Effect of the doped nitrogen on the optical properties of β-Ga2O3 nanowires

In this study, optical properties of the nitrogen-doped β-Ga₂O₃ nanowires (N-doped β-Ga₂O₃ NWs) were synthesized by exposing β-Ga₂O₃ NWs under high input power nitrogen plasma (2 kW), using a microwave plasma enhanced chemical vapor deposition (MPECVD) system. The nitrogen contents in the NWs were as-prepared about 7.4, 8.9, 9.7, 13.9, 19.3, and 26.6 at.%, respectively. Low temperature (10 K) cathodoluminescence (CL) spectra exhibit significantly different optical properties for the different nitrogen contents. The CL result of the N-doped β-Ga₂O₃ NWs (210 s N₂ plasma treatment) exhibited four distinct emission peaks at 378, 516, 759, and 970 nm. The possible light emission mechanism including the effect of the nitrogen dopant was discussed.     

On the Correction of the Melting Curve of the Eutectic Co–C for the Effect of the Thermal Inertia of the Furnace

This paper considers the influence of the thermal inertia of the furnace on the shape of the melting curve of the eutectic Co–C. To this end, melting experiments have been performed in a uniform three-zone furnace, with an inherent substantial thermal inertia. The thermal inertia has been quantified by measuring the step-response of the furnace with the sample in its solid state, just below its melting temperature. From the analysis of the effect of the thermal inertia of the furnace, it turned out that during melting the temperature distribution within the furnace, surrounding the crucible, is bound to be in a non-stationary state. This provided the key to properly finalizing the correction to be applied. The shape of the corrected curve differs considerably from that of the curve, as measured, in that the former shows a flatter melting plateau, and a larger curvature on the way down to the solidus point. As regards the liquidus temperature \(T_{\mathrm{liq}}\)—of major interest in the characterization of the transition temperature of high-temperature fixed points—it is demonstrated that the thermal inertia of the furnace shows a kind of self-compensating mechanism. But the effects of the thermal inertia of the furnace on the parameters defining the Scheil fit, involved in the correction procedure, were considerable.     

Investigation of the effect of addition of calcium stearate on the properties of low-density polyethylene/poly(ε-caprolactone) blends

Low-density polyethylene (LDPE) was blended with poly(ε-caprolactone) (PCL), prepared in proportions of 75/25, 50/50, and 25/75 (LDPE/PCL, wt/wt%). The effect of the addition of calcium stearate (CaSt) of these polymers was assessed by melting flow index, differential scanning calorimetry, tensile test, scanning electron microscopy (SEM), biodegradation in simulated soil with calcium determination, and enzymatic degradation. The addition of CaSt reduced the MFI of the PCL and of the 75/25 blend. The incorporation of 25 % of PCL slightly increased the T _m of LDPE. The tensile strength had no significant changes with the addition of CaSt and the polymers showed that they are incompatible according to this property. SEM showed poor interfacial interaction between PCL and LDPE, as well as that they are immiscible, and showed no significant changes on the morphology of the materials with the addition of CaSt. The results show that polymer samples after biodegradation in simulated soil present more calcium content than initial samples polymer. The soil analysis shows that the soil that contains the polymers submitted to thermal aging show smaller calcium content than the samples that were not aged. Lipase enzyme reinforced its specificity over PCL, and the addition of CaSt reduced the degradation of PCL and the 75/25 PCL/LDPE blend, however, it increased the rate of degradation of 50/50 and 25/75 blends.     

On the Use of the Co–C Fixed Point for Calibration of Pt/Pd Thermocouples

At INRIM, different Co–C fixed-point cells have been constructed and investigated. Two cells of different design and volume and filled with highly pure cobalt (99.998%) were used to extend the fixed-point calibration of five Pt/Pd thermocouples that had been previously calibrated at the triple point of water and at the fixed points of In, Sn, Zn, Al, and Ag. The calibration at the Cu point was also added during this exercise. Because a previous calibration from 962 °C up to 1,500°C against the local standard radiation thermometer was available, a comparison was possible with the Co–C fixed-point calibration. Agreement within 0.10 °C was found when the value of 1,324.0 °C, the same value proposed for the Co–C point to be included as a secondary reference point of the ITS-90, was assumed.     

