共查询到20条相似文献,搜索用时 31 毫秒
1.
Georgi Avdeev José María Rojo Rosa María Rojas 《Journal of solid state chemistry》2009,182(12):3226-5242
Lithium manganese titanium spinels, LiMn2−yTiyO4, (0.2≤y≤1.5) have been synthesized by solid-state reaction between TiO2 (anatase), Li2CO3 and MnCO3. Li+ was leached from the powdered reaction products by treatment in excess of 0.2 N HCl at 85 °C for 6 h, under reflux. The elemental composition of the acidic solution and solid residues of leaching has been determined by complexometric titration, atomic absorption spectroscopy and X-ray fluorescence analysis. Powder X-ray diffraction was used for structural characterization of the crystalline fraction of the solid residues. It has been found that the amount of Li+ leached from LiMn2−yTiyO4 decreases monotonically with increasing y in the interval 0.2≤y≤1.0 and abruptly drops to negligibly small values for y>1.0. The content of Mn and Li in the liquid phase and of Mn and Ti in the solid (amorphous plus crystalline) residue, were related to the composition and cation distribution in the pristine compounds. A new formal chemical equation describing the process of leaching and a mechanism of the structural transformation undergone by the initial solids as a result of Li+ removal has been proposed. 相似文献
2.
A TiO2 membrane supported on a planar porous Ti–Al alloy was prepared by combination of electrophoretic deposition and dip-coating. In the electrophoretic deposition process, the membrane thickness increased linearly with the square root of the deposition time, while increased with decrease of the suspension viscosity. The perfect TiO2/Ti–Al composite membrane was obtained by further dip-coating modification. SEM images showed that the surface of the membrane was defect-free. XRD result indicated that rutile TiO2 still remained in the membrane bulk as the main phase, while a new phase titanium oxides with the form of TixOy, where y is less than 2x, was also observed. The supported TiO2/Ti–Al composite membrane had an average pore size of 0.28 μm, a thickness of 40 μm or so and a pure water flux of 3037 L m−2 h−1 bar−1. 相似文献
3.
M.T. ColomerJ.R. Jurado 《Journal of solid state chemistry》2002,165(1):79-88
[(ZrO2)0.92(Y2O3)0.08]0.9(TiO2)0.1 (titania-doped yttria stabilized circonia, 10TiYSZ) samples were prepared by solid state reaction from mixtures of 8 mol% yttria-doped ZrO2 (YSZ) and TiO2 and characterized in terms of structure, microstructure, and electrical properties. [(ZrO2)0.97(Y2O3)0.03]0.9(TiO2)0.1 (titania-doped tetragonal zirconia polycrystalline, 10TiTZP) was also prepared for comparison in some specific studies. Ionic transport properties were measured by impedance spectroscopy in air as a function of temperature. DC techniques including electromotive force (EMF) and Ion Blocking measurements (IB) were carried out in order to determine the electronic contribution to the total conductivity. The addition of titania to YSZ induces the tetragonal zirconia phase formation, thus [(ZrO2)0.92(Y2O3)0.08]0.9(TiO2)0.1 is a composite material and is constituted by two solid solutions, titania-doped yttria-stabilized zirconia (67.7 mole fraction) and titania-doped tetragonal zirconia (32.3 mole fraction). A decrease in bulk ionic conductivity, of one order of magnitude, when TiO2 is added to YSZ is observed in the whole temperature range. Furthermore, in the bulk conductivity vs the reciprocal of the temperature plot, a bending (from 550°C to higher temperatures) toward higher activation energies was detected. The bending could indicate the existence mainly of Ti4+-Vö associated pairs with an association energy of 0.43±0.02 eV. It could mean that Ti-O bonds become stronger and shorter and could produce the formation of microdomains of a ZrTiO4-like structure. The addition of titanium is effective in increasing the electronic conductivity under reducing conditions. Conductivity as a function of Po2 and IB results cannot be related to the formation of small polarons during the reduction process. Furthermore, according to the calculations based on the small polaron theory, inconsistent values for the radius of a small polaron (rp) are obtained in both 10TiYSZ and 10TiTZP. However, large polarons can explain the transport properties in these materials under reducing conditions in agreement with the experimental data. 相似文献
4.
