bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct current-voltage failure in lead magnesium niobate-based multilayer ceramic capacitors
Authors: Cao Jiang Li , Li Long Tu , Zhang Ning Xin , Gui Zhi Lun
Published: March 2008

Resistance measurement, P–E hysteresis measurement, and transmission electron microscope and energy dispersive analysis of x-rays (TEM-EDAX) analysis were used to study the resistance failure of lead magnesium niobate-based multilayer ceramic capacitors (MLCC) under dc voltage. It was found that the failure rate of MLCC with 1/9 Pd/Ag internal electrodes was 10 times that of MLCC with 3/7 Pd/Ag electrodes after the temperature–humidity–bias test (THB). Voltage shifts of hysteresis loops showed that an internal bias field between electrodes of MLCC was formed after THB test. Ag diffusion from electrodes into the ceramics during cofiring was examined through TEM-EDAX analysis. It was also found that the degraded specimens could be partially restored after storing under natural condition. On the basis of these results, the failure mechanism was established that oxygen vacancies induced by Ag diffusion accumulated under the external bias field, which increased the concentration of electronic defects, thereby resulting in the resistance failure of MLCC.
Low-temperature preparation and structural characterization of Pr-doped ceria solid solutions
Authors: López-Navarrete E. , Caballero A. , González-Elipe A. R. , Ocaña M.
Published: March 2008

We report a method for preparing Pr-doped ceria by pyrolysis at 600 °C of aerosols consisting of aqueous solutions of Ce(III) nitrate and Pr(III) chloride. This procedure involves an important decrease of the temperature of solid solution formation (several hundred degrees) when compared with the ceramic and other previously reported methods, and does not require the addition of fluxes. The prepared samples and their products after thermal treatment were characterized in terms of particle shape and size distribution, composition, and crystalline structure. The color properties of these solid solutions were also evaluated as a function of the heating temperature and composition; the optimum red pigment was obtained for samples with a Pr/Ce mole ratio = 0.063 heated for 3 h at 600 °C. The oxidation state of the Pr cations and their
distribution in the CeO2 matrix were investigated by x-ray absorption near-edge spectroscopy and x-ray photoelectron spectroscopy. A mixture of trivalent and tetravalent Pr was detected in all studies samples. The Pr(IV)/Pr(III) ratio increased as the Pr content or the heating temperature increased. These Pr(III) cations were found to be mainly located in the particles' outer layers, in which an enrichment of Pr was detected for all samples heated at 600 °C. The further calcination of the pigments at 1200 °C gave rise to a certain diffusion of the Pr cations toward the particle core, which was more significant for the sample with the highest Pr content (Pr/Ce mole ratio 4 0.091).
Nanoindentation studies of brittle thin films on a titanium alloy substrate
Authors: Fujisawa N. , Swain M. V. , James N. L. , Tarrant R. N. , Woodard J. C. , McKenzie D. R.
Published: March 2008

The mechanical properties of a range of tribological mitigating and biocompatible films deposited on a titanium alloy substrate have been investigated using nanoindentation. For a range of carbon films investigated, the ratio of hardness to modulus was almost constant at around 0.1. The onset of film–substrate interactions of a coated system upon progressive loading could be determined as the depth of penetration at which the slope of the force versus depth curve deviated from that of an analytically derived “bulk film” system that incorporated the indenter tip effect on the contact area. For the carbon-coated systems investigated, the corresponding force, or the critical load-carrying capacity of a localized contact event by a sharp indenter, appears to scale with the elastic modulus mismatch between film and substrate.
Effect of thermal aging on the Néel temperature of a Fe–Cr–Ni–Mo alloy
Authors: Shek C. H. , Lai M. W. , Lai J. K. L.
Published: March 2008

Numerous previous investigations on the magnetic properties of Fe–Cr–Ni or similar alloys show that the Néel temperature of this class of material is usually in the range 20–40 K and never exceeds 60 K. In this paper, we report on the discovery that the Ne’el temperature of a Fe–Cr–Ni–Mo alloy can be substantially increased to approximately 80–100 K by long-term thermal aging at 800 °C and above. This discovery has raised many questions on the detailed mechanism of magnetic transition on this class of material and is expected to open up a new line of investigation for researchers in this field.
Monte Carlo Simulation of Phase Separation Behavior in a Cu-Co Alloy Nanoparticle
Authors: Shim Jae-Hyeok , Lee Byeong-Joo , Ahn Jae-Pyoung , Cho Young Whan , Park Jong-Ku
Published: March 2008

The phase separation behavior in a Cu–Co nanoparticle was investigated using Monte Carlo (MC) simulation. The modified embedded atom method (MEAM) was adopted to describe the interatomic potentials for the Cu–Co alloy system. Some of the cross potential parameters were fitted with experimental data such as mixing enthalpy and lattice constants of Cu–Co alloys. The present MC simulation combined with the MEAM potential describes well the phase separation between face-centered-cubic (fcc) Cu and fcc Co during the annealing of the particle.
Lead Zirconate Titanate Thick Film Prepared by Electrophoretic Deposition from Oxide Mixture
Authors: Zhang R. F. , Ma J. , Kong L. B.
Published: March 2008

Lead zirconate titanate (PbZr0.52Ti0.48O3; PZT) thick film with a thickness of 70 µm was prepared by the electrophoretic deposition method from a raw oxide mixture of PbO, ZrO2, and TiO2. X-ray diffraction and scanning electron microscopy were used to characterize the sintered PZT thick film. Single phase PZT was observed in the films sintered at 900 °C and above. The film sintered at 1000 °C for 30 min exhibited a dielectric constant of 1050 with a dielectric loss of about 0.05 measured at 1 kHz, a maximum polarization of 29 µC/cm2, a remnant polarization of 19 µC/cm2, and a coercive field of 21 kV/cm. This simple process to form PZT thick films may also be applied to the preparation of other multicomponent ceramics and ceramic films.
Retarded Cross-linking in ZnO-low-density Polyethylene Nanocomposites
Authors: Hong J.I. , Cho K. S. , Chung C. I. , Schadler L. S. , Siegel R. W.
Published: March 2008

