Structural investigations on Nd-doped silica nanocomposites: effect of sintering temperature and dopant concentration

Neodymium-doped silica nanocomposites were prepared from an acid-catalysed sol–gel solution followed by heat treatment. The structural and microstructural properties of the prepared samples as a function of sintering temperature and Nd concentration are reported. Fourier transform infrared spectra show that phase separation occurs during heat treatment. The presence of Nd₂O₃ and α-Nd₂Si₂O₇ phases in the samples was established by X-ray diffraction (XRD), and transmission electron microscopy (TEM) micrographs revealed the microstructure of the nanocomposites. From XRD patterns, the crystallite size was determined using the Debye–Scherrer formula, while the particle size was estimated from TEM micrographs. The results suggest that sintering at high temperature enhances the crystallinity and density of Nd₂O₃–SiO₂ nanocomposites, while the high concentration of neodymium prevents the crystallization of SiO₂.     

Reversible phase transition in vanadium oxide films sputtered on metal substrates

Vanadium oxide films, deposited on aluminium (Al), titanium (Ti) and tantalum (Ta) metal substrates by pulsed RF magnetron sputtering at a working pressure of 1.5 x10^?2 mbar at room temperature are found to display mixed crystalline vanadium oxide phases viz., VO₂, V₂O₃, V₂O₅. The films have been characterized by field-emission scanning electron microscopy, X-ray diffraction, differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy, and their thermo-optical and electrical properties have been investigated. Studies of the deposited films by DSC have revealed a reversible-phase transition found in the temperature range of 45–49 °C.     

Measurement of the relative strain ratios normal to the crystal planes in Cu thin films using grazing incidence X-ray diffraction

The relative strain normal to the crystal planes in Cu thin films has been experimentally measured using grazing incidence X-ray diffraction. This was performed by measuring the ratio of the strain exerted in the same specific (hkl) crystal plane parallel and perpendicular to the film surface. The strain ratios of the (1?1?1), (2?0?0), (2?2?0) and (3?0?0) planes were found to be –0.804, –1.324, –1.003, and –1.369, respectively. These values are within experimental error of those calculated theoretically under the assumptions of plane stress conditions.     

In-situ X-ray diffraction during tensile deformation of ultrafine-grained copper using synchrotron radiation

At the synchrotron facility, Super Photon Ring – 8 GeV, in-situ X-ray diffraction during tensile deformation was conducted on ultrafine-grained Cu with a grain size of about 300 nm fabricated by equal-channel angular pressing. The diffraction profile was observed with the time resolution of about 1 s using multiple MYTHEN detectors, and the diffraction angle and the full-width at half-maximum of some Bragg peaks were determined using the pseudo-Voigt function. From the analysis of Bragg peaks, it was found out that there are microscopically three regions; elastic, plastic and transition regions. The 0.2% proof stress obtained from the stress–strain curve locates within the microscopic transition region. Microstrain was evaluated using the Williamson–Hall method and the dislocation density was also obtained from the microstrain. The dislocation density starts increasing before 0.2% proof stress, which is associated with dislocation bow-out and emission from grain boundaries. The Taylor relationship seems to be still satisfied after 0.2% proof stress.     

Coexistence of adjacent vacancy-ordered and eutectic phases in Al–Cu–Ni alloys

ABSTRACT

Copper-mould-cast Al–Cu–Ni alloys show adjacent coexistence of in situ grown ordered and eutectic phases. A bimodal microstructure of α–Al and eutectic α-Al+θ-Al₂Cu phases with length-scale hierarchy evolves during solidification. Microstructural analysis through Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) shows the presence of Vacancy-ordered phases (VOPs) with different morphologies in two different compositions.     

Supercapacitor behaviour of cobalt-doped nickel oxide films

Ordered nanostructured cobalt-doped nickel oxide films were prepared on a conducting glass substrate via the sol–gel dip-coating method. X-ray diffraction analysis shows the films to be amorphous. Field-emission scanning electron microscope images showed well-defined, ordered grains with pores in between them. Supercapacitor behaviour was studied using cyclic voltammetry. A maximum specific capacitance of 1982?F/g at a scan rate of 5?mV/s with 1?M KOH was obtained for 5?wt% of cobalt-doped nickel oxide films. AC impedance analysis showed that the solution resistance was R _s?=?27?Ω and the charge transfer resistance R _ct?=?20?Ω.     

Recrystallization in a low-density low-alloy Fe–Mn–Al–C duplex-phase alloy

The recrystallization behaviour of a cold-rolled, low-density, low-alloy duplex-phase alloy (Fe–6.57Al–3.34Mn–0.18C, wt.%) has been studied. Temperature-resolved X-ray diffraction and dilatometry showed that the alloy recrystallizes at 850?°C during continuous heating. However, electron back-scattered diffraction investigations using Kernel average misorientation revealed that during annealing ferrite recrystallizes at lower temperatures while austenite remains strained up to 1200?°C. This study underlines the complexity of recrystallization of a microstructure comprising of constituents with high and low stacking fault energy.     

On the deformation mechanism of twinning-induced plasticity steel

The microstructures of an Fe–20Mn–2Si–2Al Twinning-Induced Plasticity (TWIP) steel deformed at different temperature were characterized by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Based on microstructural features revealed at various characteristic temperature regions of deformation, the necessary and sufficient conditions of TWIP effect are proposed. Likewise, the competitive characteristic deformation mechanism occurring in this TWIP steel is presented and discussed qualitatively in terms of phase stability and stacking fault energy of the austenitic matrix.     

Texture development during cross rolling of a dual-phase Fe–Cr–Ni alloy: experiments and simulations

Texture development during multi-step cross rolling of a dual-phase Fe–Cr–Ni alloy has been investigated. X-ray diffraction was used to investigate changes in crystallographic texture of both the constituent phases (austenite and ferrite) through changes in orientation distribution function. After deformation, rotated brass (rotated along φ₁, i.e. the sample normal direction ND), along with a weak cube texture was observed in austenite, while a strong rotated cube texture was obtained in ferrite. Texture was also simulated for various strains using a co-deformation model by self-consistent visco-plastic (VPSC) formulation. Simulations showed strong rotated brass texture in austenite and a strongly rotated cube, α-fibre (sample rolling direction RD //<1 1 0>) and γ-fibre (ND //<1 1 1>) in ferrite after highest strain (ε_t = 1.6). VPSC models could not effectively capture the change in crystallographic texture during cross rolling. In ferrite, simulations showed an overestimation of γ-fibre component and an underestimation of rotated cube component. Simulated texture of austenite, on the other hand, showed an overestimation of rotated brass with an absence of cube component. The results are rationalised based on the possible role of shear banding and activation of non-octahedral slip system during cross rolling, both of which are not incorporated in conventional VPSC models.     

Defect chemistry of La2CuO4, Nd2CuO4 and Pr2CuO4 doped by tetravalent cations: Relevance to high-T c behaviour

Abstract

The calculated defect chemistry of La₂CuO₄, Nd₂CuO₄, and Pr₂CuO₄ shows why the former material exhibits (super) conductivity apparently only via holes and the latter two materials only via defect electrons