A quantitative analysis of In concentration in InGaN/GaN multiquantum wells in light-emitting diodes was carried out using high-resolution transmission electron microscopy (HRTEM) and high-angle annual dark-field scanning TEM (HAADF-STEM). The In composition in InGaN was evaluated by the precise measurement of c-lattice parameters in the HRTEM micrographs, which increase with increasing In composition. The reliability of the results was confirmed by high-resolution x-ray diffraction measurements and Rutherford backscattering spectrometry. Quantitative In compositions can, therefore, be determined using HRTEM. We tried to determine the quantitative In compositions in InGaN by analyzing the intensity profiles of the HAADF-STEM images. However, several problems were encountered, such as differences in the thickness of the region observed, carbon contamination, and ion beam damage during specimen preparation. Therefore, relative differences in composition were observed in the HAADF-STEM images.

Powders of BaSnO3 were synthesized to obtain gas sensor thick films (using the screen printing technique) for the detection of O2 and CO. Impedance spectroscopy was used at different atmospheres and temperatures. In the presence of O2, the films showed a maximum value of sensitivity at 300 °C, with the powders formed by Pechini presenting greater reproducibility and sensitivity (with an order of magnitude greater than that for the powders formed by precipitation). Results showed that the films formed with powders obtained using the Pechini method presented a better response to CO, with a maximum sensitivity at 450 °C. In addition, in the presence of CO and for T > 250 °C, these films showed an anomalous behavior regarding their sensitivity as a function of time when platinum electrodes were used: a great increase in the electrical resistance value for exposure times greater than 10 min.

The dissimilar lattice-evolution of the isostructural layered Li(Ni,Co,Al)O2 (NCR) and Li(Ni,Co,Mn)O2 (CGR) cathodes in commercial lithium-ion batteries during overcharging/discharging was examined using operando neutron powder-diffraction. The stacking axis (c parameter) of both cathodes expands on initial lithiation and contracts on further lithiation. Although both the initial increase and later decrease are smaller for the CGR cathode, the overall change between battery charged and discharged states of the c parameter is larger for the CGR (1.29%) than for the NCR cathode (0.33%). We find these differences are correlated to the transition metal to oxygen bond (as measured through the oxygen positional-parameter) which is specific to the different cathode chemistries. Finally, we note the formation of and suggest a model for a LiCx intermediate between graphite and LiC12 in the anode of both batteries.

In the present article, the intermixing and clustering of U/Nd, O, and vacancies were studied by both laboratory and synchrotron-based x-ray diffraction in U1−yNdyO2−x alloys. It was found that an increased holding time at the high experimental temperature during initial alloy preparation results in a lower disorder of the Nd distribution in the alloys. Adjustment of the oxygen concentration in the U1−yNdyO2−x alloys with different Nd concentrations was accompanied by the formation of vacancies on the oxygen sublattice and a nanocrystalline component. The lattice parameters in the U1−yNdyO2−x alloys were also found to deviate significantly from Vegard's law when the Nd concentration was high (53%) and decreased with increasing oxygen concentration. Such changes indicate the formation of large vacancy concentrations during oxygen adjustment at these high temperatures. The change in the vacancy concentration after the oxygen adjustment was estimated relative to Nd concentration and oxygen stoichiometry.

The strain hardening effect and dynamic recovery behavior of a Ni-based superalloy are studied by isothermal compressive tests. A new unified dislocation-density based constitutive model is developed to characterize the strain hardening effect and dynamic recovery behavior of the studied superalloy. In the developed constitutive model, some material parameters (yield stress, strain hardening coefficient, and dynamic recovery coefficient) are assumed as functions of initial grain size, deformation temperature, and strain rate. An iterative algorithm is designed to predict the high-temperature deformation behaviors under time-variant hot working conditions. The hot deformation parameters and material parameters can be updated in each strain increment. Comparisons between the experimental and calculated flow stresses indicate that the developed constitutive model can accurately describe the high-temperature deformation behavior of the studied superalloy. Furthermore, the developed constitutive model is also successfully used for analyzing time-variant hot working processes.