ZnO nanoparticles were mixed with branched low-density polyethylene and were found to increase the resistance of the polymer to thermal degradation without changing other thermal properties. Submicron-size ZnO particles were mixed with low-density polyethylene for comparison, and it was found that the increased thermal stability of the nanocomposite was due to the surface properties of nanoparticles smaller than approximately 100 nm in diameter.
Polymorphism of Ti3SiC2
Authors: Yu R. , Zhan Q. , He L. L. , Zhou Y. C. , Ye H. Q.
Published: March 2008

We investigated the crystal structure of Ti3SiC2 by means of high-resolution electron microscopy (HREM). Two polymorphs, α– and β–Ti3SiC2, were identified. The amount of the α phase was larger than the β phase, indicating that the former has lower energy than the latter. We also found that the bright spots in HREM images of Ti3SiC2 do not necessarily correspond to the atomic columns; thus an intuitive interpretation of the image contrast in terms of the stacking sequences of the close-packed layers should be made cautiously
Upgrading the Triboluminescence of ZnS:Mn Film by Optimization of Sputtering and Thermal Annealing Conditions
Authors: Agyeman O. , Xu C. N. , Suzuki M. , Zheng X. G.
Published: March 2008

A statistical method of the design of experiments and analysis of variance (ANOVA) was used to obtain optimized sputtering conditions for oriented ZnS thin films doped with 5% manganese on glass substrates. The effects on the five sputtering factors—substrate temperature, radio frequency power, sputtering pressure, sputtering time, and pre-sputtering time—were simultaneously investigated by using the design of experiments and ANOVA. Through only 16 experiments, it was proved statistically at the 5% level that the substrate temperature was the only significant control factor. ZnS films were then deposited under the optimized sputtering conditions on fused quartz and thermally annealed in a reducing ambient (5% H2 diluted in Ar) at 500, 600, 700, and 800 °C. It was found that the crystallinity and triboluminescence intensity of the films were enhanced by postannealing up to 700 °C.
Contact Deformation Regimes Around Sharp Indentations and the Concept of the Characteristic Strain
Authors: Mata M. , Anglada M. , Alcalá J.
Published: March 2008

Finite element simulations are performed to analyze the contact deformation regimes induced by a sharp indenter in elastic – power-law plastic solids. As the yield strength (σys) and strain hardening coefficient (n) decrease or, alternatively, as Young's modulus (E) increases, the contact regime evolves from (i) an elastic–plastic transition, to (ii) a fully plastic contact response, and to (iii) a fully plastic regime where piling-up of material at the contact area prevails. In accordance with preliminary analyses by Johnson, it is found that Tabor's equation, where hardness (H) = 2.7σr, applies within the fully plastic regime of elastic – power-law plastic materials. The results confirm the concept of the uniqueness of the characteristic strain, ∈r = 0.1, that is associated with the uniaxial stress, σr. A contact deformation map is constructed to provide bounds for the elastic–plastic transition and the fully plastic contact regimes for a wide range of values of σ ys, n, and E. Finally, the development of piling-up and sinking-in at the contact area is correlated with uniaxial mechanical properties. The present correlation holds exclusively within the fully plastic contact regime and provides a tool to estimate σ ys and n from indentation experiments.
Photoluminescent Properties of Hydrogenated Amorphous Silicon Oxide Powders
Authors: Su Wei-Fang , Guo Hong-Ru
Published: March 2008

The photoluminescence properties of hydrogenated amorphous silicon oxide powder SiO0.92H0.53 were investigated. The powder was prepared by reacting lithium with trichlorosilane in tetrahydrofuran. The luminescence peak energy was located between 1.0 and 1.61 eV. The samples were treated under different conditions such as annealing, hydrolysis, and hydrolysis plus HF etching. The changes of the photoluminescent intensity and location on the treated powders can be explained by the electronic density of state model of amorphous semiconductors. The temperature dependence of luminescence properties of the powders can be described by the relationship of thermal quenching effect: ln[Io/I(T) – 1] = ED/Eo = T/To at temperatures between 100 and 300 K.
Interfacial Particle Bonding Via an Ultrathin Polymer Film on Al2O3 Nanoparticles by Plasma Polymerization
Authors: Shi Donglu , He Peng , Wang S. X. , Ooij Wim J. van , Wang L. M. , Zhao Jiangang , Yu Zhou
Published: March 2008

To study interfacial particle-to-particle bonding mechanisms, an ultrathin film of pyrrole was deposited on alumina nanoparticles using a plasma polymerization treatment. High resolution transmission electron microscopy experiments showed that an extremely thin film of the pyrrole layer (2 nm) was uniformly deposited on the surfaces of the nanoparticles. In particular, the particles of all sizes (10–150 nm) exhibited equally uniform ultrathin films indicating well-dispersed nanoparticles in the fluidized bed during the plasma treatment. Time-of-flight secondary ion mass spectroscopy experiments confirmed the nano-surface deposition of the pyrrole films on the nanoparticles. The pyrrole-coated nanoparticles were consolidated at a temperature range (approximately 250 °C) much lower than the conventional sintering temperature. The density of consolidated bulk alumina has reached about 95% of the theoretical density of alumina with only a few percent of polymer in the matrix. After low-temperature consolidation, the micro-hardness test was performed on the bulk samples to study the strength that was related to particle-particle adhesion. The underlying adhesion mechanism for bonding of the nanoparticles is discussed.
Microstructure and Mechanical Properties of SiC/zirconia-toughened Mullite Nanocomposites Prepared from Mixtures of Mullite Gel, 2Y-TZP, and SiC Nanopowders
Authors: Jin X. H. , Gao L. , Gui L. H. , Guo J. K.
Published: March 2008

