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1.
Annealed titanium monoxide TiO1.087 has been studied by the electron diffraction method. A cubic model of the Ti5O5 superstructure (Ti5O5 (Ti90?18O90??18)) of nonstoichiometric titanium monoxide Ti x O z has been proposed on the basis of experimental data and representations about the disorder-order transition channel. It has been shown that reflections observed on the electron diffraction pattern are identified in the space group $Pm\bar 3m$ . The period of the unit cell of the cubic Ti5O5 superstructure is larger than that for the B1 basic disordered structure of Ti x O z monoxide by a factor of 3. The disorder-order transition channel Ti x O z (space group $Fm\bar 3m$ )-Ti5O5 (space group $Pm\bar 3m$ ) includes 75 superstructure vectors of seven stars {k 10}, {k 7}, {k 6(1)}, {k 6(2)}, {k 4(1)}, {k 4(2)}, and {k 1}. The distribution functions of Ti and O atoms over the sites of the cubic Ti5O5 (space group $Pm\bar 3m$ ) superstructure have been calculated.  相似文献   

2.
A model of the atomic structure with the short-range order in the vacancy distribution for the disordered cubic phase of titanium monoxide TiO1.0 has been proposed. The effect of the short-range order on the electronic structure and the stability of the compound has been studied by the supercell method within the DFT-GGA approximation with the use of pseudopotentials. It has been established that the appearance of the short-range order considerably decreases the total energy. The decrease in the energy is comparable with the energy gain during the ordering of the vacancies according to the type of monoclinic superstructure Ti5O5 to the long-range order parameter η = 0.7. It has been shown that the discrepancies between the theoretical and experimental electronic spectra of titanium monoxide can be explained by allowance for the short range order.  相似文献   

3.
4.
J. He  E.I. Meletis 《哲学杂志》2013,93(15):1686-1710
Barium titanate thin films deposited on MgO (0?0?1) by RF magnetron sputtering are composed of two new superstructures Ba4Ti5O10 and Ba4Ti4O11 formed as epitaxial nanodomain structures. Due to the nanometre scale size of domains and the complexity of the structure in the film, the single-crystal X-ray diffraction technique does not have the capability for the crystallographic structure determination of the two new superstructures. We used nanobeam electron diffraction to reconstruct the three-dimensional diffraction space and hence the symmetry of the new superstructures. Both Ba4Ti5O10 and Ba4Ti4O11 are monoclinic structures with a space group of Cm (b-unique axis). Ba4Ti5O10 has a lattice parameter a?=?16.49?Å, b?=?3.94?Å, c?=?8.94?Å and β?=?103°, while Ba4Ti4O11 has a?=?17.88?Å, b?=?3.94?Å, c?=?7.21?Å and β?=?98°. Atomic structural models for the two new superstructures were established by reconstructing the high-resolution transmission electron microscopy (HRTEM) images taken from the three major axes and refined by matching the simulated HRTEM images and calculated electron diffraction patterns with the experimental results. The two superstructures are epitaxially grown on MgO with their b-axis parallel to the growth direction.  相似文献   

5.
The disordered and ordered structures of nonstoichiometric titanium monoxide TixOz≡TiOy(y=z/x) containing structural vacancies simultaneously in the nonmetallic and metallic sublattices were studied. In the stoichiometry range from TiO0.9 to TiO1.1, an ordered monoclinic phase [space group C2/m (A12m/1)] of the Ti5O5 type is formed in the TiOy monoxide at temperatures below 1300 K. The disorder-order TiOy?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.  相似文献   

6.
Symmetry analysis is carried out for the ordered phases of cubic monoxide TiOy with relative oxygen contents y<1 and y>1. It is established that a partially ordered orthorhombic phase (space group Immm)—a derivative of the orthorhombic M3X2□ superstructure (at y<1.0) or the inverse superstructure M2■X3 (at y>1)—may arise in TiOy. The distribution of Ti and O atoms, oxygen vacancies □, and titanium vacancies ■ in unit cells of the orthorhombic ordered phases is determined. The phases are formed through the order-disorder transition channel along two rays of a non-Lifshitz star {k 4}, and the ordering proceeds as a first-order phase transition. The distribution functions of Ti atoms over the sites of metallic and O atoms over the sites of nonmetallic sublattices are calculated for the orthorhombic superstructures of cubic titanium monoxide TiOy.  相似文献   

