The magnetic properties of single-crystalline Tb2Fe17−xSix (x = 0, 1, 2, 3, and 3.3) have been investigated. The Si substitution constricted the lattices by 1.5% and caused the Th2Ni17 transfer to Th2Zn17. The Curie temperature increased from 413 to 526 K, and the spontaneous magnetic moment decreased from 82.6 to 46.4 emu/g with the increase of Si. The stronger anisotropy and coercivity were generated by Si occupying the Fe sublattices. A domain wall pinning-dominated mechanism was responsible for increasing the coercivity force from 0.01 T (x = 1) to about 0.36 T (x = 3.3) at 1.5 K.

It has been shown that sintering temperature can be lowered and the density, hardness, and toughness of MoSi2 raised by using nanophase MoSi2 and ZrO2 additives. A minimum hot-pressing temperature of 1350 °C is needed for complete densification without a significant increase in grain size.

An in situ method has been developed to produce a Ni alloy composite coating reinforced by in situ reacted and gradiently distributed TiC particles by one-step laser cladding. The dispersed, ultrafine TiC particles in the coating are observed. Most of TiC particles, evidently with a gradient distribution, are uniformly distributed within interdendritic regions due to the trapping effect of advanced solid–liquid interface. The TiC/γ–Ni interface is clean and free from deleterious surface reactions. The microhardness of the coating also has a gradient variation, with the highest value being 1250 Hv 0.2.

The early stages of oxidation of aluminum nitride have been studied by transmission electron microscopy and electron diffraction. It has been found that the oxide layer grows by the Stranki–Krastonow mechanism, where an initial uniform layer is followed by island formation. The onset of oxidation occurs at 800 °C and the initial oxide phase that forms is γ–Al2O3, one of the transition aluminas. The orientation relationship between the oxide layer and the underlying nitride is (440)γ∥(1120)AIN and [112]γ∥[0110]AIN.

A novel sol-gel-hydrothermal process for preparation of highly oriented thin films of Pb(Zr0.52Ti0.48)O3 is reported. Pb(Zr0.52Ti0.48)O3 thin films with fully (111) orientation were successfully prepared on platinized silicon substrates at low temperature (100–200 °C) by combining a conventional sol-gel process and hydrothermal method, i.e., sol-gel-hydrothermal technique. The x-ray rocking curve for the (111) reflection as measured by a high-resolution four-crystal diffractrometer showed a narrow full width at half-maximum value of 0.20° for the as-prepared films. A dense, pinhole-free, and uniform surface morphology was observed from atomic force microscopy images of the films. The low leakage current density of the prepared films was also found.

Epitaxially laterally overgrown GaN on sapphire was used to reduce the number of threading dislocations originating from the interface of the GaN epilayer with the sapphire substrate. The GaN layer above the SiO2 mask area surrounding the window and corresponding to the lateral overgrowth was nearly free of threading dislocations. A high density of threading dislocations was observed in the vicinity of GaN grown in the window regions. InGaN multiquantum well-structure laser diodes (LDs) grown on pure GaN substrates, which were fabricated by removing the sapphire substrate, were demonstrated. The LDs with an output power of 5 mW exhibited a lifetime of more than 290 h and an estimated lifetime of 10,000 h despite a relatively large threshold current density. The far-field pattern of the LDs with a cleaved mirror facet revealed single-mode emission without any interference effects.

New structural planar defects in Ba-deficient Y1Ba2Cu3O7−δ (YBCO) (1:1.6:3) thin films grown on NdGaO3 and SrTiO3 substrates by metalorganic chemical vapor deposition have been observed by means of high-resolution electron microscopy. The defects are associated with perturbations of the YBCO “1:2:3” stacking sequences along the c direction, which give rise to structural variants with locally “2:5:7,” “3:4:7,” or “4:6:10” cationic stoichiometries. The defects can be consistently interpreted as CuO–YO–CuO/CuO conversions or YO/BaO (BaO/YO) interconversions in the (a,b) planes and extending over a few nanometers along the c axis. Structural models based on image matching with simulations are proposed for two particular cases. It is thought that these structural imperfections can be effective sites of flux pinning.

The microstructures and the solidification behavior in unidirectionally solidified Y–Ba–Cu–O/Ag (YBCO/Ag) superconducting current leads were investigated. The solidification model of this system was discussed by the Y2Ba1Cu1O5–Ba3Cu5Ox–Ag quasiternary phase diagrams constructed by analysis of the solute compositions in the melt. The diffusion fields and the spacing between silver particles in the YBCO/Ag system were discussed. The relationship between the shapes of entrapped silver particulates, the miscibility gap in the phase diagram, and the wetting behavior at the growth interface in two-dimensional monotectic reactions were also discussed.

