Definitive evidence on the variable degrees of order/disorder in the layered perovskite La2Ba2Cu2Ti2O11 is presented. This oxide was prepared by the ceramic method with varying reaction times and cooling rates; the average and local structures of the resulting solids were studied by x-ray diffraction, electron diffraction, and transmission electron microscopy (low and high resolution). The data clearly show the presence of an ap × ap × 4ap layered perovskite superstructure with a high concentration of defects in samples prepared over 48 h but with increasing degree of order for samples with longer reaction times. For samples reacted over 17 days, the order is complete and identical to that found for other related derivatives such as Ln2Ba2Cu2Ti2O11 (Ln = Nd, Eu, Tb). This behavior clearly indicates the existence of a kinetic control of order in this phase.

The reactions of rare earth (RE) acetates with iron acetylacetonate in 1,4-butanediol at 300 °C (glycothermal reaction) yielded two novel phases depending on the ionic size of the RE element: one was obtained for Er-Lu and the other for Tb and Dy. The former phase was hexagonal REFeO3, while the latter phase has not been identified. The reaction of Y or Ho acetate yielded the mixture of these two phases. When the reactions were carried out in the presence of seed crystals of yttrium aluminum garnet (Y3Al5O12), these phases were not formed but RE iron garnet (RE3Fe5O12) grew on the seed, which suggests that spontaneous nucleation of RE iron garnet does not occur, but crystal growth proceeds easily under the glycothermal conditions. Hydrothermal reaction of the same starting materials yielded a mixture of Fe2O3 and an amorphous RE phase.

The morphological stability of ultrahigh vacuum deposited Ag film on (001)Si has been drastically improved by the deposition of 1 to 5 nm thick interposing Au layers. In Ag/(001)Si samples, Ag islands were found to form after annealing at 200 °C for 1 h. In contrast, continuous and uniform metal layer persisted after annealing at 500 °C for 1 h in samples with a thin intermediate Au layer. The significantly improved morphological stability is attributed to the strong intermixing between Au and Ag atoms at the metal/Si interface. The intermixing lowers the interface energy between metal layer and (001)Si.

Superplastic behavior of aluminum matrix composites with discontinuous reinforcements has been investigated in a temperature range below the melting temperature measured by differential scanning calorimetry. The experimental results of the mechanical properties revealed that the rate-controlling process of superplastic flow was associated with dislocation movement controlled by lattice self-diffusion. The strengthening due to the presence of reinforcements was retained. It is suggested that the strongest strengthening process of the dislocation-pileup mechanism and the diffusional relaxation-limitation or dislocation bypass mechanism affects the rate-controlling process.

Gd-doped amorphous silicon films have been prepared by the electron beam evaporation technique, employing the experimental methods of dc conductivity temperature properties, ESR (electron spin resonance) spectra, and optical band gap Eopt measurements. We have investigated the optical and electrical properties of the films. The results show that at 290 K < T < 330 K, hopping conduction in Gd impurity states near Fermi level is predominant, and at 330 K < T < 500 K extended state conduction dominates due to electrons exited from the impurity states. At a Gd concentration of about 1.0 at.% spin density Ns, peak-peak width ΔBpp and line-shape factor l of ESR spectra change their dependence on Gd contents. The optical gap of the films narrows with increasing Gd contents in the films from 1.68 eV to 0.42 eV. The results were explained on the basis of the partial compensation of Gd atoms for dangling bonds .

Morphology of carbide grain in WC–12 wt.% Co–0.5 wt.% VC was examined by HREM and EDS with a special interest in the segregation of V at the WC/Co interfaces. A small addition of VC in WC-Co is effective to suppress the grain growth of carbide grains. HREM observation revealed that the WC/Co interfaces are faceted and consist of mainly two kinds of habit planes, (1010) and (0001), respectively. EDS analyses clearly showed the segregation of doped V along the interfaces. In addition, the concentration of segregated V is higher at the (0001) type habit plane than (1010) one. The retardation of the grain growth of carbide grains in the VC-doped WC-Co is closely related to the formation of the faceted WC/Co interface.

In an attempt to take advantage of charged particle irradiation for studying the effects of irradiation on the mechanical properties of metals, we developed an experimental procedure based on the combination of transmission electron microscopy (TEM) and submicron indentation of ion-implanted layers. We applied this technique to industrial 316L steel, irradiated with krypton ions up to 10 dpa at 873 K. A domain where the penetration range of the ions and the indentation depth are compatible has been identified. The indentation tests then yielded a good estimate of hardness and bulk modulus, while the TEM observations provide microstructural information in the plastic regime. It is shown that the combination of the two techniques is necessary for rationalizing the observed results.

