-containing alumina catalyst (10Zr@MA). The highest oil phase selectivity and isoparaffin selectivity in oil phase values were obtained in the presence of 10Zr@MA as 17.22% and 80.96%, respectively. 10Zr@MA catalyst showed the best catalytic activity compared to other catalysts, with 9.54% coke formation.

Resistive switching behaviors of oxygen-rich TaOx films prepared by reactive magnetron sputtering

ABSTRACT In this work, Ta2O5 films were first deposited on Si substrates by reactive magnetron sputtering of a Ta metal target at various substrate temperatures, RF powers and sputtering pressures. The crystal characteristics of these films can be effectively tailored by controlling the sputtering process. Based on the optimized process parameters, tantalum oxide (TaOx) films with different oxygen component content were sputtered on ITO buffered Si substrates and comparatively investigated. The results show that the film with Ta/TaOx/ITO structure has a resistance switching (RS) behavior and its conduction mechanism is closely related to the O2-/O concentration related to the oxygen partial pressure at the dielectric layer and electrode interface. This study provides an in-depth understanding of the component/structure design and structure-activity relationship for high-performance TaOx-based resistive memory.

Predicting properties of high entropy carbides from their respective binaries

Using Density Functional Theory calculations, this paper addresses two questions: (1) to what degree can the properties of high entropy carbides created by equi-molar combinations of five of the set of eight refractory metals Hf, Nb, Mo, Ta, Ti, V, W, and Zr be predicted from their respective binary compounds, and (2) can empirical relationships from properties of the binary compounds be used to predict phase stability for these materials. For the former question, it is found that lattice constant, binding energy and bulk modulus are well approximated by binary carbide averages, but carbon vacancy formation energies are less predictable. To address the second question, correlations are explored between binary properties and the entropy forming ability (EFA) of all 56 possible five-element combinations of the eight refractory elements. Significant correlations are not found between cohesive energies or lattice constants of the binary constituents of each composition and that composition’s EFA, but there is a correlation between EFA and the standard deviation of the distribution of bulk moduli of the constituent binaries.

In Situ Reactive Formation of Mixed Oxides in Additively Manufactured Cobalt Alloy.

Oxide-dispersion-strengthened (ODS) alloys have long been considered for high temperature turbine, spacecraft, and nuclear reactor components due to their high temperature strength and radiation resistance. Conventional synthesis approaches of ODS alloys involve ball milling of powders and consolidation. In this work, a process-synergistic approach is used to introduce oxide particles during laser powder bed fusion (LPBF). Chromium (III) oxide (Cr2O3) powders are blended with a cobalt-based alloy, Mar-M 509, and exposed to laser irradiation, resulting in reduction-oxidation reactions involving metal (Ta, Ti, Zr) ions from the metal matrix to form mixed oxides of increased thermodynamic stability. A microstructure analysis indicates the formation of nanoscale spherical mixed oxide particles as well as large agglomerates with internal cracks. Chemical analyses confirm the presence of Ta, Ti, and Zr in agglomerated oxides, but primarily Zr in the nanoscale oxides. Mechanical testing reveals that agglomerate particle cracking is detrimental to tensile ductility compared to the base alloy, suggesting the need for improved processing methods to break up oxide particle clusters and promote their uniform dispersion during laser exposure.

Friction and wear behaviors of Ta-based nanocrystalline composite coating under extreme sliding conditions

Although a great interest of researchers is focused on Tantalum (Ta) due to its unique physicochemical properties, the tribological investigation on Ta-based materials has been rarely reported. In this work, the friction and wear behaviors of a Ta-based nanocrystalline composite coating fabricated by plasma spray were studied under extreme sliding conditions via a SRV friction tester and an extremely low wear rate (4.14 × 10−8 mm3/N·m) was achieved under extreme friction condition (i.e., reciprocating friction at 50 N and 60 Hz with hard Al2O3 ball as the counterpart). The results show that with the increase of the severity of test condition, the dominant wear mechanism of the coating gradually changed from mild abrasive wear to fatigue wear, and then to noteworthy plastic deformation and a special delamination wear, which is characterized by the peeling of the whole thermal sprayed splat along its formation boundary and occurred under the most extreme sliding condition (100 N, 120 Hz) investigated. However, under the same extreme test conditions the Ta-based coating with high hardness and toughness (as well as the superb ductility of metal Ta) revealed much improved anti-wear and friction reducing performance than the widely-used hard chromium (Cr) coating. Furthermore, three factors related to the Ta-based coating, namely, the slightly higher content of oxides, the enhancement of (110) plane preferred orientation of α-Ta, and the increased ordering degree of amorphous carbon tribofilm generated at the sliding surfaces, seem to have some correlation with its better tribological behaviors under extreme conditions. This research provides a reference and basis for the application of Ta-based coating under harsh operating situation.

