Magneli Phases Research Articles

Synthesis, Characterisation, and Applications of TiO and Other Black Titania Nanostructures Species (Review)

Black titania, a conductive ceramic material class, has garnered significant interest due to its unique optical and electrochemical properties. However, synthesising and properly characterising these structures pose a considerable challenge. This diverse material family comprises various titanium oxide phases, many of them non-stoichiometric. The term “black TiO2” was first introduced in 2011 by Xiaobo Chen, but Arne Magneli’s groundbreaking discovery and in-depth investigation of black titania in 1957 laid the foundation for our understanding of this material. The non-stoichiometric black titanium oxides were then called the Magneli phases. Since then, the science of black titania has advanced, leading to numerous applications in photocatalysis, electrocatalysis, supercapacitor electrodes, batteries, gas sensors, fuel cells, and microwave absorption. Yet, the literature is rife with conflicting reports, primarily due to the inadequate analysis of black titania materials. This review aims to provide an overview of black titania nanostructures synthesis and the proper characterisation of the most common and applicable black titania phases.

Electrochemical advanced oxidation of PFOA by Ti4O7 reactive electrochemical membrane anode

In recent years, per and polyfluoroalkyl substances (PFAS) have garnered significant attention due to their persistent and harmful effects on the environment and human health. Traditional treatment methods often fall short of effectively removing PFAS from water, prompting the need for innovative techniques. One promising approach is electrochemical advanced oxidation, based on highly reactive chemical species generated through electrochemical reactions to degrade organic pollutants. In this study, a specific reactive electrochemical membrane (REM) anode was used to degrade perfluorooctanoic acid (PFOA). The anode is a tubular Ti4O7-based REM (mixture of Ti4O7 and Ti5O9 Magneli phases) with a water permeability of 3300 L m−2 h−1 bar−1. The impact of various operating parameters, including current density, flux through REM, and feed concentration, on PFOA degradation efficiency was investigated. It was found that higher current densities, feed concentrations and lower flux through REM led to increased PFOA removal rates. With this type of REM, a total degradation of PFOA was observed at PFOA flux (passing throw the REM) under 0.2 g h−1 m−2 even at the lowest current density (71 A/m2). The degradation mechanism was investigated by evaluating the generated by-products after several degradation cycles, and the results confirmed that the degradation occurs via the decomposition cycle of CF2. Energy consumption has been taken into account, as it is the major limitation of advanced oxidation processes, exhibiting value under 5 kWh/g for the lowest current density and the highest PFOA flux. The originality of this study relies on the use of a specific anode; a tubular shape Ti4O7-based REM (by Saint Gobain Company). Such concentric REM reactor is optimal for the treatment of recalcitrant effluent containing PFOA as it significantly improved mass transfer leading to a very interesting energy efficient system that can easily be scale up.

Plasma synthesis of Ti–O and carbon nanoparticles and their modification with an anionic surfactant to obtain stable dispersions

Ti–O Magneli phases and carbon nanoparticles modified in sodium dodecyl sulfate solutions formed stable dispersions in water.

Anisotropic magneli phase Ti-suboxides in β- cyclodextrin template - Enhanced charge separation upon gold doping

Substoichiometric titanium oxides i.e. Magneli phase (MP) TiOx are attractive due to their conductive nature. However, their synthesis is challenging. In this work, Anisotropic MP- Ti4O7 nanoparticles and Au doped nanocomposites were synthesized using β- cyclodextrin as template. The MP nanomaterials were 20-30 nm in size. The synthesis conditions were mild. These MP- TiOx nanomaterials show efficient charge separation upon light excitation i.e. they (i) act as efficient photocatalysts; (ii) they can be sensitized by a fluorescent dye; (iii) finite element method (FEM) simulations indicate substantial interfacial plasmonic charge generation at the metal-semiconductor interface in the doped nanocomposites.

High temperature friction and galling properties of nanolayered (Cr,V)N coatings and effect of V content