Karl R. Whittle Gregory R. Lumpkin Robert D. Aughterson Nestor J. Zaluzec 《Journal of solid state chemistry》2010,183(10):2416-2420
Thin crystals of La2O3, LaAlO3, La2/3TiO3, La2TiO5, and La2Ti2O7 have been irradiated in situ using 1 MeV Kr2+ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La2O3 remained crystalline to a fluence greater than 3.1×1016 ions cm−2 at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (Tc) of 647 K for LaAlO3, 840 K for La2Ti2O7, 865 K for La2/3TiO3, and 1027 K for La2TiO5. The Tc values observed in this study, together with previous data for Al2O3 and TiO2, are discussed with reference to the melting points for the La2O3-Al2O3 and La2O3-TiO2 systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between Tc and melting temperature (Tm) in the two systems. More complex relationships exist between Tc and crystal structure, with the stoichiometric perovskite LaAlO3 being the most resistant to amorphisation. 相似文献
5.
Mesoporous TiO2-CeO2 nanopowders responding to visible wavelength were synthesized by using a surfactant assisted sol-gel technique. They were obtained using metal alkoxide precursors modified with acetylacetone (ACA) and laurylamine hydrochloride (LAHC) as surfactant. The samples were characterized by XRD, nitrogen adsorption isotherm, SEM, TEM, and selected area electron diffraction (SAED), respectively. The 95 mol% TiO2-5 mol% CeO2 system yielded single anatase phase, however, further addition of the CeO2 formed cubic CeO2 structure while anatase TiO2 decreased. Additions of 5 and 10 mol% CeO2 increased the surface area, but those of 25, 50, and 75 mol% CeO2 did not affect it very much. By using this mixed metal oxides system, TiO2 can be modified to respond to the visible wavelength. The mixed metal oxides had catalytic activity (evaluating the formation rate of I3−) about 2-3 times higher than pure CeO2, while nanosize anatase type TiO2 materials had no catalytic activity under visible light. The catalytic activity was almost proportional to the specific surface area. The formation rate of I3− was much improved by changing the calcination temperature and calcination period. Highest catalytic activity in this study was obtained for the 50 mol% TiO2-50 mol% CeO2 nanopowders calcined at 250 °C for 24 h. 相似文献
6.
Nitrogen substituted yellow colored anatase TiO2−xNx and Fe-N co-doped Ti1−yFeyO2−xNx have been easily synthesized by novel hydrazine method. White anatase TiO2−δ and N/Fe-N-doped samples are semiconducting and the presence of ESR signals at g ∼1.994-2.0025 supports the oxygen vacancy and g∼4.3 indicates Fe3+ in the lattice. TiO2−xNx has higher conductivity than TiO2−x and Fe/Fe-N-doped anatase and the UV absorption edge of white TiO2−x extends in the visible region in N, Fe and Fe-N co-doped TiO2, which show, respectively, two band gaps at ∼3.25/2.63, ∼3.31/2.44 and 2.8/2.44 eV. An activation energy of ∼1.8 eV is observed in Arrhenius log resistivity vs. 1/T plots for all samples. All TiO2 and Fe-doped TiO2 show low 2-propanol photodegradation activity but have significant NO photodestruction capability, both in UV and visible regions, while standard Degussa P-25 is incapable in destroying NO in the visible region The mid-gap levels that these N and Fe-N-doped TiO2 consist may cause this discrepancy in their photocatalytic activities. 相似文献
7.
ABO3 amorphous materials, such as BaTiO3 (BT), SrTiO3 (ST), PbTiO3 (PT), and BaxSr1−xTiO3 (BST) have recently attracted a good deal of attention due to their ferroelectric and electro-optical properties. Intense photoluminescence at room temperature was observed in amorphous titanate doped with chromium (BaxSr1−xTi1−yCryO3) prepared by the polymeric precursor method. Results indicated that substantial luminescence at room temperature was achieved with the addition of small Cr contents to amorphous BaxSr1−xTi1−yCryO3. Further addition of Cr or crystallization were deleterious to the intensity of the luminescent peak obtained for excitation using λ=488.0 nm. 相似文献
8.
