Ti Atoms Research Articles

Stabilizing effects of atomic Ti doping on high-voltage high-nickel layered oxide cathode for lithium-ion rechargeable batteries

Stabilizing effects of atomic Ti doping on high-voltage high-nickel layered oxide cathode for lithium-ion rechargeable batteries

Visualizing the evolution from Mott insulator to Anderson insulator in Ti-doped 1T-TaS2

The electronic evolution of doped Mott insulators has been extensively studied for decades in search of exotic physical phases. The proposed Mott insulator 1T-TaS2 provides an intriguing platform to study the electronic evolution via doping. Here we apply scanning tunneling microscopy (STM) to study the evolution in Ti-doped 1T-TaS2 at different doping levels. The doping Ti atom locally perturbs the electronic and spin state inside the doped star of David and induces a clover-shaped orbital texture at low-doping levels (x < 0.01). The insulator to metal transition occurs around a critical point x = 0.01, in which small metallic and large insulating domains coexist. The clover-shaped orbital texture emerges at a broader energy range, revealing a competition with the electron correlation. It transforms to a disorder-induced Anderson insulating behavior as doping increases. We directly visualize the trapped electrons in dI/dV conductance maps. The comprehensive study of the series of Ti-doped 1T-TaS2 deepens our understanding of the electronic state evolution in a doped strong-correlated system.

Tunable electronic properties of porous graphitic carbon nitride (C[formula omitted]N[formula omitted]) monolayer by atomic doping and embedding: A first-principle study

Motivated by the successful synthesis of the porous graphitic carbon nitride (C6N7) monolayer very recently, we investigate the structural and electronic properties of C6N7 with doped and embedded with various atoms by means of spin-polarized density functional theory calculations. C6N7 monolayers doped with B, N, C, and O atoms have been revealed as stable and predicted to be feasible for experimental fabrication as free-standing monolayers based on the energy and thermal stability. Our computations demonstrate that while the C6N7 is a semiconductor, the doped C6N7 monolayers can be metal, dilute-magnetic semiconductor or half-metal. Further, a non magnetic moment is discovered in three of the doped C6N7 models and their electronic properties are disclosed to depend strongly on the spin configurations. The electronic properties of C6N7 depend on the doping atoms and doping sites. Furthermore, the effect of embedding of common nonmetal atoms such as B, C, N, S, O, Al, Si and P as well as transition metal including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn atoms on the electronic and magnetic behavior of the C6N7 are studied. The charge transfer analysis shows that all embedded atoms act as electron donors, expect N, O and S atoms which act as electron acceptors when interacting with C6N7. The modification of the electronic band structure of C6N7 as the underlying mechanism for the changes in its electronic properties has been investigated. The intention is to demonstrate how entering the above mentioned impurities changes the nature of C6N7 into a metal, ferromagnetic-metal or dilute-magnetic semiconductor. These findings give not only an insight into the physical properties of doped and embedded C6N7 monolayer by different atoms, but also can serve as a guide to discover future possible applications of this novel material.

Theoretical Study of Small Molecules Adsorption on Pristine and Transition Metal Doped GeSe Monolayer for Gas Sensing Application.

By using first-principles calculations, the sensing properties of pristine and transition metal (TM) atoms (Ti, V, and Co) embedded germanium selenide (GeSe) monolayer toward small gas molecules (H2, NH3, CO, O2, SO2, NO, and NO2) were investigated. The adsorption energies, electronic structure, optical properties, and recovery time of the adsorption systems were calculated and analyzed in detail. The results indicate that TM doped GeSe has stronger interaction with gas molecules compared with the pristine GeSe monolayer. Especially for Ti- and V-GeSe monolayer, the absolute value of adsorption energies are up to 2 eV for O2, NO, and NO2. The doping with TM atoms also changes the charge transfer and electronic structures of adsorption systems. Combined with the result of the calculated optical properties and recovery time, it can be concluded that Ti-GeSe monolayer has great potential for NH3 detection, while Co-GeSe monolayer can be very promising SO2 gas sensors.

