Morphotropic phase boundaries and temperature dependent phase transitions of (1 – x) PbZrO3 + x (Na1/2Bi1/2)TiO3 (0.01 ≤ x ≤ 0.15) solid solutions were investigated by x-ray diffraction, differential scanning calorimetry (DSC), and dielectric property analysis. Two morphotropic phase transitions at room temperature were found at x = 0.1 and 0.13, which were from antiferroelectric orthorhombic (with 4 × 4 × 2 superlattice [orthorhombic (I)]) to antiferroelectric orthorhombic (with 2 × 2 × 2 superlattice [orthorhombic (II)]) and from orthorhombic (II) to ferroelectric rhombohedral, respectively. With increasing temperature, the samples with 0.01 ≤ x < 0.1 showed two phase transitions, i.e., from orthorhombic (I) to orthorhombic (II) and from orthorhombic (II) to cubic. The other samples had only one phase transition with increasing temperature. Phase transition temperatures of all the samples were measured using DSC, and a phase diagram for the solid solutions was constructed. A model illustrating the antiparallel shift of Pb ions in the orthorhombic (II) phase was also proposed.

The compatibility of 1.4914 martensitic steel and 316 L austenitic stainless steel has been studied in the presence of static liquid gallium. It was shown that the materials are severely attacked by the liquid metal. The corrosion is characterized by the formation of a reaction layer identified as FeGa3. Depending on the steel, the growth kinetics and the morphology of the layer are found to be different. In the case of 1.4914 steel, the growth law is linear, which implies an interface controlled regime. Moreover, the layer formed from an initially rectangular substrate exhibits a typical cruciform pattern. In the case of 316 L steel, a parabolic growth is found after a transient period, indicating a process mainly controlled by diffusion. Contrary to the martensitic steel, the morphology of the layer occurring during the solid-liquid interaction leads to complete coverage of the 316 L substrate, with rounded edges.

The synthesis of nanocrystalline Fe, Fe–4 wt% Al, and Fe–10 wt% Al solid solutions by SPEX ball milling has been studied. The microstructural evolution during ball milling, as well as subsequent heat treatment, has been characterized. The results demonstrate that ball milling promotes the formation of αFe–4 wt% Al and αFe–10 wt% Al solid solutions by reducing the activation energy of these alloys and generating thermal energy during this process. For Fe–10 wt% Al powders milled for various time intervals up to approximately 20 min, the FeAl intermetallic compound is formed. For alloys annealed at temperatures ranging from 600 to 1000 °C, the addition of 10 wt% Al to Fe significantly enhances the thermal stability of the nanocrystalline Fe–Al alloys. Interestingly, the addition of Al within the range of 4–10 wt% seems to have little effect on the thermal stability of these alloys annealed under the same conditions. Also, the thermal stability improves for alloys milled in air as opposed to those processed using Ar.

We have analyzed the anisotropic behavior of surface roughening in Si1−xGex/Si(001) heterostructures by use of methods of elastic analysis of undulated surfaces and perturbation analysis on the basis of global energy variations associated with surface evolution. Both methods have shown that the two-dimensional stage of surface roughening preferentially takes place in the form of ridges aligned along the two orthogonal 〈100〉 type directions. This prediction has been confirmed by ex situ experimental observations of surface evolution by use of atomic force microscopy and transmission electron microscopy in both subcritically and supercritically thick Si1−xGex films grown on Si(001) substrates. Further experiments in supercritically thick films have revealed a remarkable interplay between defect formation and surface evolution: the formation of a network of 〈110〉?misfit dislocations in the latter stages alters the evolution process by rotating the ridge formations toward the 〈110〉 type directions.