Edisson Morgado Jr. Bojan A. Marinkovic Marco A.S. de Abreu 《Journal of solid state chemistry》2009,182(1):172-9510
One-dimensional (1-D) nanostructured sodium trititanates were obtained via alkali hydrothermal method and modified with cobalt via ion exchange at different Co concentrations. The resulting cobalt-modified trititanate nanostructures (Co-TTNS) were characterized by TGA, XRD, TEM/SAED, DRS-UV-Vis and N2 adsorption techniques. Their general chemical formula was estimated as NaxCoy/2H2−x−yTi3O7·nH2O and they maintained the same nanostructured and multilayered nature of the sodium precursor, with the growth direction of nanowires and nanotubes along [010]. As a consequence of the Co2+ incorporation replacing sodium between trititanate layers, two new diffraction lines became prominent and the interlayer distance was reduced with respect to that of the precursor sodium trititanate. Surface area was slightly increased with cobalt intake whereas pore size distribution was hardly affected. Besides, Co2+ incorporation in trititanate crystal structure also resulted in enhanced visible light photon absorption as indicated by a strong band-gap narrowing. Morphological and structural thermal transformations of Co-TTNS started nearly 400 °C in air and the final products after calcination at 800 °C were found to be composed of TiO2-rutile, CoTiO3 and a bronze-like phase with general formula Na2xTi1−xCoxO2. 相似文献
9.
Titania-lanthanum phosphate nanocomposites with multifunctional properties have been synthesized by aqueous sol-gel method. The precursor sols with varying TiO2:LaPO4 ratios were applied as thin coating on glass substrates in order to be transparent, hydrophobic, photocatalytically active coatings. The phase compositions of the composite powders were identified by powder X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). The anatase phase of TiO2 in TiO2-LaPO4 composite precursors was found to be stable even on annealing at 800 °C. The glass substrates, coated with TL1 (TiO2-LaPO4 composition with 1 mol% LaPO4) and TL50 (composite precursor containing TiO2 and LaPO4 with molar ratio 1:1) sols and annealed at 400 °C, produced contact angles of 74° and 92°, respectively, though it is only 62° for pure TiO2 coating. The glass substrates, coated with TL50 sol, produced surfaces with relatively high roughness and uneven morphology. The TL1 material, annealed at 800 °C, has shown the highest UV photoactivity with an apparent rate constant, kapp=24×10−3 min−1, which is over five times higher than that observed with standard Hombikat UV 100 (kapp=4×10−3 min−1). The photoactivity combined with a moderate contact angle (85.3°) shows that this material has a promise as an efficient self-cleaning precursor. 相似文献
10.
Shinji Kosaka Takumi Fujiwara Takayuki Komatsu 《Journal of solid state chemistry》2005,178(6):2067-2076
The ternary BaO-TiO2-B2O3 glasses containing a large amount of TiO2 (20-40 mol%) are prepared, and their optical basicities (Λ), the formation, structural features and second-order optical nonlinearities of BaTi(BO3)2 and Ba3Ti3O6(BO3)2 crystals are examined to develop new nonlinear optical materials. It is found that the glasses with high TiO2 contents of 30-40 mol% show large optical basicities of Λ=0.81-0.87, suggesting the high polarizabity of TiOn polyhedra (n=4-6) in the glasses. BaTi(BO3)2 and Ba3Ti3O6(BO3)2 crystals are found to be formed as main crystalline phases in the glasses. It is found that BaTi(BO3)2 crystals tend to orient at the surface of crystallized glasses. The new XRD pattern for the Ba3Ti3O6(BO3)2 phase is proposed through Rietvelt analysis. The second harmonic intensities of crystallized glasses were found to be 0.8 times as large as α-quartz powders, i.e., I2ω(sample)/I2ω(α-quartz)=0.8, for the sample with BaTi(BO3)2 crystals and to be I2ω(sample)/I2ω(α-quartz)=68 for the sample with Ba3Ti3O6(BO3)2 crystals. The Raman scattering spectra for these two crystalline phases are measured for the first time and their structural features are discussed. 相似文献
11.
