High-temperature deformation and specific features of dislocation structure of Ti<Subscript>3</Subscript>Al

The transmission electron microscopy was used to examine the dislocation structure of intermetallic Ti₃Al after deformation at temperatures T = 1073–1273 K. It is established that its microstructure contains mobile 2c + a and superdislocations. Possible models describing the destruction of barriers associated with 2c + a superdislocations in pyramidal planes are discussed using the results of computer simulation of the superdislocation core structure in Ti₃Al.     

Electron-microscopic study of microcracks in single-crystal Ti<Subscript>3</Subscript>Al

Microcracks in a Ti₃ Al alloy subjected to indentation at room temperature were studied by transmission electron microscopy. The microcracks are shown to grow on \(\{ 0\overline 1 11\} \) pyramidal planes and in the slip bands of 2c + a superdislocations on \(\{ 20\overline 2 1\} \) and \(\{ 11\overline 2 1\} \) pyramidal planes. It is found that, due to the formation of a slip band in the basal plane at a microcrack tip, the propagating microcrack becomes steplike rather than straight. It is shown that a microcrack can nucleate at the line of intersection of \(\{ 11\overline 2 1\} \) pyramidal and \(\{ 0\overline 1 10\} \) prismatic planes.     

Formation of microcracks in an indented Ti<Subscript>3</Subscript>Al intermetallic compound

Microcracks in the Ti₃Al alloy indented at room temperature have been analyzed by electron microscopy. Analysis of the microstructure has revealed that microcracks propagate in the {0\(\overline 1 \)11} pyramidal planes and in the slip bands of the 2c + a superdislocations in the {20\(\overline 2 \)1} and {11\(\overline 2 \)1} pyramidal planes. It is found that the formation of a slip band in the basal plane at the microcrack tip leads to a change in the character of microcrack propagation from straight-line to steplike.     

Dislocation structure of intermetallic Ti3Al subjected to high-temperature deformation

Transmission electron microscopy was used to examine the dislocation structure of intermetallic Ti₃Al subjected to deformation at tempertures T = 1073–1273 K. The microstructure of samples subjected to high-temperature deformation is established to contain mobile superdislocations of a and 2c + a types, and single dislocations with Burgers vector [0001] are also observed on the prismatic planes. Possible models of destruction of barriers associated with 2c + a superdislocations on the pyramidal planes are discussed using the results of computer simulations of the structure of a superdislocation core in in Ti₃Al.     

Microcrack formation upon interaction of superdislocations belonging to different slip planes in Ti<Subscript>3</Subscript>Al

The interaction reactions between the superdislocations accomplishing deformation in the basal, prismatic, and pyramidal (I and II types) planes in Ti₃Al single crystals have been investigated. The types of interactions leading to the formation of dislocation barriers (microcrack nuclei) are established. The microcrack types are classified according to the orientations of the deformation axes of single crystals. Stereographic triangle regions, characterized by a preferred type of crack opening, are found.     

Superdislocation core structure in pyramidal slip planes and temperature anomalies of Ti<Subscript>3</Subscript>Al intermetallic deformation behavior

For Ti₃Al intermetallic with the D0₁₉ superlattice, the computer-aided simulation of the superdislocation core structure in the basal, prismatic, and type I and type II pyramidal planes is performed. A model of thermally activated transformation of 2c + a glissile edge superdislocations into dislocation barriers in the pyramidal planes is used to account for the anomalous temperature dependence of the yield stress of single-crystal Ti₃Al compressed in the [0001] direction.     

Magnetic structure of the quasi-one-dimensional frustrated antiferromagnet LiCu<Subscript>2</Subscript>O<Subscript>2</Subscript> with Spin <Emphasis Type="Italic">S</Emphasis> = 1/2

The magnetic properties of LiCu₂O₂ single-crystal samples without twinning are investigated using electron spin resonance and nuclear magnetic resonance spectroscopy. The experimental results obtained are described in terms of the model of a planar spiral antiferromagnet for the orientation of the magnetic field H ‖ b or H ‖ c and the model of a collinear spin-modulated antiferromagnet for the orientation of the static magnetic field H ‖ a.     

