Interaction of Water with GeCl4 , SnCl4 , and AsCl3

The interaction of water with GeCl₄, SnCl₄, and AsCl₃ was studied by IR spectroscopy. The results demonstrate that these chlorides contain molecular water in monomeric form. At water concentrations above 10^–2 mol/l, GeCl₄ also contains H₃O⁺ ions. The mechanisms of GeCl₄ and AsCl₃ hydrolysis were studied over a wide range of water concentrations.     

Synthesis and properties of LiZr2(AsO4)3 and LiZr2(AsO4) x (PO4)3 − x

The LiZr₂(AsO₄)₃ arsenate and LiZr₂(AsO₄) _x (PO₄)_{3 ? x} solid solutions have been prepared through precipitation followed by heat treatment, and characterized by X-ray diffraction, X-ray structure analysis, IR spectroscopy, and impedance spectroscopy. We have established conditions for the crystallization of the arsenate and a continuous series of arsenate phosphate solid solutions (0 ≤ x ≤ 3), which have been obtained as two polymorphs: monoclinic and hexagonal. Using the Rietveld method, we have refined the crystal structures of the polymorphs of LiZr₂(AsO₄)₃ (sp. gr. P2₁/n, a = 9.1064(2), b = 9.1906(2), c = 12.7269(3) Å, β = 90.844(2)°, V =1065.03(5) ų, Z = 4; sp. gr. R $\bar 3$ c, a = 9.1600(4), c = 22.9059(13) Å, V = 1664.44(14) Å, Z = 6) and LiZr₂(AsO₄)_1.5(PO₄)_1.5. Their structural frameworks are built up of AsO₄ tetrahedra—or (As,P)O₄ tetrahedra occupied by arsenic and phosphorus atoms at random—and ZrO₆ octahedra, with the lithium atoms in between. The ionic conductivity of the materials has been measured. The cation conductivity of monoclinic LiZr₂(AsO₄) _x (PO₄)_{3 ? x} with 0 ≤ x ≤ 1 has been shown to exceed the conductivity of lithium zirconium phosphate.     

Particles-Vortex Interactions and Flow Visualization in 4He

Recent experiments have demonstrated a remarkable progress in implementing and use of the Particle Image Velocimetry (PIV) and particle tracking techniques for the study of turbulence in ⁴He. However, an interpretation of the experimental data in the superfluid phase requires understanding how the motion of tracer particles is affected by the two components, the viscous normal fluid and the inviscid superfluid. Of a particular importance is the problem of particle interactions with quantized vortex lines which may not only strongly affect the particle motion, but, under certain conditions, may even trap particles on quantized vortex cores. The article reviews recent theoretical, numerical, and experimental results in this rapidly developing area of research, putting critically together recent results, and solving apparent inconsistencies. Also discussed is a closely related technique of detection of quantized vortices by negative ion bubbles in ⁴He.     

Cathodoluminescence of Cd4SiS6 , Cd4SiSe6 , and Si-Doped CdS, CdSe, and CdTe Crystals

CdS, CdSe, and CdTe single crystals were vapor-phase-doped with the corresponding silicon chalcogenides under nearly equilibrium conditions. Cathodoluminescence studies revealed that the Si dopant produced new luminescence centers in the crystals. The cathodoluminescence spectra of Cd₄SiS₆and Cd₄SiSe₆crystals were measured. Metastable, sphalerite CdSSi and CdSeSi films were grown under highly nonequilibrium conditions. The maximum of edge emission in their spectra was redshifted as compared to the stable materials. The CdSSi and CdSeSi crystals were shown to be photosensitive.     

Excitation of 4G°, 4H°, and 4I° Levels of Vanadium Atom by Slow Electrons

The excitation of ⁴ G°, ⁴ H°, and ⁴ I° levels of vanadium atom in electron–atom collisions is investigated using the methods of extended crossing beams and optical spectroscopy. The total excitation cross sections at the electron energy of 30 eV are determined for these levels. The maximum values of the cross sections (about 2 × 10^–16 cm²) correspond to the ⁴ F(¹ P)x ⁴ G° _J levels.     

Thermal properties and radiation damage in NaNH4XO4·2H2O single crystals (XO4=SO4,SeO4)

Differential thermal analysis (DTA) studies of NaNH₄SO₄·2H₂O, NaND₄SO₄·2H₂O, and NaNH₄SeO₄·2H₂O single crystals were performed in the temperature range of the ferroelectric-paraelectric phase transition and of the dehydration process. The first-order phase transition at the Curie point was confirmed for NaNH₄SO₄·2H₂O, whereas the transition in the isomorphous NaNH₄SeO₄·2H₂O at the Curie temperature was found to be similar to a contineous (second order) with considerable higher transition enthalpy. Dehydration process of the crystals studied was found to proceed in two stages, with maximum dehydration rates at 355 and 400K. A linear decrease in thermal energy related to the long-range ordering in NaNH₄SO₄·2H₂O crystals was observed with the dose of -cobalt-60 irradiation and discussed with respect to the radiation induced decrease in spontaneous polarization.     

