Ta Metal Research Articles

Tantalum oxide and nitride spectral features from a laser-produced plasma

We report measurements of time-resolved Ta, TaO and TaN emission spectroscopic signatures from a laser-produced plasma. Plasmas were generated using 1064 nm, 6 ns pulses from an Nd:YAG laser focused onto a pure Ta metal target in a gaseous environment with varying percentages of O2/N2 for controlling gas-phase oxidation/plasma chemistry. Time-resolved analysis showed that Ta oxide emission is prominent at later times in plasma evolution, whereas strong atomic emission is present at early times in air. Emission spectral features as a function of O2 partial pressure showed that TaO emission intensity increases, while the peak intensity of TaO appears earlier with increasing O2 availability. We also report emission spectra of TaN, and show that plasma chemistry favors TaO formation instead of TaN when O2 is present in the environment.

Relative importance of magmatic and hydrothermal processes for economic Nb-Ta-W-Sn mineralization in a peraluminous granite system: The Zhaojinggou rare-metal deposit, northern China

Highly evolved granitic melts typically experience late-stage melt-melt and fluid-melt immiscibility as well as fluid-melt and fluid-rock interaction. These processes are particularly important in the formation of deposits of the rare metals Nb, Ta, W, and Sn. We document the relation between immiscibility and alteration processes and the partitioning behavior of rare metals for the Zhaojinggou rare-metal deposit of northern China. This deposit shows a systematic change from a magmatic to a hydrothermal system, including the reaction of the exsolved fluid with earlier crystallized granite and the formation of late-stage quartz veins. The magmatic stage (Stage I) includes biotite alkali-feldspar granite (BAG) with moderate Nb-Ta mineralization. Extreme fractional crystallization of BAG eventually resulted in melt-melt immiscibility and the separation of a hydrosaline melt. Fractional crystallization of this hydrosaline albite granite (AG) melt finally exsolved a magmatic fluid. Therefore, the magmatic-hydrothermal transition (Stage II) includes a melt-dominated Stage IIa with strong Nb-Ta-Sn mineralization in AG and a fluid-dominated Stage IIb with minor Nb-Ta-Sn mineralization in muscovite and biotite greisen. Late hydrothermal processes (Stage III) formed quartz veins with important W mineralization. There are several texturally and chemically distinct generations of cassiterite and columbite-group minerals (CGM) in BAG and AG reflecting crystallization from an evolving magma. The porous and patchy-zoned reaction rims of tantalite-(Mn) and wodginite on CGM in AG are the result of fluid-melt interaction. Texture and compositions show that wolframite in AG is hydrothermal and formed through interaction of early exsolved magmatic fluids with the host granite. CGM and cassiterite in the biotite greisen and Ta-rutile in the muscovite greisen, as well as wolframite and scheelite in quartz veins that formed when fluid-rock interaction reduced the availability of H+ or F− or the temperature of the fluid decreased. The distribution and importance of mineralization demonstrate that Nb, Ta, W, and Sn strongly partitioned into the hydrosaline melt during melt-melt immiscibility and that W partitioned into the magmatic fluid during fluid-melt immiscibility. Exsolved magmatic fluids interacted with earlier crystallized rocks mobilizing rare (Nb, Ta, and Sn) and base (Fe and Ti) metals from Li-Fe mica, providing the ore elements for subordinate Nb-Ta-Sn mineralization in AG and in biotite and muscovite greisen. Thus, magmatic processes (with later metal redistribution by magmatic fluids) dominantly control economic Nb-Ta-Sn mineralization, whereas hydrothermal processes mainly control the formation of economic W mineralization.