Aldol Condensation and Esterification over Ti-Substituted *BEA Zeolite: Mechanisms and Effects of Pore Hydrophobicity

Aldol condensation and esterification reactions provide paths to upgrade ethanol and acetaldehyde to higher-value molecules useful as fuels or intermediates for the synthesis of polymers. Transition-metal-substituted BEA zeolites (M-BEA) catalyze these reactions; however, the mechanisms for these processes in M-BEA and the effects of incidental or purposefully included silanol groups are not reported. Here, we combine kinetic and spectroscopic measurements obtained during catalytic reactions of acetaldehyde (CH3CHO), ethanol (C2H5OH), and hydrogen (H2) mixtures over a series of Ti-BEA catalysts that possess a known range of silanol group densities to examine the kinetic relevance of intervening steps and the impact of silanol groups on catalytic rates. Across all Ti-BEA, rates for aldol condensation and esterification increase with the pressure of CH3CHO; however, C2H5OH and H2O weakly inhibit the rates of these reactions. The substitution of CD3CDO for CH3CHO decreases aldol condensation rates slightly (∼10%) but leads to greater esterification rates (2- to 5-fold). The kinetic isotope effects together with the measured dependence of rates on reactant pressures suggest that aldol condensation and esterification occur on unoccupied Ti sites and involve multiple kinetically relevant steps. CH3CHO deprotonates irreversibly, and the kinetically relevant nucleophilic attack of the enolate to CH3CHO* (i.e., adsorbed CH3CHO on Ti sites) leads to aldol products, while the nucleophilic attack of the enolate to C2H5OH* gives esters. Selectivities toward aldol condensation increase with the ratio of CH3CHO to C2H5OH pressure and with increases in the silanol density of the as-synthesized Ti-BEA. During catalysis, in situ infrared spectroscopy demonstrates that these silanol groups react with C2H5OH to form ethoxysilane groups (i.e., SiOC2H5) that modify the polarity of the environment near Ti active sites. As initial silanol densities increase, steady-state turnover rates for aldol condensation and esterification increase by factors of 5 and 2, respectively. The changes in rates and selectivities among Ti-BEA catalysts likely reflect changes in excess free energies of transition states for enolization and nucleophilic attack of the enolate to adsorbed coreactants. The differences in excess stability report on the interactions among reactive intermediates at framework Ti atoms and the ethoxysilane and remaining silanol groups present. The in situ modification of these pore environments confers changes in the stability of reactive species in a manner that contradicts intuition when considering the initial state of the catalyst but can be reconciled after accounting for the formation of persistent alkoxy surface moieties in the pores.

First-principles study of structural, electronic and magnetic properties of transition metal doped Sc2CF2 MXene

The electronic and magnetic properties are investigated for pristine Sc2CF2, Sc2CF2-VSc (Sc2CF2 with single Sc vacancy), and Sc2CF2-dTM (Sc2CF2 doped with transitional metals TM, TM = Cr, Fe, Hf, Mn, Mo, Nb, Re, Ta, Ti, V, W, Y, or Zr) by first-principles calculation. The result indicates that Sc2CF2-dTM (TM = Ti, Zr, Nb, Hf, Ta, or W) monolayers are more stable than the other systems through the analysis of binding energies. The introduction of the Sc-vacancy and substitution doping of Hf, Mo, Nb, Re, Ta, Ti, W, or Zr atoms result in the semiconductor–metal transition for the Sc2CF2 monolayer, while the introduction of doped Cr, Fe or Y atoms doesn’t change the semiconductor character of Sc2CF2 monolayer and the introduction of doped V or Mn atoms results in the semimetal character. The substitution doping of V, Cr, Fe, or Mn atoms leads to significant magnetism. Charge transfer is further explored by the analysis of the charge density difference, the planar averaged charge density, and Bader charge. The effective mass and electron localization function are also analyzed.

