Photofragmentation of mass-selected titanium oxide cluster cations

In this paper we present the photofragmentation spectra of mass-selected positive titanium oxide cluster ions Ti _x O _y ⁺. The clusters are generated by the combination of laser ablation of a titanium target and the supersonic nozzle expansion of oxygen and are detected by time-of-flight mass spectrometry. Small clusters are mass-selected and photodissociated at a wavelength of 308 nm. The recorded photofragmentation spectra indicate that for all parent clusters the main fragment is TiO⁺ and, in some cases, Ti₂O₃ ⁺ is also observed. This is consistent with the assumption that small Ti _x O _y ⁺ clusters are built from a TiO⁺ core with TiO₂ building blocks.     

Role of structural vacancies in the stabilization of the basic B1 structure in nonstoichiometric titanium monoxide TiO y

The electron structures and formation enthalpies of vacancy-free cubic TiO, vacancy-ordered monoclinic Ti₅O₅, and vacancy-disordered cubic TiO _y have been investigated using DFT+GGA calculations. Ti₅O₅ was found to be the stablest phase and TiO was found to be the least stable. The reason for the stability of the titanium and oxygen vacancies in the basic B1 structures of Ti₅O₅ and TiO _y has been deduced. The titanium vacancies lead to a decrease in the Fermi energy. Oxygen vacancies cause strengthening in covalent Ti-Ti bonding.     

Two-sublattice ordering in titanium monoxide

The disordered and ordered structures of nonstoichiometric titanium monoxide Ti_xO_z≡TiO_y(y=z/x) containing structural vacancies simultaneously in the nonmetallic and metallic sublattices were studied. In the stoichiometry range from TiO_0.9 to TiO_1.1, an ordered monoclinic phase [space group C2/m (A12m/1)] of the Ti₅O₅ type is formed in the TiO_y monoxide at temperatures below 1300 K. The disorder-order TiO_y?Ti₅O₅ phase-transition channel involves Lifshitz {k₁₀} and non-Lifshitz {k₄} and {k₁₁} star rays. The ordering proceeds as a first-order phase transition with a decrease in the volume of the basal cubic lattice. The titanium and oxygen distribution functions in the metallic and nonmetallic sublattices of titanium monoxide are calculated. The domain of allowed values is determined for the long-range order parameter.     

Relationship between short- and long-range orders in nonstoichiometric titanium monoxide (TiO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>)

The relationship between the short- and long-range orders in various phases of nonstoichiometric titanium monoxide (TiO _y ) has been analyzed for the first time. The types of the local environment of lattice sites in the metal and nonmetal (oxygen) sublattices of Ti₅O₅, Ti₃O₂, Ti₂O₃, and Ti₄O₅ superstructures are described. It is established that, in phases where ordering takes place simultaneously in both sublattices, all parameters of the superstructural short-range order determining the positions of atoms and vacancies in the first three coordination spheres can be uniquely expressed via the long-range order parameters. If the ordering takes place only in one sublattice, then five of the six short-range order parameters vanish. It is shown that, using data on the maximum absolute values of six short-range order parameters and on the fractions of occupied atomic positions in titanium and oxygen sublattices, it is possible to predict the type of ordered phase expected to form in the nonstoichiometric titanium monoxide TiO _y .     

Thermodynamic properties of titanium dioxide,niobium dioxide and their solid solutions at high temperature

