bluuebunny/crossref_metadata_2025 huggingface dataset:
The preparation of metal–polymer composite materials using ultrasound radiation: Part II. Differences in physical properties of cobalt–polymer and iron–polymer composites
Authors: Wizel S. , Margel S. , Gedanken A. , Rojas T. C. , Fernández A. , Prozorov R.
Published: March 2008

Composite materials containing amorphous iron embedded in poly(methylacrylate) or poly(methylmethacrylate) and amorphous cobalt embedded in poly(methylacrylate) were formed using a sonochemical method. The physical and thermal properties of the composite materials were probed. A significant difference in the solubility of the iron–poly(methylacrylate) and cobalt–poly(methylacrylate) in various solvents was observed. This difference is accounted for by the stronger interaction existing between the cobalt and the surrounding polymer. For iron–poly(methylacrylate) this interaction is weakened due to the formation of an iron complex.
Preparation of nanocrystalline titania powder via aerosol pyrolysis of titanium tetrabutoxide
Authors: Ahonen P. P. , Kauppinen E. I. , Joubert J. C. , Deschanvres J. L. , Tendeloo G. Van
Published: March 2008

Nanocrystalline titanium dioxide was prepared via aerosol pyrolysis of titanium alkoxide precursor at 200–580 °C in air and in nitrogen atmospheres. Powders were characterized by x-ray diffraction, thermogravimetric analysis, Brunauer–Emmett–Teller analysis, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, x-ray fluorescence, Raman and infrared spectroscopy, and Berner-type low-pressure impactor. The anatase phase transition was initiated at 500 °C in nitrogen and at 580 °C in air. Under other conditions amorphous powders were observed and transformed to nanocrystalline TiO2 via thermal postannealing. In air, smooth and spherical particles with 2–4-μm diameter were formed with an as-expected tendency to convert to rutile in the thermal postannealings. In nitrogen, a fraction of the titanium tetrabutoxide precursor evaporated and formed ultrafine particles via the gas-to-particle conversion. At 500 °C thermally stable anatase phase was formed in nitrogen. A specific surface area as high as 280 m2 g−1 was observed for an as-prepared powder.
Reaction synthesis of mullite–silicon carbide–yttria-stabilized zirconia composites
Authors: Lin Yung-Jen , Chen Lee-Jen
Published: March 2008

SiC/mullite/zirconia composites were fabricated by controlling the oxidation of powder compacts of SiC, alumina, and 3 mol% yttria-stabilized zirconia. The powder compacts were first oxidized in air at 1100 °C for various times to obtain proper amounts of amorphous silica. Subsequent reaction sintering at 1500 °C for 2 h combined the amorphous silica with alumina to form mullite with planned amounts. The incorporation of 3 mol% yttria-stabilized zirconia promoted mullite formation and enhanced the densification of the samples. With ≥10 vol% of 3 mol% yttria-stabilized zirconia in the samples, the temperature of mullite formation was lowered from 1400 to 1300 °C, and mullitization was near completion after sintering at 1500 °C for 2 h. The densification of the samples depended on the contents of SiC and 3 mol% yttria-stabilized zirconia. Samples with 20 vol% SiC and 10–20 vol% 3 mol% yttria-stabilized zirconia could be sintered to reach approximately 97% of theoretical density after sintering at 1500 °C for 2 h.
Epitaxial growth of PbZr0.5Ti0.5O3 thin films on (001) LaAlO3 by the chemical solution deposition method
Authors: Kim J. H. , Lange F. F.
Published: March 2008

Epitaxial PbZr0.5Ti0.5O3 (PZT) thin films were grown on (001) LaAlO3 substrates (∼6.1% lattice mismatch) by the chemical solution deposition method. The sequence of epitaxy during heating between 375 and 700 °C/1h was characterized by x-ray diffraction and transmission electron microscopy. At approximately 375 °C/1h, a nanocrystalline metastable fluorite phase of PZT was formed from the pyrolyzed amorphous precursor. At higher temperatures (400–425 °C/1h), thermodynamically stable PZT crystallites were first observed at the interface; with increasing higher temperatures, these nuclei grew across the interface and through the film toward the surface by consuming the metastable nanocrystalline fluorite grains. PZT thin films annealed above ∼500 °C/1h were observed to be dense with an epitaxial orientation relationship of [100](001)PZT‖[100](001)LAO. The metastable nanocrystalline fluorite to the stable single-crystal perovskite transformation gives an extra driving force by providing an additional decrease in free energy in addition to a driving force from the elimination of grain boundary area for epitaxy.
Dislocations emission and crack extension at the atomistic crack tip in body-centered-cubic metal Mo
Authors: Tang Qiheng , Wang Tzuchiang
Published: March 2008

