Ti Valence Research Articles

Hydrothermal Synthesis of Na0.5La0.5TiO3–LaCrO3 Solid‐Solution Single‐Crystal Nanocubes for Visible‐Light‐Driven Photocatalytic H2 Evolution

Cubic perovskite structure photocatalysts of Na(0.5)La(0.5)TiO(3) and (Na(0.5)La(0.5)TiO(3))(1.00)(LaCrO(3))(0.08) solid solution that consisted of well-defined single-crystal nanocubes were successfully prepared by means of facile and surfactant-free hydrothermal reactions for the first time. The results from different instrumental characterizations and theoretical calculations consistently confirmed the formation of nanocubic single-crystal solid solution of (Na(0.5)La(0.5)TiO(3))(1.00)(LaCrO(3))(0.08), and clearly revealed the modification of its physicochemical properties compared with those of Na(0.5)La(0.5)TiO(3). In particular, the effective narrowing of the bandgap (from 3.19 to 2.25 eV) by Cr(3+) in the solid solution made it possible to utilize visible light. The solid-solution configuration maintained the charge balance to preserve the valence of Cr(3+) rather than Cr(6+), and accommodated Cr(3+) with high content to form new energy bands instead of localized impurity levels. The hydrothermal preparation strategy ensured the formation of single crystals with high purity, few defects, and regulated morphology; it also guaranteed the valences of Ti(4+) and Cr(3+) in the solid solution. Consequently, the recombination of photogenerated carriers could be effectively suppressed to benefit photocatalytic H(2) evolution. (Na(0.5)La(0.5)TiO(3))(1.00)(LaCrO(3))(0.08) nanocubic single-crystal solid solution showed stable photocatalytic activity, and thus was proved to be a promising candidate for visible-light-driven photocatalytic H(2) evolution.

Second Phase and Defect Formation in Bi0.5Na0.5-xKxTiO3 Ceramics

The second phase and defect formation mechanisms of [Bi0.5(Na1-xKx)0.5]TiO3 (BNKT100x) ceramics were investigated using electron microscopy, X-ray photoelectron spectroscopy (XPS), and electrical properties measurement. Experimental results indicated that second phase formation induces Bi-rich regions and compositional inhomogeneity within the matrix owing to the thermodynamic stability of potassium titanate. The Ti valence transition for BNKT ceramics sintered in air might be ascribed to the formation of secondary phase and low oxygen atmosphere, rather than simply attributed to the volatilization of bismuth. Li substitution at the A-site in BNKT ceramics suppresses formation of the second phase and Ti valence transition. Appropriate atmosphere control during material processing, such as sintering at higher oxygen pressure, and post oxidization annealing suppress oxygen vacancies and titanium valence transition, and therefore decrease the leakage current as well as improve electrical properties.

TiO2/Carbon Composites Prepared from Rice Husk and the Removal of Bisphenol A in Photocatalytic Liquid System

photoelectron spectroscopy (XPS) results showed that the Ti-O bond was weaker in the carbon/TiO2 composite than in the pure TiO2, resulting in an easier electron transition from the Ti valence band to the conduction band. The carbon/TiO2 composite absorbed over the whole UV-visible range, whereas the absorption band in the pure TiO2 was only observed in the UV range. These results agreed well with an electrostatic force microscopy (EFM) study that showed that the electrons were rapidly transferred to the surface of the carbon/TiO2 composite compared to the pure TiO2. The photocatalytic performance of the BPA removal was optimized at a Ti:C ratio of 9.5:0.5, and this photocatalytic composite completely decomposed 10.0 ppm BPA after 210 min, whereas the pure TiO2 achieved no more than 50% decomposition under any conditions.

