Non-stoichiometric Titanium Oxide Research Articles

Aluminum doped non-stoichiometric titanium dioxide as a negative electrode material for lithium-ion battery: In-operando XRD analysis

Lithium-ion batteries (LIB) with titanium dioxide as anode material emerged as one of the most energy-storage systems. In this study, we investigate aluminum-doped non-stoichiometric titanium dioxide synthesized using sol-gel method and subsequent reduction treatment. Different analysis techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) tests are conducted for the analysis of material and performance of the battery. The XRD results affirmed that the sample consisted of pure titanium-dioxide phases with no other precipitated phases, such as aluminum oxide (α-Al2O3 or γ-Al2O3). XPS analysis evident that aluminum was successfully incorporated into the titanium-dioxide lattice and the presence of Ti3+ and oxygen vacancy signals confirmed its non-stoichiometric nature. TEM images implies that doping and its extent did not significantly affect the size and morphology of the nanoscale particles. The selected area electron diffraction shows that the sample consisted of a mixture of the anatase and rutile phases. The best-performing electrode was found to be the one composed of 1 % aluminum-doped non-stoichiometric titanium dioxide. After 200 charge-discharge cycles, the battery maintained a capacity of 195 mAh/g, retaining 97.5 % of its reversible capacity. Cyclic stability test under high current condition shows that the capacity remained at 157 mAh/g without any noticeable decay after 750 charge-discharge cycles at a 1 C rate. This material exhibited the lowest impedance and the highest lithium-ion diffusion rate. Additionally, in situ synchrotron-based XRD indicates coexistence of three phases such as a new reversible intermediate phase LiTiO2, a partially irreversible intermediate phase Li0.55TiO2, and the anatase phase. The analysis results indicated that the peak intensities and angular shifts were associated with the phase changes that occurred during charge and discharge of the electrochemical processes. The interaction mechanism study between lithium ions and the lattice of mixed phase (anatase, rutile) identified the occurrence of non-uniform stress resulting from lithium-ion insertion in the rutile phase, in addition to the irreversible reactions in both the rutile and anatase phases. Through the synergistic effect of heteroatom doping and oxygen vacancy treatment, the conductivity of titanium dioxide is enhanced, leading to improved performance in capacity, impedance, cycle life, and rate as an anode material in LIBs.

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.

An in-Operando XRD Study of TiO2 Based Anode Materials for Secondary Li Ion Batteries Application

In recent years, lithium-ion batteries (LIB) have emerged as one of the most representative rechargeable energy-storage systems. Among the various anode materials used, titanium dioxide stands out for its excellent stability, superior safety, and high cycling performance. Moreover, its remarkable stability in high-capacity charge–discharge cycles is useful for developing fast-charging batteries. Therefore, this material has attracted significant attention from researchers. In this study, we investigate aluminum-doped and carbon-coated non-stoichiometric titanium dioxide for in operando X-ray diffraction (XRD) analysis using synchrotron radiation to explore the behavior of lithium ions intercalating into and deintercalating from the titanium dioxide lattice and draw insights from the variations in the characteristic lattice diffraction peaks.In Al-TiOx part, the lithium-ion intercalation and deintercalation behaviors within the mixed-phase titanium dioxide used herein (anatase and rutile). During discharge, a new reversible intermediate phase, LiTiO2, as well as a partially irreversible intermediate phase, Li0.55TiO2, are generated in the anatase phase. This is the first reported experimental observation of the coexistence of these three phases. The irreversible reaction kinetics of these phases contribute to capacity decay. In the rutile phase, the diffraction peaks exhibit a trend of broadening and narrowing during charge–discharge, resembling an hourglass-like structure. This phenomenon implies non-uniform stress within the material due to lithium-ion diffusion through a relatively faster channel. By using in situ XRD, we propose an interaction mechanism between lithium ions and the lattice of mixed-phase (anatase, rutile) titanium dioxide. In C@TiOx part, the rutile TiO2 undergoes a non-uniform strain at a rate of 0.5 C, causing the peak to broaden and shift left after lithiation. The capacities of C@TiO 𝑥 batteries were lowered from 109.0 to only 79.2 mAh/g at 5 C. It is believed that the carbon coating protect the inner TiO 𝑥 core from phase transition so that nanosized rutile TiO2 was retained after lithiation at 0.5 C, which means lithiated rutile is not equivalent to lithium titanate. Instead, the lattice distortion occurs when Li ions are intercalated in the rutile TiO2 matrix. This means that the fast lithium-ion diffusion channel in the c axis of rutile is blocked by the carbon coating and phase transition was prohibited. Furthermore, high reversibility is observed in by the overlap of initial and final curves, which can be taken as an extra evidence for the high Coulombic efficiency.In this study, we propose the concept of aluminum and carbon co-doped non-stoichiometric titanium dioxide for in operando XRD study. Our aim is to further enhance the conductivity of titanium dioxide and its battery performance in lithium-ion batteries through the synergistic effects of heteroatom doping and non-stoichiometric treatment. This includes improvements in the capacity, impedance, cycling lifespan, and high-rate performance of the titanium dioxide material within the battery system.Keyword: Al-doped TiO2, C coated TiOx, in operando XRD, Anode materials, Li-ion batteries