Galvanomagnetic properties of atomically disordered Sr<Subscript>2</Subscript>RuO<Subscript>4</Subscript> single crystals

The effect of neutron-bombardment-induced atomic disorder on the galvanomagnetic properties of Sr₂RuO₄ single crystals has been experimentally studied in a broad range of temperatures (1.7–380 K) and magnetic fields (up to 13.6 T). The disorder leads to the appearance of negative temperature coefficients for both the in-plane electric resistivity (ρ_a) and that along the c axis (ρ_c), as well as the negative magnetoresistance Δρ, which is strongly anisotropic to the magnetic field orientation (H ∥ a and H ∥ c), with the easy magnetization direction along the c axis and a weak dependence on the probing current direction in the low-temperature region. The experimental ρ_a(T) and ρ_c(T) curves obtained for the initial and radiation-disordered samples can be described within the framework of a theoretical model with two conductivity channels. The first channel corresponds to the charge carriers with increased effective masses (～10m _e , where m _e is the electron mass) and predominantly electron-electron scattering, which leads to the quadratic temperature dependences of ρ_a and ρ_c. The second channel corresponds to the charge carriers with lower effective masses exhibiting magnetic scattering at low temperatures, which leads to the temperature dependence of the ρ_{a, c}(T) ∝ 1/T type.     

Polarized optical absorption of MnGa<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

Optical absorption of MnGa₂S₄ single crystals is studied at two light polarizations (E ||C and E⊥ C). The polarization splitting of the absorption edge points to a splitting of the valence band of MnGa₂S₄. A contribution to the crystal-field splitting is made by two factors, namely, by a difference in the pseudopotential of cationic sublattice atoms and by tetragonal compression of the lattice along the C axis. A scheme of optical transitions in MnGa₂S₄ in the Brillouin zone center is suggested, according to which the optical transitions Г₃ + Г₄ → Г₁ occur in the polarization E ⊥ C, and the Г₂ → Г₁ transitions occur in the polarization E || C.     

Formation of the incommensurate ordered phase in TaC<Subscript>y</Subscript> carbide

Structural neutron diffraction studies indicate that only one ordered phase arises after the disorder-order transition in nonstoichiometric cubic tantalum carbide TaC_y. This phase arises in the composition range y = 0.79–0.89 due to long-term annealing with a decrease in temperature from 1600 to 300 K. It is incommensurate in the [1–11]_B1 direction, but it is close to commensurate M₆C₅ structures (C2/m and P3₁ space groups) in mutual arrangement of atoms and vacancies in nonmetallic (1–11)_B1 planes. The disorder-order transition channel that is associated with the formation of the incommensurate superstructure in TaC_y carbide includes two arms k ₅ ⁽⁶⁾ ≈ 0.473b₂ and k ₅ ⁽⁵⁾ = ?k ₅ ⁽⁶⁾ of the {k₅} star and arms of the {k₄} and {k₃} stars. The translation period of the incommensurate phase in the [1–11]_B1 direction is 8.9–9.1 nm, which is larger than that in the commensurate phase M₆C₅ by a factor of about 18.     

V<Subscript>52</Subscript>O<Subscript>64</Subscript> tetragonal superstructure of cubic vanadium monoxide with vacancies in the metal sublattice

The atom-vacancy ordering of cubic vanadium monoxide VO_1.29, which has basis cubic structure B1 and structural vacancies in the metal sublattice, has been studied using the x-ray diffraction method. It has been shown that the formation of the tetragonal (space group I4₁/amd) ordered phase V₅₂O₆₄ of cubic vanadium monoxide VO_y proceeds as a first-order phase transition through the disorder-order channel including 22 nonequivalent superstructure vectors of four stars {k ₁₀}, {k ₄}, {k ₃}, and {k ₂}. The distribution function of the vanadium atoms in the V₅₂O₆₄ tetragonal superstructure has been calculated.     

