Ti-O Bond Research Articles

Synthesis and Characteristics of MgO Coated BST-Mg2TiO4 Composite Ceramics

The (Ba, Sr)TiO3 (hereafter BST) ceramics are promising candidate for applying in tunable devices. MgO coated BST-Mg2TiO4 (BSTM-MT) composite ceramics were prepared to obtain the low dielectric constant, low dielectric loss, good dielectric constant temperature stability, and high tunability of BST ceramics. The Ba0.55Sr0.40Ca0.05TiO3 nanoparticles were coated with MgO using the precipitation method and then mixed with Mg2TiO4 powders to fabricate BSTM-MT composite ceramics. The morphologies, phases, elements, and dielectric properties of the sintered ceramics were investigated. The core-shell structure of BST powder wrapped with MgO was clearly observed from the TEM image. After sintered at 1100 °C for 2 h, the composite ceramics expressed dense microstructures from SEM images and two main phases BST and Mg2TiO4 were detected in the XRD patterns. The dielectric constant and loss tangent were both reduced after the coating. The reduced dielectric constant and loss tangent of BSTM-MT were 190, 0.0011 (2MHz), respectively. The ceramics exhibited the diffuse phase transition near the Curie temperature and the Curie temperature shifted from 10 °C to 5 °C after the coating. Since the continuous Ti-O bonds were disconnected with the MgO coating, the tunability was reduced to 15.14 % under a DC bias field of 1.1 kV/mm. The optimistic dielectric properties made it useful for the application of tunable capacitors and phase shifters.

Influence of Copper doping on physical properties of Barium Titanate

A finest possible sample of Copper (Cu) doped micro particles of BaTiO3 (BTO) with possible tetragonal structure via a solid-state route was prepared. Prepared samples of BaTi1−xCuxO3 (x=0.05) were structural characterized by X-ray diffraction (XRD). Fourier Transform Infrared spectroscopy (FTIR) technique used for determines the Ti-O bond shifting as an influence of Cu in BTO. Finally Dielectric Constant measurements of the sample above and below the Curie temperature were carried out.

Density Functional Theory Study of Ti<sub>n</sub>O<sub>2n-m </sub>Clusters (n=1-4, m=0,1)

Using density functional theory, the equilibrium geometries of TinO2n and TinO2n-1 clusters (n=1-4) have been obtained. It suggests that the structures of these two corresponding clusters are changed slightly, except for the number of terminal oxygen atoms. The electronic properties have also been investigated. The bond between Ti and terminal oxygen atom is found to be more covalent than other Ti-O bonds. It also indicates that by deleting one terminal oxygen atom, HOMO is mainly derived from titanium atoms with least coordination, but not from singly-coordination oxygen atoms as that in the stoichiometric clusters. Highest energy levels of least-coordination Ti atoms shift highly and they become more reactive. In addition, HOMO-LUMO energy gaps and binding energies were observed. The calculated results show that the energy gaps decrease quickly, except for Ti4O7 clusters and all the binding energies are relatively large.

A red anatase TiO2 photocatalyst for solar energy conversion

Narrowing the bandgap of wide-bandgap semiconductor photocatalysts (for instance, anatase TiO2) by introducing suitable heteroatoms has been actively pursued for increasing solar absorption, but usually suffers from a limited thermodynamic/kinetic solubility of substitutional dopants in bulk and/or dopant-induced recombination centres. Here we report a red anatase TiO2 microsphere with a bandgap gradient varying from 1.94 eV on its surface to 3.22 eV in its core by a conceptually different doping approach for harvesting the full spectrum of visible light. This approach uses a pre-doped interstitial boron gradient to weaken nearby Ti-O bonds for the easy substitution of oxygen by nitrogen, and consequently it substantially improves the nitrogen solubility. Furthermore, no nitrogen-related Ti3+ was formed in the red TiO2 due to a charge compensation effect by boron, which inevitably occurs in common nitrogen doped TiO2. The red anatase TiO2 exhibits photoelectrochemical water splitting activity under visible light irradiation. The results obtained may shed light on how to increase high visible light absorbance of wide-bandgap photocatalysts.