Photocatalytic Activity and Hole-Scavenging Behaviors on Rutile TiO2(100) Surfaces: A Theoretical Study

A rutile TiO2(100) surface usually shows better photoactivity than other surfaces, and its mechanism is not well understood yet. In this work, we found larger charge accumulation on its bridging oxygen/adsorbents and lower symmetry of its surface Ti atoms. This enables (100) a better surface to accommodate the hole, which could be one key reason for its high photoactivity. Interestingly, the localized hole on the (100) surface can be reliably simulated using a density functional theory (DFT) method without Hubbard U corrections, which affords an unbiased platform to study the hole-scavenging behavior for extensive adsorbents and functional groups. Then, the hole-mediated proton dissociations of water, alcohol, amine, and alkane on the (100) surface have been studied in detail. The hole-scavenging ability of the groups is in the order hydroxyl < alkoxyl < aminyl < alkyl. Moreover, we found a good correlation between the hole-scavenging ability and the density of states. With this correlation, we predict that the facet hole-scavenging ability for most groups is in the order rutile (100) > anatase (101) > rutile (110) > rutile (001), which is in good agreement with the experimental observations and would provide suggestions for further photocatalytic studies.

Synergistic Size–Surface Effects on Martensitic Transformation of Shape Memory Alloy Nanorods for Micro/Nanoelectro-Mechanical Systems

Martensitic transformation (MT) of shape memory alloys (SMAs) deserves promising applications in various smart devices including micro/nanoelectro-mechanical systems owing to the material’s large reversible deformation from cyclic MT. However, such systems always suffer from critical fatigue problems under cyclic loadings with microdamage accumulations closely related to hysteresis energy and residual strain. Here, the synergistic effects of the sample size and surface composition on the MT of SMA nanorods are systematically investigated by combining global responses and atomic evolutions based on molecular dynamics. It is found that the surface energy plays a resisting role in MT and the resistance increases with decreasing sample size, which in turn increases the critical stress, hysteresis, and residual strain. Intriguingly, the nucleated austenite–martensite transition zone during MT can be influenced by surface composition, and an ultralow hysteresis and residual strain with little size-dependence can be achieved in the nanorod with the surface composed of alternate Ni and Ti atoms. The low energy density of the transition zone indicates better microscopic lattice compatibility and smaller dissipations during MT. This reveals that the surface modification is promising for modulating the size effect and improving the reversibility and the fatigue resistance of the superelastic SMA nanostructures.

Characterizing the Chemical Structure of Ti3C2Tx MXene by Angle-Resolved XPS Combined with Argon Ion Etching.

Angle-resolved XPS combined with argon ion etching was used to characterize the surface functional groups and the chemical structure of Ti3C2Tx MXene. Survey scanning obtained on the sample surface showed that the sample mainly contains C, O, Ti and F elements, and a little Al element. Analyzing the angle-resolved narrow scanning of these elements indicated that a layer of C and O atoms was adsorbed on the top surface of the sample, and there were many O or F related Ti bonds except Ti–C bond. XPS results obtained after argon ion etching indicated staggered distribution between C–Ti–C bond and O–Ti–C, F–Ti bond. It is confirmed that Ti atoms and C atoms were at the center layer of Ti3C2Tx MXene, while O atoms and F atoms were located at both the upper and lower surface of Ti3C2 layer acting as surface functional groups. The surface functional groups on the Ti3C2 layer were determined to include O2−, OH−, F− and O−–F−, among which F atoms could also desorb from Ti3C2Tx MXene easily. The schematic atomic structure of Ti3C2Tx MXene was derived from the analysis of XPS results, being consistent with theoretical chemical structure and other experimental reports. The results showed that angle-resolved XPS combing with argon ion etching is a good way to analysis 2D thin layer materials.

Influence of the orientation of Ti-Al interphase boundary on the mutual diffusion rate at the solid and liquid states of aluminium: molecular dynamics simulation