FTIR Spectra of the M(EDTA)n? Complexes in the Process of Sol-Gel Technique

Sol-gel is one of the effective techniques for preparing YBa₂Cu₃O_{7 –} (YBCO) coatings at relatively low cost. Its process from gel to oxide coatings, however, was not yet fully understood. This is one of the obstacles for achieving YBCO coatings with good superconducting properties. In this paper, we chose EDTA as the complexant to prepare gels with different kinds of M(EDTA)^n– complexes, where M is any combination of Y, Ba, and Cu cations, in order to investigate the decomposition process of the gels with the help of Fourier transform infrared (FTIR) spectra. Comparing the FTIR spectra of the gel powders with those of the calcined powders, we found that the decomposed temperatures were different for different M(EDTA)^n– complexes. We considered this was the cause of the Ba segregation (as BaCO₃) in the coatings at low heating temperature, which in turn blocked the formation of high quality YBa₂Cu₃O_7–.     

Applicability of the polymeric precursor method to the synthesis of nanometric single- and multi-layers of Zn1?xMnxO (x?=?0–0.3)

Polymeric precursor method (Pechini) was employed to fabricate single- and multilayers of Zn_1−x Mn _x O (x = 0–0.3) on glass substrates. X-ray diffraction measurements revealed that crystal structure of Zn_1−x Mn _x O multilayers is the typical hexagonal würzite structure of pristine ZnO. A reduced peak intensity and widened full width half maximum (FWHM) value of prominent peaks suggested that the Mn²⁺ ions have substituted the Zn²⁺ ion without changing the würzite structure of pristine ZnO up to Mn concentrations x ≤ 0.2. A distinct redshift of the absorption edge was observed as the Mn concentration x was increased. Additionally, the absorption edge was less sharp due, probably, to s–d and p–d interactions, which give rise to band gap bowing. Nevertheless, amorphous states appearing in the band gap as a consequence of reduced crystallinity may also be responsible for the shrinking of the band gap in this material. Interestingly, the field dependence of the magnetization showed typical paramagnetic behavior for all the chosen Mn concentrations with no evidence of ferromagnetic ordering. Probably, the absence of ferromagnetism in the studied Zn_1−x Mn _x O films is strongly related to defects (say Mn impurities at the interface between nano-crystallites) in ZnO due to partial substitution of host Zn ions by Mn ions.     

The influence of BaGeO3 on the properties of Ba(Ti1?xSnx)O3 ceramics on the basis of sol-gel powders

Ba(Ti_1−x−y Sn _x Ge _y )O₃ (BTSG-x-y; x = 0, 0.05; y = 0–0.05) powders were synthesized by a sol-gel (SG) method and for comparative purposes also by a mixed-oxide (MO) method. In this system, BaGeO₃ functions as sintering additive. Due to smaller particle sizes of the SG powders a higher sintering activity was found, which resulted in reduced grain growth and in a more homogenous grain size distribution for the corresponding ceramics. The dependence on the paraelectric ⇆ ferroelectric phase transition, i.e. the phase transition temperature, the width of the transition region and completeness were examined by dielectric measurements, DTA as well as by SEM, EDX and XRD investigations with respect to the BaGeO₃ content, synthesis method and sintering temperature. The phase transition temperatures of the SG ceramics are remarkably higher than those of the MO ceramics with the same nominal compositions. The reason is a lower tin concentration within the grains of SG ceramics as confirmed by EDX and XRD investigations. The presence of BaGeO₃ in barium titanate–stannate system on the basis of a SG method caused an improved incorporation of tin in the BaTiO₃ lattice.     

Improvement of the Irreversibility Line of the 1212 Compound Tl0.5Pb0.5Sr2CaCu2O7?δ

The superconducting properties and the irreversibility line of the Tl_0.5Pb_0.5Sr₂CaCu₂O_7– were studied by ac susceptibility on both ceramic and powder samples prepared in sealed quartz tube at 960°C. In parallel, carefull investigations by DTA/Tg, X rays diffraction and plasma emission spectroscopy were performed on each sample after each thermal treatment. It is shown that the superconducting properties are strongly dependent on further heat treatments and that the irreversibility line may be optimized. Nevertheless, the results obtained suggest that further improvement of the irreversibility line might be expected.     