Mineral Characteristics and the Mineralization of Leptynite-Type Nb–Ta Ore Deposit in the Western Qilian Orogenic Belt

A large Nb–Ta ore deposit was found in the Yushishan leptynite in the west Qilian Orogenic Belt (QOB). Based on a field geological survey and using a Mineral Liberation Analyser (MLA, including scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS)) methods, eight Nb minerals (fergusonite, polycrase, columbite, Nb-rutile, aeschynite, pyrochlore, microlite, and ilmenorutile) were found to occur in the leptynite. This accounted for approximately 69% of Nb, with fergusonite, polycrase, and columbite being the dominant phases. The other 17.90% Nb as a minor element was dispersed in titanium magnetite–maghemite, and another 13.00% Nb was dispersed in gangue minerals. Nb minerals are formed mainly by two metallogenesis stages. The first stage is magmatic genesis to form four Nb minerals, euhedral-subhedral fergusonite, polycrase, pyrochlore, and microlite, which are crystallized within or between primary minerals, such as quartz and feldspar. Late alteration phenomena are locally observed. The second stage is the hydrothermal genesis of columbite, anhedral fergusonite, Nb-rutile, and aeschynite, which are dispersed in the fissures of the wall rocks as irregular veins and lump assemblages. Meanwhile, they are closely associated with metasomatic chlorite, albite, and secondary quartz. Furthermore, direct metasomatism among different Nb minerals is also found at the local scale. The Nb percentage of these two Nb mineral mineralization types is approximately equal, which reflects two main mineralizing periods. The first stage of mineralization occurred in the Neoproterozoic Era (834–790 Ma). Magmatism of this period produced early niobium and formed fergusonite, polycrase, pyrochlore, microlite, and zircon. The initial enrichment of Nb, Ta, and other rare metals occurred during this stage. The second stage of mineralization occurred in the Caledonian period (490–455 Ma). Large-scale and intense tectonic–magmatic thermal events occurred in the western part of the QOB due to the plate subduction and convergence (510–450 Ma). Hydrothermal activity in this period formed columbite, fergusonite, Nb-rutile, and aeschynite. Moreover, rare metal elements in the Nb-bearing rocks activated and migrated at short distances, forming in situ Nb–Ta-rich ore deposits.

Effects of refractory metal additives on diboride‐based ultra‐high temperature ceramics: A review

AbstractDiboride‐based ultra‐high temperature ceramics (UHTCs) are a special class of ceramics with excellent comprehensive properties, which have extensive potential applications in extreme environments. However, their practical applications are limited, mainly due to the poor fracture toughness and thermal shock resistance. Refractory metals have high melting points, good ductility, and high toughness, which have huge potential to improve the properties of diboride‐based ceramics. As a special class of additives, they have been adopted to promote densification, improve microstructure, and properties. However, diboride‐based ceramics containing refractory metals have not received adequate attention due to relatively weak practical effects on property improvement. The present review highlights the progress and existing problems of transition metal diborides with refractory metal additives, including W, Ta, Mo, Nb, Hf, V, Cr, and Zr, focusing mainly on the microstructure change and property improvements, followed by challenges and possible future development strategies.

Two-Level 3D Column-like Nanofilms with Hexagonally-Packed Tantalum Fabricated via Anodizing of Al/Nb and Al/Ta Layers-A Potential Nano-Optical Biosensor.

Reanodizing metal underlayers through porous anodic alumina has already been used extensively to fabricate ordered columns of different metal oxides. Here, we present similar 3D multilayered nanostructures with unprecedented complexity. Two-level 3D column-like nanofilms have been synthesized by anodizing an Al/Nb metal layer in aqueous oxalic acid for forming the first level, and an Al/Ta layer in aqueous tartaric acid for forming the second level of the structure. Both levels were then reanodized in aqueous boric acid. The Ta layer deposited on partially dissolved porous anodic alumina of the first level, with protruding tops of niobia columns, acquired a unique hexagonally-packed structure. The morphology of the first and second levels was determined using scanning electron microscopy. Prolonged etching for 24 h in a 50%wt aqueous phosphoric acid was used to remove the porous anodic alumina. The formation mechanism of aluminum phosphates on the second-level columns in the process of long-time cold etching is considered. The model for the growth of columns on a Ta hexagonally-packed structure of the second level is proposed and described. The described approach can be applied to create 3D two- or three-level column-like systems from various valve metals (Ta, Nb, W, Hf, V, Ti), their combinations and alloys, with adjustable column sizes and scaling. The results of optical simulation show a high sensitivity of two-level column-like 3D nanofilms to biomedical objects and liquids. Among potential applications of these two-level column-like 3D nanofilms are photonic crystals for full-color displays, chemical sensors and biosensor, solar cells and thermoresponsive shape memory polymers.