The behaviors of a crack in body-centered-cubic metal Mo under different loading modes were studied using the molecular dynamics method. Dislocation emission was observed near the crack tip in response to mode II loading with θ = 0° in which θ is the inclination angle of the slip plane with respect to the crack plane, and two full dislocations were observed at the stress level ofKII= 1.17 MPa m1/2without any evidence of crack extension. Within the range of 0° ≤ θ ≤ 45°, crack extension was observed in response to mode I loading, and the effect of crystal orientation on the crack propagation was studied. The crack propagated along the [111] slip direction without any evidence of dislocations emission.
Reduction of copper oxide with graphite by mechanical alloying
Authors: Liu L. , Zhang T. J. , Cui K. , Dong Y. D.
Published: March 2008

The reduction of CuO with different amounts of C (CuO:C = 2:1, 2:1.5, and 2:2 molar ratios) driven by mechanical alloying was examined by x-ray diffraction and transmission electron microscopy. It was found that reduction behaviors are closely related to the carbon content. The reduction of CuO for the mixture with 1 mol of carbon follows a two-step process; i.e., CuO → Cu → Cu2O. However, the CuO can be completely converted to Cu for the mixtures with higher carbon content. A tentative model in terms of solid-state reactions at the interfaces is proposed to explain the effect of carbon content. Additionally, the thermal responses of the premilled mixtures were investigated by thermogravity and differential thermal analysis followed by x-ray identification. Contrary to mechanical alloying, reduction of CuO during thermal treatment follows a transition sequence of CuO → Cu2O → Cu. The preferential formation of Cu2O at the early annealing stage is probably due to the involvement of gaseous reduction.
Pyramidal indentation load–depth curve of viscoelastic materials
Authors: Shimizu S. , Yanagimoto T. , Sakai M.
Published: March 2008

The indentation load P versus depth h curves are examined to investigate the time-dependent surface deformation of viscoelastic materials. The viscoelastic P–h curves significantly depend on the temperature of measurement and the penetration rate of indentation. Sneddon's elastic solution of a conical indentation is extended to a viscoelastic one for a conical or a pyramidal indentation in terms of the hereditary integral. Several types of viscoelastic problems are discussed in relation to the test techniques and analyses for determining the relaxation modulus E(t) and the creep compliance D(t). The superposition rules of time–temperature, penetration depth–temperature, and penetration depth–penetration rate are examined. The viscoelastic indentation tests (constant rate penetration test and constant load creep test) of amorphous Se are conducted at temperatures from 10 to 42 °C. The theoretical considerations and the test results encourage pyramidal indentation as an efficient microprobe for the viscoelastic characterization, in particular, of extremely small-size test specimens and ceramic, metal, and polymer thin films coated on substrate.
Sintering characteristics of Y–Ba–Cu–oxide–Agx superconductors
Authors: Pathak L. C. , Mishra S. K. , Bhattacharya D. , Chopra K. L.
Published: March 2008

The sintering characteristics of Y–Ba–Cu–oxide (YBCO)–Agx (x = 0 to 1.2) using thermomechanical analyzer were systematically investigated to understand the sintering mechanism of the metal superconductor composites. The addition of Ag was observed to lower the sintering temperatures, and the apparent densities of the sintered compacts increased with x from 0 to 0.6. A further increase of x above 0.6 decreased the apparent densities of the sintered compacts. The presence of Ag globules in the YBCO–Ag compacts was observed by scanning electron microscopy and energy dispersive x-ray spectroscopy. The apparent activation energies for sintering of the powder compacts were estimated and observed to vary between 900 to 2000 kJ/mol. The formation of AgOx by absorbing oxygen from YBCO and sintering atmosphere possibly controls the sintering and superconducting behavior. Incorporation of Ag into the matrix modifies the weak-link characteristics from superconductor–insulator– normal–superconductor (S–I–N–S) to superconductor–normal–superconductor (S–N–S) type.
Investigation of optical anisotropy of refractive-index-profiled porous silicon employing generalized ellipsometry
Authors: Zangooie S. , Jansson R. , Arwin H.
Published: March 2008