A theoretical model is proposed to explain the degree of texture achieved in high-Tc superconductors during melt-processing under an elevated magnetic field. The degree of grain alignment is quantified through a factor F which is defined as ranging from 0 (random alignment) to 1 (completely oriented). Intermediate values of F clearly characterize intermediate states of alignment in which there is still some tendency for the grains to align their c axes with the magnetic field. The model suggests that the enhancement in texture is primarily obtained through grain rotation during the early stages of grain growth from the liquid. At the later stages of growth, grains interact with each other, which hinders the phenomena of magnetic-field–induced grain alignment.

Grain boundaries in laser-deposited YBa2Cu3O7−δ (YBCO)/MgO thin films have been investigated by high-resolution transmission electron microscopy. The films exhibit perfect texturing with YBCO(001)/MgO(001) giving rise to low-angle [001] tilt grain boundaries resulting from the grains with the c axis normal to the substrate surface and with misorientation in the a-b plane. The atomic structure of the grain boundaries was analyzed by using a dislocation model. Low-angle grain boundaries have been found to be aligned along (100) and (110) interface planes. For the (110) boundary plane, the low-energy dislocation configuration was found to consist of an array of alternating [100] and [010] dislocations. We have calculated the energy of various configurations and shown that the energy of the (110) boundary with dissociated dislocations is comparable to that of the (100) boundary, which explains the coexistence of (100) and (110) interface facets along the boundary. We have also modeled critical current transport through grain boundaries with various structures and found that the low-energy (110) grain boundary with dissociated dislocation array is expected to transport a lower superconducting current (by 25% for 6° misorientation) than (100) boundaries.

High normal current fluences have long been reported to produce major changes in the x-ray diffraction pattern of YBa2Cu3O7−x (YBCO). These x-ray diffraction effects have now been shown to result from the removal of barium from the YBCO near-surface lattice together with the formation of a thin barium oxide overlayer. Neutron diffraction reveals that the bulk crystallographic structure remains unaltered by charge fluences of more than 40 million C/cm2, and Auger electron spectroscopy confirms the presence of surface barium enrichment.

Transmission electron microsopy (TEM), Hall effect, and Fourier transform infrared (FTIR) transmission measurements were performed to investigate the structural, electrical, and optical properties of indium-doped Hg0.8Cd0.2Te epitaxial layers grown on Cd0.96Zn0.04Te (211) B substrates by molecular-beam epitaxy. The TEM measurements showed that high-quality Hg0.8Cd0.2Te epitaxial layers with interfacial abruptnesses were grown on the Cd0.96Zn0.04Te substrates. The Van der Pauw Hall effect measurements on typical indium-doped Hg0.8Cd0.2Te/Cd0.96Zn0.04Te heterostructures with a doping concentration of 6 × 1016 cm−3 at 10 K in a magnetic field of 0.5 T yielded a carrier density and a mobility of 2.2 × 1016 cm−3 and 40,000 cm2/V s, respectively. The FTIR spectra showed that the absorption edges of the indium-doped Hg0.8Cd0.2Te/Cd0.96Zn0.04Te heterostructures shifted to a shorter wavelength range than those of the undoped samples, which was caused by the Burstein–Moss effect. The FTIR spectra also showed that the transmittance intensities of the indium-doped Hg0.8Cd0.2Te/Cd0.96Zn0.04Te heterostructures increased compared with those of the undoped heterostructures, which is due to the compensation of the Hg vacancy defects by the indium atoms. These results indicate that the indium-doped Hg0.8Cd0.2Te epitaxial layers were high-quality n-type layers and that p-HgxCd1−xTe epilayers can be grown on indium-doped Hg0.8Cd0.2Te/Cd0.96Zn0.04Te heterostructures for the fabrication of HgxCd1−xTe photoconductors and photodiodes.

Recent deformation experiments on semiconductors have shown the occurrence of a break in the variation of the critical resolved shear stress of the crystal as a function of temperature. These and many other examples in the literature evidence a critical temperature at which a transition occurs in the deformation mechanism of the crystal. In this paper, the occurrence of a similar transition in two polytypes of SiC is reported and correlated to the microstructure of the deformed crystals investigated by transmission electron microscopy, which shows evidence for partial dislocations carrying the deformation at high stresses and low temperatures. Based on these results and data in the literature, the explanation is generalized to other semiconductors and a possible relationship to their brittle–ductile transition is proposed.

Room-temperature photovoltaic spectroscopy was applied to study undoped GaN, n-type GaN, and InGaN quantum well structures. Clear exciton absorption was observed in the photovoltaic spectra of the undoped GaN, and polarization measurements were made to identify the exciton absorption. For the n-type GaN sample, instead of the exciton absorption we observed only bulk absorption edge, which may be due to the free carrier screening effect. For the InGaN quantum well structures, the photovoltaic spectra showed relatively complicated line shape due to the overlap of the signals from different layers. By changing the reference phase of the lock-in amplifier, we were able to suppress some of the signals and thus identify the origin of the corresponding signal.

