Variation of defects in deformed L12 Al67Mn8Ti25 ordered intermetallic alloy during annealing

The isochronal recovery of deformation-induced defects in L1₂ Al₆₇Mn₈Ti₂₅ ordered alloy was investigated by positron lifetime measurement and in situ electron transmission microscopy. Three recovery stages of the positron lifetime were observed for the deformed samples during isochronal anneals. Vacancy migration was proposed to explain the first stage from room temperature to 200°C; The second stage, between 200 and 400°C, was assigned to be the dissociation of superdislocations with superlattice intrinsic stacking fault (SISF) or antiphase boundary (APB); The third stage, occurring up to 800°C, was attributed to the only dissociation scheme of dislocation with antiphase boundary (APB) accompanied by a relaxation of antiphase domain.     

Investigation of interfacial segregation at antiphase boundaries in a ternary alloy 84.8Ni–12.8Al–2.4Ta

A thin interphase layer (4 nm) between the merging γ′ precipitates in a chosen model alloy 84.8Ni–12.8Al–2.4Ta was investigated. It is demonstrated that interfacial segregation may occur at an antiphase boundary (APB) interface between the thin layer and one of the merging γ′ precipitates. The magnitude of the lattice displacement (about 1/10[010]) caused by interfacial segregation has been measured both by comparing experimental images with computer simulations, and from high resolution electron microscopy (HREM) fringe spacings using linear regressional analysis. These measurements show a consistent lattice spacing reduction across the APB. Image simulations also highlight the way that the contrast of the bounding partial dislocation affects the APB interface image and can be used to obtain the lattice shift across the interface when the segregation effects on -fringe contrast are significant.     

Crystallization of gallium analog of zeolite Nu-23/ferrierite

The synthesis of pure Ga-substituted Nu-23 zeolite in the presence of cetyltrimethylammonium bromide (CTMA-Br) as templating agent has been carried out using the gel composition 2 (CTMA)₂O:6.25 Na₂O:M₂O₃:21.75 SiO₂:800 H₂O at 453 K. The phase purity and % crystallinity of the zeolite product was estimated by XRD, sorption, i.r. and MAS n.m.r. measurements. Thermoanalytical curves (d.t.a./t.g.) indicated that the templating species were occluded in the pores of the Ga-Nu-23 zeolite phase and the same was decomposed around 973 K. The MAS n.m.r. spectra of the calcined sample indicated partial removal of Ga from the framework position. It is surprising to note that replacement of the source of Ga³⁺ by Al³⁺ in the above gel composition yields mordenite instead of Nu-23.     

Branch-shaped NaGdF4:Eu3+ nanocrystals: Selective synthesis,and photoluminescence properties

The branch-shaped NaGdF₄:Eu³⁺ nanocrystals (NCs) were synthesized by using polyvinylpyrrolidone (PVP) as a capping agent in ethylene glycol (EG) solution. The NCs were readily dispersed into water or ethanol to form a relatively stable suspension, which may facilitate their applications in biological fields. Meanwhile, the crystal structures of the NCs were tunable from the mixture of the α-(cubic) and β-(hexagonal) phases to the pure β-phase by varying the F^?/Ln³⁺ molar ratio or the reaction temperature. The pure β-phase NCs were obtained at relatively high F^?/Ln³⁺ molar ratio and reaction temperature. In addition, the Eu³⁺-doping concentration—dependent optical properties of the NaGdF₄:Eu³⁺ NCs were investigated in detail. The result shows that the emissions from high energy level transitions (e.g., ⁵D₁, ⁵D₂, and ⁵D₃) are significantly impaired with increasing the Eu³⁺-doping concentration due to the cross-relaxation process, and the emission at 612 nm is predominant since the doped Eu³⁺ ions locate in the crystal fields without inversion center.     

Oxygen dissociation pressure of ndmno3

Measurement of oxygen partial pressures at the lower phase boundaries in neodymium manganite have been made in the temperature range 1173–1473 K. The electrical conductivity method was used to detect the decomposition reaction with flowing H₂- CO₂ mixtures in order to fix the oxygen potential. The oxygen partial pressure of dissociation over the compound NdMnO₃: NdMnO₃ (s) = $\text{1}\text{2}$ Nd₂O₃ (s) + MnO (s) + $\text{1}\text{4}$ O₂ (g) is given by the equation:

$\text{log (P}{}_{\mathrm{O2}}\text{/atm) = ?}\text{(2.762 ± 0.019) · 10}{}^4\text{T}\text{+ (9.02 ± 0.14)}$

The molal enthalpy and entropy of the reaction for the abovementioned reaction were determined as ΔH^O_R,1323 = 132.2 KJ mol^?1 and ΔS^O_R,1323 = 43.2 J mol ^?1K^?1, respectively.     