Chromium nitride (CrN) coating is considered as one of the best candidates for wear protection in many forming application where adhesive wear and galling dominate. However, its relatively high coefficient of friction against soft metals hinders its applicability. Vanadium nitride (VN), on the other hand has attracted increasing interest as VN is easily oxidized to form Magneli phase vanadium oxides with easy slipping shear planes, on one hand leading to self-lubricating properties but also to deteriorated wear resistance. This can be overcome by forming CrVN coatings. However, there is a lack of information how such coatings perform in terms of galling resistance and V-concentration in typical forming conditions and against soft metals.Therefore, the aim of this work was to study friction properties of nano-layered PVD (Cr,V)N coatings at room and elevated temperature and how V-content influences on friction and galling resistance against typical work materials. Nanolayered (Cr,V)N coatings with V in concentrations from 15 to 30 % were deposited by industrial DC magnetron sputtering system and tested using Load-Scanner against AA2024 aluminum alloy and low-carbon steel at room and elevated temperature of 300 °C and 600 °C, respectively. Results were evaluated in terms of coefficient of friction level and stability, critical loads for galling initiation and volume of adhered work material. Results show that (Cr,V)N coatings do not necessarily improve galling resistance, being strongly dependent on V concentration and contact temperature. For forming Al alloys positive results are obtained with coatings containing 20–25 at.% V and for low-carbon steels above 25 at.%, with marked improvement obtained only at elevated temperatures.

Porous single crystalline-like titanium dioxide monolith with enhanced photoelectrochemical performance

Macro-sized porous single crystalline-like (PSC-like) TiO2 is endowed with unique structural advantages due to its structural consistency and porosity in a large area, which would significantly enhance its photoelectrochemical function. However, there are significant technical challenges in the growth of porous single crystalline-like monoliths. The consistency of structure dominates the structure so that the grain boundary is reduced to the minimum, which is in contradiction with the three-dimensional percolation structure. Here we report a lattice reconstruction strategy based on solid-solid transformation to grow porous single crystal-like anatase TiO2 dominated by (200) and (101) facets at 2 cm scale. In comparison with the traditional definition of porous single crystal, it has two different lattice orientations, but still has good photoelectrochemical properties. The band gap engineering introduces Ti3+ gap into the lattice to generate TinO2n−1 with Magneli phase, limiting the created active structure to the lattice with two-dimensional surface, which would open a new avenue to create highly active surfaces to capture photons and transport electrons stably. The PSC-like TinO2n−1 provides enhanced exciton lifetime (3–5 ns) as a photocatalytic catalyst and shows significant visible light absorption. The independent PSC-like TinO2n−1 delivers high photocurrent of 1.8–5.5 mA · cm−2 at room temperature and does not decay for 10 h.

Ag/Ti-suboxides as non-PGM anode electrocatalyst for PEM water electrolysis

Minimization of high-cost metal electrocatalyst is necessary to achieve cost-effective green hydrogen production by proton exchange membrane (PEM) water electrolysis (WE). The large increase of the cost of Ir recently observed requires individuating alternative catalyst solutions for the oxygen evolution reaction (OER) in PEMWE. The OER is the rate determining step of the electrolysis process requiring high-cost noble metals with significantly high loading. A non-platinum group metal (non-PGM) anode catalyst based on silver and titanium suboxide was prepared and used for the oxygen evolution reaction in a PEMWE cell. By using a solid-state synthesis procedure, a silver nitrate and titanium suboxides (TinO2n-1) with Magneli phase powders were mixed and subjected thereafter to a thermal treatment at 300 °C in a 50% H2/N2 gas stream to promote the inclusion of silver within the Ti-suboxides structure. A membrane – electrode assembly (MEA), consisting of the anode Ag/TinO2n−1 and conventional Pt/C cathode catalysts deposited on a 212 NAFION® membrane (thickness 50 μm), was investigated to assess the performance and durability of the PGM free oxygen evolution catalyst in an acidic environment.A promising performance, of 0.6 A cm−2 at 2 V/cell at 80 °C, and an excellent stability (degradation rate < 14 μV/h during a 1000 h test) were achieved for the electrolysis cell based on a cost-effective metal anode electrocatalyst.

Hydrothermal Process to Prepare Novel Phase Titanium Sub-Oxide Ti6O11 from Nano Rutile Titanium Dioxide Particles with Different Autodave Reactors

Hydrothermal process method using different dimensions reactors with volume 100 ml (homemade) was employed to prepare titanium sub-oxide Ti6O11, where one gram of TiO2 nanoparticles 30-50 nm and 3M (20 ml) of NaOH as suspension was used . The samples are characterized using X-ray diffraction, Raman spectroscopy, and Field Emission Scanning Electron Microscopy (FE-SEM). X-ray diffraction revealed the formation of sub- oxide titanium Ti6O11 of triclinic structure with Magneli phase, when the temperature applied was 363K for 9h.While FE-SEM showed uniform hierarchical structures with planar grass-like shapes. A novel phase has been found from rutile titanium.