7.
The interpretation of diffraction spectra of ordered high-temperature phases of solid solutions and strongly nonstoichiometric compounds is discussed. It has been shown that variations of the intensities of superstructure reflections, which cannot be explained within simple ordering models, can be due to the superposition of superstructures with different symmetries in the matrix of the basis crystal structure. Using an example of atom–vacancy ordering in TiO1.0 titanium monoxide, a model of the order–order transition state formed by the superposition of low-temperature monoclinic (space group A2/m (C2/m)) and high-temperature cubic (space group Pm3?m) M5X5 superstructures has been proposed. It has been shown that the transition state is thermodynamically equilibrium and should be implemented instead of the M5X5 cubic superstructure. The transition state model can be considered as an M(5–i)X(5–i) superstructure (i = 1, 14/18, 11/18) with the monoclinic symmetry (space group P1m1).  相似文献   

8.
Conductivity and magnetic susceptibility of disordered cubic titanium monoxide TiOy(0.920≤y≤1.262) are studied. Temperature dependences of the conductivity of TiOy monoxides with y≤1.069 are described by the Bloch-Grüneisen function with Debye temperature 400–480 K, and temperature dependences of the susceptibility include Pauli paramagnetism of conduction electrons. The behavior of conductivity and susceptibility of TiOy with y≥1.087 is typical of semiconductors with nondegenerate charge carriers obeying Boltzmann statistics. The band gap ΔE between the valence and conduction bands of TiOy(y≥1.087) is 0.06–0.17 eV, and effective mass of charge carriers is equal to 7–14 electron masses.  相似文献   

9.
The structure of annealed titanium monoxide TiO1.087 containing monoclinic ordered phase Ti5O5 was studied by electron diffraction. Along with the set of structural, superstructural, and extra reflections, the diffraction pattern of titanium monoxide shows a set of plane diffuse fringes in the (112)B1* section of the reciprocal lattice of the basis cubic structure B1. It is shown that some of the extra reflections are due to the twinning of the monoclinic superstructure along the (?1?11) plane of the reciprocal lattice of the basis cubic structure. The diffuse contours enclose plane areas of the reciprocal space with the fixed values of wave vectors K100 ~ ±(h+0.07)k100, K010 ~ ±(k+0.07)k010, and K001 ~± (l+0.07)k001 of the B1 structure. Their appearance is associated with the short-range displacement order.  相似文献   

10.
Electron diffraction was used to study the annealed titanium monoxide TiO1.087 containing the monoclinic ordered phase Ti5O5. The diffraction pattern of titanium monoxide in the (112)* B1 plane of the reciprocal lattice of the parent B1 cubic structure contains not only structural, superstructural, and additional reflections but also a system of planar diffuse strips. It has been established that part of the additional reflections are twins of the superstructure reflections of the monoclinic ordered phase; the twinning plane is the ( $\overline 1 \overline 1 1$ ) plane of the reciprocal lattice of the parent cubic phase. The diffuse scattering contours cover finite plane areas in the reciprocal space characterized by the wave vectors K 100 ~ ± (h + 0.07)k 100, K 010 ~ ±(k + 0.07)k 010, and K 001 ~ ±(l + 0.07)k 001 in the B1 structure. The diffuse scattering is caused by short-range displacement order. Short-range substitution order and the corresponding diffuse scattering are absent.  相似文献   