In a moderately rapidly solidified Ga46Fe23Cu23Si8 alloy, a face-centered-cubic (fcc) superstructure (a = 1.78 nm) and a hexagonal superstructure (ahex = 2.18 nm and chex = 0.77 nm), based on the same body-centered-cubic (bcc) γ-brass structure (a = 0.89 nm), were found—by means of micro-area electron diffraction—to coexist with the decagonal quasicrystal. The fcc superstructure is probably similar to one of the F-centered-γ-brass structure and has a parallel orientation relationship with the bcc fundamental structure. The hexagonal superstructure has its (001) parallel to the (111) of the bcc γ-brass structure and its chex = abcc[111]/2, and their lattice correspondence relationship has been derived. Electron diffraction evidence is presented to show that these two superstructures are possibly crystalline approximants of the decagonal quasicrystal.

The effect of thermal aging at 473 K on martensitic transformation characteristics have been studied in the Cu–Al–Ni shape memory alloys. An increase of martensitic transformation temperatures as a result of aging has been observed. Furthermore, the martensitic transformation shows an evolution with aging time from a single β3 ⇒ β′3 structural transformation to a β3 ⇒ γ′3 + β′3 transformation. Using internal friction and thermoelectric power measurements, as well as specific thermal treatments, it has been determined that the mechanism responsible for this evolution is an increase in the degree of order, thus rejecting the participation of a γ1 precipitation process. Finally, the increase of order at the next nearest neighbors has been established as the main factor responsible of the evolution of the martensitic transformation characteristics.

Grain growth behavior in reactive spray deposited Al–Mg–Mn alloy 5083 and 5083 + Zr was quantitatively studied at 500, 530, and 560 °C. Results show that reactive spray deposited 5083 processed using N2–5% O2, in which no significant volume fraction of oxide particles was found, experienced significant grain growth when annealed at 500, 530, and 560 °C following recrystallization. On the other hand, reactive spray deposited 5083 atomized with N2–10% O2 and 5083 + Zr atomized with N2–5% O2 exhibited very slow grain growth below 530 °C and limited grain growth at 560 °C. This behavior is attributed to the retardation effect of the secondary phase particles that were formed in these alloys.

The influence of ternary additions Cr, Fe, Mn, Ni, Zr, Nb, Mo, Hf, Ta, Si, Ga, Ge, In, and Sb, as well as the anti-site defects of both Ti and Al, on lattice parameters of TiAl were studied by the first principles electronic structure calculations with a discrete variational cluster method. The results of the calculation show that the effect of ternary additions on the distortion of TiAl lattice varies with the substitution behavior of the individual alloying element involved. The addition of alloying elements in TiAl causes a change in the electronic structure and the density of states of the system and results in variation of the bond strength between the atoms. The total and partial density of states (DOS) of binary TiAl and of ternary TiAl–M, M = Cr, Zr, and Sb, etc., were comparatively examined. The relationship between the DOS and the bond strength is discussed. The present work suggests that the origin of the lattice distortion of the ternary TiAl–M systems lies in the variation of the electronic structure.

(Ti,Al)N films with increasing nitrogen content were grown by reactive cosputtering and characterized by auger electron spectroscopy, grazing x-ray diffraction, polarization curves, electrochemical impedance spectroscopy, nanoindentation, and atomic force microscopy. For Ti/Al ≈ 1 the Ti1−x AlxN phase is always present, but lower nitrogen contents lead to an additional phase, probably α–Ti(Al), which causes a decrease in hardness and Young's modulus. The increase of nitrogen content results ina decrease of surface roughness or a more compacted surface coating, according to the impedance results.

Disk-shaped, two-phase, full-density W–Ti alloy billets have been fabricated by a new, hot-explosive-compaction technique. As part of a characterization effort, the compressive behavior of the alloy was investigated. Quasistatic and split Hopkinson pressure bar (SHPB) tests of cylindrical samples, taken from a 83W–17Ti at.% alloy billet, demonstrate the propensity of this material to fail via shear localization at high strain rates. The effects of strain rate, orientation of the matrix phase with respect to the direction of the SHPB compression, and spatial location within the billet (i.e., periphery or core) were evaluated. At quasistatic strain rates, the alloy deformed in a ductile mode and exhibited a definite spatial location sensitivity. At high strain rates, spatial location sensitivity was absent. Shear localization was unaffected by density variations, matrix orientation in the alloy, or the presence of coarsened substructural features in the matrix. These experiments and the microstructural characteristics of the resultant localized regions are discussed.