Formation of chlorate and perchlorate during electrochemical oxidation by Magnéli phase Ti4O7 anode: inhibitory effects of coexisting constituents

Formation of chlorate (ClO3−) and perchlorate (ClO4−) as by-products in electrooxidation process has raised concern. In the present study, the formation of ClO3− and ClO4− in the presence of 1.0 mM Cl− on boron doped diamond (BDD) and Magneli phase titanium suboxide (Ti4O7) anodes were evaluated. The Cl− was transformed to ClO3− (temporal maximum 276.2 μM) in the first 0.5 h on BDD anodes with a constant current density of 10 mA cm2, while approximately 1000 μM ClO4− was formed after 4.0 h. The formation of ClO3− on the Ti4O7 anode was slower, reaching a temporary maximum of approximately 350.6 μM in 4.0 h, and the formation of ClO4− was also slower on the Ti4O7 anode, taking 8.0 h to reach 780.0 μM. Compared with the BDD anode, the rate of ClO3− and ClO4− formation on the Ti4O7 anode were always slower, regardless of the supporting electrolytes used in the experiments, including Na2SO4, NaNO3, Na2B4O7, and Na2HPO4. It is interesting that the formation of ClO4− during electrooxidation was largely mitigated or even eliminated, when methanol, KI, and H2O2 were included in the reaction solutions. The mechanism of the inhibition on Cl− transformation by electrooxidation was explored.

Structural and phase features of zinc selenide nanoparticles obtained by laser evaporation

The first production of weakly agglomerated zinc selenide nanopowders by evaporation of a target of the required chemical composition in argon using a fiber ytterbium laser is reported. Nanoparticles have the shape of polyhedrons and, more rarely, spheres with an average size of 18 nm. According to XRD data, the obtained nanopowders contain two phases: a stable cubic phase (sphalerite, 40 wt.%) and a metastable hexagonal phase (wurtzite, 60 wt.%). An analysis of HRTEM showed that most of the nanoparticles have structural defects. Due to superstoichiometry, defects in the crystal structure of the crystallographic shift type are formed in nanoparticles. Magneli phases, Wadsley defects and various kinds of heterogeneity inside the particles were found. Keywords: Laser evaporation, zinc selenide, nanoparticles, high resolution transmission electron microscopy (HRTEM), defects, phase composition, crystallographic shift, Magnelli phase, Wadsley defects.

Структурные и фазовые особенности наночастиц селенида цинка, полученных лазерным испарением

The first production of weakly agglomerated zinc selenide nanopowders by evaporation of a target of the required chemical composition in argon using a fiber ytterbium laser is reported. Nanoparticles have the shape of polyhedrons and, more rarely, spheres with an average size of 18 nm. According to XRD data, the obtained nanopowders contain two phases: a stable cubic phase (sphalerite, 40 wt. %) and a metastable hexagonal phase (wurtzite, 60 wt. %). An analysis of HRTEM showed that most of the nanoparticles have structural defects. Due to superstoichiometry, defects in the crystal structure of the crystallographic shift type are formed in nanoparticles. Magneli phases, Wadsley defects and various kinds of heterogeneity inside the particles were found.

Плазмодинамический синтез оксидов металлов в среде углекислого газа на примере систем Ti – O и Fe – O

The issues of decarbonization, which have recently received increased attention from the world community, mainly due to global warming, require the search for new solutions related to the utilization of carbon dioxide. The main problem of carbon dioxide conversion is the need to overcome the high stability of its molecules that requires the supply of a significant amount of energy. This paper presents the experimental results on the high-energy plasma dynamic synthesis of metal oxides in a carbon dioxide medium using the Ti – O and Fe – O systems as an example. By applying a sectioned capacitive energy storage device and a coaxial magnetoplasma accelerator with titanium and steel electrodes, which are the main elements of the plasma dynamic synthesis system, nano- and micropowders of iron and titanium oxides were obtained by utilizing CO2. Synthesis of powders was carried out as a result of plasma-chemical reactions occurring during high-speed sputtering of carbon electric discharge plasma into the atmosphere of a reactor chamber filled with carbon dioxide. The possibility of controlling the volume of CO2 utilized in the synthesis process by changing the type of electrodes and the number of successive power supply pulses is shown. It has been established that when using titanium electrodes and a multi-pulse operating mode in the considered system, it is possible to utilize up to 15 vol. % of CO2 to obtain up to ~ 9 g of dispersed products. It should be noted that when titanium electric discharge plasma is sputtered in a CO2 medium, the formation of “classical” rutile and anatase phases, as well as Magneli phases and titanium carbide without traces of pure metal is observed. This indicates that when implementing the plasma dynamic synthesis, it is possible not only to utilize carbon dioxide, but also to obtain useful powder products, which can later be used as feedstock for various applications.