This work aims to synthesize PtPd catalytic clusters and to study the effect of the particle size, the curvature and possible alloying on the catalytic activity for oxygen reduction reaction, electrochemical stability, the mass-transfer of redox active species toward catalytic sites and the electro-kinetic of the oxygen reduction reaction (ORR) process. The curvature and the chemical composition of the catalyst surface significantly influence the electrochemically active surface area and catalytic activity toward oxygen reduction, regardless the particle size. The best catalytic activity was accomplished for 45 nm clusters due to possible alloying that enhance the O2 adsorption and dissociation. The complementary impedance studies demonstrated that 45 nm cluster has also the shortest effective diffusion length and the highest reaction rate constant among all morphologies, indicating on superior reactant transport to the catalytic sites. In addition, the 45 nm clusters showed improved electrochemical stability that is believed to be the combined effect of alloying and the compactness of the structure.

The growth kinetics of gold nanoparticles (NPs) during the reduction of HAuBr4 by hydrazine in the reverse micelles of oxyethylated surfactant Tergitol NP 4 was studied in situ by UV–vis spectroscopy. Kinetic mechanism includes the steps of slow, continuous nucleation and fast, autocatalytic surface growth. Both steps are under kinetic control of the precursor reduction. The rate of nucleation is limited by reaction in the droplets of the aqueous phase forming the cores of reverse micelles, and growth rate is limited by the reaction on the surface of gold NPs growing inside the micelles. The chemical mechanism of reduction of halogenated forms of gold AuX4– by hydrazine is the same in the case of X = Cl, Br and includes the equilibria of formation and redox decomposition of the intermediate complexes AuIII(N2H4)X3 and AuI(N2H4)X. The initial form of AuX4– (X = Cl, Br) does not affect the size of the final NPs synthesized in micellar solution of oxyethylated surfactant.

The effect of high-energy electropulsing treatment (EPT) on the microstructure evolution, mechanical properties, and fracture behavior of as-treated Ti–6Al–4V alloy strips was investigated. EPT was found to accelerate phase transition and microstructure evolution of quasi-single-phase titanium alloy strips at a relatively low temperature, and obtain characteristic duplex microstructure and Widmanstatten microstructure. The EPT-induced microstructural changes increased elongation-to-failure remarkably with a slight decrease in tensile strength. Fracture surface observation and three-dimensional analysis showed that transition from small-shallow dimple colony to big-deep colony fracture took place with an increase in frequency of EPT. The rapid phase change of the Ti–6Al–4V alloy strip under EPT was attributed to the enhancement of nucleation rate and atomic diffusion resulting from the coupling of the thermal and athermal effects. It is supposed that EPT can provide a highly efficient method for the intermediate-softening annealing of titanium alloy sheet/strips.

In this study, a method using dual triangular pyramidal indenters is suggested for material property evaluation. First, we demonstrate that the load–depth curves and the projected contact areas from conical and triangular pyramidal indentations are generally different. Nonequal projected contact areas of two indenters and nonplanar contact line of Berkovich indenter are the main sources of different indentation characteristics of two indenters. For this reason, an independent approach to the triangular pyramidal indentation is needed. With finite element (FE) indentation analyses for various materials, we investigate the relationships between material properties, indentation parameters, and load–depth curves. Based on the FE solutions, we suggest mapping functions for evaluating material properties from indentations by two triangular pyramidal WC indenters, which differ in their centerline-to-face angles. Elastic modulus, yield strength, and strain hardening exponent are obtained with an average error of <3%.

Semisolid powder processing (SPP) was used to fabricate n-type bismuth telluride-based polycrystalline bulk materials with improved thermoelectric properties. The minimum lattice thermal conductivity and the maximum ZT value of the SPP sample obtained in this study are 0.163 W m−1 K−1 at 383 K and 0.89 at 423 K, respectively. This ZT value exhibited a significant enhancement of 65.7 and 101.3% compared with the hot-pressing and the die-casting counterparts, respectively. The reduction of the lattice thermal conductivity is mainly due to the nanoscale grains and the mesoscale pores induced by the SPP. The grain boundaries and the interfaces brought by the porosities could scatter the phonons with mean free paths extensively from 300 nm to 1 μm. The remarkable enhancement of the ZT value and the convenient fabricating process suggest that the SPP is a promising method for mass production of high-performance bismuth telluride-based polycrystalline bulk materials.