Research progress and clinical translation of three-dimensional printed porous tantalum in orthopaedics.

With continuous developments in additive manufacturing technology, tantalum (Ta) metal has been manufactured into orthopaedic implants with a variety of forms, properties and uses by three-dimensional printing. Based on extensive research in recent years, the design, processing and performance aspects of this new orthopaedic implant material have been greatly improved. Besides the bionic porous structure and mechanical characteristics that are similar to human bone tissue, porous tantalum is considered to be a viable bone repair material due to its outstanding corrosion resistance, biocompatibility, bone integration and bone conductivity. Numerous in vitro, in vivo, and clinical studies have been carried out in order to analyse the safety and efficacy of these implants in orthopaedic applications. This study reviews the most recent advances in manufacturing, characteristics and clinical application of porous tantalum materials.

Assessment of Selected Metals in Onion Bulbs and Leaves Collected from Samaru Market, Zaria, Kaduna State, Nigeria

This study examined the levels of metals (Mg, Al, Si, P, S, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Zr, Nb, Mo, Ag, Sn, Sb, Ta, Pt, Au, Pb, and Bi) in onion bulbs and leaves in light of the latent toxicity, unsolvable character, and snowballing behaviour of heavy metals. The onion bulbs and leaves were randomly selected from the Samaru market chopped, dried, and ground into a powder for X-Ray Fluorescence Spectrometer (XRF) measurement. Except for concentrations of Si, Ti, Zr, and Ag, with the value of 9.996, 4.051, 2.047 and 2.082 mg/kg in the onion bulbs and 20.23, 5.861, 1.175 and 1.538 mg/kg in the onion leaves respectively, which were higher than the permissible level of 0.800, 0.530, 0.000005 and 0.014 respectively, all the metals analysed were at or below the World Health Organization's (WHO) permissible limit. The findings generally indicated that Si, Ti, Zr, and Ag poisoning could result from eating onion bulbs and leaves from the Samaru market due to the Si, Ti, Zr, and Ag health risks. To avoid metal poisoning and subsequent bioaccumulation of the metal in the systems of consumers and the ecosystem at large, there is a need for a quarterly examination of the metal content in the onion bulb and onion leaf in the Samaru market.

Quantitative determination of heavy metals around schools and automobile workshops near frequented roads in Kaduna State, Nigeria

Heavy metals are metallic elements with high density compared to other metals and are toxic even at minute concentrations. The concentration of these metals around schools and automobile workshops near frequented roads in Kaduna State, Nigeria, was reported in the present work. Soil samples were collected at varying distances from the major roads (0 – 10m) and at different depths (0 – 60cm). The elemental composition of the samples was determined using Next-Generation Cartesian Geometry Energy Dispersive X-Ray Fluorescence Spectrometer (NEX CG EDXRF) and the statistical correlation and clustering analysis were carried out using SPSS and Mini tab, respectively. The heavy metals Sn, Hf, Ta, V, Cr, Zn, Ir, Pt, Au, Mn, Fe, Co, Ni, Cu, Pb, Th, Ga, As, U, and Zr were considered in the analysis, and their concentrations were presented as Average ± standard deviation. Pearson correlation coefficient indicated different levels of relationships among the heavy metals, while Clustering analysis grouped the soil samples into three major clusters, further confirming the interrelationship among the samples. The concentrations of As, Pb, Cd, Co, Ni were found to be of serious health concern, considering that in almost all the zones in Kaduna state, their average concentrations were greater than the threshold provided by WHO/FAO. Findings from this study indicated that it is unsafe for children to play near schools /auto-mechanic workshops located along highways.

