Pure Β-phase Research Articles

Crystalline phase dependent spin current efficiency in sputtered Ta thin films

We report on the optical detection of the spin Hall effect (SHE) as a function of the crystalline structure of sputtered Ta thin films using a magneto-optical Kerr system. The growth rate of Ta films is found to influence the crystalline phase of Ta films. At a lower growth rate, GR the pure α-phase of Ta is formed, which changes to the pure β-phase for GR ≥ 1.44 Å/s. For an intermediate growth rate, 0.62 Å/s ≤ GR < 1.44 Å/s, an admixture of α and β phases is formed. We optically detect spin accumulation due to the spin Hall effect in Ta films by applying a square wave current and using Fourier analysis in a magneto-optical Kerr effect setup that uses spatially modulated incident light. We show that there exists a threshold current density (Jth) above which spin current can be detected via the optical technique. Jth, which is a measure of spin current efficiency, is found to be the lowest in the mixed phase of Ta and is strongly correlated with the crystalline phase of Ta films.

Epitaxial gallium oxide on a SiC/Si substrate

Well-textured gallium oxide β-Ga2O3 layers with a thickness of ~1 μm and a close to epitaxial layer structure were grown by the method of chloride vapor phase epitaxy on Si(111) wafers with a nano-SiC buffer layer. In order to improve the growth, a high-quality silicon carbide buffer layer ~100 nm thick was preliminarily synthesized by the substitution of atoms on the silicon surface. The β-Ga2O3 films were thoroughly investigated using reflection high-energy electron diffraction, ellipsometry, X-ray diffraction, scanning electron microscopy, and micro-Raman spectroscopy. The investigations revealed that the films are textured with a close to epitaxial structure and consist of a pure β-phase Ga2O3 with the (\(\overline 2 01\)) orientation. The dependence of the dielectric constant of epitaxial β-Ga2O3 on the photon energy ranging from 0.7 to 6.5 eV in the isotropic approximation was measured.

Microstructure and mechanical properties of the near-beta titanium alloy Ti-5553 processed by selective laser melting

The aerospace industry continuously demands new materials with high strength and low density like the investigated near-β titanium alloy Ti-5553. Lately, a new need for parts with designs concerning the force flow instead of the process ability with conventional methods is rising. Therefore, additive manufacturing methods are gaining more and more in importance. In this study we processed the Ti-5553 alloy by selective laser melting (SLM), which is one of these methods. Bulk samples with a density of 99.95% were built. X-ray and electron backscatter diffraction show a pure β-phase microstructure. Mechanical tests exhibit a tensile strength of about 800MPa and a strain up to 14%. These results demonstrate the possibility of processing this alloy by SLM.

Structural and transport properties of doped LAMOX — Electrolytes for IT SOFC

Doped La2−xRxMo2−yWyO9 (R=Bi, Gd, Pr, Sm, Nd; x=0–0.5, y=0.5–1) were synthesized via polymerized precursors method or high power mechanical milling (MM). The study of doped LAMOX genesis and structural properties using thermal analysis, XRD, TEM has revealed that for all cations substituting La-position, the pure cubic β-phase is formed from polymerized precursors after calcination at 700°C. W-doped LAMOX have been obtained via low temperature calcination of MM products. Due to a high dispersion of powders, high density pellets of doped LAMOX ceramics have been already obtained after sintering at 950°C. Their electrical conductivity measured by impedance spectroscopy varies in the range of 2.3–5.6·10−3S/cm at 630°C depending on the doping cation nature. The self-diffusion coefficient (DO) values calculated from corresponding conductivities is in the range of 6–14·10−9cm2/s at 630°C agreeing well with those from the data of C18O2 SSITKA for oxygen isotope exchange with powders of LAMOX.

