Synthesis of a phase-pure orthorhombic YBa2Cu3Ox under low oxygen pressure

Reaction of Y₂O₃, BaCo₃ and CuO for 4 h at 800 °C in flowing O₂ with a total pressure of about 2.7 × 10² Pa, followed by cooling in O₂ at ambient pressure, has produced phase-pure orthorhombic YBa₂Cu₃O_x. Keeping the ratio of O₂ to evolved CO₂ above 50 was necessary to ensure phase purity. The resultant powder yielded pressed and inserted pellets with improved superconducting properties.     

Structure and thermal conductivity of powder injection molded AlN ceramic

AlN powders doped with Y₂O₃ (5 wt.%) were compacted by employing powder injection molding (PIM) technique. The binder consisted of paraffin wax (PW, 60 wt.%), polypropylene (PP, 35 wt.%) and stearic acid (SA, 5 wt.%). The feedstock was prepared with a solid loading of 62 vol.%. The binder was removed through debinding process in two steps, solvent debinding followed by thermal debinding. At last, the debound samples were sintered in flowing nitrogen gas at atmospheric pressure. The result reveals that thermal debinding atmosphere has significant effect on the thermal conductivity and structure of AlN ceramics. The thermal conductivity of injection molded AlN ceramics thermal debound in flowing nitrogen gas is 231 W m^?1 K^?1.     

Thermal stability and annealing behavior of photoluminescence from Eu doped YAG

Eu₂O₃ doped Y₃Al₅O₁₂ (YAG) crystals have been grown using a floating zone technique and evaluated thermal stability and annealing behavior of PL for a fluorescence thermo-sensor application. Color of the crystals grown varies from deep purple to colorless with O₂ concentration of the growth atmosphere and annealing in air. Photoluminescence (PL) peaking at λ = 590, 607, 624, 647 and 709 nm due to Eu³⁺ ions are observed from the crystals under UV excitation. Anomalous temperature dependence of PL intensity, which is observed in as-grown crystals, is improved greatly by annealing through the heat cycle. From annealing behavior of optical absorption spectra, residual Eu²⁺ ions are suggested to be responsible for the de-coloration and the improvement of anomalous temperature dependence of Eu doped YAG crystals.     

Characterization of Ni nanowires after annealing

The effect of Ni nanowires, fabricated by electrodeposition in self-ordered AAO templates, was studied. NiO and Ni₂O₃ nanofibers were fabricated by simple heat-treatment in air and in an atmosphere of pure O₂. Ni nanowires after vacuum annealing exhibit pronounced preferential orientation of Ni (111) at 600 °C. Grain growth resulted in size effects and induced the transformation of NiO to Ni₂O₃ during annealing in air. Ni was oxidized to Ni₂O₃ (∼ 500 °C) in an atmosphere of pure O₂. The stable Ni-oxides Ni₂O₃ are formed during annealing at a higher temperature (∼ 900 °C) in air and in an atmosphere of pure O₂.     

Synthesis of Co3(OH)2V2O7·1.7H2O nanosheets and its application in lithium ion batteries

Cobalt vanadium oxide hydroxide hydrate (Co₃(OH)₂V₂O₇·nH₂O) nanosheets are successfully synthesized by a simple hydrothermal method. The composition of Co₃(OH)₂V₂O₇·nH₂O is studied by thermal gravity (TG) analysis in N₂ atmosphere and subsequent X-ray powder diffraction (XRD) characterization of the sample obtained via annealing Co₃(OH)₂V₂O₇·nH₂O nanosheets in N₂ atmosphere at 800 °C for 6 h. The results indicate that there are 1.7 water molecules in a Co₃(OH)₂V₂O₇·nH₂O molecular formula. Electrochemical properties of Co₃(OH)₂V₂O₇·1.7H₂O nanosheets as negative electrode of lithium ion batteries are studied by conventional charge/discharge test, which show an initial capacity of 730 mAh g^?1 with steady plateau near 0.9 V at a current density of 0.05 mA cm^?2.     