Electronic reconstruction atn-typeSrTiO3/LaAlO3interfaces

Electron-energy-loss spectroscopy (EELS) is used to investigate single layers of LaAlO3 grown on SrTiO3 having an n-type interface as well as multilayers of LaAlO3 and SrTiO3 in which both n- and p-type interfaces occur. Only minor changes in Ti valence at the n-type interface are observed. This finding seems to contradict earlier experiments for other SrTiO3/LaAlO3 systems where large deviations in Ti valency were assumed to be responsible for the conductivity of these interfaces. Ab initio calculations have been carried out in order to interpret our EELS results. Using the concept of Bader charges, it is demonstrated that the so-called polar discontinuity is mainly resolved by lattice distortions and to a far lesser extent by changes in valency for both single layer and multilayer geometries.

Electrical properties changes induced by electron radiation at TiO2/Si interface

TiO2/Si structures were fabricated by electron beam evaporation, and exposed to electron beam irradiation to investigate their electrical properties using the high frequency capacitance–voltage measurements. It was found that samples annealed in oxygen became more radiation resistant than un-annealed samples, which can be explained by the Ti valence variations induced by radiation. The samples were characterized by X-ray diffraction to show the Ti2O3 crystalline phase transformed to anatase-crystalline phase after oxygen annealing.

Relationship between Electrode Performance and Chemical Bonding Nature in Mesoporous Metal Oxide-Layered Titanate Nanohybrids

We investigated the applicability of mesoporous MOx-layered titanate (M = Fe or Ni) nanohybrids as a lithium intercalation electrode to elucidate the relationship between electrode activity and chemical bonding nature in these materials. Electrochemical measurements clearly demonstrate that the mesoporous nanohybrids show better performance of lithium cation intercalation electrodes, compared with the pristine titanate. This finding underscores that hybridization with metal oxide nanocrystals is quite effective in improving the electrochemical property of titanium oxide. The anode performance of the NiOx-layered titanate nanohybrid can be further improved by a postcalcination at 300 °C whereas there is less significant increase in the discharge capacity of the iron oxide homologue after the heat-treatment at the same temperature. Such different effects of the postcalcination can be understood in terms of local structural evolution of guest species; the nickel species in the as-prepared NiOx-layered titanate nanohybrid exist in the form of nickel hydroxide and the postcalcination at ≥300 °C induces a structural transformation to rocksalt-structured nickel oxide. On the contrary, the local structure around iron ions in the FeOx-layered titanate nanohybrid does not experience any notable modifications upon the postcalcination. According to X-ray absorption spectroscopic analyses for the chemically lithiated nanohybrids, the lithium insertion via n-BuLi treatment decreases the oxidation states of iron and nickel ions with negligible change in Ti valency. This result strongly suggests that the insertion of Li+ ions into the present nanohybrids can be achieved by a redox process of hybridized iron oxide or nickel oxide, and hence this functionality is strongly dependent on the chemical bonding nature of hybridized guest species.

Switching Ti Valence inSrTiO3by a dc Electric Field

A (001) SrTiO3 wafer has been investigated in situ at room temperature under application of a static electric field of varying polarity by fluorescence x-ray absorption near edge structure (XANES) analysis at the Sr-K and Ti-K absorption edges. The XANES spectra show a clear shift of the Ti-K absorption edge energy. The shift is attributed to a change of the Ti valence state in a volume invoked by diffusion of the oxygen ions and vacancies. No shift was observed for the Sr-K absorption edge energy. Theoretical calculations support these findings.

