An allotropic transition from face-centered-cubic (fcc) to hexagonal-close-packed (hcp) Ni(Si) solid solution in Ni95Si5 and Ni90Si10 during nanocrystallization by mechanical alloying is reported. The transformation was identified as a defect-induced melting accompanied by a volume expansion of 8.6% and was observed when fcc Ni(Si) reached a critical crystallite size of 10 nm. Calculation based on equation of state showed that a 37% reduction in tetragonal shear modulus and a negative pressure of about 8.7 GPa were generated at the onset of transformation.

The microstructure and chemistry of (Ba,Sr)TiO3 thin films deposited on Pt/SiO2/Si substrates by metalorganic chemical vapor deposition were studied using highresolution transmission electron microscopy and quantitative spectrum imaging in electron energy loss spectroscopy. The grain boundaries in all films with overall Ti content ranging from 50.7% to 53.4% exhibit a significant increase in Ti/Ba ratio as compared to the grain interiors. The results suggest that the deviations of Ti/(Ba + Sr) ratio from the stoichiometric value of unity are accommodated by the creation of Ba/Sr vacancies, which segregate to the grain boundary regions. The films with Ti contents equal to or greater than 52% additionally contained an amorphous Ti-rich phase at some grain boundaries and multiple grain junctions; the amount of this phase increases with increasing overall Ti content. The analysis indicates that the amorphous phase can only partially account for the significant drop in dielectric permittivity accompanying increases in the Ti/(Ba + Sr) ratio.

A new family of microporous semicrystalline silica materials (MSSMs) were developed at room temperature from acidic mixtures of alkyl-substituted silane and tetramethylalkoxysilane. Hydrolyzed alkyl-substituted silica precursors, having hydrophilic silanol groups and hydrophobic alkyl groups, presumably act not only as templates but also as sol stabilizers for continuous pore engineering of silica materials in the micropore region. Depending on the substituted alkyl (SUA) groups in initial sols, MSSMs have distinct broad x-ray diffraction peaks in low 2θ range of 2° to 12°, distinguishable thermal behavior of SUA groups, highly flexible processability, and discrete micropore size with good thermal stability of micropores after the removal of SUA groups. These designer microporous silicas are expected to be useful for molecular sieving applications.

In the present work we studied the depth of damage layer in machined silicon wafers that was incorporated with chemical etching using micro-Raman spectroscopy. Subsurface damage causes changes in the shape and intensity for the shoulder (450–570 cm−1) of the most intense band (519 cm−1) and the second band (300 cm−1) regions of the Raman spectrum. Etching reduces the thickness of the damage layer and, hence, the intensities at the shoulder and the second band. The intensities at the shoulder and the second band become stable when the damage layer is completely etched out. The shoulder consists of two Gaussian profiles: the major and the minor. The band for the major profile is independent of etching depth, but the band for the minor profile shifts toward the longer wave numbers with increasing etching period until the damage layer is completely etched out. The depth of the damage layer is determined by the profiles of the shoulder and the second band and confirmed by the band shift of the minor profile. Transmission electron microscopy (TEM) further verified the results with respect to the depth of the damage layer. TEM observation showed that dislocations and stacking faults are responsible for the subsurface damage.

SnO crystallites having a size ranging 0.1–0.2 μm were synthesized by a hydrothermal process, which consisted of prolonged solution aging under pH = 1.0, followed by hydrothermal treatment under pH = 9 to 10 at 75–95 °C. Oxidation of Sn+2 to Sn+4 during the hydrothermal stage was effectively inhibited by increasing the solution-aging time. This was attributed to the formation, upon aging, of polymeric hydrous SnO colloids, which are more oxidation resistant than aquo-hydroxo tin complex monomers. For solutions with a sufficiently long (≥240 h) aging time, the SnO yield increased with increasing pH and temperature during the hydrothermal treatment.

The mechanism of bubble formation when He is implanted into silicon is described. Many experiments are reviewed and several techniques are considered. During implantation and subsequent annealing, complex Hen–Vm clusters are formed, trapping vacancies, while Si self-interstitials recombine directly at the surface. By increasing temperature He atoms out-diffuse, and the entire process produces a supersaturation of vacancies (void formation). Their evolution is studied during isothermal and isochronal annealing, describing the mechanisms involved; that is, direct coalescence or Ostwald ripening. The internal surface is an efficient trap for self-interstitials and for metals. The gettering mechanism is governed by a surface adsorption at low impurity concentration while at high value a silicide phase is observed. The high getter capability is ensured by the large number of traps introduced (1017–1019 cm−3). Finally, voids introduce mid gap energy levels that act as minority carrier recombination centers, providing a powerful method to control lifetime locally in silicon devices. The reviewed results demonstrate that the trap levels are due to the dangling bonds present on the void surface. This property can be used in many applications.