A Ni–Al–Cr alloy with an initial grain size of ∼60 μm was subjected to torsion straining to a strain of ∼7 at room temperature, thereby reducing the grain size to ∼34 nm. Similar torsion straining with samples of pure Cu and pure Ni gave grain sizes of ∼170 and ∼130 nm, respectively. Inspection of the Ni–Al–Cr alloy after torsion straining revealed highly strained regions containing dislocations associated with lattice distortions but with an absence of any Ni3Al ordered phase. The ultrafine grains in the Ni–Al–Cr alloy were extremely stable at high temperatures, and it was possible to retain a grain size of less than 100 nm after annealing at temperatures up to ∼900 K. By contrast, there was rapid grain growth in the samples of pure Cu and Ni at annealing temperatures in the vicinity of ∼500 K. The stability of the grains in the Ni–Al–Cr alloy is attributed to the formation of a Ni3Al-based ordered phase after annealing at ∼650–700 K. The presence of this phase also leads to an apparent negative slope in the standard Hall–Petch relationship.

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.

Low-temperature synthesis of hexaluminate phases for fiber–matrix interphases in ceramic–matrix composites is necessary to minimize processing temperatures to prevent fiber-strength degradation. Citrate-gel-derived lanthanum hexaluminate was synthesized using divalent transition-metal cations to stabilize the magnetoplumbite structure. Pure, undoped LaAl11O18 was obtained in 1 h only at temperatures >1500 °C after the formation and subsequent consumption of the intermediate perovskite, LaAlO3, which first appeared at ∼1150 °C. Powders of LaMAl11O19, where M = Mg, Mn, Fe, Co, Ni, Cu, and Zn, were prepared at much lower temperatures. Highly crystalline, phase-pure powders of LaMnAl11O19 and LaCuAl11O19 were obtained at 1000 °C in 1 h directly from the amorphous powder without the formation of the intermediate perovskite. All other compositions could be obtained at 1100 °C in 1 h except for the nominal LaNiAl11O19, which formed primarily LaAlO3, NiAl2O4, and Al2O3. Powders containing dopants all had similar grain sizes and morphologies at 1200 and 1500 °C; the grain size of powders with dopants was significantly greater than that of pure LaAl11O18 powder. The introduction of a second charge-compensating quadrivalent dopant for excess divalent cation did not greatly influence synthesis or grain growth below the eutectic temperature but did seem to enhance the [0001] texture of films on single-crystal yttrium-aluminum garnet substrates compared with singly doped films.

Nanoindentations using a Berkovich diamond indenter have been made on 1, 2, and 5 μm thick 99.99% purity polycrystalline aluminum films thermally evaporated in vacuum on to 2 mm thick R-cut polished sapphire flats. The projected contact areas of the residual indentations were estimated from the unloading load-displacement curves, and some of the indentations were imaged with an atomic force microscope (AFM). It was found that a large majority of indents showed material pileup, and the projected areas of these indents, as measured with the AFM, were up to 50% greater than those calculated from the unloading curves. This discrepancy between the calculated and directly measured indentation areas has a strong influence on the derived values of Young's modulus and hardness of the aluminum films. Using a new analytical model, Young's modulus of the aluminum films has been determined to be in the range of 50–70 GPa, independent of the relative indentation depth. The composite nanohardness of the 1 and 2 μm thick films was found to have a load-independent value of 1 GPa, whereas the composite nanohardness of the 5 μm film decreased from 1 to 0.7 Gpa with increasing indenter penetration. Finally, it has been suggested that in order to improve the accuracy with which the mechanical properties of thin films or bulk specimens can be determined by nanoindentation techniques, the projected contact areas should be measured by direct methods, such as atomic force microscopy.

The validity of controlling interfacial toughness in reaction-formed composites was explored using solid-state reaction processing and microanalysis techniques. A variety of rare-earth oxides was added to a yttrium aluminum garnet (YAG)/alumina powder mixture and then melted in air. Some melts retained the crystallography and microstructure of the pure, binary YAG–alumina eutectic. Using scanning transmission electron microscopy in conjunction with energy dispersive X-ray spectroscopy, rare-earth ions were observed both to segregate to the YAG/alumina interface and to form a third phase. Some evidence of increased crack deflection at these interfaces was observed via indentation fracture.