Effect of off-stoichiometry and Ta doping on Fe-rich (Mn,Fe)2(P,Si) based giant magnetocaloric materials

The influence of off-stoichiometry and of doping with the 5d transition metal Ta has been studied in the quaternary (Mn,Fe)2(P,Si)-based compound, which is one of the most promising materials systems for magnetic refrigeration. It is found that Ta substitution can decrease the transition temperature Ttr, while the thermal hysteresis ∆Thys remains about constant. A low Ta doping enhances the magnetocaloric effect (MCE). For Mn0.6Fe1.27-yTayP0.64Si0.36 with y = 0.01 the magnetic entropy change ∆Sm shows and enhancement of 30.7% compared to the undoped material for a low magnetic field change of 1 T. The occupancy of substitutional Ta atoms is determined by XRD and DFT calculations. The Ttr shift and enhanced MCE upon Ta doping are ascribed to the competition between a weakening of the magnetic exchange interactions and a strengthening of the hybridization. Our studies provide a good strategy to further optimize the MCE of this material family.

Preparation and characterization of Ta and monovalent alkali metals (Li, Na, K) co-doping on Sr11Mo4O23 electrolyte for solid oxide fuel cells

Double perovskite-type Sr11Mo4O23 material exhibits unusual structural flexibility and oxygen ion mobility. However, the transition of Sr11Mo4O23 cubic phase to SrMoO4 tetragonal phase around 400 ℃ makes the conductivity drop by 45.8 %. Hence, it is necessary to stabilize the phase structure and improve the electrochemical performance of Sr11Mo4O23 in order to be used for implementing into intermediate temperature solid oxide fuel cells (IT-SOFCs). In this work, a novel Sr10.8A0.2Mo3.5Ta0.5O23-δ (A =Li, Na, K) electrolyte powders are synthesized by a citrate-nitrate combustion method. X-ray diffraction, scanning electron microscopy and electrochemical impedance spectroscopy are used to investigate the effects of acceptor-type Ta and alkali metals co-doping on phase structural, microstructure and electrical properties of Sr11Mo4O23. All Sr10.8A0.2Mo3.5Ta0.5O23-δ samples show the same single phases as Sr11Mo4O23 (Fdm space group, JCPDS 27-1441). Doping Ta element at the B-site of Sr11Mo4O23 can inhibit the phase transition of Sr11Mo4O23 to SrMoO4 so as to improve the structure stability of Sr11Mo4O23. On this basis, doping alkali metal at the A-site further enhances the electrical conductivity of Sr11Mo3.5Ta0.5O23-δ(SMTO). Among them, Sr10.8K0.2Mo3.5Ta0.5O23-δ (SKMTO) sample has the conductivity of 2.02 × 10−2 S/cm in the air at 800 ℃, which is ∼ 233 % higher than that measured for Sr11Mo4O23. Moreover, the reliable chemistry stability of the SKMTO samples was demonstrated under wet reducing 5 % H2 or dry 3 % CO2 atmospheres, respectively. Finally, the single cells with SKMTO and SMTO electrolytes supported were successfully prepared by screen-printing method, respectively. The power density of SKMTO-cell is improved by at least 254 % compared to SMTO-cell. It can be deduced that co-doped Sr10.8K0.2Mo3.5Ta0.5O23-δ can be considered as potential electrolyte for IT-SOFCs.