The oxidation behavior and the effect of oxidation on the flexural strength of Si3N4/SiC nanocomposites were investigated. Parabolic weight gains, with respect to the oxidation time, were observed for all the specimens containing different amounts of SiC. However, the parabolic rate constant decreased with increasing SiC content. The main oxidation product, being in equilibrium with SiO2, was Y2Si2O7. The oxidation product became denser and retained more crystalline phase as the amount of SiC increased. The flexural strength of the nanocomposites increased by up to 40%, while that of pure Si3N4 decreased after oxidation at 1300 or 1400 %C for 100 h. This excellent oxidation resistance of Si3N4 nanocomposite was attributed to the enhancement of the crystallization of the oxidation product and the grain boundary phase by the SiC nanoparticles.

Anodic conversion films of vanadium oxides on vanadium were potentiodynamically generated at high voltages in an acetate electrolyte system. The microstructure of the anodic VOx coatings was characterized by surface and solid-state techniques such as scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and x-ray photoelectron spectroscopy. An amorphous structure is proposed in which network-forming [VO4] tetrahedra in various degrees of condensation are connected by distorted [VO5] and [VO6] units. Such polyhedra lead to the formation of nanocrystalline phases of stoichiometric and substoichiometric vanadium oxides, which were observed in the amorphous phase.

Li–ZrSiO4 was synthesized by the sol-gel method. Reactions were performed with different Li:Zr molar ratios: 1, 3, 5, and 6. Cell parameters changed as follows: a0 decreased and c0 increased as the Li:Zr molar ratio increased. The x-ray photoelectron spectroscopy analysis showed two kinds of oxygen atoms. The first one was attributed to ZrSiO4 oxygens. The second one was attributed to Li–O bonds. All these results were supported by a theoretical analysis. It was concluded that lithium atoms were held in interstitial positions of the ZrSiO4 structure.

Structural and ferromagnetic transitions in shape memory Ni–Mn–Ga alloys and their martensitic structure and microstructure were found to be strongly influenced by rapid quenching from the liquid state and by subsequent aging. Detailed calorimetric and magnetic measurements, dynamic mechanical analysis, and transmission electron microscopy observations were performed to characterize the transformation behavior of thin ribbons compared to the bulk materials. The rapid quenching caused the decrease of the ferromagnetic, martensitic, and premartensitic transformation temperatures, as well as of the saturation magnetization, while the subsequent annealing brought about an increase of the depressed values. This influence was attributed to quenched-in short-range chemical disorder within sublattices, the ordering being improved by a vacancy migration mechanism upon subsequent annealing.

The room temperature mechanical properties of a mixed conducting perovskite Sm1?xSrxCo0.2Fe0.8O3 (x = 0.2 to 0.8) were examined. Density, crystal phase, and microstructure were characterized. It was found that the grain size increased abruptly with increasing Sr content. Mechanical properties of elastic modulus, microhardness, indentation fracture toughness, and biaxial flexure strength were measured. Young's modulus of 180–193 GPa and shear modulus of 70–75 GPa were determined. The biaxial flexure strength was found to decrease with increasing Sr content from ∼70 to ∼20 MPa. The drop in strength was due to the occurrence of extensive cracking. Indentation toughness showed a similar trend to the strength in that it decreased with increasing Sr content from ∼1.1 to ∼0.7 MPa m1/2. In addition, fractography was used to characterize the fracture behavior in these materials.

Carbonate precursors of Y3Al5O12 (YAG) were synthesized from a mixed solution of alum and yttrium nitrate using ammonium hydrogen carbonate as precipitant. Precipitation method (normal-strike or reverse-strike) and aging were found to have dramatic effects on cation homogeneity of the precursor, which in turn influenced the formation temperature of the YAG phase. Reactive YAG powders were produced from the reverse-strike-derived, as-synthesized precursors at temperatures ≤1200 °C. These powders densified to >98.0% of the theoretical density up to 1500 %C at a constant heating rate of 8 %C/min or to transparency by vacuum sintering at 1700 %C for 1 h without additives.

La0.67Sr0.33MnO3 thin films were grown on LaAlO3 substrate in vacuum using pulsed laser deposition to investigate the effect of changing oxygen content. Transmission electron microscopy studies showed that the epitaxial (La0.67Sr0.33)2MnO4 phase with K2NiF4 structure formed unexpectedly as a matrix with a square-shaped nanometer-sized MnO phase distributed in a regular pattern throughout the whole film like self-assembled quantum dots. The MnO phase grew epitaxially from the LaAlO3 substrate to the top of the film with no outgrowth. High-resolution image simulation indicated that Sr ions take up only positions in every other La layer in the (La0.67Sr0.33)2MnO4 structure. Basing our theory on the composition and structure of the matrix phase, we propose that it is possibly electron-doped with a mixed valence of Mn2+/Mn3+ instead of the Mn3+/Mn4+ as in the hole-doped case.

Mechanical milling of fullerene (soot containing C60/C70 fullerenes in a 8:2 molar ratio) was investigated through various characterization methods. It was found that mechanical milling would not destroy the molecular structure of fullerene C60 (C70), while the long-range order of the face-centered-cubic crystalline structure was easily modified and transformed into amorphous phase, a mixture of fullerene C60 (C70) polymers and monomers. Differential scanning calorimetry analysis revealed a recovery of polymers to pristine fullerene molecules at 678 K, which is much higher than the reported depolymerization temperature of fullerene polymers induced by photo irradiation and by high-pressure–temperature processes. It is suggested that the contaminated Fe acts as a catalyst in the polymerization process.