By means of thermogravimetric measurements, it has been possible to obtain information on the nature of the intrinsic and extrinsic defects of TiO₂, NbO₂ and solid solutions Nb_yTi_1?yO_2±x Pure TiO₂ is an oxygen-deficient oxide The main defects are oxygen vacancies, doubly ionized V^.._o or singly ionized V^._o, and interstitial titanium Ti³_i NbO₂ is a metal-deficient oxide The main defects are neutral niobium vacancies. The solid solutions Nb_yTi_1?yO_2±x may be divided into two groups If y > 0 04, the behavior is analogous to that of NbO₂; with the same defects, but the width of the homogeneity range decreases with the titanium content and Nb_{0 04}Ti_{0 96}O₂ is a stoichiometnc oxide If y < 004, the oxides are both metal deficient and oxygen deficient according to the oxygen partial pressure. We have particularly studied the solution Ti_{0 995}Nb_{0 005}O₂ In the oxygen-deficient domain, the main defects are assumed to be neutral or singly ionized oxygen vacancies In the metal-deficient domain, the main defects are metal vacancies V⁴_Ti From these results we have deduced the nature of intrinsic defects in TiO₂ to be Schottky defects: 2V^.._O + V⁴_T1.     

Electronic structure of disordered titanium monoxide TiO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> depending on stoichiometry

The electronic structure of disordered nonstoichiometric titanium monoxide TiO _y depending on the oxygen content has been studied by the supercell method in the DFT-GGA approximation with the use of pseudo-potentials. An increase in the oxygen content in TiO _y leads to a decrease in the electron density of states near the Fermi level. The calculation of the enthalpy of formation of the ordered and disordered phases has shown that the disordered phase TiO _y is more energetically favorable than the phase without the TiO structural vacancies but is less favorable than the ordered Ti₅O₅ phase. The stability of the disordered phase increases with the oxygen content.     

Synthesis of nanocrystalline multiphase titanium oxycarbide (TiC<Subscript>x</Subscript>O<Subscript>y</Subscript>) thin films by UNU/ICTP and NX2 plasma focus devices

Nanocrystalline multiphase titanium oxycarbide (TiC_xO_y) thin films composed of TiC₂, TiO_0.325, Ti₂O₃ and graphitic carbon have been deposited on titanium substrates, using energetic carbon ions delivered by the UNU/ICTP and the NX2 plasma focus devices operated at different repetition rates. X-ray diffraction (XRD) patterns of the nanocomposite films reveal the relative transformation of various oxide and carbide phases accompanied by the suppression of the TiC₂ phase when the energy flux of the ion beam and the repetition rate are increased. A field emission scanning electron microscope (FESEM) with an energy dispersive X-ray spectroscopy (EDS) attachment reveals a non-porous microcrack-free nanocrystalline granular surface morphology of the composite films with uniform carbon distribution. X-ray photoelectron spectroscopy (XPS) confirms the formation of oxycarbides (TiC_xO_y) along with significant carbon adsorbate. Raman studies of the films also verify the relative phase transformation in the TiC_xO_y nanocomposite by tuning the deposition parameters. The Vickers microhardness of the sample surface is improved more than 400%. PACS 52.59.Hq; 52.77.Dq; 68.55.Jk; 81.15.-z; 81.65.Lp     

Cluster generation under pulsed laser ablation of zinc oxide

Neutral and cationic Zn _n O _m clusters of various stoichiometry have been produced by nanosecond laser ablation of ZnO in vacuum and investigated by time-of-flight mass spectrometry. Particular attention was paid to the effect of laser wavelength (in the range from near-IR to UV) on cluster composition. Under 193-nm laser ablation, the charged clusters are essentially substoichiometric with Zn_nO_n-1⁺\mathrm{Zn}_{n}\mathrm{O}_{n-1}^{+} and Zn_nO_n-3⁺\mathrm{Zn}_{n}\mathrm{O}_{n-3}^{+} being the most abundant series. Both sub- and stoichiometric cationic clusters are generated in abundance at 532- and 1064-nm ablation whose composition depends on the cluster size. The reactivity of small stoichiometric Zn_nO_n⁺\mathrm{Zn}_{n}\mathrm{O}_{n}^{+} clusters (n<11) toward hydrogen is found to be high, while oxygen-deficient species are less reactive. The neutral plume particles are mainly stoichiometric with Zn₄O₄ tetramer being a magic cluster. It is suggested that the Zn₄O₄ loss is the dominant fragmentation channel of large zinc oxide clusters upon electron impact. Plume expansion conditions under ZnO ablation with visible and IR laser pulses are shown to be favorable for stoichiometric cluster formation.     