The influence of the orientation of Ti-Al interphase boundary on the intensity of mutual diffusion at solid-phase and solid-liquid-phase contacts was studied by the method of molecular dynamics. Four orientations of the boundary with respect to the Ti (hcp) and Al (fcc) lattices were considered: (0001) : (111), (0001) : (001), (1010) : (111), (1011) : (001). At solid-phase contact, an important phenomenon influencing the intensity of mutual diffusion was the formation, due to the mismatch of the lattices of Ti and Al, of grain boundaries in Al parallel to the interphase boundary. This boundary was both the main source and sink of structural defects, including vacancies required for diffusion to proceed. In the case of solid-liquid-phase contact, after melting of aluminium, part of it near the interphase boundary remained in the crystalline state, repeating the titanium lattice. That is, the boundary between the crystal and the liquid metal was shifted by two or three atomic planes deep into the aluminium. For the considered orientations, concentration curves were obtained after simulating mutual diffusion at different temperatures. The flatter parts of the curves, which are responsible for the diffusion of Ti atoms deep into liquid Al, turned out to be similar for all orientations. However, the parts related to the diffusion of Al atoms into crystalline Ti were different: diffusion of Al atoms in Ti proceeded more intensively with the orientation of the boundary (0001) and more slowly with the orientations (1010) and (1011). Keywords: molecular dynamics, diffusion, interphase boundary, titan, aluminum.

Влияние ориентации межфазной границы Ti-Al на скорость взаимной диффузии при твердом и жидком состояниях алюминия: молекулярно-динамическое моделирование

The influence of the orientation of Ti-Al interphase boundary on the intensity of mutual diffusion at solid-phase and solid-liquid-phase contacts was studied by the method of molecular dynamics. Four orientations of the boundary with respect to the Ti (hcp) and Al (fcc) lattices were considered: (0001):(111), (0001):(001), (101 ̅0):(111), (101 ̅1):(001). At solid-phase contact, an important phenomenon influencing the intensity of mutual diffusion was the formation, due to the mismatch of the lattices of Ti and Al, of grain boundaries in Al parallel to the interphase boundary. This boundary was both the main source and sink of structural defects, including vacancies required for diffusion to proceed. In the case of solid-liquid-phase contact, after melting of aluminium, part of it near the interphase boundary remained in the crystalline state, repeating the titanium lattice. That is, the boundary between the crystal and the liquid metal was shifted by two or three atomic planes deep into the aluminium. For the considered orientations, concentration curves were obtained after simulating mutual diffusion at different temperatures. The flatter parts of the curves, which are responsible for the diffusion of Ti atoms deep into liquid Al, turned out to be similar for all orientations. However, the parts related to the diffusion of Al atoms into crystalline Ti were different: diffusion of Al atoms in Ti proceeded more intensively with the orientation of the boundary (0001) and more slowly with the orientations (101 ̅0) and (101 ̅1).

Interfacial behaviour of the high-entropy alloy CuCoCrFeNi and TC4 joint obtained by vacuum diffusion welding

In this work, good bonding between the high-entropy alloy (HEA) CuCoCrFeNi and TC4 titanium alloy was obtained through vacuum diffusion welding at a joining temperature of 1000 °C for 60 min under a pressure of 5 MPa. The results showed that the typical interfacial microstructure of the CuCoCrFeNi/TC4 joint was TC4/diffusion layer/island structure/dendritic structure/diffusion layer/HEA. Compared with Ti atoms, atoms such as Cr and Co from the CuCoCrFeNi substrate were prone to diffuse into the other material. Intermetallic compounds Cu0.5Fe0.5Ti and Co0.15Ni0.85Ti, solid solutions Ti(Fe, Cr)ss and amorphous materials were produced in the joint. The self-diffusion activation energy formula [see formula in PDF] can be used to approximate the order of diffusion capacity of elements, which follows in Cr &gt;Fe&gt; Co &gt; Ni.

Nano TiC-Graphene-Cu composites fabrication by a modified ball-milling method followed by reactive sintering: Effects of reinforcements content on microstructure, consolidation, and mechanical properties

A two-step mechanical milling followed by a reactive sintering process was used to synthesize Nano TiC-Graphene-Cu composites from a mixture of Cu, Ti, and Graphene (GN) powders in four different compositions, and effects of reinforcements content on the microstructure and mechanical properties were studied. The results showed that a part of GN reacted with Ti atoms in the matrix, leading to the successful formation of hybrid nanocomposites. Uniform distribution of in-situ TiC with nanometer size and unreacted GN in the nanostructured Cu (Ti) solid solution were obtained. Addition of high percentage of the reinforcements led to an increase in the porosity and microhardness, coarsening of TiC nanoparticles, and decreasing the grain size of the matrix after sintering. The simultaneous presence of GN and TiC nanoparticles in the Cu matrix improved the hardness and wear resistance and reduced the friction coefficient by self-lubricating behavior. The nanocomposite with the nominal composition of Ti-40 vol % TiC showed the highest wear resistance and the lowest friction coefficient.