SiC/ZTM (zirconia-toughened mullite) nanocomposites were prepared by hot pressing mixtures of mullite gel, 2Y-TZP, and SiC nanopowders. The intimate mixing of Al2O3 and SiO2 components in the starting powder prevented intermediate ZrSiO4 phase formation during sintering. Addition of nano-sized SiC significantly retarded the matrix grain growth, making the microstructure much finer and more uniform. Transmission electron microscopy and high-resolution transmission electron microscopy revealed that many SiC nanoparticles were found in mullite and ZrO2 grains, and low-energy grain boundaries and mullite–liquid interfaces parallel to the {110} planes of rodlike mullite grains were formed. It is deduced that the formation of rodlike mullite grains is the result of the preferential development of these low-energy grain boundaries and mullite–liquid interfaces. The mechanical properties of the SiC/ZTM nanocomposite showed significant improvement over those of ZTM, and further enhancement in the mechanical properties was achieved by combinative strengthening with nano- and micro-sized SiC.
Influence of Substrates on the Crystal Structure of Pulsed Laser Deposited Pb(Mg1/3Nb2/3)O3–29% PbTiO3 Thin Films
Authors: Lee Jung-Kun , Jung Hyun-Suk , Kim Dong-Wan , Kim Chang-Hoon , Hong Kug Sun
Published: March 2008

Lead magnesium niobate–lead titanate [Pb(Mg1/3Nb2/3)O3 (PMN)–PbTiO3 (PT)] films were synthesized using pulsed laser deposition, and the effect of substrates on the deposition behavior of the PMN–PT film was investigated. Phase evolution of PMN–PT thin films was found to depend significantly on the type of the substrate used during deposition. Though a mixture of pyrochlore and perovskite was observed when films were deposited on a Pt/TiO2/SiO2/Si substrate, the oxide substrates, such as (Ba0.5Sr0.5)RuO3/Si, SrTiO3, and LaAlO3, enabled the deposition of pure perovskite. Scanning Auger microprobe, transmission electron microscope, and x-ray diffraction analysis showed that an interfacial layer between the substrates and the oxide film was central to the phase evolution behavior. On the Pt/TiO2/SiO2/Si substrate, an interfacial layer of lead–platinum (Pb–Pt) played a major role in the formation of the pyrochlore phase. However, on oxide substrates, there was no interfacial layer and interdiffusion of A-site cations was observed between the PMN film and the oxide electrodes.
Microstructural Evolution in Nanocrystalline Ni Coatings
Authors: Lau M. L. , He J. , Melmed A. J. , Lusby T. A. , Schweinfest R. , Rühle M. , Lavernia E. J.
Published: March 2008

Gas-atomized Ni powders were mechanically milled under liquid nitrogen and subsequently sprayed using a high-velocity oxygen-fuel thermal spraying system. The resultant coatings were evaluated using various analytical methods, including scanning electron microscopy (SEM), transmission electron microscopy, and atom probe field ion microscopy (APFIM). The results indicated that the majority of the grains in nanocrystalline Ni coating were equiaxed with an average grain size of 50 ± 23 nm. SEM elemental dot mapping analysis suggested that oxide particles were distributed along the prior droplet boundaries and interpass boundaries in the coatings. The APFIM analysis indicated that the distribution of oxygen was very inhomogeneous in the nanocrystalline coating samples studied. Mostly small NiO precipitates with a size range of 1–7 nm were found throughout the grains, and the average size of these precipitates was approximately 4 nm. However, large oxide precipitates with a size up to 55 nm were also observed. In addition, increased amounts of oxygen were found at the grain boundaries and at structural defects.
Microstructure of Film Growth from Filtrating Mono-dispersed Particle Suspension
Authors: Zhang Feng , Chan Siu-Wai
Published: March 2008

The deposition mechanism that determines the microstructure of colloidal films was investigated using a constant-filtration-rate procedure. In particular, we studied the dependence of the grain size on the filtration rate and the volume fraction of the particles in liquid. We correlated the surface diffusion distance to the final grain size and identified a processing window for large-grain colloidal films. The necessary conditions for homoepitaxy of colloidal crystals were successfully identified. In particular, the surface diffusion distance of deposited particles before embedment emerged as an important parameter for film microstructural control. Sufficiently long the diffusion distances correlated well with the slow deposition rates often required for crystal growth. Low deposition rates allowed more time for depositing particles to sample surface sites for low-energy configurations. This surface diffusion model for microstructure control has universal application to other film deposition methods for mono-dispersed particles.
Properties of Porous AlN Multilayered Ceramic Sandwich Substrates
Authors: Boey F. Y. C. , Tok A. I. Y. , Long Y. , Yeong H. Y.
Published: March 2008

The development of denser and higher powered integrated circuits has led to a corresponding demand on the performance of dielectric substrates. This paper reports on the fabrication and properties of an AlN multilayered sandwich substrate comprising porous tape-cast layers sandwiched between nonporous layers. Tapes were produced by nonaqueous tape casting, with the porous tapes produced using polymer microspheres as sacrificial molds. Starting from initially Al2O3-rich tapes, the multilayered sandwich substrates were reaction sintered to produce AlN substrates. No interface cracking or delamination was observed in the substrates as a result of the processing. The added porosity resulted in a decrease in the substrate dielectric constant in correspondence to porosity volume. Mechanical strength of the sandwich substrates was improved over that of nonsandwich porous substrates, while substrates having noninterconnected pores showing higher mechanical strength than substrates with connected pores. Substrates with more than 2% porosity showed porosity-dependent thermal conductivity values, while thermal conductivity of substrates with less than 2% porosity was dependent on grain boundary effects. Thermal expansion coefficient of the substrates was unaffected by porosity levels.
Identification of Cl and Na Impurities in Inclusions of a Vapor-grown CdTe Doped with Zn and Cl
Authors: Corregidor V. , Babentsov V. , Fiederle M. , Feltgen T. , Benz K. , Dieguez E.
Published: March 2008