Oxygen partial pressure dependence of the structural properties of CdO thin films deposited by a modified reactive vacuum evaporation process

Thin films of cadmium oxide were thermally deposited on glass substrates at partial pressures of oxygen, pO₂ in the range 1.33×10⁻² to 0.133 Pa at a substrate temperature of 160 °C. Energy dispersive analysis of X-ray fluorescence (EDAX) revealed that the CdO films deposited at pO₂ value of 4.00×10⁻² Pa were nearly stoichiometric. X-ray diffractometry (XRD) confirmed the polycrystalline nature of the film structure. All the films showed an fcc structure of the NaCl-type, as the dominant phase. The films exhibited preferred orientation along the (1 1 1) diffraction plane. The texture coefficients calculated for the various planes at different oxygen partial pressures (pO₂) indicated that the maximum preferred orientation of the films occurred along the (1 1 1) plane at an oxygen partial pressure of 4.00×10⁻² Pa. This was interpreted in terms of oxygen chemisorption and desorption processes. The lattice parameters determined from the diffraction peaks were in the range 4.655–4.686 Å. The average lattice parameter a₀ found by extrapolation using the Nelson–Riley function was 4.696 Å. Both the lattice parameter and the crystallite size were found to increase with increased partial pressure of oxygen. On the other hand, the strain and dislocation density were found to decrease as the partial pressure of oxygen was raised. A maximum (80%) in the optical transmittance at λ=600 nm and minimum in the electrical resistivity (9.1×10⁻⁴ Ω cm) of the films occurred at an optimum partial pressure of oxygen of 4.00×10⁻² Pa. The results are discussed.     

Low temperature synthesis,crystal structure and thermal stability studies of nanocrystalline VN particles

The simultaneous thermal decomposition and nitridation of [VO(NH₂O)₂Gly]·H₂O complex in NH₃ atmosphere at 723–973 K gives the nanocrystalline vanadium nitride (VN) having crystallite size of 8–32 nm. It shows cubic NaCl structure with lattice parameter of a = 4.137 nm. XRD pattern Rietveld analysis program for crystal structure of VN shows the space group-Fm3m. The particle sizes measured by BET and SEM techniques are in the range of 26–100 nm. The particles are spherical and distributed homogeneously and found larger than XRD crystallite size because of agglomeration of crystallites. The fundamental IR absorption of VN material is found at 995 cm⁻¹ which gives the force constant of 634.3 Nm⁻¹. The electrical resistivity and magnetic studies show the superconducting to normal transition (T_c) at 9.2 K. Thermal decomposition of VN is carried out in O₂ atmosphere which goes through the formation of an oxynitride (V–N_p–O_q) intermediate phase up to 913 K. Finally, nanocrystalline V₂O₅ is formed at 973 K. The V₂O₅ has orthorhombic structure with lattice parameters of a = 11.537, b = 3.568 and c = 4.380 Å and the XRD crystallite size of 10 nm.     

Role of environmental and annealing conditions on the passivation-free in-Ga–Zn–O TFT

We examined the characteristics of passivation-free amorphous In–Ga–Zn–O thin film transistor (a-IGZO TFT) devices under different thermal annealing atmospheres. With annealing at higher temperature, the device performed better at the above-threshold operation region, which indicated the film quality was improved with the decrease of defects in the a-IGZO active region. The mobility, threshold voltage and subthreshold swing of a-IGZO TFT annealed at 450 °C was 7.53 cm²/V s, 0.71 V and 0.18 V/decade, respectively. It was also observed that the a-IGZO was conductive after thermal annealing in the vacuum, due to the ease of oxygen out-diffusion from the a-IGZO back channel. The oxygen deficiency resultantly appeared, and provided leaky paths causing electrical unreliability when TFT was turned off. In contrast, the annealing atmosphere full of O₂ or N₂ would suppress the oxygen diffusion out of the a-IGZO back channel. The worst V_th degradation of a-IGZO TFT after positive gate bias stress and negative gate bias stress (NGBS) was about 2 V and ? 2 V, respectively. However, the V_th shift in the NGBS testing could be suppressed to ? 0.5 V in vacuum chamber. Material analysis methods including X-ray photoelectron spectroscopy and scanning electron microscopy were used to investigate the change of a-IGZO film after different thermal annealing treatments. The variation of O 1s spectra with different annealing atmospheres showed the consistence with our proposed models.     