Investigation of the Dynamics of Evaporation of Condensed Bodies on the Basis of the Law of Spectral‐Radiation Intensity of Particles

The fundamentals of radiation theory and the mechanism of evaporation of condensed bodies are presented. The distribution functions of particles of a body by energies and by the intensity of their transition from one energy level to another in the process of evaporation have been obtained based on the law of spectralradiation intensity of the body particles. The temperature dependence of the resulting vapor flow on the outer surface of a massive condensed body and a thin layer in equilibrium and nonequilibrium states, which, in the limit, transforms to the known Hertz–Knudsen formula, has been found.     

Some features of the transgranular embrittlement of α-titanium alloys under the influence of the environment

Some common features of the transgranular embrittlement of -titanium alloys in chloride solutions, hot salts, liquid metals, and air are established. These types of brittle fracture are typical symptoms of trans-granular embrittlement along the basal (near-basal) cleavage planes of metals (alloys) with hcp crystal lattices with various values of the ratioc/a. In this connection, the role of alloying elements and the mechanism of corrosion cracking of -titanium alloys in chloride solutions are reconsidered.Central Scientific Research Institute of Structural Materials Prometheus, St. Petersburg. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 1, pp. 75–77, January–February, 1994.     

Electric Field Dependence of the Flux-Flow Resistance and the Electronic Vortex Structure in the Cuprate Superconductor Nd2?xCexCuOy

In the temperature limit T T _c c-axis oriented films of the cuprate superconductor Nd_2–x Ce _x CuO _y display an intrinsic step structure of the flux- flow resistance. Under current bias hysteretic voltage steps appear, whereas under quasi voltage bias negative differential resistance (NDR) is observed. For explaining these instabilities, we propose an electronic structure in the mixed state, consisting of subbands between the Fermi energy and the superconducting energy gap. The subbands originate from the Andreev bound states in the core of an isolated vortex, because of the interaction between vortices. Bloch oscillations of the quasiparticles in the narrow subbands are proposed as the mechanism generating the NDR.     

Effect of addition of Ce in Sn–30Zn solder on the structure and properties of the Mg/Al-brazed joint

AZ31B Mg alloy and 6061 Al alloy are joined using low-temperature soldering with Sn–30Zn–xCe solder alloy. The effect of Ce content in Sn–30Zn–xCe solders on microstructure evolution and mechanical properties of the different brazed joints are investigated. The experimental results show that adding appropriate amount of Ce into Sn–30Zn solder is conducive to decreasing the amount of Mg₂Sn intermetallic compounds and increasing the amount of Al–Sn–Zn solid solutions in the soldering zone of the brazed joint, which restricts the drawback of the formation of hard and brittle Mg₂Sn intermetallic compounds and enhances the mechanical property of soldered joint. The average shear strength of the Mg/Sn–30Zn–0.05Ce/Al-brazed joint can reach 77.48 MPa. Results also indicate that the excessive content of Ce leads to the formation of some Ce–Zn and Ce–Sn intermetallic compounds in soldering zone and subsequently decreases the strength of soldered joint.     

Investigation of Nb–B Diffusion and the Superconducting Properties of MgB2/Nb/Cu Tapes

The Nb?CB diffusion behaviors and their effects on the superconducting properties of MgB₂/Nb/Cu tapes were investigated. Two relevant samples of the Nb?CB diffusion couples and monocore MgB₂/Nb/Cu tapes were prepared with the same standard in situ PIT method, respectively. And both the samples were sintered at 650, 750, 850, and 950°C for 2 hours, respectively. It has been found that Nb?CB interface is invisible in the diffusion couples sintered at low temperatures as 650°C, correspondingly the superconducting properties of MgB₂ tapes are superior to those of the ones sintered at the other three temperatures. With the heating temperature increasing, Nb?CB interface, mainly NbB₂ with a little NbB, appears and becomes thicker gradually in the Nb?CB diffusion couples. The corresponding superconducting properties of MgB₂ tapes follow the similar patterns: within the range from 650°C to 950°C, the higher the sintering temperature, the poorer the superconducting performances, because the Nb?CB diffusion in MgB₂ tapes could cause the property degradations of MgB₂/Nb tape. As extended to the actual fabrications of Nb sheathed MgB₂ tapes or wires, suitable sintering temperature range should be from 650°C to 750°C for the desired performances.     