Enhancement piezoelectricity in poly(vinylidene fluoride) by filler piezoceramics lead-free potassium sodium niobate (KNN)

Polymer–ceramic piezoelectric composites are promising materials for sensor and actuator, because of large piezoelectric response properties. Thin films composites of poly(vinylidene fluoride) (PVDF) and piezoceramics potassium sodium niobate (KNN) have been prepared by cast method on indium–tin-oxide-coated glass substrates. The β-phase in PVDF is responsible for piezoelectric property. KNN with different concentrations was used as filler in composites. Corona poling method is used to the polarized the thin films of PVDF/KNN composites. The morphology of thin films determines using SEM and the crystalline structure investigates by XRD and FTIR techniques. SEM shows the rough surface contained spherulitic structural with less porosity and the size of the spherulitic range between 1 and 3 μm in diameter. XRD demonstrated that the structure of pure PVDF film is mix of α and β-phase and converted to the pure β-phase after filler by KNN. FTIR results confirmed the XRD. The fraction β in PVDF films alter from 77.5 to 80.3 % after poling, and enhance to the 86.0 % by filler of KNN in PVDF.

Investigations into Ti–(Nb,Ta)–Fe alloys for biomedical applications

In this study, a Ti–(Ta,Nb)–Fe system was investigated with aims toward the development of high strength, biocompatible titanium alloy suitable for the development of porous orthopedic biomaterials with minimal processing. Notable findings include yield strengths of 740, 1250 and 1360MPa for the Ti–12Nb–5Fe, Ti–7Ta–5Fe and Ti–10Ta–4Fe alloys, respectively, with elastic moduli comparable to existing Ti-alloys, yielding admissible strains of 0.9±0.3, 1.2±0.2 and 1.13±0.02% for the Ti–12Nb–5Fe, Ti–7Ta–5Fe and Ti–10Ta–4Fe alloys, respectively; more than twice that of human bone. Observed microstructure varied significantly depending on alloy; near pure β-phase was seen in Ti–12Nb–5Fe, β with some ω precipitation in Ti–10Ta–4Fe, and a duplex α+β structure was observed throughout the Ti–7Ta–5Fe. In addition to suitable mechanical parameters, all investigated alloys exhibited promising corrosion potentials on the order of −0.24V SCE, equalling that seen for a C.P.-Ti control at −0.25V SCE, and substantially more noble than that seen for Ti–6Al–4V. Electrochemical corrosion rates of 0.5–3μm/year were likewise seen to agree well with that measured for C.P.-Ti. Further, no statistically significant difference could be seen between any of the alloys relative to a C.P.-Ti control regards to cell proliferation, as investigated via MTS assay and confocal microscopy. As such, the combination of high admissible strain and low corrosion indicate all investigated alloys show significant promise as potential porous biomaterials while in the as-cast state, with the Ti–10Ta–4Fe alloy identified as the most promising composition investigated. Statement of SignificanceThe findings of this paper are of significance to the field of metallic biomaterials as they detail the development of alloys of satisfactory biocompatibility and electrochemical behaviour, that furthermore display exceptional mechanical properties. Notably, both extremely high compressive yield strengths and admissible strains, up to 1.36GPa and 1.2% respectively, are reported, exceeding or rivalling that seen in traditional alloys such as Ti–6Al–4V, which typically displays compressive yield strengths and admissible strains on the order of 895MPa and 0.81% respectively, as well as modern alloys such as Gum Metal or TNZT. That this is achieved in the absence of thermomechanical processing represents a significant and novel outcome of substantial benefit for application as a porous biomaterial.

Influence of TiO2 on the electrochemical performance of pasted type β-nickel hydroxide electrode in alkaline electrolyte

Nickel hydroxide was used as the positive electrode material in rechargeable alkaline batteries, which plays a significant role in the field of electric energy storage devices. β-nickel hydroxide (β-Ni(OH)2) was prepared from nickel sulphate solution using potassium hydroxide as a precipitating agent. Pure β-phase of nickel hydroxide was confirmed from XRD and FT-IR studies. The effects of TiO2 additive on the β-Ni(OH)2 electrode performance are examined. The structure and property of the TiO2 added β-Ni(OH)2 were characterized by XRD, TG-DTA and SEM analysis. A pasted–type electrode is prepared using nickel hydroxide powder as the main active material on a nickel sheet as a current collector. Cyclic voltammetry and electrochemical impedance spectroscopy studies were performed to evaluate the electrochemical performance of the β-Ni(OH)2 and TiO2 added β-Ni(OH)2 electrodes in 6 M KOH electrolyte. Anodic (Epa) and cathodic (Epc) peak potentials are found to decrease after the addition of TiO2 into β-Ni(OH)2 electrode material. Further, addition of TiO2 is found to enhance the reversibility of the electrode reaction and also increase the separation of the oxidation current peak of the active material from the oxygen evolution current. Compared with pure β-Ni(OH)2 electrode, TiO2 added β-Ni(OH)2 electrode is found to exhibit higher proton diffusion coefficient (D) and lower charge transfer resistance. These findings suggest that the TiO2 added β-Ni(OH)2 electrode possess improved electrochemical properties and thus can be recognized as a promising candidate for the battery electrode applications.