In-situ fabrication of Al3V/Al2O3 nanocomposite through mechanochemical synthesis and evaluation of its mechanism

In this research, in situ fabrication of Al₃V based nanocomposite and its formation mechanism have been investigated. In order to synthesize Al₃V/Al₂O₃ nanocomposite, a mixture of Al and V₂O₅ powders was subjected to high-energy ball milling and the nanocomposite was produced through a mechanochemical reaction. The produced structure was isothermally heat-treated at 500–600 °C for 0.5–2 h under argon atmosphere. In order to evaluate the structural changes during milling and annealing, the synthesized powders were characterized by X-ray diffraction (XRD). Moreover, the powder morphological changes were studied by scanning electron microscopy (SEM). It was observed that the reaction between Al and V₂O₅ occurred after about 30 min and, the Al₃V and Al₂O₃ were formed in nanocrystalline structure with the continuing mechanical milling. Calculation of adiabatic temperature confirmed that reaction took place in combustion mode. In final stage of milling up to 40 h; it was observed that the Al₃V decomposed to Al and V so that the optimum time of milling to achieve fabrication of nanocomposite was determined to be about 20 h. Calculations based on Miedema’s model verified partial disordering of Al₃V during further milling and annealing of as-milled powder at 600 °C led to the ordering of Al₃V. The crystallite size of Al₃V and Al₂O₃ after annealing at 600 °C for 2 h remained in nanometer scale. So the final product appeared to be stable even after annealing.     

Effect of environment atmosphere on thermal shock resistance of the ZrB2–SiC–graphite composite

The thermal shock resistance of the ZrB₂–SiC–graphite composite was evaluated by measuring the retention of the flexural strength after the electrical resistance heating to the temperature ranging from 1000 °C up to 2500 °C. The experiment was operated in two different environment atmospheres (pure oxygen and low oxygen partial pressure which mixed O₂ and Ar with 1:9) at total pressure 2000 Pa. The residual strength for the specimen decreased gradually as the temperature increased up to 2200 °C, and it was slightly higher when heated in low oxygen partial pressure environment than in pure oxygen. In contrast to the specimen heated in low oxygen partial pressure environment, the residual strength for the specimen in pure oxygen increased steeply as the temperature increased from 1600 °C up to 1800 °C. The analysis of the SEM observations combined with EDS confirmed that the surface oxidation played a positive role in the thermal shock resistance of the ZrB₂–SiC–graphite composite with different environment atmospheres. The results here pointed out a potential method for charactering the effect of environment atmosphere on thermal shock resistance of the ZrB₂–SiC–graphite composite.     

Enhanced apatite formation on Ti metal heated in PO2-controlled nitrogen atmosphere

The oxynitridation of biomedical titanium metal under a precisely regulated oxygen partial pressure (P_O2) of 10^? 14 Pa in nitrogen atmosphere at 973 K for 1 h strongly enhanced apatite formation compared with that on Ti heated in air. The factors governing the high apatite-forming ability are discussed from the viewpoint of the surface properties of Ti heated under a P_O2 of 10^? 14 Pa in nitrogen atmosphere determined from X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. Nitrogen (N)-doped TiO₂ (interstitial N) was formed on pure Ti heated under a P_O2 of 10^? 14 Pa in nitrogen atmosphere at 973 K. The XPS O1s main peak shifted toward a lower binding energy upon heating under a P_O2 of 10^? 14 Pa. This shift may be due to the formation of oxygen vacancies. This Ti surface had a positive zeta potential of approximately 20 mV. According to time-of-flight secondary ion mass spectroscopy results, PO₄^3 ? ions were predominantly adsorbed on Ti soaked in simulated body fluid (SBF) after heat treatment, followed by calcium ions. It was concluded that the apatite formation kinetics can be described using the Avrami–Erofeev equation with an Avrami index of n = 2, which implies the instantaneous nucleation of apatite on the surface of Ti soaked in SBF after heat treatment at 973 K under a P_O2 of 10^? 14 Pa.     

Structural and optical studies on dc reactive magnetron sputtered Cu2O films

Cuprous oxide (Cu₂O) thin films were deposited by dc reactive magnetron sputtering technique onto glass substrates by sputtering of pure copper target in a mixture of argon and oxygen gases under various oxygen partial pressures in the range 8 × 10^− 3–1 × 10^− 1 Pa at a constant substrate temperature of 473 K and a sputtering pressure of 4 Pa. The dependence of cathode potential on the oxygen partial pressure was explained in terms of cathode poisoning effect. The influence of oxygen partial pressure on the structural and optical properties of Cu₂O films was systematically studied. Single phase films of Cu₂O were obtained at an oxygen partial pressure of 2 × 10^− 2 Pa. The films formed at an oxygen partial pressure of 2 × 10^− 2 Pa were polycrystalline with cubic structure and exhibited an optical band gap of 2.04 eV.     