Electron structure and photoluminescence behavior of Ti0.09Y1.91O2S

The Ti-doped yttrium oxysulfide (Ti0.09Y1.91O2S) was synthesized by sintering the mixture of sulfur (S)- and Ti-doped yttrium oxide (Ti0.09Y1.91O3); Ti0.09Y1.91O3, the same as yttrium oxide, form cubic lattice (C-type) with six coordinated polyhedron of the metal ions, but the synthesized Ti0.09Y1.91O2S displays trigonal P3¯m1 structure. X-ray photoelectron spectrograph analysis reveals that the Ti ion is in quadrivalence state, no Ti2+ and Ti3+ ions were found. Besides, the shift of core level Ti 2p and valence band top was observed, which results from the change in the lattice structure. The changes in electronic state density are attributed to an increase in sulfur and a decrease in oxygen. Under the wavelength of 514.5 nm radiation of Ar-ion Laser excited, Ti-doped Y2O3 shows an asymmetry emission spectrum at about 644 nm, and Ti0.09Y1.91O2S has two broad bands emission spectra centered at 744 and 383 nm have been observed. The two broad bands correspond to usual fluorescence and upconversion spectrum, respectively. We assume that the Ti 3d level structure is similar to the Mn 3d one of manganites. The observed emission spectra were attributed to the spin-allowed T32g-T31g and T31g-T31g transition. The relation between electron structure and luminescence behavior was discussed in detail.

N ion irradiation enhancement of photocatalytic activity of TiO2

We have prepared TiO2 (anatase-phase) films by anodic-oxidation of Ti sheet followed by oxidation at 450°C in air and studied ion irradiation effect on the photocatalytic activity of water splitting by using Hg lamp and gas-chromatograph. We find that H2 evolution from water under ultraviolet (UV) light exposure increased by a factor of ∼2 after 100keV N ion irradiation of 3×1015/cm2. X-ray diffraction (XRD) shows no appreciable change in the XRD patterns before and after the ion irradiation. Rutherford backscattering spectra (RBS) of 1.8MeV He and nuclear reaction analysis (NRA) of 1.2MeV d neither show noticeable change in the composition and the amount of carbon impurities by the N ion irradiation. Possible factors for the enhancement of photocatalytic activity by ion irradiation have been discussed: increase in the surface area, optical absorption change and modification of Ti valence. Ion irradiation enhancement has been observed also for NiO-loaded TiO2 (rutile-phase).

Effect of O<SUB>2</SUB>-Plasma Treatment on Surface Characteristics and Osteoblast-Like MG-63 Cells Response of Ti-30Nb-1Fe-1Hf Alloy

In this study, the effect of O2-plasma treatment with various powers on the surface characteristics and also the cell response of the Ti-30Nb-1Fe-1Hf alloy were investigated. Surface characteristics of Ti-30Nb-1Fe-1Hf alloy were evaluated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray powder diffractometer (XRPD) and wettability test. The results show that the surface roughness of the alloy decreases after O2-plasma treatment, and also with increased plasma power. By XPS analyses, both Ti valence states of Ti2+, Ti3+ and Ti4+ as well as Nb valence states of Nb2+, Nb4+ and Nb5+ can be detected in the oxide films. Also, the concentrations of TiO2 and Nb2O5 increase with increasing O2-plasma power. The results also show that the contact angle decreases as the alloy is modified by O2-plasma treatment, and therefore, the treated alloys can be expected to be more hydrophilic. On the other hand, for the evaluation of cell response, cell (MG-63) culture was performed. The results show that the oxidation effect on the alloy surface brought about by O2-plasma treatment enhances the spreading of cells. In addition, in vitro tests suggest that cell spreading on Ti-30Nb-1Fe-1Hf alloy is similar to that on Ti-6Al-4V alloy, whereas, cell adhesion on Ti-30Nb-1Fe-1Hf alloy is better than that on Ti-6Al-4V alloy.

Atomic control and characterization of surface defect states of TiO2 terminated SrTiO3 single crystals

By using an alternative wet-etch procedure, we have obtained high-quality atomically flat TiO2 terminated surfaces of SrTiO3 single crystals with the morphology equivalent to that of the conventional wet-etch methods. By applying a combined power of photoluminescence (PL) spectroscopy, reflection high-energy electron diffraction, atomic force microscopy imaging, and soft x-ray absorption (XAS), we were able to identify and monitor the complex evolution of oxygen defect states and Ti valency at the surface and near-surface layers. Our experiments revealed a high level of local defects resulting in the presence of the Ti3+ states at the surface. We have developed a method to control the defect states capable of a marked reduction of the defect concentration. We have demonstrated that the PL and XAS are able to distinguish the surface-related Ti3+ states from oxygen vacancies trapping charge transfer vibronic excitons that define the PL intensity. The experimental findings will have important implications for the growth of high-quality ultrathin complex oxide heterostructures.