The feasibility of transforming shaped Mg–Al2O3-bearing precursors into monolithic spinel (MgAl2O4) bodies with a retention of shape and dimensions has been demonstrated.Dense, shaped precursors (disks, bars) were fabricated by the pressureless infiltration of molten Mg into porous Al2O3 preforms. After solidification (and machining, in the case of bar-shaped specimens), the Mg-bearing precursors were oxidized in flowing O2 (g) at 430–700 °C. Postoxidation annealing at 1200 °C resulted in the conversion of MgO and Al2O3 into MgAl2O4. After sintering at 1700 °C, spinel bodies that retained the precursor dimensions (to within 0.65%) were produced. Phase and microstructural analyses at various stages of processing are discussed.

Well-crystallized Pb(Zr0.52Ti0.48)O3 thin films (4000 Å thickness) can be synthesized on Pt/Ti/SiO2/Si(100) substrate at a temperature as low as 520 °C. The polycrystalline lead zirconate titanate (PZT) perovskite phase formation was confirmed with x-ray diffraction (XRD) analysis, and growth morphologies were studied with a scanning electron microscope (SEM). The electrical properties of PZT thin films were characterized through P-E hysteresis curve, dielectric constant, and loss, fatigue, and leakage current measurements. Remanent polarization (Pr) and coercive field (Ec) of as-grown film were 8–30 μC/cm2 and 24–64 kV/cm with the variation of applied voltage (5–15 V). The post-annealing enhances the electrical properties even at 500 °C, which is below the as-grown temperatures (520 °C). The average polarization loss after applying rectangular pulse (Vp-p = 10 V) up to 1011 cycles was 40.9% for a 300 μm small dot and 22% for a 500 μm large dot, which are relatively improved values for platinum electrode. The values of dielectric constant (ε′) and tan δ measured with small signal sign wave (1 V, 10 kHz) were 1207 and 0.066 in the case of as-grown film.

Zinc oxide varistors are very complex systems, and the dominant mechanism of voltage barrier formation in these systems has not been well established. Yet the MNDO quantum mechanical theoretical calculation was used in this work to determine the most probable defect type at the surface of a ZnO cluster. The proposed model represents well the semiconducting nature as well as the defects at the ZnO bulk and surface. The model also shows that the main adsorption species that provide stability at the ZnO surface are O-, O2-, and O2.

A technique for preparing electrically conductive coatings of Cu3BiS3 powder in polyacrylic acid matrix is presented. Bi2S3 powder obtained by chemical precipitation was introduced into a freshly prepared CuS chemical deposition bath. After the initial nucleation period, CuS started to deposit on the Bi2S3 surface. The as-obtained CuS–Bi2S3 powder was mixed with polyacrylic acid aqueous solution, and the resulting mixture was used as a paste to form a screen-printed composite coating. Up to 200 °C the film behaves like a simple CuS film; the sheet resistance is around 100 and the crystallized phase in the composite is CuS (Covellite). When the temperature is equal or higher than 250 °C, atomic diffusion at the CuS–Bi2S3 interface is promoted, leading to the formation of the ternary compound Cu3BiS3 (Wittichenite) in the composite film. The formation of the compound depends on the temperature, relative abundance of the Bi2S3 and CuS components in the CuS–Bi2S3 pigment, as well as on the annealing atmosphere.

Metallurgical reactions controlling the Ti activation in brazing of Al2O3 have been studied by means of microstructural and thermodynamic analysis. The reactions of titanium with oxygen and copper are shown to be decisive in active brazing. Themiscibility gap in the Ag–Cu–Ti system divides the liquid braze into Ag-rich (L1) and TiCu-rich (L2) liquids. The liquid L2 reacts with alumina forming the mixed oxide (Ti, Al)4Cu2O. Besides with alumina, Ti reacts with oxygen that the filler alloys usually contain and forms a brittle ribbon composed of TixO and Ti–Cu–O phases in the braze. The formation of Ti oxides next to the alumina is possible only in the filler alloys of highest Ag content.

Unidirectional celsian matrix composites having 42–45 vol% of uncoated or BN-SiC coated Hi-Nicalon fibers were tested in three-point bend at room temperature. The uncoated fiber-reinforced composites showed catastrophic failure with strength of 210 ± 35 MPa and a flat fracture surface. In contrast, composites reinforced with coated fibers exhibited graceful failure with extensive fiber pullout. Values of first matrix cracking stress and strain were 435 ± 35 MPa and 0.27 ± 0.01%, respectively, with ultimate strength as high as 960 MPa. The elastic Young modulus of the uncoated and coated fiber-reinforced composites were 184 ± 4 GPa and 165 ± 5 GPa, respectively. Fiber push-through tests and microscopic examination indicated no chemical reaction at the uncoated or coated fiber-matrix interface. The low strength of composite with uncoated fibers is due to degradation of the fiber strength from mechanical damage during processing. Because both the coated- and uncoated-fiber-reinforced composites exhibited weak interfaces, the beneficial effect of the BN-SiC dual layer is primarily the protection of fibers from mechanical damage during processing.