Separation Performance of Membranes Containing Ultrathin Surface Coating of Metal-Polyphenol Network.

Metal-polyphenol networks (MPNs) are being used as versatile coatings for regulating membrane surface chemistry and for the formation of thin separation layers. The intrinsic nature of plant polyphenols and their coordination with transition metal ions provide a green synthesis procedure of thin films, which enhance membrane hydrophilicity and fouling resistance. MPNs have been used to fabricate tailorable coating layers for high-performance membranes desirable for a wide range of applications. Here, we present the recent progress of the use of MPNs in membrane materials and processes with a special focus on the important roles of tannic acid-metal ion (TA-Mn+) coordination for thin film formation. This review introduces the most recent advances in the fabrication techniques and the application areas of TA-Mn+ containing membranes. In addition, this paper outlines the latest research progress of the TA-metal ion containing membranes and summarizes the role of MPNs in membrane performance. The impact of fabrication parameters, as well as the stability of the synthesized films, is discussed. Finally, the remaining challenges that the field still faces and potential future opportunities are illustrated.

First-principles calculations for the effect of energetic point defect formation on electronic properties of the Weyl MX family (M = Nb, Ta; X = P, As)

• The unfolding technique was used for the first time to highlight the impact of point defects on the electronic band structure. • The transition metal Nb and Ta vacancies are energetically nearer to stability in the cases of NbAs and TaAs. • The pnictide P vacancy is energetically favorable among four possible point defects in both NbP and TaP. • For TaAs, the Ta vacancy concentration is significantly higher than all other types of defect concentrations. • All four of these compounds are thermodynamically, dynamically, and mechanically stable. By the first-principles of the density functional theory (DFT) approach, the structural parameters, elastic, vibrational, electronic properties, and enthalpies of formation of four stoichiometric Weyl semimetal compounds were evaluated. Besides, we calculated point defect formation energies and electronic band structures of defect-containing supercells by using an unfolding technique to highlight the effects of point defects (vacancies and anti-sites) on Weyl points in the electronic structure of these compounds. The transition metal Nb and Ta vacancies are energetically nearer to stability in the cases of NbAs and TaAs, but the pnictide P vacancy is energetically favorable among four possible point defects in both NbP and TaP. The band structure results, obtained from the unfold method, agree with defect formation energies at the ground state. Moreover, a true and accurate description of defects is based on the well-ordered compounds (NbAs, TaAs, NbP, and TaP). A relationship between temperature (K based on defect formation energies) and defect concentrations for these Weyl compounds was derived. In particular, for TaAs, the Ta vacancy concentration is significantly higher than all other types of defect concentrations.

Chemical Influence of Carbon Interface Layers in Metal/Oxide Resistive Switches.

Thin layers introduced between a metal electrode and a solid electrolyte can significantly alter the transport of mass and charge at the interfaces and influence the rate of electrode reactions. C films embedded in functional materials can change the chemical properties of the host, thereby altering the functionality of the whole device. Using X-ray spectroscopies, here we demonstrate that the chemical and electronic structures in a representative redox-based resistive switching (RS) system, Ta2O5/Ta, can be tuned by inserting a graphene or ultrathin amorphous C layer. The results of the orbitalwise analyses of synchrotron Ta L3-edge, C K-edge, and O K-edge X-ray absorption spectroscopy showed that the C layers between Ta2O5 and Ta are significantly oxidized to form COx and, at the same time, oxidize the Ta layers with different degrees of oxidation depending on the distance: full oxidation at the nearest 5 nm Ta and partial oxidation in the next 15 nm Ta. The depth-resolved information on the electronic structure for each layer further revealed a significant modification of the band alignments due to C insertion. Full oxidation of the Ta metal near the C interlayer suggests that the oxygen-vacancy-related valence change memory mechanism for the RS can be suppressed, thereby changing the RS functionalities fundamentally. The knowledge on the origin of C-enhanced surfaces can be applied to other metal/oxide interfaces and used for the advanced design of memristive devices.