Morphology and analysis of composition of inclusions were done by secondary electron microscopy and spatially resolved energy-dispersive analysis of x-ray on semiintrinsic CdTe:Cl and CdTe:Zn:Cl crystals grown from the vapor phase by the modified Markov technique and on undoped CdTe crystals grown from the melt by the Bridgman method. In CdTe:Cl and CdTe:Zn:Cl crystals nonstoichiometric inclusions of about 10–20 μm were found, which contain high concentrations of Cl and Na impurities. The Cl is concentrated in small precipitates of 1–2 μm inside these inclusions. After short-time low-temperature annealing (600 °C), the inclusions mostly disappeared.
High-temperature Thermoelectric Properties of the Ca1-xBixMnO3 System
Authors: Xu Gaojie , Funahashi Ryoji , Matsubara Ichiro , Shikano Masahiro , Zhou Yuqin
Published: March 2008

Polycrystalline samples of Ca1-xBixMnO3 (0.02 ≤ x ≤ 0.20) were studied by means of x-ray diffraction, electrical resistivity (ρ), thermoelectric power (S), and thermal conductivity (κ) at high temperature. Bi doping leads to the lattice parameters a, b, and c increasing. And the ρ and the absolute value of S decrease rapidly with Bi doping. The largest power factor, S2/ρ, is obtained in the x = 0.04 sample, which is 3.6×10−4 Wm−1 K−2 at 400 K. The figures of merit (Z = S2/ρκ) for this sample and 1.0×10−4 and 0.86 × 10−4 K−1 at 600 and 1000 K, respectively.
Comparative Study of Single Crystals and Laser-grown Films of V2O5
Authors: Janicskó-Csáthy J. , Nagy A. , Nánai L. , Marine W. , Souto S. P. , Balkanski M. , George Thomas F.
Published: March 2008

Comparative investigations are carried out for spectral (Raman) electrical and structural properties of V2O5 single crystals and polycrystalline samples obtained by IR laser light illumination of pure metallic samples in an oxidizing atmosphere (air). It is shown that the structures grown on metallic plates in the field of laser light are predominantly V2O5 polycrystals. Raman measurements reveal that the main peaks, which are characteristic for single crystals, are also present in laser-driven samples but with different intensities. Some peaks are attributed to laser-grown thick films, which are not present in the single-crystalline phase. There are shifts in the peak positions indicating the existence of different force constants for films as compared with crystals. The activation energies obtained from the electrical properties (conductivity, impedance versus temperature) yield similar values except for the anisotropic characteristics of the single crystal where the values are a bit different along different crystallographic axes (unlike the polycrystalline oxide films made by the laser). The single-crystalline phase has a well-defined layered structure with well-defined shapes showing formed units of truncated oktaeders, while the film structure shows randomly distributed tubular micron-size structures with empty holes at the peripheral part of the irradiated area, and nanoscaled long and thin tubes well oriented along the direction of the incoming laser light in the central part of the irradiation spot.
Cracking in Ceramic/metal/polymer Trilayer Systems
Authors: Zhao Hong , Miranda Pedro , Lawn Brian R. , Hu Xiaozhi
Published: March 2008

Fracture and deformation in model brittle-outerlayer/metal-core/polymer-substrate trilayer systems in concentrated loading are studied. Model systems for experimental study are fabricated from glass microscope slides glued with epoxy adhesive onto steel and aluminum sheets, and the resulting laminates glued onto polycarbonate substrate bases. Critical loads to initiate two basic fracture modes in the glass layers—cone cracks at the top surfaces and radial cracks at the undersurfaces—are measured as a function of metal thickness byin situobservation through the glass side walls. Finite element modeling (FEM) is used to quantify these competing fracture modes. The more damaging radial fracture mode is attributed to flexure of the glass layers on soft underlayers. Although much of this flexure can be eliminated by removing the soft adhesive interlayer between glass and metal, yield in the metal limits the potential increases in critical load for radial cracking. Trilayer systems consisting of porcelain fused to Co-, Pd- and Au-alloy core support layers relevant to dental crowns are then analyzed by FEM. The hardness (especially) and elastic modulus of the metal are identified as the primary controlling material parameters, with modulus and strength of the brittle layer as supplemental parameters. Guidelines for improving metal-based crownlike layer structures are thereby developed via optimization of metal properties and relative layer thicknesses.
Crystal Structure of Dielectric Ceramics in the La(Mg0.5Ti0.5)O3–BaTiO3 System
Authors: Avdeev M. , Seabra M. P. , Ferreira V. M.
Published: March 2008

The crystal structure of microwave dielectric ceramics in the (1 − x)La(Mg0.5Ti0.5)O3 (LMT)–xBaTiO3 (BT) (0 ≤ x ≤ 0.9) system has been refined by Rietveld method using x-ray powder diffraction data. LMT and BT were found to form a solid solution in the whole compositional range. The increase of BaTiO3 content results in the following sequence of structure transformations of those solid solutions: P21/n (a−a−c+, B-site ordered) → Pbnm (a−a−c+) → I4/mcm (a0a0c−) → Pm3m (a0a0a0). These structural changes are related to the disappearance of B-site cation ordering (x > 0.1), in-phase tilting (x > 0.3), and antiphase tilting (x > 0.5), respectively.
Optical Absorption of Copper Nanoparticles Dispersed within Pores of Monolithic Mesoporous Silica
Authors: Liu Xiong , Cai Weiping , Bi Huijuan
Published: March 2008