Iron-doped BaTiO3: Influence of iron on physical properties

Barium Titanate BaTiO3 is known for both its electric and magnetic properties. The synthesis and characterization of iron doped barium titanate; BaTi1-xFexO3 (x= 0.005, 0.01, 0.015) was investigated with a view to understand its structural, magnetic and electrical properties. A finest possible sample of Iron doped micro particles of BaTiO3 (BTO) with possible tetragonal structure via a solid-state route was prepared. Prepared samples of BaTi1-xFexO3 (Fe-BTO) were structural characterized by X-ray diffraction (XRD) then XRD data fitted by Rietveld refinement. Fourier Transform Infrared Spectroscopy were use to determine the Ti-O bond length position according to increment in Iron on Titanium site. The dielectric constant measurements of the samples were carried out at 1 MHz. Vibrating Sample Magnetometer (VSM) measurements revealed the magnetic nature of Iron doped BaTiO3. Magnetic Moment verses Temperature plot took at 1Tesla and Magnetic Moment verses Magnetic field plot took at low temperature (10K). Ferroelectric hysteresis loop traced at the electric field in-between -8 to +8 (KV/cm). Details of the preparation technique, experimental results, data analysis, and the interpretation will be presented.

The FTIR studies of gels and thin films of Al2O3–TiO2 and Al2O3–TiO2–SiO2 systems

In this work, samples in form of bulk ones and thin films were obtained using the sol–gel method. The bulk samples were heated at different temperatures (500°C, 850°C and 1100°C) corresponding to the annealing process of coatings, deposited on different substrates by dipping and pulling out samples from the proper sol with the stable speed. Thin films of both Al2O3–TiO2 and Al2O3–TiO2–SiO2 systems were deposited on carbon, steel and titanium substrates in two different ways: as single layers obtained from Al2O3 sol, TiO2 sol and Al2O3 sol or deposited as mixed coatings from Al2O3–TiO2 sol as well as Al2O3–TiO2–SiO2 one.All bulk samples were studied by the FTIR spectroscopy and the X-ray diffractometry while thin films were also investigated by the electron microscopy.In the IR spectra of Al2O3–TiO2 samples, as well as gels and coatings, bands due to the vibrations of AlO bonds of the octahedrally and tetrahedrally coordinated aluminum were observed.The IR spectra of samples of Al2O3–TiO2–SiO2 system differ from that of Al2O3–TiO2 ones in presence of bands assigned to the SiO bond vibrations and in positions of bands due to AlO bond vibrations. In all spectra of bulk samples and coatings, the positions of TiO bond vibrations were ascribed basing on the IR spectra of the pure anatase and rutile.

Effect of the modification of barium titanate on the permittivity of its composites with cyanoethyl ester of polyvinyl alcohol

The effect of chemical modification of submicron barium titanate particles by the deposition of M x O y (x = Ti, Co, Ni) oxide layers from aqueous solutions of the corresponding precursors is studied upon the surface properties of modified BaTiO3 particles and dielectric permittivity of organo-inorganic composites obtained by their dispersion in the matrix of cyanoethyl ester of polyvinyl alcohol and useful in electroluminescent light sources. It is shown that a significant increase (by about 25%) of the dielectric permittivity is observed only when adding Nb2O5, in comparison with a similar composite which contains unmodified BaTiO3. A correlation is found between the dielectric permittivity of the organo-inorganic composites and the presence of Brensted neutral and basic centers with pK a = 6−13, localized on the surface of a filler, being capable of interacting with the polymer matrix. It is shown that an increase of the dielectric permittivity upon deposition of niobium oxide on the surface of BaTiO3 is caused by formation of such centers and modification of the surface layer structure of BaTiO3 particles, with transformation of rutile-like Ti-O bonds to anataselike ones.