Defective blue titanium oxide induces high valence of NiFe-(oxy)hydroxides over heterogeneous interfaces towards high OER catalytic activity.

Nickel-iron (oxy)hydroxides (NiFeOxHy) have been validated to speed up sluggish kinetics of the oxygen evolution reaction (OER) but still lack satisfactory substrates to support them. Here, non-stoichiometric blue titanium oxide (B-TiOx) was directly derived from Ti metal by alkaline anodization and used as a substrate for electrodeposition of amorphous NiFeOxHy (NiFe/B-TiOx). The performed X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations evidenced that there is a charge transfer between B-TiOx and NiFeOxHy, which gives rise to an elevated valence at the Ni sites (average oxidation state ∼ 2.37). The synthesized NiFe/B-TiOx delivers a current density of 10 mA cm-2 and 100 mA cm-2 at an overpotential of 227 mV and 268 mV, respectively, which are better than that of pure Ti and stainless steel. It also shows outstanding activity and stability under industrial conditions of 6 M KOH. The post-OER characterization studies revealed that the surface morphology and valence states have no significant change after 24 h of operation at 500 mA cm-2, and also can effectively inhibit the leaching of Fe. We illustrate that surface modification of Ti which has high corrosion resistance and mechanical strength, to generate strong interactions with NiFeOxHy is a simple and effective strategy to improve the OER activity and stability of non-precious metal electrodes.

Elucidating the mechanisms of titanium–induced morphological and structural changes in catalysts on mesoporous Al2O3–TiOx mixed oxides: Effect of non–stoichiometric TiOx phase

In the present work, mesoporous Al 2 O 3 –TiO x composites with different titania loadings (4, 8 and 12 wt%) were synthesized to evaluate the effect of non-stoichiometric TiO x phases on the hydrodesulfurization (HDS) ability of the CoMo/Al 2 O 3 –TiO x catalysts. The activity of the catalysts was evaluated in the dibenzothiophene (DBT) HDS reaction carried out at 593 K, 5.5 MPa in a batch reactor. Regardless of the TiO x content, all sulfided CoMo Al 2 O 3 –TiO x catalysts were more active than the CoMo/Al 2 O 3 catalyst. For all catalysts, DBT HDS occurs mainly through the direct desulfurization (DDS) pathway (95–97% selectivity). The most active catalysts (CoMo-12 and CoMo-4) showed evidence of the presence of non-stoichiometric titanium oxides. The synthesized materials were characterized in depth to evaluate their crystallinity, textural and morphological properties, elemental composition and acidity. Their characterization showed that: (i), the Al 2 O 3 –TiO x interaction increased with decreasing TiO x content; (ii) the strong interaction between TiO x particles and alumina led to the formation of more defined TiO x structures; (iii), an increase in titania content led to the growth of TiO x crystals along the [101] direction (relative to the [001] direction), which in turn, led to the different TiO x morphologies: nanorods → nanotubes → U-shaped nanotubes. The TiCoMoS phase can be formed if the process is performed on Ti 3 O 5 instead of TiO 2 . • Titania loading influenced on the metal–support interaction and the type of titania phases. • Ti–promoted species are related to increase of the direct desulfurization route. • Non–stoichiometric titanium oxides are necessary to formation of TiCoMoS active phase.