The nucleation behavior of α(TiCrSiO), a 1/1 Fibonacci crystal approximant phase, was investigated in alloys made near the stoichiometric composition. Containerless solidification studies were made with electromagnetic radio-frequency levitation and the 105-m NASA Drop Tube. The solidification microstructures indicate that the α–Ti hexagonal solid solution was the primary crystallizing phase in these alloys, growing dendritically. The α(TiCrSiO) phase nucleated in the remaining liquid. The competition between these two phases resulted from the high oxygen concentration needed to form α(TiCrSiO), which also stabilized the hexagonal-close-packed α–Ti phase.

Static and cyclic creep tests of Al–15 vol% TiB2in situ composite were carried out at 573–623 K. The values of apparent stress exponent and activation energy for cyclic creep of the composite were much higher than that for static creep. Furthermore, the cyclic creep rate tended to decrease with increasing percentage of unloading amount but was independent of the loading frequencies under the frequency ranges investigated. Finally, the true stress exponent of the composite was equal to 8, and the true activation energy was close to the value for the lattice self-diffusion of aluminum by incorporating a threshold stress for the analysis.

Nanocrystalline zirconia powders in pure form and doped with yttria and calcia were prepared by the precipitation method. In the as-prepared condition, all the doped samples show only monoclinic phase, independent of the dopants and dopant concentration. On annealing the powders at 400 °C and above, in the case of 3 and 6 mol% Y2O3 stabilized ZrO2 (3YSZ and 6YSZ), the monoclinic phase transforms to tetragonal and cubic phases, respectively, whereas in 3 and 6 mol% CaO stabilized ZrO2 (3CSZ and 6CSZ), the volume percentage of the monoclinic phase gradually decreases up to the annealing temperature of about 1000 °C and then increases for higher annealing temperatures. The presence of monoclinic phase in the as-prepared samples of doped zirconia has been attributed to the lattice strain effect which results in the less symmetric lattice. For the annealing temperatures below 1000 °C, the phenomenon of partial stabilization of the tetragonal phase in 3CSZ and 6CSZ can be explained in terms of the grain size effect. High resolution transmission electron microscopy (HRTEM) observations reveal the lattice strain structure in the as-prepared materials. The particles are found to be a tightly bound aggregate of small crystallites with average size of 10 nm. The morphology of the particles is observed to be dependent on the dopants and dopant concentration.

Metalorganic chemical vapor deposition (MOCVD) GaSb growth using trimethylgallium and trimethylantimony as a function of substrate temperature and V/III ratio was examined. These parameters were found to have a significant effect on the growth rate and surface morphology of the GaSb films. A phase diagram is used to interpret the effect of these growth parameters on the GaSb film growth. The region of single-phase growth was found to be narrow, falling between 540 and 560 °C. The optimum growth conditions for the MOCVD growth of GaSb have been determined for a TMGa flow rate of 20 sccm and a carrier gas flow of 8 l/min. The optimum substrate temperature and V/III ratio were found to be 540 °C and 0.72, respectively. In these conditions the lowest hole concentration of 5 × 1016 cm-3 and the highest room temperature mobility of 500 cm2 V-1 s-1 were achieved, accompanied by a steep, well-resolved band edge at 0.72 eV.

Micro/nanomechanical and tribological characterization of ultrathin amorphous carbon coatings, deposited by filtered cathodic arc (FCA), direct ion beam (IB), electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD), and sputter (SP) deposition processes on Si substrate have been conducted using a nanoindenter with a nanoscratch attachment and an accelerated ball-on-flat tribometer. Coating thicknesses of 20, 10, 5 nm and, for the first time, 3.5 nm coatings have been investigated. It was found the FCA coating exhibits the highest hardness and elastic modulus, followed by the ECR-CVD, IB, and SP coatings. In general, the thicker coatings exhibited better scratch/wear performance than the thinner coatings due to their better load-carrying capacity as compared to the thinner coatings. At 20 nm, the FCA and ECR-CVD coatings show the best scratch and wear resistance, while the IB and ECR-CVD coatings show the best scratch and wear resistance at 10 nm. Five nanometer thick coatings show reasonable scratch and wear resistance, while 3.5 nm thick coatings show extremely low load-carrying capacity and poor scratch and wear resistance. It appears that the 3.5 nm coatings studied are unfeasible for scratch and wear resistance applications as of now.