Synthetics of ZnO nanostructures by thermal oxidation in water vapor containing environments

Metallic Zn films deposited on glass were wet or dry oxidized at 390 °C in pure N₂ or O₂ to understand the effects of water vapor in different oxygen partial pressure on growth of ZnO nanostructure during thermal oxidation. As-prepared ZnO oxides were characterized by a scanning electron microscope (SEM), an X-ray diffractometer (XRD), and a transmission electron microscope (TEM). Optical and electric properties of these ZnO films were characterized by photoluminescence (PL) and resistance measurements, respectively. It was found that the oxygen partial pressure and water vapor of environment significantly affect the morphologies of ZnO nanostructures. Decreasing oxygen partial pressure in dry oxidation can enhance a green light peak at 500 nm on PL spectra arising from defect-related emission and reduce the resistivity of the oxide films. High H₂O^(g)/O₂ ratio in wet oxidation will significantly increase the intensity of a green light peak and reduce the resistivity of the oxide films. The effect of oxygen partial pressure and H₂O^(g)/O₂ ratio on the PL spectra and resistivity of ZnO films are explained by the theory of defects equilibrium during oxidation.     

Crystal defects in the laves phase TiCo∼2

Both intrinsic and extrinsic stacking faults are observed on {111} in well annealed cubic TiCo_2+x alloys (x = ?0.06, 0.0, 0.13). The faults are more profuse in the stoichiometric phase than in the off-stoichiometric ones. The intrinsic/extrinsic fault populations range from 61 pct extrinsic in the nominally stoichiometric alloy to 67 pct intrinsic in the cobalt-deficient alloy. Partial dislocations bounding all faults studied in CTEM contrast experiments are Shockley-type ($\text{b}{}_{\mathrm{p}}\text{=}\text{1}\text{6}\text{〈112〉}$).     

Optical absorption and infrared studies of some silicate glasses containing titanium

The optical absorption and infrared (IR) spectra of mixed alkali silicate glasses in the system 3SiO₂–(1 − x)Na₂O–xK₂O + 2.5–20 g of TiO₂ were measured. Absorption bands due to Ti³⁺ ions, at 500 and 570 nm, were observed in the spectrum of Na₂O-free glasses. The intensities of such bands were followed with the variation in TiO₂ content from 2.5 to 20 g (per 100 g of glass). The incorporation of titanium oxide as Ti³⁺ in the Na₂O-free glass, conferring a violet hue to it, was explained on the basis of the acidity–basicity character of the glass. The IR measurements have been used to explore the structural changes throughout the compositional variations. This revised version was published online in November 2006 with corrections to the Cover Date.     

Angular momentum of the fields of a few-mode fiber: I. A perturbed optical vortex

This paper presents the results of studies of the physical nature of the electrodynamic angular momentum of a stable CV ₊₁ ⁺ vortex in a few-mode fiber. It shows that the angular momentum of a CV ₊₁ ⁺ vortex can be conventionally divided into orbital and spin angular momenta. The longitudinal component of the fundamental HE ₁₁ ⁺ mode on the axis of the fiber has a pure screw dislocation with a topological charge of e=+1. The longitudinal component of a CV ₊₁ ⁺ vortex also has a pure screw dislocation on the axis of the fiber with a topological charge of e=+2. Therefore, perturbation of a CV ₊₁ ⁺ vortex by the field of the fundamental HE ₁₁ ⁺ mode removes the degeneracy of the pure screw dislocations of the longitudinal and transverse components of the field and breaks down the structural stability of the CV ₊₁ ⁺ vortex. As a result, an additional azimuthal flux of energy with an angular momentum opposite to that of the fundamental flux is induced. An analogy is drawn between the stream lines of a perturbed CV vortex and the stream lines of an inviscid liquid flowing around a rotating cylinder. Studies of the evolution of a CV vortex in a parabolic fiber show that they are structurally stable when acted on by the perturbing field of the HE ₁₁ ⁺ mode. However, perturbing a CV ₊₁ ⁺ 1 vortex of a stepped fiber with the field of the HE ₁₁ ⁺ mode destroys the structural stability of the vortex. It is found that the propagation of a circularly polarized CV vortex can be represented as a helical wavefront screwing into the medium of the fiber. The propagation of a linearly polarized vortex in free space is characterized by the translational displacement (without rotation) of a helical wavefront. Pis’ma Zh. Tekh. Fiz. 23, 74–81 (November 12, 1997)     

On the formation of stacking faults in silicon implanted with high doses of oxygen

The stacking faults (SFs) in the silicon overlayer, which is formed after the implantation of silicon wafers by high doses (2 × 10¹⁸ cm^–2) of oxygen ions, are studied. During the implantation, a three-dimensional network of SiO₂ precipitates is formed along the 100 directions. Stacking faults appear only after a high-temperature annealing when all the SiO₂ precipitates are dissolved. Due to the very low value of the anomalous absorption coefficients of silicon, -fringe contrast profile calculations are needed for the characterization of SFs. The results show that these SFs are extrinsic in character, bounded by Frank partial dislocations.     