Specific Heat and Electrical Resistance of Metals Ta and W from the Melting Point to 7000 K under Pulsed Current Heating

Specific Heat and Electrical Resistance of Metals Ta and W from the Melting Point to 7000 K under Pulsed Current Heating

Corrosion of metal parts on satellites by iodine exposure in space

Iodine becomes increasingly popular as alternative propellant for electric propulsion (EP) systems offering several advantages over established xenon. However, iodine is also a reactive and corrosive element. Thus, a careful material selection for the EP system itself, but also for components employed on the satellite is required in the light of typical space mission durations of several years. Here, we carefully define an approach for mimicking long-term interaction of material specimens with iodine in a space environment. The space conditions cover typical iodine atmospheres (10− 1 to 10− 4 Pa), which occur in the vicinity of a satellite employing an iodine-fed EP system, and exposure times, which correspond to 10 years of mission duration. The approach is used to expose a wide range of metal specimens commonly used on spacecraft to iodine. Chemical modifications of the surfaces of the treated samples are analyzed by x-ray photoelectron spectroscopy (XPS). The elemental metals Fe, Ti, Al, and Nb chemically react with iodine, whereas the elemental metals Ni, Cr, Ta, W, and Mo are basically inert. The stainless-steel and aluminum metal alloys show the same behavior as the corresponding dominant elemental specimens, i.e., Fe and Al, respectively. Somewhat surprisingly, Cr as constituent in stainless steel reacts with iodine, in contrast to elemental Cr. Nevertheless, our studies reveal that long-term exposure to low-pressure iodine atmospheres is not critical for the macroscopic structural integrity of all tested specimens even over space mission durations of several years. The reaction with iodine is macroscopically a surface effect, which mainly affects the optical appearance.

Critical element (Nb-Ta-Zr-Hf-REE-Ga-Th-U) mineralization in Late Triassic coals from the Gaosheng Mine, Sichuan Basin, southwestern China: Coupled effects of products of sediment-source-region erosion and acidic water infiltration

The Nb-Ta-Zr-Hf-REY-Ga mineralization in the Late Permian coals in southwestern China has been well investigated by several studies and has generally been attributed to alkaline pyroclastics coupled with input from hydrothermal fluids. The Late Triassic is one of the important coal-forming periods but the critical element mineralization in coals of this geological age has not been well documented. In this paper, the mechanism of Nb-Ta-Zr-Hf-REE-Ga-Th-U mineralization in the K5 coal seam of the Upper Triassic Xujiahe Formation from the Gaosheng Mine, Sichuan Basin, southwestern China, was investigated. The K5 coal is a high-ash, low-sulfur, and low-volatile bituminous coal. The minerals in this coal include illite, kaolinite, quartz, and, to a lesser extent, anatase, calcite, chamosite, bassanite, and pyrite, along with traces of ankerite, rutile, and zircon. Compared with the averages of common world hard coals, the studied coals are enriched in critical elements including Zr (247 ppm), Hf (5.56 ppm), Nb (23 ppm), Ta (1.55 ppm), rare earth elements and yttrium (REY, 168 ppm), Ga (18.3 ppm), Th (14.1 ppm), and U (6.18 ppm) (all on a whole coal basis). The Al2O3/TiO2 ratios, Eu anomalies, and the relationships of Al2O3/TiO2 vs. Zr/TiO2 and Nb/Yb suggest that the sediment-source rocks of the Gaosheng coals were Neoproterozoic and Early-Middle Triassic felsic-intermediate igneous rocks from the southeastern Qinling and Longmenshan Orogens, along with the Hannan and Micangshan-Dabashan Uplifts. Other probable sources are contemporaneous felsic-intermediate pyroclastics from the Late Triassic volcanic areas around the Sichuan Basin (i.e., East Kunlun Orogen, West Qinling Orogen, and East Tibetan Plateau). The relationships of Al2O3/TiO2 vs. Zr/Al2O3, Al2O3/TiO2 vs. Nb/Al2O3, Ga/Al2O3, and Al2O3/TiO2 vs. LREY/Al2O3 further indicate that the elevated concentrations of Nb(Ta)-Zr(Hf)-REY-Ga in the Gaosheng coal are probably sourced from both the erosion of sediment-source regions and contemporaneous pyroclastics. The illite-kaolinite aggregates with a vermicular texture and authigenic illite, quartz, anatase, pyrite, calcite, ankerite, barite, and REE-rich minerals, REY distribution patterns, as well as elemental variation trends of the coal seam, collectively indicate that the studied coals were likely influenced by multiple-stage infiltration of various solutions. These solutions leached the fresh pyroclastics and products of erosion derived from granites in the sediment-source regions, leading to redistribution of the critical elements (e.g., Zr, Nb, and HREY) between the roof, floor, and parting mudstones and the coal benches. The concentrations of (Nb,Ta)2O5, (Zr,Hf)2O5, and Ga in the coals are 107, 1093, and 57.6 ppm, respectively, close to or higher than the marginal grade of conventional ore deposits for these elements, and thus the Gaosheng coals have potential as raw materials for the recovery of the critical metals Nb, Ta, Zr, Hf, and Ga.