Heteroepitaxial growth of δ-Bi2O3 thin films on CaF2(1 1 1) by chemical vapour deposition under atmospheric pressure

We have succeeded in achieving the heteroepitaxial growth of a δ-Bi₂O₃ thin film on a CaF₂(1 1 1) substrate by means of chemical vapour deposition under atmospheric pressure. The film grew with a strong (1 1 1) orientation. From X-ray pole figures, it was observed that the δ-Bi₂O₃ film grew on the CaF₂(1 1 1) substrate with 60° rotational in-plane domains. The growth mode was of a 3D island type, and the grain size decreased with increasing oxygen pressure during the δ-Bi₂O₃ film growth, improving the overall surface smoothness.     

Spectroscopic properties of B2O3–PbO–Bi2O3–GeO2 glass doped with Sm3+ and gold nanoparticles

Heavy metal oxide B₂O₃–PbO–Bi₂O₃–GeO₂ transparent glass doped with Sm³⁺ was synthesized and implanted with Au⁺ using energy of 300 keV and fluence of 1 × 10¹⁶ cm⁻². The annealing of the implanted glass at moderate temperature below the glass transition temperature induced the nucleation of gold nanoparticles, confirmed by the characteristic absorption band in the visible range and by transmission electron microscopy. Using Miés and Doylés theories for the surface plasmon resonance, the average size of the gold nanoparticles was about 4.6 nm, similar to the values observed by transmission electron microscopy. It was also observed the crystallization of a thin layer of the glass at the implanted surface after annealing, detected by X-ray diffraction and scanning electron microscope. Visible and near-infrared emission of Sm³⁺ was enhanced after annealing of the glass implanted with gold. Judd–Ofelt parameters and radiative parameters were calculated for the glass doped with Sm³⁺ with and without gold nanoparticles.     

Studies of solution deposited cerium oxide thin films on textured Ni-alloy substrates for YBCO superconductor

Cerium oxide (CeO₂) buffer layers play an important role for the development of YBa₂Cu₃O_7−x (YBCO) based superconducting tapes using the rolling assisted biaxially textured substrates (RABiTS) approach. The chemical solution deposition (CSD) approach has been used to grow epitaxial CeO₂ films on textured Ni–3 at.% W alloy substrates with various starting precursors of ceria. Precursors such as cerium acetate, cerium acetylacetonate, cerium 2-ethylhexanoate, cerium nitrate, and cerium trifluoroacetate were prepared in suitable solvents. The optimum growth conditions for these cerium precursors were Ar–4% H₂ gas processing atmosphere, solution concentration levels of 0.2–0.5 M, a dwell time of 15 min, and a process temperature range of 1050–1150 °C. X-ray diffraction, AFM, SEM, and optical microscopy were used to characterize the CeO₂ films. Highly textured CeO₂ layers were obtained on Ni–W substrates with both cerium acetate and cerium acetylacetonate as starting precursors. YBCO films with a J_c of 1.5 MA/cm² were obtained on cerium acetylacetonate-based CeO₂ films with sputtered YSZ and CeO₂ cap layers.     

Synthesis of the CaAl2O4 nanoceramic compound using high-energy ball milling with subsequent annealing

Monocalcium aluminate, CaAl₂O₄, is the main constituent of calcium alumina cements which have found wide applications in refractory industries. In the present work, CaAl₂O₄ nanoceramic compound was produced by high-energy ball milling of the oxide powders followed by annealing. The phase evolution and microstructural changes of the powders during the process were investigated by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that no CaAl₂O₄ was formed during ball milling even after 100 h. By subsequent annealing, the nucleation and growth of CaAl₂O₄ took place at 1000 °C after 2 h. Depending on milling time, the amount of CaAl₂O₄ increased with increasing annealing temperature. The CaAl₂O₄ single phase was obtained by milling the sample for 100 h and subsequently annealing at 1200 °C for 2 h. The quantitative phase analysis was used to measure CaAl₂O₄ phases in these processes. The average particle diameter of the sample milled for 100 h and annealed at 1200 °C was found to be less than 100 nm as measured by transmission electron microscopy.     