Nano-sized copper particles are loaded into the pores of monolithic mesoporous silica by soaking and drying, followed by thermal reduction of copper nitrate [Cu(NO3)2]in a hydrogen atmosphere at 973 K for 90 min. It has been shown that copper nanoparticles are isolated from each other and highly uniformly dispersed inside the pores of silica. It is found that the surface plasmon resonance peak of the copper particles shows a significant red-shift with decreasing the particle size, which is in contrast to the corresponding fully embedded system. The peak decreases with exposure time to air and exhibits a linear relation with logarithmic exposure time. This red-shift phenomenon and decrease are explained on the basis of the structural features of this new composite or coexistence of local porosity and the nanoparticle's free surface in contact with air.
Filling of Chrysotile Nanotubes with Metals
Authors: Métraux C. , Grobéty B. , Ulmer P.
Published: March 2008

Nanowires were produced by injection of molten Hg and Pb into chrysotile nanotubes. The breakdown of chrysotile and the surface tension of the molten metals are the limiting factors for the filling procedure. The thermal stability of chrysotile nanotubes was investigated by infrared spectrometry, thermogravimetry, differential thermal analysis, and x-ray diffraction analyses. For short-term thermal annealing (30 min) the tube morphology remains stable up to 700 °C. The high surface tension of both molten Pb and Hg (γLV > 200 mN/m) requires external pressure for the melts to penetrate into the tubes. Filling of the tubes was achieved under high pressure and high temperature conditions compatible with the stability range for chrysotile determined in the annealing experiments. Transmission electron microscopy observations confirmed high filling yields for both metals. Almost all nanotubes were partially filled with lead. The length of continuous wires ranged from tens to hundreds of nanometers. Additional experiments with tin were not successful.
Formation of in situ Reinforced Microstructures in α-sialon Ceramics: Part II. In the Presence of a Liquid Phase
Authors: Peng Hong , Shen Zhijian , Nygren Mats
Published: March 2008

In situ reinforced microstructures with well-dispersed elongated grains, up to 10 μm in length, embedded in matrices consisting of submicron equiaxed grains, were developed by hot pressing Y-, Yb-, and (Y + Yb)-doped a-sialon ceramics containing approximately 3 vol% extra liquid phase at a comparatively low sintering temperature, 1800 °C. The liquid phase, thermodynamically compatible with a-sialon, was introduced by raising the oxygen content of an already oxygen-rich α-sialon composition, e.g., by increasing the O/N ratio in RExSi12-(3x+n) Al3x+nOnN16−n. Two different α–Si3N4 precursor powders, one fine-grained and one coarse, and one coarse β–Si3N4 powder were used, and the influence of particle size and crystalline modification of the precursor Si3N4 powder on the formation of elongated a-sialon grains was investigated. The formation of elongated α-sialon grains was promoted by introducing an extra liquid phase and by using a fine-grained α–Si3N4 powder, whereas the coarse β–Si3N4 powder did not yield any elongated grains at all. The obtained in situ reinforced α-sialon ceramics were both hard and tough, with a Vickers hardness and a fracture toughness of 21 GPa and approximately 5 MPa m1/2, respectively.
Simplified Area Function for Sharp Indenter Tips in Depth-sensing Indentation
Authors: Thurn Jeremy , Cook Robert F.
Published: March 2008

A two-parameter “area function” characterizing the depth-dependent projected area of an indenter was introduced and applied to a Berkovich tip. The two parameters have physical meaning, corresponding to the effective tip radius and effective cone angle. The indenter tip was calibrated on a commercial load-controlled Nano Indentert® XP (MTS Systems Corp., Eden Prairie, MN). All calibrations were carried out using the procedure of Oliver and Pharr [J. Mater. Res. 7, 1564 (1992)] using several homogeneous materials. Plane-strain modulus and hardness values deconvoluted from indentation load–displacement traces using the calibrated two-parameter area function compared well with the values determined using the empirical eight-parameter area function of Oliver and Pharr.
Wet Synthesis and Characterization of MSe (M = Cd, Hg) Nanocrystallites at Room Temperature
Authors: Yang Qing , Tang Kaibin , Wang Chunrui , Zhang Chunjuan , Qian Yitai
Published: March 2008

Semiconductor selenides of MSe (M = Cd, Hg) nanocrystalline powders were synthesized through the reactions between metal chlorides and sodium selenosulfate in the ammoniacal aqueous solution at room temperature for 6–10 h. The samples were characterized by x-ray powder diffraction, transmission electron microscopy, electron diffraction, x-ray photoelectron spectroscopy, and elemental analysis. The average diameters of CdSe and HgSe nanocrystallites are 4 and 8 nm, respectively. The storage and an interesting phase transition under hydrothermal conditions have been presented. The absorption spectrum of the as-prepared samples exhibits obvious blue shift due to the size confinement.
Highly Ordered Nanoporous Alumina Films: Effect of Pore Size and Uniformity on Sensing Performance
Authors: arghese Oomman K. , Gong Dawei , Paulose Maggie , Ong Keat G. , Grimes Craig A. , Dickey Elizabeth C.
Published: March 2008