Ta(B, C, N) and (Ta, Mi)(B, C, N) (Mi = Nb, W) ceramics by high‐energy ball milling: processing and solution mechanisms

AbstractIn order to study the solid‐solution process between amorphous BCN and metal Ta, Ta(B, C, N), (Ta, Nb)(B, C, N), and (Ta, W)(B, C, N) ceramics were prepared by high‐energy ball milling, and their phase composition, microstructures, and binding bonds have been analyzed. The results show that all the three ceramics are hard agglomeration state, formed by stacking of nanoparticles. The mechanical alloying process is accompanied by the formation of chemical bonds, such as B–Ta, N–Ta, C–Ta, and O–Ta for Ta(B, C, N) ceramic, and the order of solid solution is C > N > B. When heated at 1500°C, a second diboride phase precipitates from (Ta, Nb)(B, C, N) ceramic, whereas the second phase of WC gradually dissolved from (Ta, W)(B, C, N) ceramic. This work provides theoretical and data supporting to analyze the solid‐solution process of Ta(B, C, N) ceramic.

Petrogenesis of Paleozoic–Early Mesozoic Granites and Pegmatites in the Yuechengling Pluton of South China

Abstract Although pegmatites are volumetrically minor in the upper continental crust, these rocks host abundant rare metal deposits (e.g., Li, Be, Rb, Ta, and Nb). Pegmatites can be formed either by extensive fractional crystallization of granitic magmas or by low-degree partial melting of metasedimentary rocks. The Mao’ershan–Yuechengling composite batholith in the Nanling Range in the South China Block (SCB) is of early Paleozoic–Triassic age (440–381 and 236–204 Ma, respectively). Recently, hundreds of pegmatites associated with Nb, Ta, Be, Rb, and Li mineralization have been identified in this batholith. These pegmatites are hosted by granitic wall rocks. However, the relationships between the pegmatites and granitic wall rocks are not well constrained. To address this, we investigated the Mao’antang (MAT) and Tongzuo (TZ) pegmatites and their biotite granite wall rocks in the middle part of the Yuechengling pluton. Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb ages revealed that the MAT pegmatites formed during the Permian (269 Ma) and Triassic (231 Ma) and that the MAT biotite granite wall rock records two stages of magmatic activity (271 and 231 Ma) that are coeval with the pegmatites. The TZ pegmatites probably formed during the Triassic (235 Ma), and the TZ biotite granite wall rock formed during the Silurian (435 Ma). The MAT biotite granite and pegmatites (εNdt=−12.0 to −10.6; εHft=−8.0 to −1.0), TZ pegmatites (εNdt=−10.4 to −6.1), and TZ biotite granites (εNdt=−9.1 to −8.7; εHft=−7.7 to −4.1) have enriched whole-rock Nd and zircon Hf isotopic compositions that are similar to those of early Paleozoic and Triassic S-type granites in the SCB. In addition, the whole-rock Pb isotopic compositions of the MAT and TZ pegmatites and granites are distributed along the upper crust evolution line. We suggest that the MAT and TZ biotite granites were mainly derived from Paleoproterozoic metasedimentary rocks in the middle crust. The MAT pegmatites are fractional crystallization products of the MAT biotite granites, whereas the TZ pegmatites were formed by fractional crystallization of hidden parental S-type granites. We propose that the MAT and TZ pegmatites have potential for rare metal (Nb, Ta, Be, and Li) mineralization, as they record high degrees of fractional crystallization. The MAT and TZ areas in the middle of the Yuechengling pluton are promising targets for rare metal exploration.