Effect of current density and temperature on nanostructure of PbO2 coating on Ti/SnO2 substrate provided by pulse electrodeposition process

In this paper the results are presented of a study on the use of electro-catalytic coating of PbO2 on Ti/SnO2 substrate. The experiments were conducted using continuous and pulse DC electrodeposition in a nitrate type electrolyte. Electrodeposition parameters, such as current density and electrolyte temperature were changed to produce a coating with a high surface roughness, small crystal size and high active surface area. The samples were studied using a number of techniques that included scanning electron microscopy (SEM), roughness measurement and cyclic voltammetry (CV). The results showed that a combination of 65°C and 33 mA cm−2 are the optimum temperature and current density that yield a good coating of pure β-phase. The morphology of coating under these electrodeposition conditions included fine flakes with a length about 0·75–10 μm and compact crystallites. Scanning tunnelling microscopy (STM) observation of the surface revealed that the coating also included PbO2 nano-particles with an average diameter in the range of 7–21 nm.

Low-Temperature Synthesis, Structural and Transport Properties of Doped LAMOX – Electrolytes for IT SOFS

Doped La2-xRxMo2-yWyO9 (R= Bi, Gd, Pr, Sm, Nd; x=0-0.5, y=0.5-1) were synthesized via polymerized precursors method or high power mechanical milling (MM). The study of doped LAMOX genesis and structural properties using thermal analysis, XRD, SEM, IR and Raman spectroscopy has revealed that for all cations but Bi substituting La-position, the pure cubic β-phase is formed from polymerized precursors after calcination at 700°C. W-doped LAMOX have been obtained via low temperature calcination of MM products depending on W concentration. Due to a high dispersion of powders, high density pellets of doped LAMOX ceramics have been already obtained after annealing at 950°C. Their electrical conductivity measured by impedance spectroscopy depends on the doping cation nature being sufficiently high (up to 5.6∙10-3 S/cm at 630 ºC) at temperature below 650°C.

Facile hydrothermal synthesis of Mn doped ZnS nanocrystals and luminescence properties investigations

Abstract Mn doped ZnS is considered as one of the most important group II–VI semiconductors in the last two decades since its good character of stable emission, heavy metal free and environmental friendly. A facile, effective and green hydrothermal protocol was reported to synthesize Mn doped ZnS nanocrystals. The obtained nanocrystals are pure β-phase, spherical, mono-dispersed and narrow in size distribution. Besides the well-known Mn: 4T1–6A1 energy transition, photoluminescence (PL) spectra indicated that the transition also occurred between the surface-defect state to the Mn 4T1 state, leading to the emission changing from green to orange. By investigating the steady state and time-resolved PL spectra, a novel energy transition and transfer mechanism is established.

Branch-shaped NaGdF 4:Eu 3+ nanocrystals: Selective synthesis, and photoluminescence properties

The branch-shaped NaGdF 4:Eu 3+ 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 −/Ln 3+ molar ratio or the reaction temperature. The pure β-phase NCs were obtained at relatively high F −/Ln 3+ molar ratio and reaction temperature. In addition, the Eu 3+-doping concentration—dependent optical properties of the NaGdF 4:Eu 3+ NCs were investigated in detail. The result shows that the emissions from high energy level transitions (e.g., 5D 1, 5D 2, and 5D 3) are significantly impaired with increasing the Eu 3+-doping concentration due to the cross-relaxation process, and the emission at 612 nm is predominant since the doped Eu 3+ ions locate in the crystal fields without inversion center.