Recent Progress in the Synthesis and Potential Applications of Two‐Dimensional Tungsten (Sub)oxides

AbstractWhile WO3 is one of the most studied metal‐oxides in bulk, it is increasingly gaining interest as a two‐dimensional (2D) material as it exhibits different behaviour compared to bulk. In addition, many substoichiometric WO3–x (0≤x≤1) phases exist both in bulk and 2D form. These Magneli phases have different physical and chemical properties than their WO3 counterparts. By introducing oxygen vacancies, the physical and chemical properties of 2D tungsten (sub)oxide nanomaterials can be further altered. This review focuses on synthesis pathways of 2D tungsten (sub)oxides reported so far, and their subsequent use for various applications. The different stoichiometries and additional oxygen vacancies that appear in these materials, combined with their low thickness and high surface area, make them interesting candidates for gas sensing, catalytic application or in electronic devices.

Effects of composition of hydroxyapatite/gray titania coating fabricated by suspension plasma spraying on mechanical and antibacterial properties

While several metallic implants with bioactive coatings have been developed thus far for treating bone deformations or deterioration, a multifunctional coating with the desired mechanical and antibacterial properties has not been demonstrated. This study aimed to reveal the effect of the composition of hydroxyapatite (HAp)/gray titania coatings on the mechanical and antibacterial properties for biomedical applications. Suspension plasma spray (SPS) aided successful deposition of HAp/gray titania coatings on the surface of titanium substrates. The microstructure of coatings with different compositions was then characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy to identify the crystal structure. All results consistently demonstrated that SPS could transform Ti2O3 into TiO2 with mixed Magneli phases, such as Ti4O7 and Ti3O5, which could typically demonstrate photocatalytic activity. Hardness, Young’s modulus, and interfacial strength of composite coatings commonly increased with an increase in the weight percentage of TiO2. A multi-modal damage assessment combining acoustic emission (AE), infrared ray camera (IR), and digital-image-correlation (DIC) was performed to monitor the damage process of HAp composite coating, which successfully revealed initiations of microcracks and nonlinear deformation at interface until fracture. Antibacterial test performed for examining the cytotoxic effects against E. coli under LED light irradiation conditions revealed that SPS HAp/gray titania coating could significantly enhance the antibacterial properties. Enhanced antibacterial properties can be attributed to an increase in the number of Magneli phases and better bacterial adhesion was attributed to hydrophilic properties conferred by submicron-sized particles. Hence, SPS can help fabricate visible light-responsive antibacterial coating, which can be used for medical devices.

Simulation of TiN/HfO2/Pt memristor I–V curve for different conductive filament thickness

The operation of the TiN/HfO2/Pt bipolar memristor has been simulated by the finite elements method using the Maxwell steady state equations as a mathematical basis. The simulation provided knowledge of the effect of conductive filament thickness on the shape of the I-V curve. The conductive filament has been considered as the highly conductive Hf ion enriched HfOx phase (x &lt; 2) whose structure is similar to a Magneli phase. In this work a mechanism has been developed describing the formation, growth and dissolution of the HfOx phase in bipolar mode of memristor operation which provides for oxygen vacancy flux control. The conductive filament has a cylindrical shape with the radius varying within 5–10 nm. An increase in the thickness of the conductive filament leads to an increase in the area of the hysteresis loop of the I-V curve due to an increase in the energy output during memristor operation. A model has been developed which allows quantitative calculations and hence can be used for the design of bipolar memristors and assessment of memristor heat loss during operation.

Simulation of TiN/HfO2/Pt memristor I–V curve for different conductive filament thickness

The operation of the TiN/HfO2/Pt bipolar memristor has been simulated by the finite elements method using the Maxwell steady state equations as a mathematical basis. The simulation provided knowledge of the effect of conductive filament thickness on the shape of the I–V curve. The conductive filament has been considered as the highly conductive Hf ion enriched HfOx phase (x &amp;lt; 2) whose structure is similar to a Magneli phase. In this work a mechanism has been developed describing the formation, growth and dissolution of the HfOx phase in bipolar mode of memristor operation which provides for oxygen vacancy flux control. The conductive filament has a cylindrical shape with the radius varying within 5–10 nm. An increase in the thickness of the conductive filament leads to an increase in the area of the hysteresis loop of the I–V curve due to an increase in the energy output during memristor operation. A model has been developed which allows quantitative calculations and hence can be used for the design of bipolar memristors and assessment of memristor heat loss during operation.