Cluster-type analogue memristor by engineering redox dynamics for high-performance neuromorphic computing

Memristors, or memristive devices, have attracted tremendous interest in neuromorphic hardware implementation. However, the high electric-field dependence in conventional filamentary memristors results in either digital-like conductance updates or gradual switching only in a limited dynamic range. Here, we address the switching parameter, the reduction probability of Ag cations in the switching medium, and ultimately demonstrate a cluster-type analogue memristor. Ti nanoclusters are embedded into densified amorphous Si for the following reasons: low standard reduction potential, thermodynamic miscibility with Si, and alloy formation with Ag. These Ti clusters effectively induce the electrochemical reduction activity of Ag cations and allow linear potentiation/depression in tandem with a large conductance range (~244) and long data retention (~99% at 1 hour). Moreover, according to the reduction potentials of incorporated metals (Pt, Ta, W, and Ti), the extent of linearity improvement is selectively tuneable. Image processing simulation proves that the Ti4.8%:a-Si device can fully function with high accuracy as an ideal synaptic model.

Characterisation of Electrochemical Properties for Molten Titanium(IV) Oxide - Sodium Oxide and Expansion into Other Binary Oxide Systems for the Electrolytic Reduction of Valuable Metals

Molten oxide electrolysis is a promising route to reduce harmful environmental effects that occur when compared to more common industrial metal extraction techniques. This method can provide a stepping stone to decarbonise metal production and to do this suitable supporting electrolyte ore combinations need to be found. For the application of extracting titanium metal, due to the lack of electrochemical information on complex multi-component titanium metal oxide systems, designing an electrolytic cell and predicting ultra-high temperature (above 1500°C) behaviours becomes difficult. Hence, to gain insight into this electrochemical information a binary system, TiO2 – Na2O, was investigated via experimentation and the use of FactSage 7.2 (a thermodynamic predictive software). This system was chosen as the phase diagram indicated deep eutectics either side of a congruently melting line compound situated at approximately 40 wt% TiO2, hence providing suitable operating temperature and composition ranges. Additionally, FactSage predicted that the relative potentials of the half-cell reactions 2Na2O → 4Na + O2 and TiO2 → Ti + O2, change order when the composition of TiO2 is increased from below the congruently melting line compound, to above, indicating that above approximate 40 wt% TiO2, titanium metal may be favourably reduced first when electrolytically reducing the melt. Lab scale experimental process conditions (temperature and composition) were studied to determine the feasibility of electrolytically reducing titanium metal from the molten oxide mixture. From our research, expansion into other binary oxide systems for different metals of interest, specifically neodymium and tantalum, will be discussed. Specifically, systems that contain congruently melting line compounds with adjacent eutectic reactions were hypothesised to have a similar reordering of the half-cell potentials, favouring the reduction of the desired metals (Nd or Ta). Understanding simplified binary systems will scaffold insight into more complex, industrially-relevant molten oxide mixtures at ultra-high temperatures, potentially contributing to the discovery of new and more sustainable electrochemical pathways for technology-critical metals.