In this paper, we describe the structural and sensing properties of high-k PrYxOy sensing films deposited on Si substrates through reactive co-sputtering. Secondary ion mass spectrometry and atomic force microscopy were employed to analyze the compositional and morphological features of these films after annealing at various temperatures. The electrolyte-insulator-semiconductor (EIS) device incorporating a PrYxOy sensing membrane that had been annealed at 800 °C exhibited good sensing characteristics, including a high sensitivity (59.07 mV pH−1 in solutions from pH 2 to 12), a low hysteresis voltage (2.4 mV in the pH loop 7 → 4 → 7 → 10 → 7), and a small drift rate (0.62 mV h−1 in the buffer solution at pH 7). The PrYxOy EIS device also showed a high selective response towards H+. This improvement can be attributed to the small number of crystal defects and the large surface roughness. In addition, the enzymatic EIS-based urea biosensor incorporating a high-k PrYxOy sensing film annealed at 800 °C allowed the potentiometric analysis of urea, at concentrations ranging from 1 to 16 mM, with a sensitivity of 9.59 mV mM−1. 相似文献
12.
SrCo1−yNbyO3−δ (y = 0.025–0.4) were synthesized for oxygen separation application. The crystal structure, phase stability, oxygen nonstoichiometry, electrical conductivity, and oxygen permeability of the oxides were systematically investigated. Cubic perovskite, with enhanced phase stability at higher Nb concentration, was obtained at y = 0.025–0.2. However, the further increase in niobium concentration led to the formation of impurity phase. The niobium doping concentration also had a significant effect on electrical conductivity and oxygen permeability of the membranes. SrCo0.9Nb0.1O3−δ exhibited the highest electrical conductivity and oxygen permeability among the others. It reached a permeation flux of ∼2.80 × 10−6 mol cm−2 s−1 at 900 °C for a 1.0-mm membrane under an air/helium oxygen gradient. The further investigation demonstrated the oxygen permeation process was mainly rate-limited by the oxygen bulk diffusion process. 相似文献
13.
Qiang Dong Yoshinori Yonesaki Takahiro Takei Nobukazu Kinomura 《Journal of solid state chemistry》2011,184(7):1899-1902
A new pyrochlore-type Na0.32Bi1.68Ti2O6.46(OH)0.44 with the cubic cell of a=10.339(5) Å was prepared by hydrothermal reaction using TiO2 (anatase) and Bi2O3 in NaOH solution. This compound was obtained when the molar ratio of NaOH/TiO2 was above 2 and the reaction temperature was above 240 °C. The TG-curve of as-prepared sample showed a mass loss of 0.8 mass% which was caused by release of OH group. This compound decomposed to a pyrochlore-type compound and a layered-type Na0.5Bi4.5Ti4O15 above 800 °C. The optical band gap of Na0.32Bi1.68Ti2O6.46(OH)0.44 was estimated to be 2.5 eV. 相似文献
14.
Nik Reeves-McLaren Matthew C. Ferrarelli Yuan-Wei Tung Derek C. Sinclair Anthony R. West 《Journal of solid state chemistry》2011,184(7):1813-1819
Subsolidus phase relations in the CuOx-TiO2-Nb2O5 system were determined at 935 °C. The phase diagram contains one new phase, Cu3.21Ti1.16Nb2.63O12 (CTNO) and one rutile-structured solid solution series, Ti1−3xCuxNb2xO2: 0<x<0.2335 (35). The crystal structure of CTNO is similar to that of CaCu3Ti4O12 (CCTO) with square planar Cu2+ but with A site vacancies and a disordered mixture of Cu+, Ti4+ and Nb5+ on the octahedral sites. It is a modest semiconductor with relative permittivity ∼63 and displays non-Arrhenius conductivity behavior that is essentially temperature-independent at the lowest temperatures. 相似文献
15.