Collision-induced dissociation studies on gas-phase titanium oxide cluster cations

Titanium oxide cluster cations $\mathrm{Ti}_{x}\mathrm{O}_{y}^{+}$ are produced in a molecular beam by combining laser ablation of titanium with the supersonic expansion of oxygen into vacuum. The size distribution of the clusters produced is analyzed by time-of-flight reflectron mass spectrometry. The stable clusters appearing in the mass spectrum can be described by the general formula $(\mathrm{TiO})_{m}(\mathrm{TiO}_{2})_{n}(\mathrm{O}_{2})_{k}^{+}$ (with m,n=0,1,2,?? and k=0,1). Additionally, collision-induced dissociation studies of mass selected clusters colliding with Kr atoms in a gas cell have been performed. The results show that the clusters lose neutral O₂, TiO and/or (TiO₂) _n units, and the remaining charged fragments are those with the lowest ionization potentials. From these results the fragmentation cross section of the selected clusters is obtained.     

Effect of different doped elements on visible light absorption and ultraviolet light emission on Er3+:Y3Al5O12

In this progress report, seven kinds of novel carefully designed and fabricated up-conversion luminescence agents, Er³⁺:Y₃Al₅O₁₂, Er³⁺:Yb_nY_3?nAl₅O₁₂, Er³⁺:Y₃B_aAl_5?aO₁₂, Er³⁺:Y₃Ga_bAl_5?bO₁₂, Er³⁺:Y₃Al₅N_xO_12?x, Er³⁺:Y₃Al₅F_yO_12?y and Er³⁺:Yb_nY_3?nB_aGa_bAl_5?a?bN_xF_yO_12?x?y, are successfully synthesized using sol–gel methods. After that, their corresponding photocatalysts, Er³⁺:Y₃Al₅O₁₂/TiO₂, Er³⁺:Yb_nY_3?nAl₅O₁₂/TiO₂, Er³⁺:Y₃B_aAl_5?aO₁₂/TiO₂, Er³⁺:Y₃Ga_bAl_5?bO₁₂/TiO₂, Er³⁺:Y₃Al₅N_xO_12?x/TiO₂, Er³⁺:Y₃Al₅F_yO_12?y/TiO₂ and Er³⁺:Yb_nY_3?nB_aGa_bAl_5?a?bN_xF_yO_12?x?y/TiO₂, are also prepared by sol–gel coating process. The obtained up-conversion luminescence agents and photocatalysts were characterized by using XRD, XPS, SEM, UV–vis and fluorescence spectrophotometer. Synchronously, several kinds of organic dyes are used to test their photocatalytic degradation using prepared photocatalysts. It indicates that the up-conversion luminescence ability of Er³⁺:Y₃Al₅O₁₂ can be improved obviously through doping of some elements. And then, the photocatalytic activity of TiO₂ is markedly enhanced by modified up-conversion luminescence agents which can transform much visible light into ultraviolet light.     

(Mo + N) codoped TiO2 for enhanced visible-light photoactivity

A series of Ti_1−xMo_xO_2−yN_y samples were prepared by using sol-gel method and characterized by X-ray diffraction, transmission electron microscopy and UV-vis absorption spectroscopy. All Ti_1−xMo_xO_2−yN_y samples are anatase phase. It is found that Mo, N mono-doping can increase visible light absorption, while (Mo + N) co-doping can greatly enhance absorption in whole visible region. Results of our first-principles band structure calculations reveal that (Mo + N)-doping, especially passivated co-doping can increase the up-limit of dopant concentration and create more impurity bands in the band gap of TiO₂, which leads to a greatly increase of its visible-light absorption without a decrease of its redox potential. It reveals that (Mo + N) co-doped TiO₂ is promising for a photocatalyst with high photocalystic activity under visible light.     