CuCr2–xSbxS4 and Cu1–ySbyCr2S4 solid solutions

CuCr_2–ySb_xS₄ and Cu_1–ySb_yCr₂S₄ solid solutions with the spinel structure were synthesized, and their magnetic and electrical properties were studied. The limits of solid solutions in these systems were found to bex = 0.5 andy = 0.22. Models of the cation distributions in the solid solutions are proposed. The CuCr_2-xSb_xS₄ solid solutions with 0.10 <x < 0.15 are magnetic semiconductors with high ferromagnetic ordering temperatures.     

Specific heat and superfluid density of bulk and confined4He near the λ-transition

The specific heat and superfluid density of liquid⁴He are calculated using a vortex-ring renormalization group theory, both for the bulk fluid and for confinement in a sphere of diameter L. In the finite geometry the superfluid density remains finite and universal at T, in agreement with Monte Carlo simulations and with finite-size scaling. The specific-heat peak is flattened in the finite geometry, and the onset temperature of the deviation from bulk behavior approaches T more closely as L is increased.     

X-ray crystallographic data on aluminum silicon carbide, α-Al4SiC4 and Al4Si2C5

Single-crystal and powder X-ray crystallographic data on -Al₄SiC₄ and Al₄Si₂C₅ are given, and their respective space groups are P6₃ mc and R¯3m. Powder X-ray diffraction lines are individually indexed in the 2-range from 5° to 110°. The unit cell dimensions obtained from a least-square computer program are a=3.2771 Å (±0.0001 Å), c= 21.676 Å (±0.002) for -Al₄SiC₄ and a=3.2512 Å (±0.0002 Å), c=40.1078 Å (±0.0027 Å) for Al₄Si₂C₅. In addition, it is proposed that the crystal structures of -Al₄SiC₄ and Al₄Si₂C₅ may be formed by substituting SiC-layers for AIN-layers in the Al₅C₃N and Al₆C₃N₂ structures.     

Growth and Properties of KTi1 – xSnxOPO4Crystals

Single crystals of KTi_{1 – x} Sn _x OPO₄solid solutions and KSnOPO₄were grown from off-stoichiometric flux, and their structure and physical properties were studied. The replacement of Ti by Sn was found to increase the unit-cell parameters, shift the ferroelectric transition to lower temperatures, and decrease the nonlinear optical susceptibility. Near t _C, some of the crystals exhibit a jump in electrical conductivity, typical of superionics.     

Microstructural and electromagnetic characterization of La2−xSrxCuO4

A microstructural electromagnetic characterization of samples of La_2xSr_xCuO₄ has been made. Evidence of percolative behaviour was seen in a.c. and d.c. magnetization measurements. Transport current densities were of the order of 1 A cm ², about ten times smaller than the magnetization current density. The superconducting cluster size was estimated to be of the order of 1 1 μm. A detailed microchemical analysis was made over multiple regions of the sample, both within grains and at grain boundaries. No evidence was seen for the second phase, nor was there any large variation in chemical composition. Isolated dislocations and sub-grain boundaries were seen within the grains. We were not able to find any convincing microstructural evidence for percolative behaviour.     

Corrosion and corrosion-fatigue behavior of cp-Ti and Ti–6Al–4V laser-marked biomaterials

The aim of this work was to determine the influence of laser surface modification treatments on mechanical and electrochemical behavior in Ti and Ti–6Al–4V implants. For each metal, different samples were laser modified simulating the markings according to the international requirements. (It is necessary in each metallic biomaterial to mark the serial, batch and company numbers.) Microstructural changes produced by this treatment were observed: (a) the melting zone with small grain sizes and martensitic structures in above-mentioned metals and (b) the heat-affected zone (HAZ) with alpha phase in cp-Titanium with bigger grain sizes and Widmanstatten structure in Ti–6Al–4V. Positive tensile residual stress was determined by means X-ray analysis in the zones marked by laser. Furthermore, corrosion behavior was studied in a simulated body fluid at 37°C. Pitting was observed in different zones near the HAZ and the results showed a decrease of the corrosion resistance in the laser treated samples. Residual stresses and the martensitic microstructures favoured the decrease of the corrosion-fatigue life around 20% of both metals under physiological conditions.     