11.
谢东  冷永祥  黄楠 《物理学报》2013,62(19):198103-198103
TiO在微电子结构器件中有重要的应用前景. 本文以CO2作反应气体, 采用直流反应磁控溅射方法成功制备出C掺杂TiO薄膜. 采用XRD, XPS和四探针电阻计对薄膜结构、成分和电阻率进行表征. 在实验结果的基础之上建立起TiO和C掺杂TiO的计算模型并采用第一性原理 方法计算其能带结构和电子态密度. 实验结果表明薄膜相结构为面心立方的岩盐结构, C取代O的阴离子掺杂为主要掺杂方式, 薄膜电阻率为52.2 μΩ·cm. 第一性原理计算结果表明, 费米能级穿过TiO的导带, TiO具有金属性导电的能带结构特征; C掺杂TiO 后, 其金属性导电的能带结构没有改变, 只是在费米面附近出现C 2p态提供的杂质能级, 杂质能级扩展了TiO的导带宽度并提高了费米面附近的电子能态密度, 从而导至TiO电导增加, 电阻率降低. 第一性原理计算结果与实验结果一致. 关键词: C掺杂TiO 直流反应磁控溅射 第一性原理 电子结构  相似文献   

12.
The electronic structure of titanium monoxide TiO y (0.810 ≤ y ≤ 1.262) in the high-temperature cubic phase with vacancies randomly distributed over the titanium and oxygen sublattices is calculated in the coherent potential approximation. The changes in the electronic spectra with the concentration of vacancies are retraced. The calculated spectra are compared to the available experimental data.  相似文献   

13.
The influence of the ordering of titanium and oxygen atoms on the Madelung energy has been studied using the computer simulation. The dependence of the Madelung constant on the crystal size for the titanium monoxide with ordered and disordered distributions of atoms and vacancies has been obtained for the first time. It has been demonstrated that the Madelung energy in the ordered titanium monoxide is considerably (by 6%) lower than that in the disordered monoxide. The electrostatic interaction between titanium and oxygen ions stabilizes the ordered phase in titanium monoxide up to high temperatures and should substantially affect the disordering processes that occur in this compound at high temperatures.  相似文献   

14.
利用密度泛函BLYP方法优化得到了TiO分子的稳定构型,并计算了TiO分子基态在外场作用下前线轨道变化情况,然后利用杂化组态相互作用CIS-DFT方法,比较了TiO分子在外电场下的激发特性.结果表明,在一定的电场范围内,随着电场的增大,α轨道的最高占据轨道与最低空轨道能隙逐渐变小,β轨道能隙逐渐变大,同时可跃迁的低激发态跃迁波长随电场的增大而变长,高激发态波长变化相对复杂,且基态跃迁至激发态的耦合强度随外电场的增大而加强.  相似文献   

15.
Local atomic environment of vacancies in nonstoichiometric titanium monoxide ranging in composition from TiO0.74 to TiO1.26 was studied by electron-positron annihilation. Analysis of the Doppler broadening spectra of the annihilation gamma line for titanium and liquid oxygen showed that positrons in titanium monoxide are trapped by titanium vacancies. Experiments revealed that the lifetime of positrons in ordered and disordered titanium monoxide TiO y increases with increasing oxygen content y and varies from 184 to 210 ps. Data on the valence electron density permitted the prediction that the lifetime of free positrons in stoichiometric titanium monoxide is about 140 ps and the lifetime of positrons localized in an oxygen vacancy is about 170 ps. The method used to analyze the gamma-line Doppler broadening spectra makes it possible to determine the type and number of atoms around a vacancy and to investigate order-disorder phase transformations in nonstoichiometric compounds.  相似文献   

16.
Structural vacancies were directly observed in nonstoichiometric ordered titanium monoxide using high-resolution transmission electron microscopy under a magnification of 4×106. The observation of structural vacancies became possible due to their ordering and the formation of continuous vacancy channels in certain crystallographic directions. Microdiffraction was employed to orient the sample in the direction permitting the observation of vacancy channels. Transmission electron microscopy providing a magnification of tens of thousands of times revealed that titanium monoxide grains do not contain cracks and macropores and confirmed that the free volume detected picnometrically in the titanium monoxide is concentrated in structural vacancies on the titanium and oxygen sublattices.  相似文献   