Luminescence response and CL degradation of combustion synthesized spherical SiO2:Ce nanophosphor

This study was aimed to systematically investigate the luminescence response of SiO₂:Ce³⁺ nanophosphors with different excitation sources. The powders were synthesized by using an urea assisted combustion method. SiO₂:Ce_1m% samples were also annealed at 1000 °C for 1 h in a charcoal environment to reduce incidental Ce⁴⁺ to partial Ce³⁺ ions. High resolution transmission electron microscopy (HRTEM) images of the as synthesized and annealed powder samples confirmed that the particles were spherical and in the size range of 3-8 nm in diameter. X-ray diffraction (XRD) and electron dispersion spectroscopy (EDS) results showed that the SiO₂ was crystalline and pure. Diffused reflectance, photoluminescence (PL) and cathodoluminescence (CL) results of the SiO₂:Ce³⁺ samples were obtained and compared with each other. The CL degradation and the surface reactions on the surface of the SiO₂:Ce³⁺ were studied with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). A clear improvement in the chemical stability of the SiO₂:Ce³⁺ annealed at 1000 °C were obtained.     

Six Birds with One Stone: Versatile Nanoporphyrin for Single-Laser-Triggered Synergistic Phototheranostics and Robust Immune Activation

Simultaneous photodynamic therapy (PDT) and photothermal therapy (PTT) can reduce the risks of drug leakage, body burden, and preparation complexity in traditional combination PDT/PTT. Here, a versatile nanoporphyrin (Pp18-lipos) self-assembled from lipid–purpurin 18 conjugates (Pp18-lipids) and pure lipids is presented. The as-prepared Pp18-lipos with 2 mol% Pp18-lipids can perform effective PDT and fluorescence imaging. The Pp18-lipos with 65 mol% Pp18 can perform potent PTT and photoacoustic imaging. The chelation of Mn²⁺ endows the Pp18-lipids-Mn²⁺ a high T₁-weighted magnetic resonance imaging contrast. Notably, pretreatment of low-dose PDT facilitates the endocytosis and tumor accumulation of Pp18-lipos, thus achieving synergistic PDT/PTT. Upon exposure to a single 705 nm-laser, the combination of PDT/PTT achieves a significantly higher tumor growth inhibition rate than PDT or PTT alone. In addition, it is found that the synergistic PDT/PTT triggers more potent anti-tumor immune response including tumor infiltration of immune cells and release of related cytokines.     

The a.c. conductivity of CuO-containing lead silicate glasses

The a.c. conductivity of copper-free and copper-containing lead silicate glasses of the base composition 80PbO–20SiO₂ (wt %), equivalent to 51.5PbO–48.5SiO₂ (mol %), was measured at different temperatures and frequencies. The ratio Cu²⁺/Cu_total as a function of CuO content in the glasses studied was quantitatively determined by ESR. The results were used to derive the mechanism of conduction in lead silicate glasses. Values of a.c. conductivity, dielectric loss and dielectric constant decreased with the addition of CuO up to 0.25 g/100 g glass and increased with further additions of CuO. This may be due to the gradual decrease in the ratio Cu²⁺/Cu_total (as indicated by ESR) with increasing CuO content, through reduction of some Cu²⁺ ions to Cu⁺ ions, which have higher mobility. The a.c. conductivities agreed with the Anderson and Stuart model and indicated that the conduction mechanism was ionic in character.     

Effect of Isovalent Ba-Site Substitutions on the Properties of (Ba1 – x – y M y Y x )TiO3(M = Ca, Sr, Pb) PTCR Ceramics

An approach is proposed for fabricating fine-grained, low-resistivity BaTiO₃-based PTCR ceramics via partial isovalent substitutions on the Ba site. The grain size of the ceramics thus prepared is shown to decrease as the ratio of ionic radii r(Ba²⁺)/r(M²⁺) (M = Ca, Sr, Pb) increases. Isovalent substitutions on the Ba site narrow down the range of donor dopant (yttrium) concentrations in which PTCR materials can be prepared. The experimental results agree well with thermodynamic calculations under the assumption that the materials contain the Y³⁺Ti³⁺O₃ phase, as suggested by ESR data, which point to the presence of Y³⁺–Ti³⁺ associates. Partial calcium, strontium, and lead substitutions on the Ba site reduce the average grain size of PTCR ceramics, which is probably due to the lattice strain arising from the isovalent substitution. Partial replacement of Ba²⁺ with mixtures of different isovalent elements (e.g., Sr²⁺ and Pb²⁺) offers the possibility of obtaining fine-grained, low-resistivity PTCR ceramics, without changing the phase transition temperature.     