Effect of a Rare-Earth Ion on the Structural Instability in RFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> Crystals

The dynamics of the crystal lattice of RFe₃(BO₃)₄ (R = Pr, Nd, Sm, Gd, Tb, Dy, and Ho) compounds in the high-symmetry R32 phase has been calculated. Significant changes in spectra of compounds with various rare-earth ions have been obtained only near the edge Λ point of the Brillouin zone (qΛ = 1/3(?2b₁ + b₂ + b₃, where b₁, b₂, and b₃ are the reciprocal lattice vectors) for acoustic oscillation branches. A decrease in the frequency of an acoustic mode at the point Λ has been revealed in all studied compounds. This frequency depends on the type of rare-earth ion and decreases from a compound with Pr to a compound with Ho down to imaginary values. Such a behavior of the frequency of the unstable acoustic mode is in good agreement with experimental data on the dependence of the temperature of the R32 → P3₁21 structural phase transition on the type of rare-earth ion in ferroborates.     

Magnetic structure of Er<Subscript>5</Subscript>Ge<Subscript>3</Subscript> at 4.2 K

A symmetry analysis of the possible magnetic structures of Er₅Ge₃ in the ground state is performed using the results of measurements of elastic magnetic neutron scattering at 4.2 K. It is shown that the minimum discrepancy factor R _m ≈9.5% corresponds to a modulated collinear magnetic structure in which the magnetic moments of erbium atoms are oriented along the a ₃ axis of the unit cell of the crystal structure and induce an antiferromagnetic longitudinal spin wave (AFLSW). The magnetic structure is characterized by the wave vector k=2π(0, 0, μ /a ₃) (where μ≈0.293) and the modulation period λ≈3.413a ₃. The magnetic ordering temperature T _N ≈38 K is determined from the temperature dependence of the intensity of magnetic reflections. __________ Translated from Fizika Tverdogo Tela, Vol. 45, No. 9, 2003, pp. 1653–1659. Original Russian Text Copyright ? 2003 by Vokhmyanin, Dorofeev.     

Ordering of the lowest tungsten carbide W<Subscript>2</Subscript>C

Atomic-vacancy ordering of the lowest tungsten carbide W₂C with the basis hexagonal structure of the L’3 type is analyzed by neutron and x-ray diffraction studies. It is found that the trigonal phase ?-W₂C (space group \(P\bar 3\) 1m) is the only ordered phase in the temperature range from ～2700 to 1370 K. The disorder-order phase transition channel associated with the formation of the trigonal ?-W₂C phase is found to include three superstructure vectors k ₁₅ ⁽¹⁾ , k ₁₅ ⁽²⁾ , and k ₁₇ ⁽¹⁾ of two stars {k ₁₅} and {k ₁₇}. The distribution function of the carbon atoms in the trigonal ?-W₂C superstructure is calculated.     

Anisotropy of magnetic properties of Sm<Subscript>0.55</Subscript>Sr<Subscript>0.45</Subscript>MnO<Subscript>3</Subscript> single crystals

Anisotropy of the magnetic properties of Sm_0.55Sr_0.45MnO₃ single crystals has been studied. A significant increase in the antiferromagnetic component of magnetization in the case of orientation of an external magnetic field H close to the c axis has been found. Magnetization for a field lying in the ab plane seems typical of a ferromagnet. Anisotropy of susceptibility reaches 2.2 in weak fields and nearly vanishes at H > 1 T.     

Influence of the ground state of the Pr<Superscript>3+</Superscript> ion on magnetic and magnetoelectric properties of the PrFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> multiferroic

The magnetic, magnetoelectric, and magnetoelastic properties of a PrFe₃(BO₃)₄ single crystal and the phase transitions induced in this crystal by the magnetic field are studied both experimentally and theoretically. Unlike the previously investigated ferroborates, this material is characterized by a singlet ground state of the rare-earth ion. It is found that, below T _N = 32 K, the magnetic structure of the crystal in the absence of the magnetic field is uniaxial (l ∥ c), while, in a strong magnetic field H ∥ c (H _cr ～ 43 kOe at T = 4.2 K), a Fe³⁺ spin reorientation to the basal plane takes place. The reorientation is accompanied by anomalies in magnetization, magnetostriction, and electric polarization. The threshold field values determined in the temperature interval 2–32 K are used to plot an H-T phase diagram. The contribution of the Pr³⁺ ion ground state to the parameters under study is revealed, and the influence of the praseodymium ion on the magnetic and magnetoelectric properties of praseodymium ferroborate is analyzed.     