The effect of pore size and uniformity on the humidity response of nanoporous alumina, formed on aluminum thick films through an anodization process, is reported. Pore sizes examined range from approximately 13 to 45 nm, with a pore size standard deviations ranging from 2.6 to 7.8 nm. The response of the material to humidity is a strong function of pore size and operating frequency. At 5 kHz an alumina sensor with an average pore size of 13.6 nm (standard deviation 2.6 nm) exhibits a well-behaved change in impedance magnitude of 103 over 20% to 90% relative humidity. Increasing pore size decreases the humidity range over which the sensors have high sensitivity and shifts the operating range to higher humidity values. Cole–Cole plots of 5 to 13 MHz measured impedance spectra, modeled using equivalent circuits, are used to resolve the effects of water adsorption and ion migration within the adsorbed water layer. The presence of impurity ions within the highly ordered nano-dimensional pores, accumulated during the anodization process, appear highly beneficial for obtaining a substantial variation in measured impedance over a wide range of humidity values.
Effect of Silver on Superplastic Deformation in YBa2Cu3O7–x/Ag Composites
Authors: Yun Jondo , Chou Ye T. , Harmer Martin P.
Published: March 2008

Superplastic deformation was studied in fine-grained (0.7–1.1 μm) YBa2Cu3O7–x/Ag composites containing 2.5–25 vol% Ag. The compression tests were conducted in the temperature range of 750–875 °C and at strain rates of 10−5 to 10−3/s. For the YBa2Cu3O7−x/25%Ag composites with grain size of 0.7–1.1 μm, deformed at 800–850 °C and 10−5 to 10−3/s, the stress exponent, grain size exponent, and the activation energy of deformation were 2.0 ± 0.1, 2.5 ± 0.7, and 760 ± 100 kJ/mol, respectively. These values were the same as those of the pure YBa2Cu3O7−x, indicating that the deformation of the composite was controlled by that of the rigid YBa2Cu3O7−x phase. However, the strain rate was increased by the addition of silver as explained by the soft inclusion model of Chen. The dependence of the flow stress on the silver content was in close agreement with the prediction of the model.
Bi2O3 Solubility of Bi-based Pyrochlores and Related Phases
Authors: Nino Juan C. , Youn Hyuk J. , Lanagan Michael T. , Randall Clive A.
Published: March 2008

Bismuth oxide solubility in Bi2O3–ZnO–Nb2O5 and Bi2O3–MgO–Nb2O5 (BMN) pyrochlore systems was investigated and the solubility limits were identified. Differences in the solubility behavior between the two Bi-pyrochlore systems investigated were analyzed and explained through crystal chemistry concepts. For the BMN system, the dielectric constant was enhanced, and a systematic shift occurred in the dielectric relaxation loss peak to higher temperatures with increases in the excess bismuth are reported in the BMN system. The relationship between solubility and the shift in the dielectric loss curve was analyzed under the scope of possible relaxation mechanisms.
Effect of Buffer on the Optical Properties of Irradiated Hydroxyethyl Methacrylate Copolymer
Authors: Chou K. F. , Han C. C. , Lee Sanboh
Published: March 2008

The effect of buffer and γ irradiation on the optical properties of hydroxyethyl methacrylate (HEMA) copolymer was investigated. The transmission of HEMA copolymer decreased with the increase of irradiation dose and/or pH value of the buffer. The cutoff wavelength of HEMA copolymer exhibits a bathochromic shift as the γ-ray dose and/or pH value of buffer increases. The influence of atmosphere during γ-ray irradiation on the optical properties of HEMA copolymer was investigated. The change of optical properties of HEMA copolymer irradiated in air was more pronounced than that irradiated in vacuum. Light was scattered by holes in the polymer. The relationship between scattering intensity (Is) and incident wavelength (λ) can be described by the formula Is ∝ λ−n. The span of holes increases with the irradiation dose regardless of radiation atmosphere and pH value in the range of 4.1–6.5. A boundary between the inner and outer layers of HEMA copolymer irradiated in air was observed, separating two differential morphologies of holes.
Novel Ferroelectric Ceram-glass of [(SrO)(y)(BaO)(1−y)(Nb2O5)](1−x) Tellurite
Authors: Kortan A. R. , Kopylov N. , Greene B. I. , Glass A. M.
Published: March 2008

We report a new SBN-tellurite ceram-glass system, where the [(SrO)(y)(BaO)(1−y) (Nb2O5)](1−x) (SBN) ferroelectric crystallites precipitate on a tellurite (TeO2)x glass surface with nominal compositions x < 0.8 and y = 0.6 to 0.75. X-ray diffraction, calorimetry, and electro-optic measurements confirmed the ferroelectric nature of the SBN crystallites. In principle, this system has the potential for high transparency and the property tunability to match the application needs of optical devices.
Translucent Ceramics of 12CaO · 7Al2O3 with Microporous Structure
Authors: Hayashi Katsuro , Hirano Masahiro , Hosono Hideo
Published: March 2008

We examined the densification of 12CaO · 7Al2O3 (C12A7), which has a microporous lattice framework with a cavity of approximately 0.4 nm. Fully densified translucent ceramics are obtained when hydrated C12A7 powders prepared as precursors are sintered in a dry oxygen atmosphere at 1300 °C. The average transmittance between 400–800 nm for 1-mm-thick samples is improved up to approximately 70% with a 48-h increase in the sintering time. Dissociation of water molecules at the grain–pore interface into grains which entraps hydroxide ions in the crystallographic cage, and the release of the hydroxide ions into the atmosphere during the sintering procedure are considered to play crucial roles in the pore-annihilation processes.
Self-affine Fracture Surface Parameters and Their Relationship with Microstructure in a Cast Aluminum Alloy
Authors: Hinojosa M. , Aldaco J.
Published: March 2008