Band-engineered Zn2TiO4 nanowires for hydrogen generation from water using visible light: A first-principles study

The electronic structure and optical properties of inverse-spinel Zn2TiO4 nanowires and bulk material were investigated for hydrogen generation from water by visible-light photocatalysis using first-principles density calculations. In our theoretical studies, the bandgap of the Zn2TiO4 nanowires was much smaller than that of the bulk material. New intermediate states appeared in the mid-bandgap as a result of Zn and Ti atoms on the surface of ZnO-terminated and ZnTiO-terminated nanowires. These deep-level states could become recombination centers for photogenerated electron–hole pairs, indicating that these two types of nanowires would no longer meet the requirements for photocatalytic water splitting. In contrast, the electronic states arising from oxygen elements on the surface of the TiO-terminated nanowires resulted in an upward movement of the edge of the valence band, whereas the surface electronic states made no difference to the edge of the conduction band. Moreover, the optical property calculations showed that the optical absorption edge of the nanowire would be red-shifted. These calculations revealed that inverse-spinel Zn2TiO4 nanowires were appropriate for visible-light photocatalytic water splitting reactions.

Single Mo atoms paired with neighbouring Ti atoms catalytically decompose ammonium bisulfate formed in low-temperature SCR

We developed a TiO2-supported single-atom Mo catalyst (Mo1/TiO2) where single Mo atoms paired with the neighboring surface Ti atoms function as Mo–Ti acid–base dual sites, realizing the decomposition of ABS at ∼225 °C.

ВЛИЯНИЕ ХИМИЧЕСКОГО СОСТАВА НА ТВЕРДОРАСТВОРНОЕ И ДЕФОРМАЦИОННОЕ УПРОЧНЕНИЕ МОНОКРИСТАЛЛОВ ГЦК ВЫСОКОЭНТРОПИЙНЫХ СПЛАВОВ

A characteristic feature of high-entropy alloys is high strength at maintaining plasticity, wear and corrosion resistance, and fracture toughness at cryogenic temperatures. Currently, CoCrFeNiMn is the best-investigated high-entropy compound. However, its application is limited in the high-temperature region due to the low values of the deforming stress level at the plasticity breaking point at T&gt;296 K. One of the common ways to improve the material durability is the addition of substitution atoms of larger atomic radius, and Al, Ti, and Mo are some of these atoms. The paper presents the analysis of the mechanical behavior of single crystals of CoCrFeNiMn and CoCrFeNiMо FCC high-entropy alloys (at. %) oriented along the [001] direction: the author studied the temperature dependence of critical shear stresses τcr(T) within the temperature range of T=77–973K, the type of dislocation structure, strain hardening coefficient θII, plasticity and fracture at Т=296 K under tension. The study shows that the alloying with Mo atoms 4 at. % of the CoCrFeNi system (at. %) causes the solid solution hardening, and critical shear stresses τcr increase within the entire studied temperature range. The onset of plastic deformation is associated with slip at all temperature tests. At T=296 K, the author identified a planar dislocation structure with flat dislocation pile-ups and dislocation networks in CoCrFeNiMo while in equiatomic CoCrFeNiMn, at such test temperature, a uniform distribution of dislocations was observed in several systems without flat pile-ups. Work hardening coefficient, plasticity, and the level of stresses before fracture turn out to be similar in [001]-crystals of CoCrFeNiMo and CoCrFeNiMn high-entropy alloys, which are determined by the development of slip deformation simultaneously in several systems. Crystals are destroyed viscously at 296 K at the same level of stress.