Anchoring functional molecules on TiO2 surfaces: A comparison between the carboxylic and the phosphonic acid group

The adsorption of formic acid on clean TiO2 anatase (101) and rutile (110) surfaces is studied by density-functional-based methods and compared with the results for coupling related phosphonic acids to titania surfaces. The preferred adsorption mode of the formic acid on both surfaces is a dissociative bridging bidentate complex, which is similar to the adsorption geometry of phosphonic acid. Higher adsorption energies and shorter Ti-O bond lengths indicate that phosphonic acid binds more strongly to TiO2 than formic acid. The preference for the bidentate adsorption mode is supported by a detailed analysis of the charge distribution in the adsorption complexes. The strong interfacial electronic coupling between the adsorbate orbitals and the electronic states of the anatase (101) surface slab leads to additional states in the band gap of the clean surface. For rutile (110) no or only weak coupling of the adsorbate orbitals and the surface states occurs at the band edges, which leads to an increase of the band gap.

Hydrogen donors and Ti3+ ions in reduced TiO2 crystals

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) are used to identify and characterize the neutral hydrogen donor in TiO2 crystals having the rutile structure. These spectra are best observed near 5 K. The neutral donors are present without photoexcitation in crystals that have been slightly reduced at high temperature in a nitrogen atmosphere. The same defects can be photoinduced at low temperature in oxidized crystals. The neutral hydrogen donor in this lattice consists of a substitutional Ti3+ ion adjacent to a substitutional OH– molecular ion. The axis of the OH– molecule lies in the basal plane with the hydrogen ion extending out from the oxygen in a direction perpendicular to the Ti-O bonds. Spin-Hamiltonian parameters are obtained from the angular dependence of the EPR and ENDOR spectra (principal values are 1.9732, 1.9765, and 1.9405 for the g matrix and –0.401, + 0.616, and –0.338 MHz for the 1H hyperfine matrix). The principal axis associated with the + 0.616 MHz principal value is in the basal plane 22.9° from a [110] direction and the principal axis associated with the –0.338 MHz principal value is along the [001] direction. Our results show that interstitial Ti3+ ions are not the dominant shallow donors in slightly reduced TiO2 (rutile) crystals.

Structural evolution across the insulator-metal transition in oxygen-deficient BaTiO3−δstudied using neutron total scattering and Rietveld analysis

Oxygen-deficient BaTiO${}_{3\ensuremath{-}\ensuremath{\delta}}$ exhibits an insulator-metal transition with increasing $\ensuremath{\delta}$. We performed neutron total scattering measurements to study structural evolution across an insulator-metal transition in BaTiO${}_{3\ensuremath{-}\ensuremath{\delta}}$. Despite its significant impact on resistivity, slight oxygen reduction ($\ensuremath{\delta}=0.09$) caused only a small disturbance on the local doublet splitting of Ti-O bond. This finding implies that local polarization is well preserved under marginal electric conduction. In the highly oxygen-deficient metallic state ($\ensuremath{\delta}=0.25$), however, doublet splitting of the Ti-O bond became smeared. The smearing of the local Ti-O doublet is complemented with long-range structural analysis and demonstrates that the metallic conduction in the highly oxygen-reduced BaTiO${}_{3\ensuremath{-}\ensuremath{\delta}}$ is due to the appearance of nonferroelectric cubic lattice.

Correlations of dielectric properties with electronic structure and phonon vibration of low loss tunable Ba0.4Sr0.6Ti1-yMnyO3 ceramics

Correlations of dielectric properties with electronic structure and phonon vibration of Ba0.4Sr0.6Ti1-y MnyO3 (y = 0.00-0.20) ceramics were studied by using spectroscopic techniques. High level of Mn substitution prevented the reduction of Ti4+ and enhanced the charge ordering of Ti3+/Ti4+, leading to materials with high Q values. An increase in the concentration of Mn resulted in hardening of the softest mode, which led to a reduction in relative permittivity, dielectric loss, and tunability with increasing y. Raman spectra revealed that higher vibration frequency of Ti-O bonds was related to lower relative permittivity, and narrower width of Mn-O stretching corresponded to a higher Q × f.