Photoelectron spectroscopy of PbTiO 3:Mn single crystals

The XPS measurements of the PbTiO 3: x%Mn single crystals revealed that in spite of a small manganese concentration the significant changes of the XPS line shapes are observed. This is caused probably by the change of the valency of Ti, Pb and Mn and due to possibility of the replacement of both Ti and Pb ions by Mn.

Charge compensation and mixed valency inLaAlO3∕SrTiO3heterointerfaces studied by the FLAPW method

The electronic structures and properties of heterointerfaces in the perovskite oxide superlattices ${\mathrm{LaAlO}}_{3}∕{\mathrm{SrTiO}}_{3}\phantom{\rule{0.3em}{0ex}}[001]$ are presented using the first-principles all-electron full-potential linearized augmented plane-wave (FLAPW) method. Superlattices with three types of interfaces, (i) electron-doped, (ii) hole-doped, and (iii) both electron- and hole-doped, are studied and compared. For the electron-doped interface, the mixed valency of Ti along with the Jahn-Teller effect are found to explain the metallicity, in agreement with experiment, whereas for the hole-doped interface metallicity is found, in contrast to experiment. Oxygen vacancies introduce an additional $n$-type carrier to compensate the holes present at the interface, which now becomes insulating and agrees well with experiment. For a system with both types of interfaces, the metallicity found for the unrelaxed structure is changed to insulating after relaxation is included. For all cases, the relaxation results in a complicated buckled geometry, which is a good indication of the adjustment due to polarity discontinuity. Our findings support recent experimental results, namely, (i) the mixed-valence character of Ti at the electron-doped interface, and (ii) the existence and importance of oxygen vacancies at the hole-doped interface.

Titanium incorporation and VITi3+ -IVTi4+ charge transfer in synthetic diopside

A series of Ti-doped diopside samples synthesized by fluxgrowth methods under reducing conditions were investigated by microanalytical methods and optical absorption spectroscopy, to assess Ti incorporation mechanisms, valence states, and related electronic transitions. Chemical characterization show that Ti occurs both in the tri-and tetravalent states, with Ti4+ preferentially ordered to the tetrahedral position whereas Ti3+ is restricted to the M1 position. Charge-balance is maintained by incorporation of Na and minor B, stemming from the flux compound. Polarized optical absorption spectra reveal three major absorption features. Two relatively narrow bands centered at 18 500 and 15 700 cm-1, mainly polarized in the crystallographic c-direction, display absorbance values that correlate with the calculated Ti3+ (M1) concentration, and are assigned to spin-allowed d-d transitions in Ti3+. A broader band centered around 24 500 cm-1 displays absorbance values that are well correlated with the product of VITi3+ and IVTi4+. Based on the spectral characteristics of this band, including a strong polarization in the crystallographic b-direction, we assign this band to an M1Ti3+-TTi4+ intervalence charge transfer process.

Investigations on Raman and X-ray photoemission scattering patterns of vanadium-doped SrBi4Ti4O15 ferroelectric ceramics

Abstract Vanadium incorporation in SrBi 4 Ti 4 O 15 results in an improvement of electric properties. Raman scattering reveals that V-addition brings about the local disorders of structure, charge, and internal stress. The chemical valence of Bi and Ti does not increase after V-doping. The electric property improvement is originated from the restraint of oxygen vacancies, mobility weakening of the defects, and the vacancies produced at A -site.