Ab initio расчет зонной структуры и свойств модификаций соединения Ti-=SUB=-3-=/SUB=-Sb, допированного литием

Using the density functional theory (DFT) in the local electron spin density approximation (LSDA), 2×2×2 supercells based on the Ti3Sb compound have been studied. The supercells contained their own vacancies and doped lithium atoms replacing Ti and/or Sb. The DFT-LSDA method was used to calculate the structural, electronic, and magnetic properties, the enthalpy of formation, and the cohesion energy of supercells of two modifications of the Ti3Sb compound. We studied supercells with cubic system (A15 type structure; a = 5.217 Å) and tetragonal system (D8_m type structure; а = 10.457 Å, с = 5.258 Å). It has been established that the distribution of the density of states of the Ti3Sb cubic system has a more metallic character than for the D8_mTi3Sb modification. The enhancement of "metallicity" in the cubic modification A15 Ti3Sb is associated with an increase in the Ti–Sb interatomic distance in the crystal. Due to this, the degree of metallic bonding increases during the electronic interaction between Ti and Sb atoms near the Fermi level in Ti3Sb. In DFT calculations, the spin-polarized density of states was taken into account. It has been established that in both modifications (A15 and D8_m) of Ti3Sb near the Fermi level for s, p, d-states with spin "up" and spin "down" there is a spin imbalance in the population of energy levels. Defect-containing supercells based on Ti3Sb were studied by DFT-LSDA calculations. It is shown that Ti and/or Sb vacancies in the lattices of Ti3Sb crystals of both modifications (A15 and D8_m) increase the magnetic moment (M) as compared to the value of M (M_tot = 0.08 μ_B) of a “pure” Ti3Sb crystal. Considering that Al5 Ti3Sb is also interesting as a material for Li-ion batteries, we studied Ti3Sb–Li supercells doped with lithium. Li-doping and the creation of own Ti and/or Sb vacancies changes the distance between atoms in Ti3Sb. Correspondingly, the resulting local magnetic moments near the Ti or Sb vacancies also change. The enthalpy of formation and magnetic moment of Ti3Sb and Ti3Sb–Li based supercells are calculated. DFT calculations of the structural stability of binary compounds (phases) have been carried out, and the stability of conodes between phases in the Ti–Sb–Li system has been established. The isothermal section of the Ti–Sb–Li system was plotted at 298 K. It is shown that the introduction of various lithium concentrations (&lt;6.25 at. % Li) into the Ti3Sb (Space group Pm3 ̅n; № 223; a = 5.217 Å) crystal lattice reduces the partial magnetic moment of Ti in the Ti3Sb–Li supercell.

Ab initio calculation of the band structure and properties of modifications of the Ti-=SUB=-3-=/SUB=-Sb compound doped with lithium

Using the density functional theory (DFT) in the local electron spin density approximation (LSDA), 2x2x2 supercells based on the Ti3Sb compound have been studied. The supercells contained their own vacancies and doped lithium atoms replacing Ti and/or Sb. The DFT-LSDA method was used to calculate the structural, electronic, and magnetic properties, the enthalpy of formation, and the cohesion energy of supercells of two modifications of the Ti3Sb compound. We studied supercells with cubic system (A15 type structure; a=5.217 Angstrem) and tetragonal system (D8m type structure; a=10.457 Angstrem, c=5.258 Angstrem). It has been established that the distribution of the density of states of the Ti3Sb cubic system has a more metallic character than for the D8m Ti3Sb modification. The enhancement of &amp;quot;metallicity&amp;quot; in the cubic modification A15 Ti3Sb is associated with an increase in the Ti-Sb interatomic distance in the crystal. Due to this, the degree of metallic bonding increases during the electronic interaction between Ti and Sb atoms near the Fermi level in Ti3Sb. In DFT calculations, the spin-polarized density of states was taken into account. It has been established that in both modifications (A15 and D8m) of Ti3Sb near the Fermi level for s-, p-, d-states with spin &amp;quot;up&amp;quot; and spin &amp;quot;down&amp;quot; there is a spin imbalance in the population of energy levels. Defect-containing supercells based on Ti3Sb were studied by DFT-LSDA calculations. It is shown that Ti and/or Sb vacancies in the lattices of Ti3Sb crystals of both modifications (A15 and D8m) increase the magnetic moment (M) as compared to the value of M (M=0.08 μB) of a &amp;quot;pure&amp;quot; Ti3Sb crystal. Considering that Al5 Ti3Sb is also interesting as a material for Li-ion batteries, we studied Ti3Sb-Li supercells doped with lithium. Li-doping and the creation of own Ti and/or Sb vacancies changes the distance between atoms in Ti3Sb. Correspondingly, the resulting local magnetic moments near the Ti or Sb vacancies also change. The enthalpy of formation and magnetic moment of Ti3Sb and Ti3Sb-Li based supercells are calculated. DFT calculations of the structural stability of binary compounds (phases) have been carried out, and the stability of conodes between phases in the Ti-Sb-Li system has been established. The isothermal section of the Ti-Sb-Li system was plotted at 298 K. It is shown that the introduction of various lithium concentrations (≤6.25 at.% Li) into the Ti3Sb (Space group Pm3 n; N 223; a=5.217 Angstrem) crystal lattice reduces the partial magnetic moment of Ti in the Ti3Sb-Li supercell. Keywords: Ti3Sb intermetallic compounds, A15 cubic modification, D8m tetragonal modification, doping with lithium, Ti3Sb-Li, DFT-LSDA calculations, supercell, electronic and magnetic properties, Ti-Sb-Li phase stability.

