A. A. Rempel

Ordering of Cubic Titanium Monoxide into Monoclinic Ti5O5

The structures of ordered and disordered cubic TixOz= TiOy(y= z/x) phases containing both Ti and O vacancies were studied by x-ray diffraction. The results demonstrate that annealing TiOywith y= 0.9–1.1 below 1300 K leads to the formation of a monoclinic ordered Ti5O5phase (sp. gr. C2/m(A12m/1)). Symmetry analysis of the monoclinic Ti5O5superstructure indicates that the TiOy–Ti5O5ordering transition is defined by the {k10} Lifshits and {k4} and {k1} non-Lifshits wavevector manifolds. The ordering is shown to be a first-order transition accompanied by a decrease in the unit-cell volume of the parent lattice. The Ti and O distribution functions in titanium monoxide are calculated, and the Ti- and O-site near-neighbor environments in the monoclinic Ti5O5superstructure are identified. The region of possible long-range-order parameters is outlined.

Atomic ordering and hardness of nonstoichiometric titanium carbide

Abstract A study is made of the structure of a nonstoichiometric titanium carbide TiC y in the disordered state and in the as-annealed condition. Annealing carbides with different carbon content is found to give rise to various types of ordered phases. On annealing, a nonstoichiometric titanium carbide exhibits an increase in microhardness. It is assumed that microhardness increases owing to the grain being comminuted as a result of the formation of ordered phases.

Two-sublattice ordering in titanium monoxide

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.

Observation of structural vacancies in titanium monoxide using transmission electron microscopy

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.

Atomic structure of cadmium sulfide nanoparticles

A method for calculating the x-ray diffraction patterns of cadmium sulfide nanoparticles with a disordered internal structure, a real surface, shape, and size is proposed within the kinematic theory of scattering. A computer analysis has revealed that the characteristic shape of the experimental x-ray diffraction patterns of cadmium sulfide films and powders is determined by a specific disordered nanoparticle structure differing from the crystal structures of wurtzite and sphalerite. According to the computer simulation, cadmium sulfide nanoparticles synthesized through chemical deposition have a shape similar to a hexagonal prism with a characteristic size of approximately 5 nm.

Incommensurate ordered phase in non-stoichiometric tantalum carbide

By the neutron diffraction structure analysis method, an ordered phase of non-stoichiometric tantalum carbide with the base B1(NaCl) structure has been detected. It is shown that the superstructural reflections observed correspond to an incommensurate superstructure close to type. With allowance for ordering of , the phase diagram of the Ta - C system has been calculated and constructed. The effects of non-stoichiometry and ordering on the period of a base B1-type lattice of tantalum carbide and on the superconducting critical temperature have been studied.

Synthesis of nanocrystalline silver sulfide

Silver sulfide (Ag2S) powders have been synthesized through chemical precipitation from aqueous solutions of silver nitrate, sodium sulfide, and sodium citrate or Trilon B as a complexing agent and stabilizer. The synthesized Ag2S powders have a monoclinic (sp. gr. P21/c) acanthite (α-Ag2S) structure. The colloidal stock solutions decanted from the synthesized precipitate have been shown to be stable for at least a year. The particle size of the silver sulfide in the colloidal solutions and precipitated powders has been evaluated by dynamic light scattering, X-ray diffraction, and BET measurements. The results demonstrate that, varying the relative reactant concentrations in the starting reaction mixture, one can precipitate Ag2S nanoparticles of tailored average size in the range from ≃ 500 to ≃20–30 nm. The size of Ag2S nanoparticles in the stable colloidal solutions obtained is 15–20 nm.

Preparation of stable colloidal solution of cadmium sulfide CdS using ethylenediaminetetraacetic acid

By the method of chemical condensation a stable aqueous colloidal solution of nanoparticles of cadmium sulfide was obtained. The solution obtained in the daylight had a bright lemon-yellow color. For the temporary stabilization of the solution was used an organic complexone, disodium ethylenediaminetetraacetate (EDTA), that prevented coagulation of colloidal particles up to several months at 4°C. At room temperature, the solution remained stable during a month. The structure and properties of the disperse phase were studied by the X-ray diffraction, optical fluorescence, and electron microscopy. The solid particles size is about 3 nm, they have a disordered close-packed structure with the space group P6mm and possess the photoluminescence color from green to orange depending on the duration of keeping the solution. The size of coagulates was 10 nm, 100 nm, and 1 μm after keeping for 1, 2, and 4 months, respectively.

Electrical Conductivity and Magnetic Susceptibility of Titanium Monoxide

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.

Sizes and fluorescence of cadmium sulfide quantum dots

Cadmium sulfide quantum dots have been synthesized by wet chemical deposition from an aqueous solution. The sizes of the quantum dots determined by dynamic light scattering directly in the colloidal solution and by intermittent-contact atomic force microscopy in the dry sediment agree with each other. It has been found that splitting of the fluorescence peaks of the quantum dots can be affected by the disorder of the atomic structure of cadmium sulfide quantum dots.