Phase interactions in TiN<Subscript>x</Subscript>(TiB<Subscript>x</Subscript>)-<Emphasis Type="Italic">n</Emphasis>-Si-<Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript>-Si contacts and their thermal degradation due to rapid thermal annealing

The temperature stability of TiN_x(TiB_x)-n-Si-n ⁺-Si, Au-TiN_x(TiB_x)-n-Si-n ⁺-Si, and Au-Ti(Mo)-TiN_x(TiB_x)-n-Si-n ⁺-Si Schottky-barrier contacts subjected to rapid thermal annealing in hydrogen at temperatures T=400, 600, and 800°C is studied. It is shown that structural and morphological transformations and the related degradation of electrophysical characteristics in interstitial alloys (titanium nitrides and borides) start at 600°C. Reasons for the degradation of the barrier properties of titanium borides and nitrides are discussed.     

Preparation of nitrogen-doped titanium dioxide with visible-light photocatalytic activity using a facile hydrothermal method

Nitrogen-doped TiO₂ (N-TiO₂) nanoparticles have been successfully prepared via a direct and simple hydrothermal reaction of a commercial Degussa P25 with triethanol amine as solvent and nitrogen source. As-prepared N-TiO₂ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible light (UV-vis) absorption spectra, electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS) techniques. The results confirm that hydrothermal reaction is an effective way to incorporate nitrogen into the TiO₂ lattice, especially nitrogen substitute for titanium. The nitrogen concentration in TiO₂ can be as high as 21% (molar ratio), which is described as Ti_1−yO_2−xN_x+y (in this paper, x=0.36, y=0.27, i.e., Ti_0.73O_1.64N_0.63). The chemical statuses of N have been assigned to N-Ti-O and O-N-O in the TiO₂ lattice as identified by XPS. Photocatalytic degradation of methyl orange has been carried out in both UV-vis (simulated solar light) and the visible region (λ>400 nm). N-TiO₂ exhibits higher activity than the Degussa P25 TiO₂ photocatalyst, particularly under visible-light irradiation. This study has developed a promising and practical pathway to new nitrogen-doped photocatalysts.     

Spectroscopic and dielectric studies on PbO–MoO3–B2O3 glasses incorporating small concentrations of TiO2

This paper deals with the investigation of a variety of physical properties including dielectric constant (over a wide range of frequency and temperature), optical absorption, luminescence, electron spin resonance (ESR) and infrared spectra of a TiO₂-doped lead molybdenum borate glass system. The composition chosen for the study is 30PbO–4MoO₃–(66–x)B₂O₃:xTiO₂ (with x ranging from 0.2 to 2.0). Quantitative analysis of the results of this study shows that, when the content of TiO₂ is around 0.8 mol%, the titanium ions exist predominantly in the tetravalent state and occupy substitutional positions in the glass network. A substantial increase in the insulating strength of these glasses on TiO₂ doping has also been observed. When the concentration of TiO₂ is increased beyond 0.8 mol%, it is observed that titanium ions exist primarily in the Ti³⁺ state and molybdenum ions in the Mo⁵⁺ state; analysis of the results further suggests that both of these ions participate in the depolymerization of the glass network.     

The Fixed Point of a Generalization of the Renormalization Group Maps for Self-Avoiding Paths on Gaskets

Let W(x,y) = ax ³+ bx ⁴+ f ₅ x ⁵+ f ₆ x ⁶+ (3 ax ²)² y+ g ₅ x ⁵ y + h ₃ x ³ y ² + h ₄ x ⁴ y ² + n ₃ x ³ y ³+a ₂₄ x ² y ⁴+a ₀₅ y ⁵+a ₁₅ xy ⁵+a ₀₆ y ⁶, and X = , , where the coefficients are non-negative constants, with a > 0, such that X ²(x,x ²)−Y(x,x ²) is a polynomial of x with non-negative coefficients. Examples of the 2 dimensional map Φ: (x,y)↦ (X(x,y),Y(x,y)) satisfying the conditions are the renormalization group (RG) maps (modulo change of variables) for the restricted self-avoiding paths on the 3 and 4 dimensional pre-gaskets. We prove that there exists a unique fixed point (x _f ,y _f ) of Φ in the invariant set . 2000 Mathematics Subject Classification Numbers: 82B28; 60G99; 81T17; 82C41.     