Microstructure and high-temperature mechanical properties of co-continuous (Ti3AlC2+ Al3Ti)/2024Al composite fabricated by pressureless infiltration

Ti 3 AlC 2 /2024Al composites with a co-continuous structure were successfully fabricated from 2024Al powders and Ti 3 AlC 2 porous preforms (with porosity of 48%, 41% and 35%, respectively) by pressureless infiltration at 930 °C. Long-rod like Al 3 Ti was in situ formed due to reaction of Ti atoms de-intercalated from Ti 3 AlC 2 and liquid 2024Al, which interpenetrated with Ti 3 AlC 2 to form a new continuous framework. The mechanical properties in relationship with the initially different volume fractions of Ti 3 AlC 2 and 2024Al at room temperature and high temperature were investigated. At room temperature, 59 vol%Ti 3 AlC 2 /2024Al has the best comprehensive mechanical properties, with the flexural strength of 510 MPa, compressive strength of 729 MPa, and compressive strain of 5.49%. Due to the co-continuous structure and the excellent high temperature of Al 3 Ti, all samples exhibit well mechanical properties at 300 °C. Among them, 52 vol%Ti 3 AlC 2 /2024Al has the best performance with the ultimate compressive strength of 532 MPa, which is only 18.7% lower than room temperature. And even at 400 °C,it still has an objective compression strength of 394 MPa due to the highest content of Al 3 Ti. In addition, after quenching from 400 °C to room temperature, the residual flexural strength of 52 vol%Ti 3 AlC 2 /2024Al can be reached to 450 MPa with the mere reduction rate of 7.4%. And no cracks are observed at the boundary of each phase, which means the good thermal shock resistance of the composites.

In situ synchrotron Х-ray diffraction study of heat-induced structural changes in TiOy/HAp nanocomposites

In situ synchrotron Х-ray diffraction (XRD) was used to study the interactions between an important biomaterial for tissue engineering and regenerative medicine, hydroxyapatite, and titanium monoxide additives of different stoichiometry, in nanocomposite materials. The study was carried out in the temperature range from ambient to 900 °C in a flow of dry air. During the temperature evolution of the nanocomposites, the mutual influences of the matrix and additives were observed. The dynamics of changes in the phase composition and the effects of TiOy on the thermal stability of the matrix were considered. The addition of 10 wt% TiOy increased the decomposition temperature of HAp by approximately 100 °C. Different additive stoichiometries shifted the temperature ranges of the phase transitions in the nanocomposites. Opposite trends were observed for the dependence of the weight content of the matrix and that of the additive on temperature in the range from 300 to 800 °C. This behaviour was explained by a partial substitution of Ti atoms for Ca atoms. After heat treatment to 900 °C, all nanocomposite phases were biocompatible. The oxyapatite and TiO2 phases retained the nanostates of their initial components, while the α- and β-ТСР phases were microcrystalline. In situ synchrotron XRD method proved to be a highly informative and precise technique for studying new biomaterials.