The oxidative dehydrogenation of n-hexane over Ni–Mo–O catalysts

The effect of chemical composition on nickel–molybdenum catalysts in the oxidative dehydrogenation of n-hexane was studied. The catalysts consisted of the following phases: nickel oxide, molybdenum trioxide, nickel molybdate (α-NiMoO 4 and β-NiMoO 4) and a solid solution of nickel in a lattice of nickel molybdate. Characterization of the catalysts was carried out using ICP-OES, BET, XRD, FTIR, SEM, TPR and XPS techniques. The effect of phase composition of the catalysts on their catalytic activity and selectivity to the products obtained in the temperature range 300–500 °C was also studied. The most selective catalyst for the synthesis of hexenes was the pure β-NiMoO 4, which gave 25% selectivity to 1-hexene and 10% selectivity to 2-hexenes and 3-hexenes at 9% conversion. The pure phases NiO and MoO 3, although active in hexane ODH, showed poor selectivity to hexenes, particularly to 1-hexene at comparable conversions suggesting that they are not responsible for the catalytic activity of the NiO–MoO 3 system. The pure β-phase was more selective towards the hexenes than the α-phase with the difference in the molybdenum coordination believed to be the reason for the different activities and selectivities of the two modifications of NiMoO 4. The α-phase with MoO 3 was more active, suggesting that a synergetic effect plays an important role in modifying catalytic activity.

Combustion synthesis of Ga2O3 nanoparticles

Nanophase of Ga2O3 has potentially important applications in photocatalysis. We report the synthesis of nanophase of the metastable γ- and stable β-Ga2O3 and demonstrate that it is possible to prepare a continuously varying mixture starting from the pure metastable γ- to the pure β-phase. This is achieved by employing a facile and reliable combustion route, using urea as a fuel. Typical grain sizes, as estimated from XRD studies, are about 3 nm. Given the importance of surface chemistry for potential applications, thermogravimetric coupled with mass spectrometry is used in conjunction with FTIR to elucidate the chemistry of the adsorbed surface layer. Studies on the γ-Ga2O3 phase indicate the occurrence of weight loss of 8.1% in multiple steps. Evolved gas analysis and FTIR studies show presence of physisorbed H2O molecules and chemisorbed –(OH) ions bonded to active surface states and accounts predominantly for the observed weight loss.

Poly(9,9-dioctylfluorene)-based light-emitting diodes with pure β-phase emission

The authors report on poly(9,9-dioctylfluorene) (PFO)-based light-emitting diodes exhibiting an emission spectrum which was previously attributed to the so-called β phase. These devices were prepared by drop cast from dilute toluene solutions. Photoluminescence and electroluminescence spectra, recorded at room temperature, show no evidence of the usual amorphous phase emission. Devices with pure β-phase emission exhibit a higher color stability, upon increase of the driving voltage, than those based on amorphous PFO.

Morphology, polymorphism behavior and molecular orientation of electrospun poly(vinylidene fluoride) fibers

The morphology, polymorphism behavior and molecular orientation of electrospun poly(vinylidene fluoride) (PVDF) fibers have been investigated. We found that electrospinning of PVDF from its N, N-dimethylformamide/acetone solutions led to the formation of β-phase. In contrast, only α- and γ-phase was detected in the spin-coated samples from the same solutions. In the aligned electrospun PVDF fibers obtained using a rotating disk collector, the β-phase crystallites had a preferred orientation along the fiber axis. The degree of orientation did not, however, vary significantly with the speed of the rotation disk collector, and the β-phase was also not significantly enhanced with the increase in the rotation speed or the decrease in the size of spinnerets. These facts indicated that the orientation was likely to be caused by Columbic force rather than the mechanical and shear forces exerted by the rotating disk collector and spinnerets. The Columbic force may induce local conformational change to straighter TTTT conformation, and hence promote the β-phase. The addition of 3 wt.% of tetrabutylammonium chloride (TBAC) into the polymer solutions effectively improved the morphology of the electrospun fibers, and led to almost pure β-phase in the fibers. With spin coating, PVDF–TBAC did not, however, show any strong β-phase diffraction peak. The synergistic β-enhancement effect of TBAC and electrospinning is possibly due to the fact that while TBAC could induce more trans conformers, electrospinning promotes parallel packing, and hence inter-chain registration.