Fatigue crack growth tests of NiAl bronze (NAB) alloy heat treated at different temper temperature after quenching at 920 °C are performed using direct current potential drop method. The influences of heat treatment on the fatigue crack growth behavior of NAB alloy are investigated. The results show that the fatigue crack growth rate (FCGR) of NAB alloy decreases with the increase of temper temperature. A few large secondary cracks are obtained as the sample is tempered at 350 °C and the secondary cracks diminish with the increase of temper temperature. With further increasing temper temperature to 550 °C, a large number of small secondary cracks are obtained, which is responsible for its lower FCGR. The as-cast NAB alloy has a lower FCGR than that tempered at 550 °C at low stress intensity factor range (ΔK) region, and the lower FCGR is attributed to the crack deflection effect of the as-cast microstructure. At high ΔK region, the crack deflection effect diminishes, which leads to the higher FCGR of as-cast sample.

The effects of heat treatment for recovering microstructure of a Ni-based single crystal superalloy with carbon addition have been evaluated. The heat treatment resulted in increased levels of chemical homogeneity. All the samples experienced more γ′ coarsening than as-cast samples. Significant changes to as-cast carbide morphologies were observed. Script-type, MC carbide networks transformed during heat treatment to smaller, spherical Ta-rich MC carbides. Heat treatment caused significant MC carbide decomposition and formation of Cr-rich secondary carbides on or near to decomposed carbides in all modifications. The size of carbides after heat treatment was less than that of cast alloy obviously, and the distribution of carbides became more and more dispersion than in cast alloy.

Phase maps of Co–Cr alloys bonded to dental porcelain cycled through an incremental number of porcelain firings at two separate thicknesses (0.5 and 1 mm) were analyzed. Bulk hexagonal close-packed (hcp) phase vol% of the alloy was found to increase with the number of porcelain firings for both 0.5 and 1 mm specimens. At the metal-porcelain interface, a uniform fine-grained hcp phase was observed. The depth and grain size of this hcp layer increased with the number of porcelain firings with the thicker specimens undergoing more substantial growth and transformation. Simple heat transfer modeling of the specimens during heat treatment cycles indicated that the thicker specimen had more time at high temperature to affect the face-centered cubic to hcp phase transformation. Therefore, the amount of porcelain firings and the thickness of the alloy should be considered and kept to a minimal when manufacturing metal-porcelain restoration.

The influence of substitution of Fe by Ni or Co on the glass forming ability (GFA) and soft magnetic properties of the Fe71−xNb6B23Nix (x = 1–5) and (Fe1−x−yNixCoy)71Nb6B23 (x = 0.1–0.2, y = 0.1–0.2) amorphous ribbons was systematically studied. The Ni or Co substitution for Fe enhances the GFA and decreases the thermal stability for Fe–Nb–B–Ni and (Fe, Ni, Co)–Nb–B alloy systems. The alloys with Ni and Co substitution have lower glass transition temperature and wider supercooled liquid region than that with Ni substitution. The (Fe0.7Ni0.1Co0.2)71Nb6B23 alloys achieved the maximum supercooled liquid region of 78 K. The saturation magnetization decreased and the coercivity increased with increasing Ni or Co content. The (Fe0.8Ni0.1Co0.1)71Nb6B23 amorphous ribbons exhibited the best soft magnetic properties with high saturation and low coercivity. The findings of Fe-based multicomponent alloys with large GFA, low cost, and good magnetic properties are encouraging to develop new soft magnetic materials.

With its particular ability to image solute clusters in three dimensions and impurity segregation to selected interfaces and grain boundaries, atom probe tomography has provided unique insight into the effects of irradiation on materials microstructures. This article reviews the contribution of atom probe tomography to our understanding of behaviors and responses of structural materials under irradiation. Possible atom probe tomography based approaches and common data analysis methods to analyze the microstructural features often observed in irradiated materials are described. In particular, the analysis of solute clustering, solute segregation, and void imaging are discussed in the context of radiation-induced hardening of austenitic steels and reactor pressure vessel steels, and the development of oxide dispersion strengthened steels, radiation-induced solute segregation to grain boundaries for stress corrosion cracking or corrosion issues, and to understand the swelling response of irradiated materials. While highlighting the unique information that atom probe tomography can offer, common limitations, current challenges, and outstanding technical questions regarding data analysis and interpretation are also presented.