Porosity depth profiles in porous silicon were realized by time modulation of the applied current density during electrochemical etching of crystalline silicon. The samples were investigated by variable angle spectroscopic ellipsometry. Using a basic optical model based on isotropy assumptions and the Bruggeman effective medium approximation, deviations from an ideal profile in terms of an interface roughness between the silicon substrate and the porous silicon layer and a compositional gradient normal to the surface were revealed. Furthermore, optical anisotropy of the sample was investigated by generalized ellipsometry. The anisotropy was found to be uniaxial with the optic axis tilted from surface normal by about 25°. The material was also found to exhibit positive birefringence.
Evolution of microstructure and phases inin situprocessed Ti–TiB composites containing high volume fractions of TiB whiskers
Authors: Sahay S. S. , Ravichandran K. S. , Atri R. , Chen B. , Rubin J.
Published: March 2008

A series of titanium composites, with varying volume fractions of titanium monoboride (TiB) whiskers, were made by mixing various proportions of titanium (Ti) and titanium diboride (TiB2) powders followed by hot pressing. The phases present were identified by x-ray diffraction. Microstructural examination revealed three different types of TiB whisker morphologies: (i) long and needle-shaped TiB whiskers that are isolated and randomly oriented in the Ti matrix at relatively low volume fractions (0.3), (ii) colonies of refined and densely packed TiB whiskers from intermediatevolume (0.55) to high volume (0.73 and 0.86) fractions, and (iii) coarse and elongated TiB particles with a few needle-shaped whiskers at the highest volume fraction (0.92). In all the composites, TiB was found to be the predominant reinforcement. However, in Ti–TiB composites with 0.86 and 0.92 volume fractions of TiB, a significant amount of TiB2was also present. The relative volume fractions of Ti, TiB, and TiB2phases were estimated from the integrated intensities of diffraction peaks by the direct comparison method employing the calculated structure factors and Lorentz polarization factors. The composite microstructure, as well as the evolution of different morphologies, of TiB whiskers is discussed.
Infiltration of C/SiC composites with silica sol-gel solutions: Part II. Infiltration under isostatic pressure and oxidation resistance
Authors: Aparicio Mario , Durán Alicia
Published: March 2008

An infiltration process that uses silica sol-gel solutions was developed to protect C/SiC composites against oxidation. The infiltration is assisted using isostatic pressure. Different process parameters including substrate porosity and solution concentration and viscosity were varied to optimize the infiltration effectiveness. Applied pressure enhances penetration of solutions, reducing the importance of viscosity, an important process variable for dipping infiltration. The effectiveness of the isostatic pressure infiltration method, evaluated through the total weight gains and pore-size distribution of infiltrated samples, is compared with results of dipping infiltration. The oxidation behavior of the infiltrated samples, was evaluated by stepwise oxidation test as well as isothermal tests at 1200 and 1600 °C. The infiltrated SiO2 protects the C/SiC substrate, reducing the burnoff rate of C fibers at low temperature and delaying the oxidation of SiC.
Reactive hot pressing of aluminum matrix composites
Authors: Brinkman H. J. , Duszczyk J. , Katgerman L.
Published: March 2008

A method is described for the production of dense aluminum matrix composites from elemental powders in one processing step by reactive hot pressing (RHP). It encompasses both the exothermic conversion of reactants to composite product and the following hot compaction of the porous composite product. The RHP method described in this paper takes into account the gas evolution accompanying the exothermic process, ensures complete conversion of reactants, and avoids adverse reactions between aluminum matrix and graphite tooling material. In situ sample temperature measurements enable proper process control, in particular the timing of the full densification step of the hot reaction product.
Effect of substituents with different valences on antiferroelectric stability of antiferroelectric lead zirconate ceramics
Authors: Tan Qi , Xu Z. , Viehland Dwight
Published: March 2008