A Water-Soluble Fluorescent Probe for SO<Subscript>2</Subscript> Derivatives in Aqueous Solution and Serum Based on Phenanthroimidazole Dye

A water-soluble fluorescent SO₂ derivatives probe PI-SO ₂ based on a phenanthroimidazole dye, and a sensitive SO₂ recognition site, aldehyde was constructed. The probe PI-SO ₂ exhibits desirable properties such as high sensitivity, high selectivity and good water-solubility. Significantly, we have demonstrated that the probe PI-SO ₂ is suitable for rapidly fluorescence detecting of SO₂ derivatives in aqueous solution and serum. The application of the novel probe PI-SO ₂ proved that it was not only a useful tool for the detection of SO₂ derivatives in vitro, but also a potential assay for investigating the effects of SO₂ derivatives, and demonstrating its value in practical applicationin of complex biological samples.     

An efficient and facile synthesis of new tetracyclic fused pyrazolo[4,3-<Emphasis Type="Italic">c</Emphasis>][1,2,4]triazino[4,5-<Emphasis Type="Italic">a</Emphasis>]quinolin-4(5<Emphasis Type="Italic">H</Emphasis>)-ones

Reaction of amidrazones 1a–1i with (1,5-dihydro-3-methyl-5-oxo-1-phenyl-4H-pyrazol-4-ylidene)propanedinitrile (2) in ethyl acetate solution in one-step reaction led to the formation of unprecedented pyrazolo[4,3-c][1,2,4]triazino[4,5-a]quinolin-4(5H)-ones 3a–3g along with pyrazolo[4,3-c][1,2,4]triazino[4,5-a]quinolin-12b-oles 3h–3m in moderate to excellent yields. These novel heterocycles were formed via a Michael addition reaction followed by intramolecular cyclization via a dearomatization process.     

First- and second-order Raman scattering from MoTe<Subscript>2</Subscript> single crystal

We report on Raman experiments performed on a MoTe₂ single crystal. The system belongs to the wide family of transition metal dichalcogenides which includes several of the most interesting two-dimensional materials for both basic and applied physics. Measurements were performed in the standard basal plane configuration, by placing the ab plane of the crystal perpendicular to the wave vector k _i of the incident beam to explore the in-plane vibrational modes, and in the edge plane configuration with k _i perpendicular to the crystal c axis, thus mainly exciting out-of-plane modes. For both configurations we performed a polarization-dependent study of the first-order Raman components and detailed computation of the corresponding selection rules. We were thus able to provide a complete assignment of the observed first-order Raman peaks, in agreement with previous literature results. A thorough analysis of the second-order Raman bands, as observed in both basal and edge plane configurations, provides new information and allows a precise assignment of these spectral structures. In particular, we have observed and assigned Raman active modes of the M point of the Brillouin zone previously predicted by ab initio calculations but never previously measured.     

States of cobalt fluoride in a strong magnetic field

The behavior of the magnetic subsystem of cobalt fluoride is investigated in a strong magnetic field oriented in an arbitrary direction in space. In the case where the magnetic field is out of the planes passing through the easiest magnetization axis A and the axis [100] ‖ X or through the easiest magnetization axis A and the axis [010] ‖ Y, it follows from the derived system of equations that the antiferromagnetic vector l does not change direction to be align with the basal plane, provided the magnetic field has a nonzero component along the A axis. It is demonstrated that the antiferromagnetic vector l becomes parallel to the basal plane only when the magnetic field is perpendicular to the A axis. The case of the magnetic field directed parallel to the [110] axis is examined thoroughly. The critical value of the magnetic field is determined at which the antiferromagnetic vector l becomes parallel to the basal plane and perpendicular to the external magnetic field H for H _⊥ → ∞.