Size and strain induced phase formation and ferromagnetism in reduced TiO2 powders

We investigate the strain evolution, phase formation and ferromagnetism of nanocrystalline TiO2 powders prepared by high energy planetary ball milling technique. Pure TiO2 shows the anatase phases in the structural analysis and more than 0.25 h of milled powder turns into Rutile and Magneli phases. The crystallite size and strain were calculated from the X-ray diffraction pattern using the Williamson-Hall equation and the uniform deformation energy density model. Pure TiO2 exhibits paramagnetic nature, which transforms into ferromagnetic one with a moderate moment 0.15 emu/g for 60 h milled powders at an applied field of 12 kOe. The Micro-Raman analyses show the presence of Magneli phase (Ti3O5) along with a shift in the active Eg(1) band for milled powders. X-ray photoelectron spectroscopy results show an oxygen-deficiency peak at 457.7 eV in milled powders. The electron paramagnetic resonance study shows the evidence of oxygen-deficiency which is clear from the resonance signal at 338 mT in milled powders. Further, the electronic structures are investigated by the spin-polarized plane-wave self-consistent field calculation based on density functional theory (DFT) with generalized gradient approximation (GGA) and Hubbard U corrections. The elastic properties are also calculated for pure, oxygen vacancies TiO2 and pure Magneli phase (Ti3O5) crystal. Our results demonstrate the effects of size and strain engineering on the formation of the Magneli phase due to defect induced oxygen vacancy and show the ferromagnetism in TiO2 nanoparticles, which are important for spintronics and other potential applications.

Surface modification of blue TiO2 with silane coupling agent for NOx abatement

The role of hydroxyl-functionalization of reduced TiO2 (Blue TiO2) for the photocatalytic oxidation of toxic NOx was systematically explored in the present study. A hydrogenation technique was used to reduce the rutile phase in P25 TiO2 giving rise to a Magneli phase. Then, the process was followed by the surface functionalization of the Blue TiO2 with Trimethoxy (Propyl) Silane (TPS). The fabricated nanoparticles were structurally characterized, and photocatalytically tested for NOx abatement. OH-functionalized Blue TiO2 showed strong photo-oxidation of NOx with NOx removal efficiency of 80.2%. The broad-band light absorption (UV and visible) and the formation of a higher number of radicals on the surface of OH-functionalized Blue TiO2 made the material more efficient than other samples. In addition, the lowest NO2 selectivity of 2.7% proved the effective suppression of toxic NO2 and formation of nitrate ions. The reusability test was carried out for five cycles of 1 ​h and had 10% loss in NOx removal efficiency. The role of surface OH groups for the oxidation of NO and NO2 has been discussed in this manuscript. A possible mechanism for NOx photo-oxidation is proposed based on FTIR, ESR, and ion chromatography test.

Evolution of structural and magnetic properties of Ar2+ ion irradiated TiO2 thin films annealed under argon atmosphere

In this report, the evolution of structural as well as magnetic state of 900 °C annealed TiO2 films under argon (Ar) environment have been examined before and after irradiating with the Ar2+ ions of energy 500 keV. The pristine film stabilized with Magneli phase (Ti4O7), the film retains its crystallinity but phase get transformed to anatase TiO2, irradiating with the lowest fluence, 1 × 1014 ions/cm2. After rising up to 5 × 1016 ions/cm2 ion fluence, film again stabilize with the Magneli phase (Ti4O7). In the previous report, we have demonstrated an unusual phase change from anatase TiO2 to brookite, where films are annealed in O2 atmosphere. In contrast to that here we have obtained TiO2 from Ti4O7 at lowest fluence but at highest fluence again Ti4O7 is obtained. The energy deposited by the ion beam passed to the lattice and collision cascades are formed which brings atomic displacement in the lattice, results the structural transformation. Surface topography is not affected much after the irradiation as observed from atomic force microscopy (AFM). Interesting, ferromagnetic behavior at room temperature stems in all the films as a consequence of the controlled introduction of anionic defects (oxygen vacancies).

Electron-hole asymmetry in electron systems with orbital degeneracy and correlated hopping

Microscopic models of electronic subsystems with orbital degeneracy of energy states and non-diagonal matrix elements of electron interactions (correlated hopping) are considered within the configuration-operator approach. Equations for arbitrary-temperature numerical calculation of the doublon concentration for the integer band filling $n=1$ at different forms of the model density of states are derived. The energy spectra obtained within the Green function method are discussed with special emphasis on the role of correlated hopping in transition from itinerant to localized behavior observed in vanadium Magneli phases V$_n$O$_{2n-1}$, transition-metal dichalcogenides NiS$_{2-x}$Se$_x$, fulleride A$_n$C$_{60}$ systems.