Influence of annealing temperature on sensing properties of TIOx thin films prepared by magnetron sputtering

This work describes the influence of the annealing temperature on the optical and surfaceproperties of non-stoichiometric titanium oxide (TiOx) thin films. The results were related to theinvestigation of the sensing response toward H2 gas. The samples were prepared by the magnetronsputtering method using Ar:O2 plasma with low oxygen content (20% and 30%). An increase in theamount of oxygen in the gas mixture supplied to the magnetron led to a decrease in the deposition rate.The thickness of the deposited thin films, determined by the use of an optical profiler, was found tobe 600 nm and 200 nm, respectively. The coatings were then annealed in an ambient air atmosphereat a temperature in the range from 100C to 800C. Additionally, the roughness of the coating surfacewas measured. To investigate the optical properties of the thin films, transmission and reflection spectrawere measured, and parameters such as transmission coefficient, cutoff wavelength value, and opticalband gap value were determined as functions of the annealing temperature. The sensing propertiesof the thin films were characterised on the basis of changes in a resistance value as a response to amix of Ar:3.5% H2. It was found that the oxidation of the thin films has a key influence not only onthe response time of the TiOx thin films, but also on the character of the response.Keywords: materials engineering, titanium oxides, thin films, magnetron sputtering, optical properties,gas sensing properties

Gas Sensors Based on Titanium Oxides (Review)

Nanostructured titanium compounds have recently been applied in the design of gas sensors. Among titanium compounds, titanium oxides (TiO2) are the most frequently used in gas sensing devices. Therefore, in this review, we are paying significant attention to the variety of allotropic modifications of titanium oxides, which include anatase, rutile, brukite. Very recently, the applicability of non-stoichiometric titanium oxide (TiO2−x)-based layers for the design of gas sensors was demonstrated. For this reason, in this review, we are addressing some research related to the formation of non-stoichiometric titanium oxide (TiO2−x) and Magnéli phase (TinO2n−1)-based layers suitable for sensor design. The most promising titanium compounds and hetero- and nano-structures based on these compounds are discussed. It is also outlined that during the past decade, many new strategies for the synthesis of TiO2 and conducting polymer-based composite materials were developed, which have found some specific application areas. Therefore, in this review, we are highlighting how specific formation methods, which can be used for the formation of TiO2 and conducting polymer composites, can be applied to tune composite characteristics that are leading towards advanced applications in these specific technological fields. The possibility to tune the sensitivity and selectivity of titanium compound-based sensing layers is addressed. In this review, some other recent reviews related to the development of sensors based on titanium oxides are overviewed. Some designs of titanium-based nanomaterials used for the development of sensors are outlined.

Compositional, electrical and thermal properties of nonstoichiometric titanium oxide thin films for MEMS bolometer applications

Nonstoichiometric titanium-oxide (TiOx) films are being extensively studied for MEMS bolometer applications. To have superior bolometer performance, the TiOx layers should have a high value of temperature coefficient of resistivity (TCR) and a low value of thermal conductivity. This paper presents the evolution of the electrical and thermal properties of RF sputtered TiOx films with the film thickness and stoichiometry. A series of amorphous TiOx films of 100 nm, 200 nm, and 400 nm thickness are deposited with different oxygen flow rates. X-ray photoelectron spectroscopy (XPS) study revealed the presence of only Ti4+ and Ti3+ oxidation states in the deposited films, and no TiO phase exists (no Ti2+ state). The oxygen-titanium atomic ratios (O/Ti) of the films are 1.5, 1.7, and 1.9. The TCR of the films is increased (from -1.1 %/K to -4.8%/K) with the increased oxygen content. The cross-plane thermal conductivities of the films are by the 3-ω technique. The thermal conductivity of the TiOx films is increased (0.5 W/m-K to 2.4 W/m-K) with the increase in film thickness and is independent of its ‘x’ values. Characteristics of MEMS bolometer pixel (17 mm pitch) are simulated based on the measured properties of the TiOx films. The film having 2.75 %/K TCR and 1.12 W/m-K thermal conductivity, exhibited minimum NETD (37.3 mK) with decent voltage responsivity (1.62x106 V/W).