Ingots of composition Nd9Fe85B6, Nd9Fe85B6 + 1 at.% (Ti + C), Nd9Fe85B6 + 2 at.% (Ti + C), and Nd9Fe85B6 + 5 at.% (Ti + C) were prepared by plasma arc-melting the constituent elements from 99.95 wt% Nd, 99.99 wt% Fe, 99.97 wt% Ti, spectrographic grade C, and ferroalloy Fe–B (19.6 wt% B). Effect of Ti + C addition and its content on quenchability and magnetic properties of Nd9Fe85B6 alloy were investigated by melt-spinning. The results showed that the added Ti and C elements reacted with each other to form TiC compound that was solid solutioned, precipitated, or both in the cast ingots. The Ti + C addition can increase the glass-forming ability (GFA) of an α–Fe/Nd2Fe14B–type nanocomposite permanent material: the more the additive, the stronger the GFA; but only approximately 2 at.% Ti + C addition could enormously increase the magnetic properties.

Ultrafine Fe, Fe–Ni, and Ni particles were prepared by using the hydrogen plasma-metal reaction method in a mixture of H2 and Ar of 0.1 MPa. The particles were characterized by x-ray diffraction, transmission electron spectroscopy, energy disperse spectroscopy, chemical analysis, and Mössbauer spectroscopy. In contrast with bulk Fe–Ni alloys, the distinguishing features in corresponding ultrafine particles are that two phases with fcc and bcc structures coexist in a wide composition range. Ultrafine Fe–Ni particles have higher resistance to oxidation than Fe and Ni particles. The mechanism of forming particles was analyzed by means of structural and magnetic measurements. It was found that quenching is a dominant mechanism for forming paramagnetic particles. Hyperfine interactions were studied by Mössbauer spectroscopy in comparison with those in bulk Fe–Ni alloys.

Wetting behavior of eutectic SnPb and pure Sn on Au(500 Å)/Cu(1 μm)/Cr(800 Å) layered thin films were monitored in situ in a ramping temperature profile using a scanning electron microscope (SEM) with a vacuum of 10−5–10−6 Torr. We found that the wetting behavior of these two solders in SEM was dramatically different from their behavior in RMA soldering flux; a smaller wetting angle and rough wetting front morphology were observed. Very surprisingly, no dewetting could be observed inside the SEM chamber, yet dewetting happened to the same sample when it was removed from the SEM and immersed in RMA soldering flux. We estimate the interfacial energy between liquid Sn and solid Cr and assume the reduction of surface and interfacial energies caused by possible oxidation of Cr and liquid Sn surface in the SEM in order to explain the above-mentioned wetting and dewetting behaviors.

Recently, it was demonstrated that grain refinement in undercooled Cu30Ni70 is brought about by a remelting of those initially formed dendrites (termed novel dendrites) which are unstable against melting. Also, it was found that in the same transition regime, there is a sharp drop in the specific volume of the undercooled specimens. Before entering into the transition regime, the novel dendrites found in an undercooled specimen are arranged in a regular pattern and the microstructures consist of large dendrites. Voids are found mainly at the dendritic spacings of the large dendrites. On the other hand, near the upper end of the transition regime, the microstructures consist of equiaxed refined grains. Furthermore, each of these grains contains a novel dendrite. Voids have moved to the interdendritic or grain boundaries. Based on these observations, a solidification mechanism of undercooled molten Cu30Ni70 is proposed.

A detailed study of the sintering behavior of titanium carbide (TiC) powder synthesized by the self-propagating high-temperature synthesis (SHS) route was carried out with varying percentages of nickel. With an increase in the nickel content, porosity was found to increase along with Ni2.67Ti1.33 secondary phase at grain boundary. A 90–92% dense sintered body of TiC was produced from SHS-produced powder at 1800 °C with 10 wt% nickel.

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.