The local structure and crystallization behavior of Nd15Fe77Bx (x = 2−14) melt-spun alloys were studied by Nd L3 extended x-ray absorption fine structure (EXAFS). The conventional x-ray powder diffractometry studies showed that the Nd–Fe–B melt-spun ribbons had the amorphous structure regardless of the boron content. EXAFS studies of the local structure around the Nd atom confirmed that the Nd–Fe–B melt-spun alloys had the amorphous structure and virtually the same nearest neighbor distance from the Nd atom. The amorphous alloys were heated by a differential scanning calorimetry in order to investigate the variation in the local structure during the crystallization process by EXAFS measurements. Although no appreciable difference was found in the nearest neighbor distance of the Nd atom between the amorphous alloys and the crystallized alloys, the small variation in the nearest neighbor distance during the crystallization process was detected by EXAFS measurements.

This paper is the first report of the synthesis of a sinteractive single-phase microstructure yttrium disilicate precursor powder using hydrothermal processing. The effect of the pH of the precursor chemicals on the ease of formation of a single-phase material was investigated using x-ray diffraction, TEM, and SEM. Under very acidic conditions (pH 1), the formation of yttrium chloride, in addition to the yttrium disilicate precursors, produced a powder that absorbed moisture, did not sinter well, and produced a two-phase interpenetrating microstructure after sintering. At pH 6, yttrium chloride no longer formed, but the interpenetrating network persisted after sintering. Only under basic conditions (pH 10) did single-phase yttrium disilicate form after sintering. This work is noteworthy because the calcination time of 1 h required for the formation of this ceramic at 1050 °C is over an order of magnitude lower than the calcination times of over 100 h required when calcined in the temperature range 900 °C to 1150 °C, as reported previously by other workers.

This paper reviews the past, present, and future of the hydroxyapatite (HAp)-based biomaterials from the point of view of preparation of hard tissue replacement implants. Properties of the hard tissues are also described. The mechanical reliability of the pure HAp ceramics is low, therefore it cannot be used as artificial teeth or bones. For these reasons, various HAp-based composites have been fabricated, but only the HAp-coated titanium alloys have found wide application. Among the others, the microstructurally controlled HAp ceramics such as fibers/whiskers-reinforced HAp, fibrous HAp-reinforced polymers, or biomimetically fabricated HAp/collagen composites seem to be the most suitable ceramic materials for the future hard tissue replacement implants.

Ion beam nitridation (IBN) of GaAs at room temperature was studied as a function of N2+ ion incident angle at ion energy of 10 keV. The ion beam bombardment surface area of GaAs was characterized in situ by both Auger electron spectroscopy (AES) and small spot-size x-ray photoelectron spectroscopy (XPS). Thin GaN reaction layers are formed at all N2+ ion incident angles, whereas the formation of As–N bonds has not been found. However, the degree of nitridation of Ga decreases with increasing incident angle. The observed angular dependence of the N incorporation can be explained in terms of sputtering yield, indicating that the growth kinetics can be described as a dynamic process comprising the accumulation of N and sputter removal of the surface layer. N2+ ion bombardment causes the depletion of As from the surface region because of the preferential sputtering of As from GaAs. The preferential sputtering of As reduces with increasing N2+ ion incident angle. The angular dependent behavior of preferential sputtering of As by 10 keV N2+ ions can be attributed to the angular dependence of GaN surface layer formation.

A new porous material was prepared from a layered compound, K4Nb6O17, through the exfoliation of its layers. A composite of the niobate sheets and MgO particles were obtained by precipitating the exfoliated two-dimensional niobate sheets with MgO fine particles. Porous niobium oxide was obtained by removal of the MgO particles from the composite after thermal treatment. It had a large surface area and showed higher photocatalytic activity than the original H+/K4Nb6O17 for H2 evolution from various aqueous alcohol solutions.

The hydrothermal growth of epitaxial BaTiO3 thin films on single-crystal SrTiO3 substrates occurs by the island growth mode. The aqueous solution chemistry is found to control interfacial characteristics and plays an important role in controlling film formation and faceting. Island faceting can be changed by the introduction of additional cations during synthesis. Electrophoretic data, confirmed by adsorption measurements, show that barium is a potential determining counterion and adsorbs on SrTiO3 surfaces. Initial electrical measurements show that the BaTiO3 films have a dielectric constant of 141 with a loss tangent of 0.9 that decreases with heat treatment.

In this paper, positron annihilation measurements have been carried out on a-Si: H thin films deposited by plasma-enhanced chemical vapor deposition (PECVD) at high and low rates by means of the variable energy positron beam Doppler-broadening technique. The depth profiles of microvoids in the films grown under different conditions have been determined. We found a smaller void fraction in the surface region of all films compared to the bulk, and a smaller void fraction in low rate than in high growth rate films. By plotting S and W parameters in the (S, W) plane, we have shown that the vacancies in all of the high-rate and low-rate deposited intrinsic samples, and in differently doped low-rate samples are of the same nature, although there appears to be a higher density of defects in the boron than phosphorus doped films. The depth profiles of the microvoid-like defects in the a-Si: H films are extracted by use of the vepfit program.