17.
The disorder-order transition in cubic vanadium monoxide VOy (y = 1.29, 1.30) possessing a B1 type structure and containing vacancies only in the metal sublattice has been studied by X-ray diffraction and symmetry analyses. It is established that the formation of a tetragonal (space group I41/amd) ordered V52O64 phase in cubic vanadium monoxide VOy proceeds in the form of the first-order phase transition via a channel involving 22 nonequivalent superstructural vectors of four stars ({k 10}, {k 4}, {k 3}, and {k 2}). The distribution function of V atoms in the tetragonal V52O64 superstructure is calculated, and it is found that the real ordered V51.6O64 phase exhibits significant atomic displacements. The boundaries of the domain of existence of the V52O64 phase at 54–60% O are determined in the phase diagram of the V-O system.  相似文献   

18.
Single crystals of Li4 + xTi5O12 were prepared by means of electrochemical Li-ion intercalation technique using parent Li4Ti5O12 single crystals. The obtained Li4 + xTi5O12 (x = 1.35) crystallizes in the cubic spinel-related type structure, space group Fd3?m, and lattice parameters of a = 8.346(2) Å and V = 581.3(5) Å3 and Z = 8. The Li-ion intercalated sites were successfully determined to be both the 8a and 16c sites by using the difference Fourier synthesis map. The structure was determined by single-crystal X-ray structure analysis and refined to the conventional value of R = 3.7% for 132 independent observed reflections. The chemical composition has been determined to be Li5.35Ti5O12 from the result of site-population refinements. In addition, theoretical electron density distributions and total energy were calculated for three postulated compounds of “Li4.5Ti4.5O12” and “Li4.5 + xTi4.5O12” with x = 1.5 and 3.0.  相似文献   

19.
Li4Ti5O12 for anodic active material of lithium ion batteries is synthesized using different Li/Ti ratios of 3.5/5.0, 4.0/5.0 and 4.5/5.0 by a solid-state reaction between Li2CO3 and anatase TiO2 at 850?°C. All samples contain a small amount of transformed rutile TiO2 in the final Li4Ti5O12, where the amount of rutile TiO2 decreases with the increase in Li/Ti ratio. A stoichiometric Li4Ti5O12 with Li/Ti = 4.0/5.0 shows a slightly larger particle size and higher charge capacity than those of Li-deficient and Li-excessive particles, while the discharging rate capability is shown to mainly depend on particle size regardless of Li/Ti ratio. According to the time-resolved X-ray diffraction patterns using a synchrotron source, however, no significant difference is found in spite of the difference in Li/Ti ratio, indicating the structural stability of Li4Ti5O12 during the Li insertion and extraction process.  相似文献   

20.
Layered cathode Li1.5Ni0.25Mn0.75O2.5 has been synthesized and coated by Li4Ti5O12. The pristine and coated Li1.5Ni0.25Mn0.75O2.5 powders are characterized by X-ray diffraction (XRD), indicating the materials remained the layered structure before and after coating. The coated Li4Ti5O12 has been detected by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (DEX). The electrochemical performance, especially rate performance of Li1.5Ni0.25Mn0.75O2.5 electrode, is improved effectively after Li4Ti5O12 coating. The first discharge capacity, coulombic efficiency, and capacity retention of Li4Ti5O12-coated Li1.5Ni0.25Mn0.75O2.5 electrode are 244 mA h g?1, 81.5 %, and 98.3 % after 50 cycles, respectively. The Li4Ti5O12-coated Li1.5Ni0.25Mn0.75O2.5 electrode exhibits 108 mA h g?1 at 10 °C rate. Electrochemical impedance spectroscopy (EIS) results show that the charge transfer resistance (R ct) of Li1.5Ni0.25Mn0.75O2.5 electrode decreases after coating, which is due to the existence of Li4Ti5O12 with high lithium ion diffusion coefficient and suppression of the solid electrolyte interfacial (SEI) layer development and is responsible for the excellent rate capability and cyclic performance.  相似文献   

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