Structure analysis of aluminium silicon manganese nitride precipitates formed in grain-oriented electrical steels

We report a detailed structural and chemical characterisation of aluminium silicon manganese nitrides that act as grain growth inhibitors in industrially processed grain-oriented (GO) electrical steels. The compounds are characterised using energy dispersive X-ray spectrometry (EDX) and energy filtered transmission electron microscopy (EFTEM), while their crystal structures are analysed using X-ray diffraction (XRD) and TEM in electron diffraction (ED), dark-field, high-resolution and automated crystallographic orientation mapping (ACOM) modes. The chemical bonding character is determined using electron energy loss spectroscopy (EELS). Despite the wide variation in composition, all the precipitates exhibit a hexagonal close-packed (h.c.p.) crystal structure and lattice parameters of aluminium nitride. The EDX measurement of ~ 900 stoichiometrically different precipitates indicates intermediate structures between pure aluminium nitride and pure silicon manganese nitride, with a constant Si/Mn atomic ratio of ~ 4. It is demonstrated that aluminium and silicon are interchangeably precipitated with the same local arrangement, while both Mn^2 + and Mn^3 + are incorporated in the h.c.p. silicon nitride interstitial sites. The oxidation of the silicon manganese nitrides most likely originates from the incorporation of oxygen during the decarburisation annealing process, thus creating extended planar defects such as stacking faults and inversion domain boundaries. The chemical composition of the inhibitors may be written as (AlN)_x(SiMn_0.25N_yO_z)_1 − x with x ranging from 0 to 1.     

Effect of Particle Size on Magnetic and Dielectric Properties of Nanoscale Dy-Doped BiFeO3

In the present report, influence of Dy-substitution and size on the structural, magnetic and dielectric properties of BiFeO₃ nanoparticles has been investigated. The synthesis of pure and Dy-doped BiFeO₃ nanoparticles has been done successfully using sol–gel method. Size of Dy-doped BiFeO₃ nanoparticles was tailored by varying the calcination temperature. Structural analysis reveal that substitution of Dy³⁺ leads to a change in structure from rhombohedral (x=0) to orthorhombic (x=0.15). The average crystallite size varies from 6 to 15 nm. Magnetic study reveals the enhancement in magnetization with the doping of Dy³⁺. Further, this value decreases as the particle size increases. Dielectric property improves with the Dy³⁺ substitution. All the nanoparticles display Debye-type relaxation. The low dielectric loss values observed are attributed to the nanosized grains. Remarkably, enhanced saturation magnetization value (13.8 emu/g) and dielectric constant value (95.8) were observed for Dy-doped BiFeO₃ nanoparticles having the smallest particle size. Thereby, the study indicates strong correlation between size and multiferroism.     

Effect of salting-out agents on nitric acid distribution between liquid and vapor in the course of evaporation of nitric acid radioactive waste

The database on the influence of concentrations of salting-out agents with different cation valence (Li⁺, Na⁺, K⁺, Cs⁺, NH₄⁺, Mg2+, Ca²⁺, Cu²⁺, Zn²⁺, Al³⁺, Fe³⁺, La³⁺, Pu⁴⁺, UO₂²⁺ nitrates) and of H₂SO₄ on the HNO₃ distribution between liquid and vapor at atmospheric pressure was verified and expanded by performing equilibrium evaporation experiments in an evaporator without reflux with circulation of the bottoms. This equilibrium can be described by the equation \(\log {\kern 1pt} {\alpha _H} = - 2.35 + 2\log \;{X_{\Sigma N{O_3}}}\) (where \({X_{\Sigma N{O_3}}}\) is the total concentration of nitrate ions in aqueous solution), taking into account partial binding of water due to hydration of the salting-out agent and apparent hydrolysis of polyvalent cations, and also incomplete dissociation of sulfuric acid. The suggested model is valid at \({X_{\Sigma N{O_3}}}\) from 3 to 16 M (azeotrope); at \({X_{\Sigma N{O_3}}}{\text{ < }}\;3\), Raoult’s law is observed (α_H = const), which is confirmed by a number of examples. In this model, the additivity of the properties of the salting- out agents, taking into account the concentration of “free” water, is assumed, which allows calculation of the composition of the bottoms and distillate when evaporating waste of any composition from radiochemical plants.     