(Invited, Digital Presentation) Doping Gallium Oxide and Competing Ultra-Wide Bandgap Oxides

Although Ga2O3 is widely believed to be the among most promising ultrawide-bandgap semiconductors, its inability to be p-type doped hampers future applications. Moreover, alloying with aluminum increases the Ga2O3 band gap, but it is unclear if electrical conductivity of AlGO alloys can be controlled. The properties of group-IV (C, Si, Ge, and Sn) and transition metal (Hf, Zr, and Ta) substitutional dopants in AlGO alloys are systematically explored here using first-principles hybrid functional calculations. In Ga2O3, all dopants act as shallow donors. However, in Al2O3 all are deep defects, characterized by DX behavior or the emergence of positive-U (+/0) levels. Combining our calculations of dopant charge-state transition levels with information of the AlGO alloy band structure, the critical Al composition at which each dopant transitions from being a shallow to a deep donor is estimated. Si is identified as being the most efficient dopant to achieve n-type conductivity in high Al-content AlGO alloys, acting as a shallow donor over the entire predicted stability range for AlGO solid solutions. Compensation by other unintentional impurities (such as H and C) is also assessed.Other oxide materials have also emerged as potential competitors to Ga2O3, but their propensity for hole conductivity is less well known. Here the stability of hole polarons in a set of ultrawide-bandgap oxides (Ga2O3, Al2O3, ZnGa2O4, MgGa2O4, LiGaO2 and GeO2) is examined and compared, both in pristine material and in the presence of acceptor impurities. Holes spontaneously self-trap in all oxides investigated, with varying stabilities. Acceptor impurities further stabilize these trapped holes, leading to large acceptor ionization energies. Hole trapping also leads to characteristic distortions and distinct optical transitions, which may explain some experimentally-observed signals. These results indicate that achieving p-type conductivity in any of these oxides is unlikely, with the possible exception of GeO2.This work was performed in collaboration with Darshana Wickramaratne (NRL), Joel Varley (LLNL), Sai Mu (UCSB), Mengen Wang (UCSB) and Chris Van de Walle (UCSB), and was supported by the ONR/NRL 6.1 Basic Research Program.

In-depth understanding of physical mechanism of the gradual switching in AlOxNy-based RRAM as memory and synapse device

This paper reported the Pt/AlOxNy/Ta structure with oxygen scavenging metal Ta as a top electrode in order to achieve excellent data storage and the artificial synaptic function. As a series resistance layer and a thermal enhanced layer, the TaOx interface layer between the resistance switching (RS) layer and the top electrode (TE) can greatly affect the RS characteristics. These effects can be attributed to properties of the interface layer such as thermal and electrical conductivities, suggesting that properties of the interface layer should be carefully and systematically considered if excellent RS characteristics are desirable. Based on the electrical testing and current conduction mechanism analyses, the major factors affecting the bipolar gradual RS behavior can be concluded as the property of the interface layer between the RS layer and TE, the Joule heating caused by current, and the distribution of the electric field on the interface layer.

Comprehensive study of amorphous metal oxide and Ta2O5 -based mixed oxide coatings for gravitational-wave detectors

High finesse optical cavities of current interferometric gravitational-wave detectors are significantly limited in sensitivity by laser quantum noise and coating thermal noise. The thermal noise is associated with internal energy dissipation in the materials that compose the test masses of the interferometer. Our understanding of how the internal friction is linked to the amorphous material structure is limited due to the complexity of the problem and the lack of studies that span over a large range of materials. We present a systematic investigation of amorphous metal oxide and Ta$_2$O$_5$-based mixed oxide coatings to evaluate their suitability for low Brownian noise experiments. It is shown that the mechanical loss of metal oxides is correlated to their amorphous morphology, with continuous random network materials such as SiO$_2$ and GeO$_2$ featuring the lowest loss angles. We evaluated different Ta$_2$O$_5$-based mixed oxide thin films and studied the influence of the dopant in the optical and elastic properties of the coating. We estimated the thermal noise associated with high-reflectance multilayer stacks that employ each of the mixed oxides as the high index material. We concluded that the current high index material of TiO$_2$-doped Ta$_2$O$_5$ is the optimal choice for reduced thermal noise among Ta$_2$O$_5$-based mixed oxide coatings with low dopant concentrations.