Ti和蓝宝石的界面反应

在超高真空中用电子束蒸发在抛光的(1102)取向的蓝宝石(α-Al₂O₃)衬底上蒸镀500nm的Ti膜,在恒温炉中退火,然后用XRD(包括一般的和小角度的X射线衍射),AES(俄歇电子谱,包括深度剖面分布和通过界面的谱形分析)和SIMS(二次离子质谱)等表面分析技术详细研究了从室温至850℃,Ti与α-Al₂O₃的固相界面反应.结果表明室温及300℃,30min退火已有反应,Al₂O_{3< 关键词：}     

Synthesis of anatase-type TiO2 films by reactive laser ablation of a metallic Ti target in ambient O2 gas

TiO₂ films having anatase-type crystal structures were synthesized by reactive laser ablation of a metallic Ti target in ambient O₂ gas. The anatase-type TiO₂ was obtained at O₂ pressures below 0.2 Torr and at substrate temperatures above 150 °C. The films had the (101) orientation at substrate temperatures of 200–250 °C while, at substrate temperatures of 400–450 °C, the orientation of the films was (004). Rutile-type crystal was mixed in at substrate temperatures higher than 450 °C. The synthesis characteristics were compared with the fluxes of Ti, Ti⁺, and TiO toward the substrate, which were evaluated by laser-induced fluorescence imaging spectroscopy. PACS 81.15.Fg; 61.10.-i; 52.70.Kz     

Combinatorial discovery of anomalous substrate effect on the photochemical properties of transition metal-doped epitaxial SrTiO3 heterostructures

Epitaxial Sr(V_xCr_yTi_1−x−y)O₃ (0≤x+y≤0.05) ternary composition spreads were grown on two different single crystal substrates, LaAlO₃ and Nb-doped SrTiO₃, by use of combinatorial laser molecular beam epitaxy with a specially patterned slide masking plate. The photocatalytic activity on the composition spreads was evaluated by the photo-reduction of Ag⁺ in an AgNO₃ aqueous solution to deposit Ag metal on the spreads. The V-doping effect was found to depend greatly on the substrate: the photodeposition of Ag was much enhanced in the composition region of SrV_0.05Ti_0.95O₃ only on the Nb-doped SrTiO₃, but not on the LaAlO₃ and non-doped SrTiO₃.     

Phase states and ferroelectric properties of Pb(Zr, Sn, Ti)O3 ceramic

The ferroelectric and dielectric properties of Pb_0.99[(Zr_1−x Sn_x)_1−y Ti_y]_0.98Nb_0.02O₃ ceramic of composition (I) x=0.5, y=0.04–0.12 and (II) x=0.4, y=0.06–0.09 were studied, and the T-x and E-T diagrams were constructed. When zinc is substituted for tin, the range of coexistence of the ferroelectric and antiferroelectric phases extends. The range of the nonpolar phase shrinks when the titanium content is increased.     

A method for determining a solid solution of the Pb(Hf1−yZry)1−xTixO3 type used for electromechanical energy conversion

The mechanical stress-forced Ferroelectric F→Antiferroelectric AF transition energy conversion is reviewed. The temperature-composition phase diagram of PbHf_1−xTi_xO₃+1%La₂O₃ is established. The composition of a suitable material such as a ternary solid solution of the Pb(Hf_1−yZr_y)_1−xTi_xO₃+1%La₂O₃ type, characterized by a low transition pressure, is theoretically determined by a graphic construction using the Goldschmidt factor. Experimental results on the prepared material are given.