Thermodynamic Analysis of Stoichiometric Composition Changes in the TixOy Films at RF Magnetron Sputtering and Modeling of Their Conductivity

Herein, the results of experiments on the synthesis of nonstoichiometric titanium oxide films by magnetron sputtering at various partial oxygen pressures and discharge powers are presented. The thermodynamic analysis of the synthesis results is performed by minimizing the Gibbs free energy of the equilibrium thermodynamic system, which takes place in the chamber. The dependences of the concentration of the main components in the deposition chamber on the partial pressure of oxygen and the discharge power, including the concentration of synthesized titanium monoxide and dioxide, are obtained. The analysis of these dependences allows determining the conditions for the critical values of the partial pressures of oxygen at which the oxides are synthesized. The exponential dependence of the conductivity on oxygen pressure is found experimentally and explained on the basis of hopping conductivity over the states of defects on the surface of nanocrystals that form the synthesized films.

Study on the fabricated non-stoichiometric titanium dioxide by in-situ reduction with carbon powder via spark plasma sintering

Study on the fabricated non-stoichiometric titanium dioxide by in-situ reduction with carbon powder via spark plasma sintering

Synthesis and Attestation of Titanium Dioxide Nanotubes Based Photocatalyst for Water and Air Purification out of Harmful Organic Impurities

In the present work we have synthesized nanotubular TiO2 film with a nonstoichiometric layer in the vicinity of titanium foil by anodization during 120 min. The catalytic activity of nanotubular titanium dioxide films formed during the oxidation of acetone to carbon dioxide under the action of visible light with a wavelength of 450 nm was found to be approximately 2 times higher compared to standard titanium dioxide (Degussa P25). Such a pronounced enhancement of activity may be attributed to a more efficient absorption of visible light by the films due to narrowing of the optical gap because of difference in the nonstoichiometry of titanium dioxide near the interface between nanotubular film and the titanium foil substrate.
 Keywords: photocatalysis, nonstoichiometric titanium dioxide, purification of water

Sol-Gel Synthesis of Nonstoichiometric Titanium Dioxide for Photo-Oxidation of Toxic Organic Substances

Titanium dioxide (TiO2) was synthesized by sol-gel method at different values of pH = 3, 7, 8, 9, or 10. X-ray phase analysis has shown that in an acid rout, an anatase phase had crystallized, and in an alkaline rout an amorphous phase of TiO2 was achieved. After annealing for 4 hours at 350∘C, all samples were transformed into anatase phase. The particle size in the different samples varies from 7 to 50 nm depending on the pH. The diffuse reflectance spectra revealed a high value of the band gap width in the range from 2.9 to 3.4 eV and its narrowing after annealing to the range from 2.8to 3.1 eV. The specific surface area measured by BET method was changing from 80 up to 140 m2 /g.
 Keywords: Titanium dioxide, nanostructure, photocatalysis, band gap, specific surface area

Insights in the Application of Stoichiometric and Non-Stoichiometric Titanium Oxides for the Design of Sensors for the Determination of Gases and VOCs (TiO2-x and TinO2n-1 vs. TiO2).