Hiromasa Ikuta 《Thermochimica Acta》2004,414(2):227-232
The phase transition of chromium substituted lithium manganese spinel oxide, LiCryMn2−yO4 was investigated by low-temperature powder X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and electrical resistivity measurements. The sample prepared at 820 °C resulted in lowering the transition temperature Tt with Cr composition y, whereas Tt of the sample prepared at 750 °C remained constant for 0≤y≤0.17 in LiCryMn2−yO4. This would be caused by a difference in distribution of the substituted Cr3+ ion in octahedral site depending on the preparation temperature. The phase transition was suppressed with increasing the amount of Cr content. 相似文献
16.
Li4Ti5O12 thin films for rechargeable lithium batteries were prepared by a sol-gel method with poly(vinylpyrrolidone). Interfacial properties of lithium insertion into Li4Ti5O12 thin film were examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and potentiostatic intermittent titration technique (PITT). Redox peaks in CV were very sharp even at a fast scan rate of 50 mV s−1, indicating that Li4Ti5O12 thin film had a fast electrochemical response, and that an apparent chemical diffusion coefficient of Li+ ion was estimated to be 6.8×10−11 cm2 s−1 from a dependence of peak current on sweep rates. From EIS, it can be seen that Li+ ions become more mobile at 1.55 V vs. Li/Li+, corresponding to a two-phase region, and the chemical diffusion coefficients of Li+ ion ranged from 10−10 to 10−12 cm2 s−1 at various potentials. The chemical diffusion coefficients of Li+ ion in Li4Ti5O12 were also estimated from PITT. They were in a range of 10−11-10−12 cm2 s−1. 相似文献
17.
The phase system Al2O3-TiO2 was investigated in the compositional range from 48:52 to 62:38 mol% Al2O3:TiO2. The samples were prepared by melting the binary oxides in an arc-imaging furnace and the obtained samples were examined by powder X-ray diffraction. The recorded powder patterns could be interpreted in terms of intergrowth structures consisting of two basic building blocks, which were deduced from the known crystal structures of β-Al2TiO5 and Al6Ti2O13. The structure of a new ordered compound with the formula Al16Ti5O34 is proposed. The thermal stability was estimated from DTA and tempering experiments and showed that all prepared samples decompose at temperatures around 800 °C into the binary oxides corundum and titania. 相似文献
18.
The interaction of colloidal TiO2 nanoparticles with calf thymus-DNA was studied by using absorption, FT-IR, steady state and time resolved fluorescence spectroscopic techniques. The apparent association constant has been deduced (Kapp = 2.85 × 103 M−1) from the absorption spectral changes of the DNA-colloidal TiO2 nanoparticles using the Benesi–Hildebrand equation. Addition of colloidal TiO2 nanoparticles quenched the fluorescence of EtBr–DNA. The number of binding sites (n = 0.97) and the apparent binding constant (K = 6.68 × 103 M−1) were calculated from relevant fluorescence quenching data. The quenching, through a static mechanism, was confirmed by time resolved fluorescence spectroscopy. 相似文献
19.