The effects of electronic field on the atomic structure of the graphene/α-SiO(2) interface

The atomic structure of the graphene/α-SiO(2)(0001) interface under electric field F with different intensities is studied using the density functional theory method. Simulation results indicate that the atomic structure of the graphene/α-SiO(2)(0001) interface has only a slight change under the condition of F≤0.02?au. However, the distance between substrate and graphene d(0) changes evidently. Moreover, as F reaches 0.03?au, the formation of a C-O covalent bond on the interface is present, which would destroy the excellent electronic properties of graphene. Thus, there exists a maximum for F in application of the graphene.     

Preparation of the BaTiO3–SiO2 hybrid particles for the catalyst of methane steam reforming process

BaTiO₃ nano-coated SiO₂ (BaTiO₃–SiO₂) hybrid particles were prepared by liquid phase deposition and sol–gel process. The obtained BaTiO₃–SiO₂ hybrid particles have relatively high surface area (20 m² g⁻¹) at 600 °C annealing temperature. Ni component was impregnated to the obtained BaTiO₃–SiO₂ hybrid particles, and the obtained catalyst was used for the methane steam reforming process to consider the effect of the surface area on the catalytic activity. The catalytic activity of the Ni/BaTiO₃–SiO₂ catalyst was approximately three times as large as that of the reported Ni/BaTiO₃ catalyst, even in the lower process temperature. However, the limitation temperature for methane steam reforming process of this hybrid material was 600 °C, because of the diffusion of the Ba component.     

Synthesis of polyetherimide/silica hybrid membranes by the sol–gel process: influence of the reaction conditions on the membrane properties

Hybrid polyetherimide (PEI)–silica membranes were synthesized. The aim was to obtain improved materials for gas separation media. The inorganic material was prepared via the sol–gel method through the hydrolysis of tetraethoxysilane (TEOS). The influence of the reaction conditions on the final membrane morphology and properties were studied. Scanning electron microscopy (SEM), energy-dispersive X-ray analysis (SEM–EDX), and Fourier transform infrared spectroscopy (FTIR) were used to characterize the PEI and PEI–silica composite membranes. The evolution of TEOS hydrolysis and the condensation processes were verified by FTIR studies. The silica–polymer interaction was also analyzed. The SEM micrographs showed how the membranes distinct morphologies depended upon synthesis parameters and preparation techniques (presence of coupling agent, TEOS polymerization in situ or not, silica content and membranes redissolution). The permeation rates of CO₂, CH₄, O₂, N₂, and H₂ through the pure polymer and hybrid membranes were measured and showed an increase of gas permeability for hybrid membranes but, the CO₂/CH₄ and O₂/N₂ selectivities decreased compared to PEI membranes.     

The improvement of the amorphous environment of the germanate–tellurate glasses in the presence of the gadolinium ions

Glasses in the system xGd₂O₃·(100 − x)[TeO₂·GeO₂] with 0 ≤ x ≤ 50 mol% have been prepared from melt quenching method. In this paper, we investigated changes of the coordination numbers of germanium, tellurium, and gadolinium ions by investigations of FTIR, EPR, and UV–VIS spectroscopy. By analyzing the structural changes resulted from the IR spectra we found that the bending modes of [GeO₄] structural units and the deformed modes of the Te–O–Te linkages produce intercalation of the [GdO _n ] entities in the germanate–tellurate chain network and densification of the glasses by increasing the number of [GeO₆] structural units. EPR spectra of the studied samples reveal that the gadolinium ions play a role of network former. The UV–VIS spectra show broad UV absorption bands located in the 250–350 nm region. Their intensity increase with the increasing of Gd₂O₃ content showing that these stronger transitions can be due to the presence of the O=Ge bonds (n–π* excitations) of [GeO₅] structural units. The [GeO₅] structural units are more stable thermodynamically than their analogues and the [GeO₆] structural units produce the improvement of the amorphous character of these glasses.