In this review article, attention is paid towards the formation of various nanostructured stoichiometric titanium dioxide (TiO2), non-stoichiometric titanium oxide (TiO2−x) and Magnéli phase (TinO2n−1)-based layers, which are suitable for the application in gas and volatile organic compound (VOC) sensors. Some aspects related to variation of sensitivity and selectivity of titanium oxide-based sensors are critically overviewed and discussed. The most promising titanium oxide-based hetero- and nano-structures are outlined. Recent research and many recently available reviews on TiO2-based sensors and some TiO2 synthesis methods are discussed. Some promising directions for the development of TiO2-based sensors, especially those that are capable to operate at relatively low temperatures, are outlined. The applicability of non-stoichiometric titanium oxides in the development of gas and VOC sensors is foreseen and transitions between various titanium oxide states are discussed. The presence of non-stoichiometric titanium oxide and Magnéli phase (TinO2n−1)-based layers in ‘self-heating’ sensors is predicted, and the advantages and limitations of ‘self-heating’ gas and VOC sensors, based on TiO2 and TiO2−x/TiO2 heterostructures, are discussed.

Nonstoichiometry, structure and properties of nanocrystalline oxides, carbides and sulfides

The results of recent experimental studies of the influence of the size of oxide, carbide and sulfide nanoparticles on changes in their nonstoichiometry are analyzed and generalized. In relation to intrinsically nonstoichiometric titanium oxides and niobium and vanadium carbides, on the one hand, and stoichiometric silver sulfides, on the other hand, it is shown that a decrease in the particle size to the nano scale has a strong impact on the chemical composition of nanocrystalline compounds, viz., it leads to the occurrence of or increase in nonstoichiometry. A conclusion is drawn that interplay between the particle size and nonstoichiometry is common to all solid nanocrystalline substances and should be taken into account in studies on the synthesis, structure and properties of these systems.The bibliography includes 260 references.

Effect of Sample Preparation Pressure on Transformation Law of Low-Valent Titanium Oxide in a Multi-Stage Reduction Process

A novel method for preparing titanium powder by multi-stage reduction of TiO2 was proposed. Its core is the preparation of high-quality low-valent titanium oxide. In this paper, the effect mechanism of different sample preparation pressures on the preparation of low-valent titanium oxide by the primary reduction (self-propagating high-temperature synthesis mode, SHS) of the Mg-TiO2 system was studied. The results show that the generation of Mg thermal fluid is the key link of the self-sustaining chemical reaction of the Mg-TiO2 system. Titanium exists inα-Ti and TiO at the end of combustion, and constitutes a non-stoichiometric low-valent titanium oxide. The sample preparation pressure determines the proportion of pores reserved for Mg diffusion in the compacts and the contact area of the reactants, thereby determining the partitioning behavior and heat transfer effect of Mg thermal fluid during the combustion process. When the sample preparation pressure is 75 MPa (relative density is 0.66 ± 0.01), the combustion effect is optimal, and the low-valent titanium oxide with oxygen content of 15.1% can be obtained. It was subjected to deep reduction to obtain a titanium powder product with an oxygen content of 0.27%.

Self-propagating reaction mechanism of Mg–TiO2 system in preparation process of titanium powder by multi-stage reduction

The novel method for the preparation of titanium powder by multi-stage reduction was proposed. The primary reduction adopted self-propagating high-temperature synthesis (SHS) mode. This paper focuses on the primary reduction process of Mg–TiO2 system under the condition of off-balance reaction. The effects of different material ratios, material arrangement methods and reaction initiation modes on the SHS reaction process of Mg–TiO2 system and its reaction mechanism were systematically studied. SHS mode was used to Mg–TiO2 system, and non-stoichiometric low-valent titanium oxide intermediate including α-Ti (Ti2O type) and TiO was directly obtained (with oxygen content of 13.93 wt%). SHS reaction initiated by local ignition is more sufficient than by overall heating method. Compared with the loose setting materials, the compacts can increase the effective contact interface of the reactants, and SHS reaction proceeds more sufficiently, which is favorable for obtaining lower oxygen content product. The adiabatic temperatures of the Mg–TiO2 system at different initial conditions were calculated according to the improved calculation method. When the initial temperature is 298 K, the adiabatic temperature of Mg–TiO2 system is between 1363 and 2067 K at different material ratios. Therefore, unreacted or partially excess Mg at the reaction front will diffuse into the unreacted region in gas or liquid form, thereby preheating the material and initiating further SHS reaction.