LCAO calculations of SrTiO3 nanotubes

The large-scale first-principles simulation of the structure and stability of SrTiO3 nanotubes is performed for the first time using the periodic PBE0 LCAO method. The initial structures of the nanotubes have been obtained by the rolling up of the stoichiometric SrTiO3 slabs consisting of two or four alternating (001) SrO and TiO2 atomic planes. Nanotubes (NTs) with chiralities (n,0) and (n,n) have been studied. Two different NTs were constructed for each chirality: (I) with SrO outer shell, and (II) with TiO2 outer shell. Positions of all atoms have been optimized to obtain the most stable NT structure . In the majority of considered cases the inner or outer TiO2 shells of NT undergo a considerable reconstruction due to shrinkage or stretching of interatomic distances in the initial cubic perovskite structure. There were found two types of surface reconstruction: (1) breaking of Ti-O bonds with creating of Ti = O titanyl groups in outer surface; (2) inner surface folding due to Ti–O–Ti bending. Based on strain energy calculations the largest stability was found for (n,0) NTs with TiO2 outer shell.

Preparation and Characterization of Ag-Doped BaTiO3 Conductive Powders

BaTiO3 powders doped with Ag at different Ag/Ba molar ratios were prepared by sol-gel method. The resistivity reached the lowest point of 5.644 Ω·m when Ag concentration was 0.10 at% and the powders were calcined for two times at 800°C and 500°C. XRD and FTIR investigations showed that no new substance was formed after the doping and calcining process, but the particle size and the strength of Ti-O bond in modified BaTiO3 crystal cell all changed. The conductivity of Ag-doped BaTiO3 powders with different Ag concentrations and through different preparing methods was discussed by using defect theory.

Electron Dynamics in Dye-Sensitized Solar Cells: Effects of Surface Terminations and Defects

The electron dynamics in a TiO(2)/alizarin based dye-sensitized solar cell is studied by a means of ab initio nonadiabatic molecular dynamics. The effects of surface terminations and vacancy defects on photoexcited interfacial electron transfer (ET) and energy relaxation of injected electrons are examined in detail. In particular, we consider three plausible TiO(2) surface terminations which are stable at zero temperature. However, only one of them maintains structural integrity at room temperature while the other two terminations lead to broken interfacial Ti-O bonds. An ultrafast ET dynamics (4.6 fs) is observed for the intact interface, consistent with relevant experimental and theoretical results. On the other hand, the ET dynamics of the two other terminations takes either a much longer time or results in less charge transfer. The surface vacancies in TiO(2) are found to play important roles in the structural integrity, the interfacial ET dynamics, and the energy relaxation in the TiO(2) conduction bands. For example, O vacancies are observed to enhance the interfacial bonding, delocalize the photoexcited state, and facilitate nonadiabatic ET. On the other hand, Ti vacancies give rise to less stable interfacial structure and negligible ET. The energy relaxation time scale for the injected electron in the conduction band is 500 fs regardless of the vacancies. Both O and Ti surface vacancies are found to trap the injected electron while the O vacancies could increase the charge recombination at the interface.

Modification of Ag-doped BaTiO 3 powders through La gaseous penetration route

The Ag-doped BaTiO 3 (BATO) polycrystalline powders were fabricated by Sol-Gel method. Further modification by rare earth La was done through gaseous penetration route. Changes in constitution, structure, and electrical conductivity before and after modification of Ag and La were characterized. The acceptor dopant Ag owned the ability to decrease the resistivity of the doping samples from 4.30×10 9 Ω·m to 6.14×10 5 Ω·m where the resistivity fell by 4 orders of magnitude when the Ag doping ratio was 0.10%. And more doping of Ag enhanced the resistivity dramatically even beyond 2.0×10 7 Ω·m. Yet, gaseous penetration of La successively reduced the resistivity of BATO to the lowest point of 2.45×10 5 Ω·m. XRD analysis indicated that the doping process of Ag did not change the perovskite structure and main phases of the powders. However, new compound BaLa 2O 4 generated from complex reactions during the penetration process, which manifested that La 3+ penetrated into the crystal lattices in the form of substituting the Ti 4+ site. And this substitution strengthened the Ti-O bond, which led to the inhibition of blue shift in FTIR spectrum caused by doping of Ag. The morphology of La penetrated BATO powders detected by SEM and EDAX suggested that La did penetrate into the powders and this penetration process progressed the partly sintering of the powders which is in favor of the conductivity.