Neutron diffraction measurements were carried out on samples of CeO2–ZrO2 powder catalysts prepared by high-energy mechanical milling. The formation of solid solution was evidenced across the entire composition range examined. Quantitative phase evaluation by the Rietveld method indicated formation of tetragonal structure for low CeO2 content, whereas cubic solid solutions were the stable form at high CeO2 loading. In addition, a pseudocubic or tetragonal t″ cell with axial ratio of unity and with internal deformation of the oxygen sublattice was observed at intermediate composition (50 mol% CeO2). Thermal annealing up to 1000 °C showed expansion of the unit cell parameters; an increase in the degree of tetragonality at the expense of cubic and monoclinic phase was observed for composition CexZr1−xO2 (x < 0.5).

A liquid-precursor process was used to produce an epitaxial all-oxide ferroelectric memory device structure. The lanthanum strontium manganate–lead zirconate titanate–lanthanum strontium manganate (LSMO–PZT–LSMO) structure used for this device shows excellent polarization and fatigue behavior with a remnant polarization Pr of 42 µC/cm2 and a coercive field Ec of 68 keV. The polarization was found to only slightly degrade after over 1010 fatigue cycles. This behavior is contrasted with epitaxial PZT using a metal top electrode. In addition, the use of a top LSMO electrode was a sufficient barrier to Pb loss during heating to allow subsequent (or prolonged) heat treatments that would generally lead to Pb loss.

The thickness distribution of grain-boundary films during the superplastic deformation of fine-grained β–silicon nitride was investigated by high-resolution electron microscopy. In particular, grain-boundary thickness was considered with respect to the stress axis in two orientations; namely, parallel and perpendicular to the direction of applied stress. The results showed that the thickness distribution in boundaries perpendicular to the direction of applied stress was unimodal, whereas in parallel boundaries it was bimodal. Moreover, it was found that the majority of film-free boundaries were parallel to the direction of applied stress in the extremely deformed sample. The variation in spacing reflects distribution of stresses within the material due to irregular shape of the grains and the existence of percolating load-bearing paths through the microstructure.

The influence of Co addition on the glass-forming ability of slowly cooled Nd70-xFe20Al10Cox alloys (0 ≤ x ≤ 10) was studied by x-ray diffraction, constant-rate heating calorimetry, and magnetic measurements. Without addition of Co, the as-cast Nd70Fe20Al10 cylinders of 3-mm diameter show a mixture of amorphous and crystalline phases after copper mold casting. Increasing the Co content promotes amorphization, and bulk amorphous specimens can be obtained for Nd60Fe20Al10Co10. No glass transition or supercooled liquid region before crystallization was observed for the bulk Nd60Fe20Al10Co10 alloy. The bulk amorphous alloy exhibits hard magnetic behavior with a remanence (Jr) of 0.09 T, a magnetization (J1500) of 0.13 T, and a coercivity (Hc) of 298 kAm−1. The Curie temperature for the as-cast Nd70-xFe20Al10Cox cylinders increases from 480 K for x =0 to 487 K for x = 10. The enhanced glass-forming ability for the Nd–Fe–Al-based alloys upon Co addition will be critically discussed with respect to classical nucleation theory and the formation of metastable ordered clusters upon solidification.

Nanometer-sized particles of W are of interest in semiconductor device research, where such particles may store electrons inside heteroepitaxially defined structures. In this paper, we present results concerning W particles produced by thermal decomposition of tungsten hexacarbonyl. By the described method, it was possible to produce size-selected, single-crystalline W particles in the size range between 15 and 60 nm. The sintering behavior of the particles was studied between ambient temperatures and 1900 °C. The particle morphology and structure were examined with high-resolution transmission electron microscopy and electron diffraction techniques. Particles sintered at the highest temperatures typically were single crystals, with well-developed facets. Some problems concerning a yield reducing charging mechanism are discussed.

Crystals of merwinite were prepared at 1550 °C from chemical reagents, and their intracrystalline microstructures were examined by the combined use of x-ray diffraction and optical microscopy. The crystals were composed of pseudomerohedral twins. The adjacent twin domains were related by the pseudosymmetry two-fold axis parallel to ⟨011⟩with the composition surface {811} The overall twin structure was constructed by introducing the pseudo-symmetry three-fold axis normal to (100), which must originally be a symmetry element of the former high-symmetry phase. The transition from the primitive trigonal (point group 3m) to the primitive monoclinic (space group P21/a) was accompanied by the combination of reducing the order of the point group and the change in the size of the unit cell. The order of the point group was reduced from 12 to 4, resulting in three twin domains with six different interfaces. This accounted for the experimentally observed microstructure consisting of repeated lamella twins in several orientations. Because the unit lattice translation would be lost during the transition, the formation of antiphase domains was expected. The lost translation vectors were 1/2[011], 1/2[100], and 1/2[111] resulting in four antiphase domains. As a result, the total number of domains possible in the transition was 3 × 4 = 12.