Synthesis, characterization, and enhanced luminescence of CaWO4:Eu3+/SBA-15 composites

Considering the combination of lanthanide-doped CaWO₄ nanophosphor and mesoporous matrix may contribute to superior luminescent properties, CaWO₄:Eu³⁺/SBA-15 composites were successfully synthesized in a mild condition. The physicochemical properties of the resultant composites were carefully characterized by X-ray diffraction, high-resolution transmission electron microscopy, inductive coupled plasma optical emission spectroscopy (ICP), N₂ adsorption–desorption, Fourier transform infrared spectroscopy, and luminescence spectra. It’s found that the incorporation of CaWO₄:Eu³⁺ showed no obvious impact on the ordered mesostructure of the host matrix SBA-15, which, however, led to a decrease of BET surface area from 836 to 187 m² g⁻¹ for pure SBA-15 and CES (0.5), respectively. ICP results indicated that the real loaded amount of CaWO₄:Eu³⁺ in SBA-15 host was lower than the initial molar ratios (x) of CaWO₄:Eu³⁺ to SBA-15 for all samples. The maximum loaded level of CaWO₄:Eu³⁺ in SBA-15 is about 27.3 %. Moreover, the real Eu³⁺ dopant concentration increased with the initial molar ratios (x), which showed a maximum of about 6.51 % at x = 0.25. The resultant CaWO₄:Eu³⁺/SBA-15 composites exhibited enhanced-luminescent properties than that of pure CaWO₄:Eu³⁺ nanoparticles, which can be mainly attributed to the variation of Eu³⁺ dopant concentration and the host-protect effect through interaction between guest molecules and host matrix. The available large surface area, pore volume, and superior luminescent properties would facilitate future applications for the composites.     

Magnetic properties of (Co,Al) co-doped SnO<Subscript>2</Subscript> nanoparticles

The desired size of pure SnO₂ and Co (1, 3, 5 mol%) with constant 5 mol% of Al co-doped into SnO₂ nanoparticles are synthesized by chemical co-precipitation method. The raw materials used in synthesis are SnCl₂.2H₂O, AlCl₃, Co (C₂H₃O₂).4H₂O, aqueous NH₄OH and Polyethyleneglycol (PEG) from AR grade. The XRD pattern of pure and co-doped samples confirm the formation of tetragonal rutile phase of SnO₂ nanoparticles with average particle size 25 and 20 nm respectively. Micrographs of scanning electron microscope (SEM) for pure and (Co, Al) co-doped into SnO₂ show that the prepared nanoparticles are agglomerate and spherical in shape. The EDAX spectra of prepared nanoparticles indicate the presence of Co²⁺, Al³⁺, Sn⁴⁺ and O²⁺ and also confirm stoichiometric proportions of raw material in the formation of SnO₂. Transmission electron microscope (TEM) reveals that the surface morphology of pure and co-doped samples are spherical, and average size of particles is ~20 nm. Magnetization measurements from M-H curves of VSM show that the ferromagnetism at low concentration of Co and at higher concentration of Co shows weak ferromagnetism due to super exchange coupling among neighboring ions. The bound magnetic polarons model supports the observed ferromagnetic behavior.     

Phase selection controlled by sodium ions in the synthesis of FAU/LTA composite zeolite

Abstract

Zeolite faujasite (FAU), Linde type A (LTA) and FAU/LTA composite have been synthesized using tetramethylammonium cation (TMA⁺) as template, by adjusting only the concentration of Na⁺ ions in the initial solution (1.00 Al₂O₃ 4.36 SiO₂ : 2.39 (TMA)₂ O : β Na₂ O : 249.00H₂ O). Na⁺ ions alter the phase composition of the product more than TMA⁺ or OH^? ions. When Na₂ O concentration [Na₂ O] increases from 0.024 to 0.168, the product gradually changes from pure FAU to pure LTA via the formation of FAU/LTA composite with increasing LTA fraction. Interestingly, the induction periods of FAU and LTA in the FAU/LTA composite zeolite ([Na₂ O] is 0.072) are both 13 h, quite different from the induction periods of their individual pure phases—45 h for FAU and 4 h for LTA. During the crystallization, the LTA/(FAU + LTA) fraction in the composite zeolite decreases in a nearly linear fashion. Scanning electron microscopy, thermogravimetry and differential thermal analysis indicate some difference between the properties of the FAU/LTA composite zeolite and of the mechanical mixture.