The effect of Dy-doping on the dielectric nonlinearity was investigated in Mn and V-doped BaTiO3 multilayer ceramic capacitors under the same grain size condition, which was described by the Preisach model utilizing the first order reversal curve (FORC) distribution. The dielectric constants in both low and high field region could be enhanced by the Dy-doping, and it was associated with the increase of both reversible and irreversible FORC distributions near zero bias, whereas there was little variation in the saturation polarization that scales to the magnitude of spontaneous polarization. These results demonstrate that both reversible and irreversible domain wall motions are enhanced by Dy-donor incorporation in BaTiO3 resulting in softening of the dielectrics and increase of dielectric constants, which is supposed to be caused by the decrease of the pinning sources such as defect dipoles formed by the oxygen vacancies and their interaction with the domain walls.

In this work, the effects of different preparation methods on the microstructures and properties of the Ti45.7Zr33Ni3Cu5.8Be12.5 alloy were systematically studied by both experimental and numerical ways. It is found that the heating methods and the cooling rate during the process of preparation have great influences not only on the morphology and crystalline structure of the solid solutions but also on the thermal stability of the amorphous phase. Furthermore, the different crystalline structures and micromorphologies of the ductile phase will also influence the mechanical properties. And the uniaxial compression tests at room temperature verify that the Ti45.7Zr33Ni3Cu5.8Be12.5 samples obtained by different preparation methods possess different degrees of plasticity. The better comprehensive properties were found for samples with a larger size under the copper mold cooling conditions. The variation of the morphology of the solid solution phase under different preparation conditions is believed to be the vital factor that leads to the diversity in properties.

In situ curvature measurements were used to compare the stress evolution of GaN films grown directly on 6H-SiC via a two-step temperature growth to films grown with an AlN buffer layer. The two-step temperature growth consisted of an initial low-temperature and a main high-temperature GaN layer. In the case of GaN grown directly on 6H-SiC, the high-temperature layer initiated growth under compressive stress which transitioned to tensile stress. Films grown directly on 6H-SiC exhibited a reduction in the threading dislocation (TD) density and an improvement in the surface roughness compared to growth on the AlN buffer layer. Furthermore, transmission electron microscopy of the GaN grown directly on 6H-SiC revealed predominant (a + c)-type TD along with basal plane stacking faults and $\left\{ {11\bar 20} \right\}$ prismatic stacking faults. Channeling cracks were observed in the GaN film when the AlN buffer layer was not utilized. This was attributed to tensile stress induced from the thermal expansion coefficient mismatch.

The present study focuses on a quantitative analysis of electrical resistivity in monovalent-doped manganites La1−xAgxMnO3 (x = 0.05 and 0.1). The electrical resistivity data in the ferromagnetic (FM) metallic phase are analyzed by considering a temperature-independent inelastic scattering of the electrons (due to domain and grain boundaries, defects, etc.) and other temperature-dependent elastic scattering mechanisms (electron–electron, electron–phonon, and electron–magnon). The Debye and Einstein temperatures are deduced from the model Hamiltonian containing potential energy contribution from the long-range Coulomb, van der Waals (vdW) interaction, and short-range repulsive interaction up to the second-neighbor ions. The electron–phonon scattering partially describes the reported FM metallic resistivity behavior with temperature for La1−xAgxMnO3 (x = 0.05 and 0.1). The T2 and T4.5 terms accounting for electron–electron and electron–magnon interactions are essential for the correct description of resistivity. The Mott–Ioffe–Regel criterion for metallic conductivity is valid, and kFl ∼ 1, εFτ ∼ 1.

This research is devoted to the study of the effect of grain size and structural disorders on the melting behavior of Al nanocrystals under nonequilibrium conditions. The results indicate that Tm is constant and similar to Tm of perfect crystal for nanocrystals of 14 nm and higher. But, by a decrease in the grain size, Tm is significantly reduced. In addition, by further decrease in the size of the grain up to about three times the value of Al-lattice parameter, the behavior of the melt will be similar to the amorphous phase. Since it seems that these behaviors are related to high percentage of grain boundaries in nanocrystalline materials, the structural disorders of the atoms in different regions of nanocrystalline samples are separately studied during heating. The results show that premelting of boundary regions causes the melting process of nanostructure materials to be done within one temperature limit instead of at one temperature point.