Synthesis and Optical Property of β-Brass Colloid

Cu/Zn beta-phase alloy (beta-brass) colloid was successfully synthesized by reducing the organometallic complexes in the organic liquid phase. It was confirmed by X-ray diffraction that the material formed pure beta-phase. The morphology for the beta-brass particles was observed using transmission electron microscopy (TEM). The dispersion of the particle diameter was almost single modal, and the diameter was estimated at 8+/-2 nm. A clear peak around 520 nm was seen in the optical absorption spectrum for the beta-brass colloid, and it is attributed to the surface plasmon absorption. We also simulated the optical absorption spectrum using the bulk dielectric constant for beta-brass. The simulation qualitatively reproduced the experimental data well.

Structural behaviour of β-Cu 2− δSe ( δ = 0, 0.15, 0.25) in dependence on temperature studied by synchrotron powder diffraction

Superionic β-copper selenide, β-Cu 2− δ Se ( δ = 0, 0.15, 0.25), has been studied by synchrotron powder diffraction and calorimetric methods in the range 293 K < T < 823 K. Cu 1.75Se exists in the superionic phase at room temperature and remains stable in air up to 600 K. Cu 1.85Se exists at room temperature as a mixture of β and α phases, β + α → β phase transition is not detected in DCS experiment, however, pure β-phase was observed in diffraction pattern of Cu 1.85Se at 353 K; Cu 1.85Se remains stable in air up to 600 K. A copper release process starts in Cu 2Se at a temperature below the superionic–non-superionic phase transition. At T > 543 K the composition is close to Cu 1.95Se and remains stable up to 573 K. Time average structure of β-Cu 2− δ Se has been analysed in the whole temperature range of existence in air. A face centred cubic unit cell (space group F m 3 ¯ m ) is formed by the selenium anions with copper cations distributed over tetrahedral 8(c) and 32(f) ( x, x, x) split positions within the octahedral voids (1/3 < x < 1/2). The copper occupancy of the 32(f) sites increases with temperature with a simultaneous decrease in the 8(c) sites. Besides, the copper occupancy of the 32(f) lattice site also increases with the total copper content 2 − δ. A diffusion pathway of mobile Cu ions along the tetrahedral sites, in “skewed” 〈1 0 0〉 directions through the peripheries of octahedral cavities is proposed.

Sol–gel derived phase pure α-Ga 2O 3 nanocrystalline thin film and its optical properties

Single-phase α-Ga 2O 3 thin films in the nanocrystalline form were prepared by the sol–gel technique. The optimum annealing temperature was found to be 500 °C. Below this temperature, a mixed phase of α-GaO(OH) and α-Ga 2O 3 was found and above this range a mixed phase of α-Ga 2O 3 and β-Ga 2O 3 was detected. A pure β-phase was observed at higher annealing temperatures. The crystallite size of α-Ga 2O 3 was found to be about 16 nm. The optical band gap of α-Ga 2O 3, determined from transmittance measurements, was found to be 4.98 eV which was higher than that of the β-phase prepared in identical condition. The semiconducting transition of this phase was allowed direct type like β-phase.

Magnetic and transport properties of (β+γ) Ni35Co35Al30 ferromagnetic shape memory alloy across the martensitic transition

The results of dc-magnetization, resistivity and ac-susceptibility studies performed on (β+γ) Ni35Co35Al30 magnetic shape memory alloy are presented highlighting the transition between two equilibrium lattice configurations of austenite and martensite phases. The first order nature of this martensitic transition is emphasized by highlighting the presence of thermal hysteresis and phase co-existence. This transition is apparently broadened with the introduction of γ-phase in the pure β-phase Ni35Co35Al30 alloy giving rise to a relatively large thermal hysteresis.

Effects of α/β ratio in starting powder on microstructure and mechanical properties of silicon nitride ceramics

The effects of α/β ratio in the starting powder on microstructure development and mechanical properties of sintered silicon nitride ceramics were investigated. With increasing β-phase content, the microstructure became finer, the finest-grained microstructure was developed from the powder with pure β-phase, whereas a duplex microstructure was developed from high α-phase content powder. The results show that the microstructure of silicon nitride ceramics can be tailored by changing the α/β ratio in the starting powder. The mechanical properties have an optimum region where the α/β ratio equals 1. Both flexural strength and fracture toughness can be improved by controlling size, number, aspect ratio and size distribution of the rod-like β-Si 3N 4 grains