Synthesis and characterization of Al doped non-stoichiometric ratio titanium oxide at high temperature and pressure

Preparation of TiAlxO1.80-x (x = 0.06, 0.04, 0.02) under high temperature and high pressure (HPHT) can adjust the energy band gap and modify the resistivity of the material, and gives rise to special microstructure and morphology that reduce the phonon thermal conductivity. In this work, we sought to obtain improved the thermoelectric performance of oxide materials by adjusting the doping ratio of Al and Ti in TiAlxO1.80-x. The phase structures of different samples were studied by X-ray diffraction. The morphology characteristics generated by HPHT synthesis were studied by electron microscopy （FSEM, HRTEM）and the thermoelectric properties of TiAlxO1.80-x (x = 0.06, 0.04, 0.02) were evaluated. It was found that an appropriate Al and Ti doping ratio combined with the use of HPHT synthesis can reduce the resistivity of the sample and inhibit the rapid increase of thermal conductivity with increasing temperature. The best zT value (0.22) was obtained at the temperature of 973 K for the TiAl0·04O1.76 sample.

Preparation of Laser-Modified Ti-15Mo Surfaces With Multiphase Calcium Phosphate Coatings

Multiphasic bioceramic scaffolds has been enhanced for dental and orthopedic applications. In this perspective, the laser surface texturing of metallic surfaces combined to bioactive calcium phosphate coatings have shown to be promising and economically feasible for biomaterial clinical applications. Ti-15Mo alloy samples were irradiated by pulsed Yb: YAG laser beam. The formation of HA and other calcium phosphates phases by biomimetic method should occur in the presence of Ca2+, PO43-, Mg2+, HCO3-, K+ and Na+. The modified surfaces were submitted to thermal treatment at 380 and 580°C. The results showed the processes of fusion and fast solidification from the laser beam irradiation, inducing the formation of stoichiometric α-Ti, TiO2 and non-stoichiometric titanium oxides, Ti3O and Ti6O with different oxide percentages depending on applied fluency (fluency of 0.023, 0.033, 0.040 and 0.048 J/mm2). The morphological and physicochemical properties have indicated the formation of a multiphase bioceramic coatings. It was observed the formation of amorphous calcium phosphate (ACP), octacalcium phosphate (OCP), and magnesium phosphate (Mg3(PO4)2) phases at 380°C, whereas β-TCP (tricalcium phosphate), OCP, and substituted β-TCP with Ca2,589Mg0,41(PO4)2 were obtained at 580°C. Therefore, the multiphasic bioceramic modified Ti-15Mo surface could enhance osteointegration for bone regeneration.

Nanostructured titanium dioxide for medicinal chemistry

The review considers methods for the synthesis of stoichiometric and nonstoichiometric nanostructured titanium dioxide for medicinal chemistry. The influence of the synthesis method on the amorphous atomic and crystal structures, specific surface area, morphology, and photooptical properties of the material is analyzed. The review compares the results of using stoichiometric and nonstoichiometric titanium dioxide in the synthesis of new organic molecules by cross-coupling of heteroarenes, which can be utilized in drugs.

Composite Nafion Membranes with CaTiO3-δ Additive for Possible Applications in Electrochemical Devices.

A composite membrane based on a Nafion polymer matrix incorporating a non-stoichiometric calcium titanium oxide (CaTiO3−δ) additive was synthesized and characterized by means of thermal analysis, dynamic mechanical analysis, and broadband dielectric spectroscopy at different filler contents; namely two concentrations of 5 and 10 wt.% of the CaTiO3−δ additive, with respect to the dry Nafion content, were considered. The membrane with the lower amount of additive displayed the highest water affinity and the highest conductivity, indicating that a too-high dose of additive can be detrimental for these particular properties. The mechanical properties of the composite membranes are similar to those of the plain Nafion membrane and are even slightly improved by the filler addition. These findings indicate that perovskite oxides can be useful as a water-retention and reinforcing additive in low-humidity proton-exchange membranes.