Spin and charge dynamics in lightly doped CuO and La2CuO4 from NMR,NQR and μ+SR

The effects induced by charge defects on the spin dynamics and on the static properties of antiferromagnetic cuprates, as detected through NMR-NQR and ⁺SR, are addressed. Information on hole localization and evidence supporting hole segregation are presented.     

Transformations of neat and heated struvite (MgNH4PO4⋅6H2O)

Struvite (MgNH₄PO₄?6H₂O) is the mineral phase of one of the urinary tract stones of humans and animals, besides being an important phase seen in waste water treatment and purification plants. Single-phase and highly crystalline struvite powders were synthesized in this study at room temperature in aqueous solutions containing dissolved salts of MgCl₂?6H₂O and (NH₄)₂HPO₄ at the Mg/P molar ratio of 1.00. As-synthesized, crystalline struvite powders (neat powders) completely transformed into cryptocrystalline apatitic calcium phosphate (Ap-CaP), in less than 72 h, when soaked in Ca-containing saline solutions at 37 °C. Moreover, crystalline struvite powders heated at temperatures from 90° to 200 °C became x-ray amorphous. Amorphous powders stirred for 4 h at room temperature in water containing dissolved diammonium hydrogen phosphate recrystallized back into struvite.     

Microstructures and microwave dielectric properties of Ba4LiNb3O12–BaWO4 composite ceramics

Composite ceramics of (1 ? x)Ba₄LiNb₃O₁₂–xBaWO₄ (x = 0.36–0.69) had been synthesized by co-firing the mixtures of Ba₄LiNb₃O₁₂ and BaWO₄ powders. The structures and microwave dielectric properties of the ceramics were studied by XRD, SEM, and TEM. These ceramics consisted of hexagonal Ba₄LiNb₃O₁₂ and tetragonal BaWO₄. The two phases co-existed well in the ceramics, and there was not obvious reaction at interfacial areas among grains. These ceramics had low sintering temperatures and excellent microwave dielectric properties, especially the small temperature coefficients of resonant frequency (τ_f) and high quality factor (Q × f) values. For composition at x = 0.69, the ceramic sintered at 1070 °C had Q × f value of 75,500 GHz and τ_f value of +8.7 ppm/°C.     

Room temperature synthesis and formation process of α-NaYF4 nanocubes

In this article, α-NaYF₄ nanocubes were synthesized with a simple and environmentally friendly method at room temperature. The structure and morphology of the products were characterized by X-ray diffraction and scanning electron microscopy. The influence of the F^?/Y³⁺ molar ratio on the morphology of the products was examined. The products changed from spherical nanocrystals to cubic nanocrystals when the F^?/Y³⁺ molar ratio gradually increased from 4:1 to 16:1, and excessive F^? ions were necessary for the formation of regular NaYF₄ nanocubes in our synthesis procedure. The formation process of these α-NaYF₄ nanocrystals was traced via time-dependent experiments. Several nanometer-sized NaYF₄ nanocrystals changed into 100 nm sized NaYF₄ nanocrystals with prolonging of the reaction time. Additionally, the photoluminescence properties of Eu³⁺-doped samples were investigated. The excitation spectrum consists of the characteristic absorption peaks of Eu³⁺ corresponding to the direct excitation from the europium f-electrons. The charge-transfer band of Eu³⁺–F^? is not present in our measured range. The ⁵D₀ → ⁷F₁ transition is much stronger than the ⁵D₀ → ⁷F₂ transition in our samples.     

STM studies of island formation and surface ordering of Si on GaAs (001), (2×4) and c(4×4): Implications for δ-doping

Scanning tunnelling microscopy (STM) and reflection high energy electron diffraction (RHEED) have been used to study the deposition of Si below 400C onto GaAs (001) surfaces grown in situ by molecular beam epitaxy (MBE). The emphasis is on the island formation and growth, as well as surface ordering, for submonolayer quantities of Si (up to 0.2 ML) deposited on two different As-rich reconstructions of GaAs (0 0 1) (2 × 4) and c(4 × 4). For deposition on the c(4 × 4) surface, an asymmetric (3 × 1) RHEED pattern is formed, a consequence of anisotropic needle-like islands, which grow adjacent to each other along the [1 1 0] direction and produce a three-fold periodic superstructure. Individual islands grow by a site exchange process in which the additional As layer of the c(4 × 4) structure acts as a surfactant and enables the Si atoms to occupy Ga sites in the GaAs lattice. In contrast, Si deposition on the (2 × 4) surface does not lead to any new surface periodicities as monitored by RHEED. The Si atoms form poorly ordered clusters distributed randomly across the surface. The site exchange process cannot occur in this case as the (2 × 4) surface is terminated with only one layer of arsenic. Instead, the Si atoms occupy sites on top of the outer arsenic layer.