Subsolidus phase equilibria and crystal chemistry were studied for the La2O3-MgO-TiO2 system and for the ternary sections LaMg1/2Ti1/2O3-CaTiO3-La2O3 and LaMg1/2Ti1/2O3-CaTiO3-La0.833Mg0.25Ti0.75O3 in the quaternary La2O3-CaO-MgO-TiO2 system. Dielectric properties (relative permittivity and temperature coefficient of resonant frequency, τf) were measured at 5-10 GHz and mapped onto the phase equilibria relations to reveal the compositions of temperature-stable (τf=0) compounds and mixtures. Phase equilibria relations were obtained by X-ray powder diffraction analysis of approximately 80 specimens prepared by solid-state reactions in air at ∼1450°C. Six ternary phases were found to form in the La2O3-MgO-TiO2 system, including the three previously reported compounds LaMg1/2Ti1/2O3, La5Mg0.5Ti3.5O15, and “La6MgTi4O18”; and the new phases La10MgTi9O34, La9Mg0.5Ti8.5O31, and a perovskite-type solid solution (1−x)LaMg1/2Ti1/2O3-xLa2/3TiO3 (0?x?0.5). The phase previously reported as “La6MgTi4O18” was found to form off-composition, apparently as a point compound, at La6Mg0.913Ti4.04O18. Indexed experimental X-ray powder diffraction patterns are given for LaMg1/2Ti1/2O3, La5Mg0.5Ti3.5O15, La6Mg0.913Ti4.04O18, La10MgTi9O34, and La9Mg0.5Ti8.5O31. LaMg1/2Ti1/2O3 exhibits a slightly distorted perovskite structure with ordered B-cations (P21/n; a=5.5608(2) Å, b=5.5749(3) Å, c=7.8610(5) Å, β=90.034(4)°). La5Mg0.5Ti3.5O15 (Pm1; a=5.5639(1), c=10.9928(5) Å) and La6Mg0.913Ti4.04O18 (R3m; a=5.5665(1), c=39.7354(9) Å) are n=5 and n=6 members, respectively, of the (111) perovskite-slab series AnBn−1O3n. The new phases La10MgTi9O34 (a=5.5411(2), b=31.3039(9), c=3.9167(1) Å) and La9Mg0.5Ti8.5O31 (a=5.5431(2), b=57.055(1), c=3.9123(1) Å) are n=5 and n=4.5 members, respectively, of the (110) perovskite-slab series AnBnO3n+2, which exhibit orthorhombic subcells; electron diffraction revealed monoclinic superlattices with doubled c-parameters for both compounds. Extensive perovskite-type solid solutions form in the ternary sections LaMg1/2Ti1/2O3-CaTiO3-La2O3 and LaMg1/2Ti1/2O3-CaTiO3-La0.833Mg0.25Ti0.75O3. The La2O3-MgO-TiO2 system contains two regions of temperature-stable (τf=0) compositions. The quaternary La2O3-CaO-MgO-TiO2 system contains an extensive single-phase perovskite-type volume through which passes a surface of temperature-stable compositions with permittivities projected to be in the 40-50 range. Traces of this surface occur as lines of τf=0 perovskite-type phases in the ternary sections LaMg1/2Ti1/2O3-CaTiO3-La2O3 and LaMg1/2Ti1/2O3-CaTiO3-La0.833Mg0.25Ti0.75O3. 相似文献
20.
Yasuhiko Takahashi Ken-ichi Ohshima Junji Awaka Junji Akimoto 《Journal of solid state chemistry》2007,180(3):1020-1027
Single crystals of calcium ferrite CaFe2O4-type NaTi2O4 having millimeter-sized needle shapes were synthesized by a reaction of Na metal and TiO2 in a sealed iron vessel at 1473 K. Sodium-deficient NaxTi2O4 single crystals with 0.558<x<1 were successfully synthesized by a topotactic oxidation reaction using NaTi2O4 single crystals as parent materials. The crystal structures of NaxTi2O4 with x=0.970, 0.912, 0.799, 0.751, 0.717, 0.686, 0.611, and 0.558 were determined by the single-crystal X-ray diffraction method. The basic framework constructed by the Ti1O6 and Ti2O6 double rutile chains was maintained in these NaxTi2O4 compounds. Based on the results of bond valence analysis, we speculated that the Ti1 sites are preferentially occupied by Ti3+ cations over the compositional range of 0.8<x<1, while both the Ti1 and Ti2 sites are randomly occupied by Ti3+ and Ti4+ cations at x=0.558. Magnetic susceptibility data indicated that the broad maximum around 40 K observed in as-grown NaTi2O4 is suppressed by an Na deficiency and vanishes in Na0.717Ti2O4. The electrical resistivity increased with the Na deficiency; however, it was still semiconductive in Na0.799Ti2O4. 相似文献