The possible role of microstructural features in determining the self-affinity of the fracture surface of a cast aluminum alloy is explored in this work. Fracture surfaces generated both in tension and impact tests were topometrically analyzed by atomic force microscopy, scanning electron microscopy, and stylus profilometry. The roughness exponent exhibited the “universal” value ζ ≈ 0.78, and the correlation length ζ was of the order of the grain size. The brittle intermetallic compounds known to be important in crack initiation did not show any correlation with the self-affine parameters of the resulting fracture surfaces in this particular case.
Hot-stage Transmission Electron Microscopy Study of Phase Transformations in Hexacelsian (BaAl2Si2O8)
Authors: Xu Zhengkui , Shull James L. , Kriven Waltraud M.
Published: March 2008

Phase transformations in synthetic hexacelsian were investigated by hot-stage transmission electron microscopy. A second phase transformation from an orthorhombic to hexagonal structure was identified in the synthetic hexacelsian at approximately 700 °C. The hexacelsian was found to exhibit a sequence of phase transformations on heating of hexagonal (P63/mcm)–orthorhombic (Immm)–hexagonal (P6/mmm). Antiphase domain boundaries, which were observed in P63/mcm and Immm phases, were absent in the P6/mmm phase. Crystal symmetries of the three phases were determined by convergent beam electron diffraction, and space group symmetries were derived by comparison of experimental selected area electron diffraction patterns with computer-simulated patterns.
Nanocrystalline SnO2 Particles and Twofold-coordinated Sn Defect Centers in Sol-gel-derived SnO2–SiO2 Glasses
Authors: Hayakawa Tomokatsu , Enomoto Takehiro , Nogami Masayuki
Published: March 2008

Semiconductive nanocrystals of stannic oxide (SnO2) were precipitated in silica (SiO2) glasses synthesized via a sol-gel route. Kayanuma's equation, which describes the quantum confinement of an electron–hole pair in a semiconductive particle, well explained the absorption-edge shift due to the SnO2 nanocrystals in the optical absorption spectra. The adequate anneal of the SnO2–SiO2 glass ceramics in H2 gas led to the decomposition of the SnO2 nanocrystals and concurrently the production of twofold-coordinated tin atoms (Sn20 ) that provided a violet photoluminescence. The thermal behavior was studied with the x-ray diffraction measurement and photoluminescence and photoluminescence excitation spectroscopy.
Hydrogen Absorption of Nanoscale Pd Particles Embedded in ZrO2Matrix Prepared from Zr–Pd Amorphous Alloys
Authors: Yamaura Shin-Ichi , Sasamori Ken-Ichiro , Kimura Hisamichi , Inoue Akihisa , Zhang Yue Chang , Arata Yoshiaki
Published: March 2008

Nanocomposite materials consisting of ZrO2and Pd phases were prepared by heating the amorphous Zr65Pd35alloy for 24 h at 553 K in air. The maximum hydrogen absorption amount is about 2.4 mass% (H2/Pd) at 323 K and 2.2 mass% (H2/Pd) at 423 K at hydrogen pressure of 1 MPa. The absorption amount of Pd nanoparticles in the nanocomposite is a few times larger than those for the bulk and powder Pd metals. The remarkable increase in the hydrogen absorption/desorption amounts seems to result from the isolated dispersion state of Pd nanoparticles in the ZrO2phase containing a tremendously large interface area in the nanocomposite.
Thermally-induced Crack Healing in Poly(Methyl Methacrylate)
Authors: Shen Jane-Sang , Harmon Julie P. , Lee Sanboh
Published: March 2008

A microscopic theory of thermally induced crack healing in poly(methyl methacrylate) is presented. Both laser-induced cylindrical cracks and knife-induced surface cracks were analyzed. For a given temperature, the crack closure rate was constant for both types of cracks. However, the crack closure rate was lower for samples with cylindrical cracks than for those with surface cracks. The former exhibited higher activation energy for crack closure than the latter, because the knife-induced cracks had sharper crack tips. Fracture stress was proportional to surface crack healing time to the one-fourth power for thermal healing at a given temperature. Based on the reptation model of polymer chains, the activation energy of chain diffusion was calculated. The healing process was monitored via fractography and crack closure was confirmed. The results were compared with solvent healing and thermal healing in the literature.
Effects of Postdeposition in situ Heat Treatment on the Properties of Low Dielectric Constant Plasma Polymer Films Deposited Using Decahydronaphthalene and Tetraethyl Orthosilicate as the Precursors
Authors: Yang Jaeyoung , Shim Cheonman , Jung Donggeun
Published: March 2008

We investigated effects of postdeposition heat treatment (HT) on the properties of plasma polymer films deposited by plasma-enhanced chemical vapor deposition using a mixture of decahydronaphthalene and tetraethyl orthosilicate as the precursors, which were referred to as plasma-polymerized decahydronaphthalene:tetraethyl orthosilicate (PPDHN:TEOS) films. HTs at 350, 450, and 500 °C decreased the relative dielectric constant k of the PPDHN:TEOS films from 3.16, the k value of the as-deposited film, to 2.82, 2.72, and 3.02, respectively. The change of k value as a function of HT temperature was correlated with the change of Fourier transform infrared absorption peaks of O–H, C = O, and Si-related groups. As the HT temperature increased, the thermal stability of the PPDHN:TEOS film increased. PPDHN:TEOS films, as-deposited or heat treated, showed leakage current density in the order of 10−7 A/cm2 at 1 MV/cm.
Piezoelectric Properties of SrBi4Ti4O15 Ferroelectric Ceramics
Authors: Maeder Marlyse Demartin , Damjanovic Dragan , Voisard Cyril , Setter Nava
Published: March 2008