High-pressure investigation ofCaTiO3up to 60 GPa using x-ray diffraction and Raman spectroscopy

In this work, we investigate calcium titanate (CaTiO3 - CTO) using X-ray diffraction and Raman spectroscopy up to 60 and 55 GPa respectively. Both experiments show that the orthorhombic Pnma structure remains stable up to the highest pressures measured, in contradiction to ab-initio predictions. A fit of the compression data with a second-order Birch-Murnaghan equation of state yields a bulk modulus K0 of 181.0(6) GPa. The orthorhombic distortion is found to increase slightly with pressure, in agreement with previous experiments at lower pressures and the general rules for the evolution of perovskites under pressure. High-pressure polarized Raman spectra also enable us to clarify the Raman mode assignment of CTO and identify the modes corresponding to rigid rotation of the octahedra, A-cation shifts and Ti-O bond stretching. The Raman signature is then discussed in terms of compression mechanisms.

Enhanced photoelectric efficiency by surface modification of TiO2 thin film using various acidic species

This study examined the photoelectric conversion efficiency of the dye-sensitized solar cell (DSSC) when the surface of a nanometer-sized TiO2 film, which was prepared using the solvothermal method, was modified by five acid compounds. The TiO2 film exhibited an anatase structure with an average particle size in the range of 10–15 nm, and the maximum absorption band was shown in the UV-visible spectrum around 360 nm. The surface colors of the carboxylic acid-modified TiO2 films were changed to light or dark with differing energy conversion efficiencies. Particularly, the conversion efficiency was considerably enhanced from approximately 6.25% for the non-modified TiO2 film to approximately 7.50% for the film treated by acetic acid of 1.0 mole, with the N719 dye under 100 mW/cm2 of simulated sunlight. FT-IR analysis of the films after N719 dye adsorption confirmed that the IR spectrum of the modified TiO2 showed a sharp and strong band at 500 cm−1, which was assigned to a metal-O bond, due to the formation of a new Ti-O bond between the O of COO− and the Ti atom, which was relatively weaker in the non-modified TiO2. Furthermore, these results were in agreement with an electrostatic force microscopy (EFM) study showing that the electrons were transferred rapidly to the surface of the acetic acid-modified TiO2 film, compared with that on the nonmodified TiO2 film.

ChemInform Abstract: Syntheses, Structures, and Properties of RbScFAsO4 and CsScFAsO4: Scandium-Containing Analogues of Potassium Titanyl Phosphate (KTiOPO4).

The syntheses, single-crystal structures, and some properties of RbScFAsO4, and CsScFAsO4, the first scandium-containing analogues of potassium titanyl phosphate (KTiOPO4), are reported. In both phases, the distinct cis and trans ScO4F2 octahedra are essentially regular and lack the distinctive short TiO bonds seen in KTiOPO4. The powder second harmonic generation responses of these phases are much smaller that that of KTiOPO4. Crystal data: RbScFAsO4, Mr = 288.34, orthorhombic, space group Pna21 (no. 33), a = 13.687(4) A, b = 6.804(2) A, c = 11.248(2) A, V = 1047.5(5) A3, Z = 8, R = 3.15%, Rw = 3.95% [1807 reflections with I > 2σ(I)]; CsScFAsO4, Mr = 335.78, orthorhombic, space group Pna21 (no. 33), a = 13.900(2) A, b = 6.9413(8) A, c = 11.219(2) A, V = 1082.4(2) A3, Z = 8, R = 3.65%, Rw = 4.14% [2205 reflections with I > 3σ(I)].

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.

First-principles study of defect properties in tetragonal BaTiO3

Based on density functional first principles method, the defect properties in tetragonal BaTiO 3 have been studied. The results showed that the formation energies of neutral Ti vacancy and partial Schottky defect 2 V 3- Ti +3V 2+ O are the lowest under oxygen-rich condition; while under reducing condition oxygen vacancy becomes the primary defect. The calculated full Schottky formation energy is higher than that obtained in the cubic phase, which may be the result of the strong hybridization between the Ti-O bonds. The hybridization is also responsible for the Frenkel formation energy of Ti. The defect-interactions are important when dealing with Schottky defects.