Crystal growth and photoluminescence characteristics of Ca2MgSi2O7:Eu3+ thin films grown by pulsed laser deposition

Ca₂MgSi₂O₇:Eu³⁺ films were deposited on Al₂O₃ (0 0 0 1) substrates by pulsed laser deposition. The films were grown at various oxygen pressures ranging from 100 to 400 mTorr. The crystallinity and surface morphology of the films were examined by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD and AFM respectively showed that the Ca₂MgSi₂O₇:Eu³⁺ films had a zircon structure and consisted of homogeneous grains ranging from 100 to 400 nm depending on the deposition conditions. The radiation emitted was dominated by a red emission peak at 620 nm. The maximum PL intensity of the Ca₂MgSi₂O₇:Eu³⁺ films grown at 300 mTorr was increased by a factor of 1.3 compared to that of Ca₂MgSi₂O₇:Eu³⁺ films grown at 100 mTorr. The crystallinity, surface roughness and photoluminescence of the thin-film phosphors were strongly dependent on the deposition conditions, in particular, the oxygen partial pressure.     

Effect of stirring on the dissolution of coal fly ash and synthesis of pure-form Na-A and -X zeolites by two-step process

Using the coal fly ash (FA), pure-form Na-A and -X zeolites were synthesized by two-step process. The FA was pretreated in aqueous NaOH solution under stirring condition at 85 °C for 18 h. The amorphous aluminosilicate of FA was dissolved during pretreatment. Increasing the stirring speed accelerated the dissolution of FA and increased Si⁴⁺ and Al³⁺ concentrations in the solution. This fact indicated that the stirring during pretreatment significantly affected on the dissolution of FA. After pretreatment, remaining FA was removed and aqueous NaAlO₂ solution was added to the residual solution to control the molar ratio SiO₂/Al₂O₃ of 0.5–4.5. After aging the resultant at 85 °C for 24 h, white precipitates were generated over the whole SiO₂/Al₂O₃ range. Increment of Si⁴⁺ concentration by stirring during pretreatment increases the yield of the product. At SiO₂/Al₂O₃ = 0.5, the material was identified as Na-A zeolite with a trace amount of hydroxysodalite. A single phase Na-A zeolite was obtained at SiO₂/Al₂O₃ = 1.0. The Na-X zeolite was emerged at SiO₂/Al₂O₃ ? 2.0. At SiO₂/Al₂O₃ = 4.5, a single phase Na-X zeolite was formed. The cation exchange capacity of synthetic single phase Na-A and -X zeolites was respectively 4.78 and 3.88 meq./g.     

Influence of heat treatment on microstructure and adhesion of Al2O3 fiber-reinforced electroless Ni–P coating on Al–Si casting alloy

Influence of heat treatment regime on microstructure, phase composition and adhesion of Al₂O₃ fiber-reinforced Ni–P electroless coating on an Al–10Si–0.3 Mg casting alloy is investigated in this work. The pre-treated substrate was plated using a bath containing nickel hypophosphite, nickel lactate and lactic acid. Al₂O₃ fibers pretreated with demineralised water were placed into the plating bath. Resulting Ni–P–Al₂O₃ coating thickness was about 12 μm. The coated samples were heat treated at 400–550 °C/1–8 h. LM, SEM, EDS and XRD were used to investigate phase transformations. Adhesion of coating was estimated using scratch test with an initial load of 8.80 N. It is found that annealing at high temperatures (450 °C and above) leads to the formation of hard intermetallic products (namely Al₃Ni and Al₃Ni₂ phases) at the substrate–coating interface. However, as determined by the light microscopy and by the scratch test, these phases reduce the coating adhesion (compared to coatings treated by the optimal annealing regime 400 °C/1 h). The analysis of scratch tracks proves that fiber reinforcement significantly reduces the coating scaling. However, due to the formed intermetallic sub-layers, partial coating delamination may occur on the samples annealed at 450 °C and above.     

A new strategy to diminish the 4 V voltage plateau of LiNi0.5Mn1.5O4

As for spinel LiNi_0.5Mn_1.5O₄, there is 4 V voltage plateau in the charge–discharge profiles. This voltage plateau can be reduced by an annealing process, however it is hard to avoid it completely. In this study, a new strategy of partial substitution for Mn by Mg is applied. There is no 4 V voltage plateau in the charge–discharge profiles of Mg-doped compound LiNi_0.5Mn_1.45Mg_0.05O₄. This compound exhibits good electrochemical properties which can be used as cathode material of lithium ion batteries. At 1 C rate, it can deliver a capacity of around 129 mAh g⁻¹ and remain good cycle performance.