Photoemission and x-ray absorption study of the electronic structure ofSrRu1−xTixO3

We investigated the chemical states and the electronic structure of ${\mathrm{SrRu}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{3}$ at room temperature by using both photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The core-level spectra showed the absence of a macroscopic chemical inhomogeneity. The $\mathrm{Ti}\phantom{\rule{0.3em}{0ex}}2p$ core level and the $\mathrm{Ti}\phantom{\rule{0.3em}{0ex}}2p$ XAS reveal that the valency of Ti remains unchanged at $4+$. In contrast to a previous PES study that was conducted on the scraped surfaces of polycrystal samples, we observed a systematic change in the $\mathrm{Ru}\phantom{\rule{0.3em}{0ex}}4d$ band: a decrease in coherent peaks and an increase in incoherent peaks with an increase in $x$. In addition to this spectral change, we observed the depletion of the density of states near ${E}_{F}$. This depletion expands in energy and strength with an increase in $x$. Finally, the $\mathrm{Ru}\phantom{\rule{0.3em}{0ex}}4d$ spectra for $x=0.8$ exhibit a hard gap. All these spectral changes are consistent with those reported in a recent optical and transport study.

Characterisation of Grain Boundaries in CaCu3Ti4O12 using HREM, EDS and EELS

Preliminary EELS and EDS analyses undertaken on CaCu3Ti4O12 ceramics, sintered for 3 and 24 hrs at 1100°C in air, have suggested that there are differences in the composition and valence of the Cu and Ti at grain boundaries as compared with the bulk composition. For the 3 hour sinter a change was observed in the Cu valence and for the 24 hour a change in both Ti and Cu valences was detected. This variation in composition may explain the electrical properties of high permittivity at room temperature exhibited by these ceramics.

Lithiation–delithiation properties of new compound LiNi 0.5Ti 0.5O 2 with cubic structure

A new compound Li–Ni–Ti oxide-based material (LiNi 0.5Ti 0.5O 2) with cubic structure was prepared by solid state reaction at 900 °C. Powder X-ray diffraction (XRD) was used to determine the phase purity and structure of the material. The Bragg peaks of LiNi 0.5Ti 0.5O 2 can be indexed based on a cubic unit with dimension a = 4.142 Å, belonging to space group Fd3 m (SG number 225). X-ray photoelectron spectroscopy (XPS) study showed that the chemical valences of Ni and Ti were +2 and +4, respectively. The electrochemical testing indicated that the Li + ions in LiNi 0.5Ti 0.5O 2 cannot be extracted until 4.8 V. However, two initial Li ions per LiNi 0.5Ti 0.5O 2 can be intercalated into LiNi 0.5Ti 0.5O 2 and one Li + ion can be extracted reversibly.

X-ray absorption study of Ti-activated sodium aluminum hydride

Ti K-edge x-ray absorption near-edge spectroscopy was used to explore the Ti valence and coordination in Ti-activated sodium alanate. An empirical relationship was established between the Ti valence and the Ti K-edge onset based on a set of standards. This relationship was used to estimate oxidation states of the titanium catalyst in 2 and 4mol% Ti-doped NaAlH4. The results demonstrate that the formal titanium valence is zero in doped sodium alanate and nearly invariant during hydrogen cycling. A qualitative comparison of the edge fine structure suggests that the Ti is present on the surface in the form of amorphous TiAl3.

Dependence of Titanium Deposition upon Its Ionic State in Molten Salt

The ionic valence of Ti changed with electrorefining process of Ti in a bath equi-molar mixture of NaCl-KCl containing TiCln (n=2 or 3); The average valence was about 2.3 initially, and became about 2.1 after electrolysis. The cathodic current efficiency was getting better with electrolysis. It should be necessary to maintain the average ionic valence lower for efficient electrolysis in the molten salt. The dominant Ti ion and its electrode reaction changed with the addition of NaF-KF in the molten salt; The average valence shifted from about 2 to about 3, and the total amount of Ti in the bath decreased. The result indicates the disproportionation reaction: 3Ti2+ = Ti + 2Ti3+ is induced by the fluoride addition. The quantity of electricity for Ti deposition changed consequently, and the purity of the Ti deposit was also affected.