The dynamic piezoelectric response of SrBi4Ti4O15 ceramics with Aurivillius structure was investigated at high alternating stress, low frequencies (0.01 to 100 Hz), and temperatures from 20 to 200 °C. The piezoelectric nonlinearity, observed only at high pressures (>10 MPa) and elevated temperatures (>150 °C), is interpreted in terms of contributions from non-180° domain walls. At weak fields, the frequency dependence of the longitudinal piezoelectric coefficient was explained in terms of Maxwell–Wagner piezoelectric relaxation. The Maxwell–Wagner units are identified as colonies that consist of highly anisotropic grains which sinter together, and whose distribution in the ceramic is strongly dependent on sintering conditions.
Stability of ZrTiCuNiBe Bulk Metallic Glass upon Isothermal Annealing Near the Glass Transition Temperature
Authors: Wang Wei Hua , Wang Ru Ju , Yang W. T. , Wei B. C. , Wen P. , Zhao D. Q. , Pan M. X.
Published: March 2008

The stability of Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) upon isothermal annealing near the glass transition temperature has been investigated by using x-ray diffraction, differential scanning calorimetry, and the pulse echo overlap method. The density, elastic constants, and thermodynamic parameters as well as their annealing time dependence have been determined. The microstructural and properties changes of the annealed BMG were checked by acoustic measurement. Obvious structural and property changes were observed with prolonged annealing of the BMG near the glass transition temperature.
Chemical Synthesis of Crystalline, Pure or Mn-doped ZnGa2O4Powders at 90 °C
Authors: Tas A. Cuneyt , Majewski Peter J. , Aldinger Fritz
Published: March 2008

Crystalline, pure or Mn-doped ZnGa2O4powders have been preparedin situin urea (with or without enzyme urease)-containing Zn and Ga nitrate (and Mn nitrate) solutions by simply holding those for 24–48 h, at 90 °C, in screw-capped glass bottles in a constant-temperature laboratory oven. Single-phase pure or Mn-doped zinc gallate powders synthesized with the spinel crystal structure had an average particle size around 15 to 18 nm. Powders were characterized by x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, inductively-coupled plasma atomic emission spectroscopy, simultaneous thermogravimetry and differential thermal analysis, Fourier-transformed infrared spectroscopy, and carbon and nitrogen analyses. Calcination behavior of the as-filtered powders was later studied in an air atmosphere over the temperature range of 90 to 1200 °C.
Pressure Distribution During Binder Burnout in Three-dimensional Porous Ceramic Bodies with Anisotropic Permeability
Authors: Lombardo Stephen J. , Feng Z. C.
Published: March 2008

The flow of gas-phase products in three-dimensional porous bodies was modeled for the case when a source term is present. Analytical solutions to the governing partial differential equations were obtained for bodies of parallelepiped and cylindrical geometry. An important feature of the model is that it treats the case where the permeability in the body may be anisotropic. The evolution of pressure within the body depends on a number of parameters, including the rate of production of gas-phase species, and on the dimensions of the body. The model is thus able to describe the pressure within a porous ceramic body arising from flow during a number of elevated-temperature processing operations such as drying, binder burnout, and sintering.
Deformation and Failure of Zr57Ti5Cu20Ni8Al10 Bulk Metallic Glass Under Quasi-static and Dynamic Compression
Authors: Hufnagel T. C. , Jiao T. , Li Y. , Xing L-Q. , Ramesh K. T.
Published: March 2008

We have examined the mechanical behavior of Zr57Ti5Cu20Ni8Al10 bulk metallic glass under uniaxial compression at strain rates from 10−4to 3 × 103 s−1. The failure stress decreases with increasing strain rate, and shear-band formation remains the dominant deformation mechanism. A consideration of basic properties of adiabatic shear bands makes it appear unlikely that shear bands formed under quasi-static loading are adiabatic; in the dynamic case, the time scales of deformation and thermal conduction are similar, indicating that a more sophisticated calculation is required. In the dynamic tests, however, high-speed cinematography reveals evidence that the mechanism of failure involves an adiabatic component.
Dissolution Kinetics of Spinel Lithium Manganate and its Relation to Capacity Fading in Lithium Ion Batteries
Authors: Lu Chung-Hsin , Lin Shang-Wei
Published: March 2008

The dissolution behavior and kinetics of spinel lithium manganate LiMn2O4 with different particle sizes have been investigated in this study. The dissolution of manganese cations from LiMn2O4 is confirmed to occur when LiMn2O4 particles are immersed in the electrolytes. The amount of dissolved manganese ions markedly increases with a rise in temperature and a decrease in particle size, which implies that the capacity fading of LiMn2O4 at elevated temperatures is associated with manganese dissolution. On the basis of the isothermal analysis of reaction kinetics, the rate of manganese dissolution from LiMn2O4 is dominated by the rate of dissolution reaction. Smaller particles exhibit a larger reaction rate constant and higher activation energy of the dissolution process than the larger ones. Therefore, an increase in temperature has a more pronounced effect on the dissolution reaction of small particles than on that of large particles.
Aerosol-gel-derived Microcrystalline Hydroxyapatite Coatings
Authors: Manso M. , Martínez-Duart J. M. , Langlet M. , Jiménez C. , Herrero P. , Millon E.
Published: March 2008

Highly porous microcrystalline hydroxyapatite (HAP) coatings have been prepared from calcium nitrate and phosphoric acid based sols by the aerosol-gel process. The coatings were studied after sintering at different temperatures with the use of Fourier transform infrared spectroscopy, x-ray diffraction, energy disperse x-ray microanalysis, scanning electron microscopy, and transmission electron microscopy. The composition, structure, and morphology of the coatings sintered at 650 °C fit fairly well highly porous HAP. These coatings were reproduced onto TiO2/Si substrates and studied by Rutherford backscattering. It is shown that even after chemical etching, an adherent calcium phosphate phase remains attached to the TiO2/Si substrate.