The effect of lower valent substituents on the stability of the antiferroelectric phase of lead zirconate was studied by dielectric spectroscopy, Sawyer–Tower polarization methods, and electron diffraction techniques. The stability of an intermediate ferroelectric phase region was found to be enhanced with increasing lower valent substitution concentration. The influences of substituents of different ionic size and valence on the stabilization of the intermediate ferroelectric phase were differentiated. In general, lower valent substituents, such as K+ and Fe3+ affected antiferroelectric phase stability more significantly than higher valent ones.
Processing and microwave dielectric properties of barium magnesium tantalate ceramics for high-quality-factor personal communication service filters
Authors: Ra Seung-Hyun , Phulé Pradeep P.
Published: March 2008

A modified route, based on calcined MgO, Ta2O5, BaCO3, and ZrO2, was developed and used for preparation of barium magnesium tantalate (BMT) and barium zirconate (BZ)-doped BMT ceramics (BZ-BMT). The dielectric constant for BMT ceramics sintered at 1600 °C for 2 h was 24.9 at 7.28 GHz. The average long-range ordering parameter for undoped BMT ceramics was 0.81 ± 0.03 and the coresponding average quality factor and resonant frequench product (Qd · fo) was 147,000 ± 3800 GHz. A significant level of B-site long-range cation disorder was introduced as a result of BZ doping of BMT ceramics. The average ordering parameters for 3 and 4 mol% BZ-doped BMT were found to be 0.69 ± 0.06 and 0.49 ± 0.13, respectively. The decrease in ordering parameters did not lead to a dramatic decrease in the corresponding average quality factors of 3 mol% BZ-BMT (Qd · fo = 127,000 ±3800 GHz) and 4 mol% BZ-BMT (Qd · fo = 139,000 ± 4200 GHz). The results suggest that the B-site cation ordering is not a primary factor that influences the observed microwave loss in BMT ceramics. The influence of atomic level point defects, induced from raw material impurities, processing, etc., may be more important in controlling the quality factor of BMT ceramics.
Si3N4–TiN–Y2O3 ceramics derived from chemically modified perhydropolysilazane
Authors: Iwamoto Yuji , Kikuta Ko-ichi , Hirano Shin-ichi
Published: March 2008

[Si–Y–Ti–O–C–N] multicomponent powders were synthesized by pyrolysis at 1000 °C, in NH3 flow, of chemically modified perhydropolysilazane using yttrium triisopropoxide and titanium tetrachloride. [Si–Y–Ti–O–C–N] powders yielded uniform and fine-grained Si3N4–TiN–Y2O3 ceramics by heat treatment at 1800 °C in N2. The fully densified Si3N4–TiN–Y2O3 ceramics were also synthesized by heat treatment at 1800 °C, followed by powder-vehicle hot pressing at 1800 °C in N2. The resulting ceramics revealed that TiN was dispersed as particles having a size range of about 60–600 nm and the fine particles less than 80 nm were dispersed within the β–Si3N4 matrix grains.
Pyrochlore-to-perovskite transformation during rapid heating of sol-gel (Pb,La)TiO3 thin films
Authors: Algueró Miguel , Calzada M. Lourdes , Pardo Lorena
Published: March 2008

Phases appearing in lanthanum-modified lead titanate thin films prepared by a diol-based sol-gel method and crystallized by rapid heating were studied. The results clearly indicate that a phase transformation from a pyrochlore structure to the perovskite phase occurs in Pb-deficient films during the thermal treatment, which involves a heating rate higher than 500 °C min−1. The rate of this transformation is a function of the lead content of the films, decreasing as lead volatilizes. Temperatures higher than 650 °C or soak times longer than 2 h make possible the complete pyrochlore-to-perovskite transformation without any lead excess in the films.
Optical properties of AlN determined by vacuum ultraviolet spectroscopy and spectroscopic ellipsometry data
Authors: Jones D. J. , French R. H. , Müllejans H. , Loughin S. , Dorneich A. D. , Carcia P. F.
Published: March 2008

Precise and accurate knowledge of the optical properties of aluminum nitride (AlN) in the ultraviolet (UV) and visible (VIS) regions is important because of the increasing application of AlN in optical and electro-optical devices, including compact disks, phase shift lithography masks, and AlN/GaN multilayer devices. The interband optical properties in the vacuum ultraviolet (VUV) region of 6–44 eV have been investigated previously because they convey detailed information on the electronic structure and interatomic bonding of the material. In this work, we have combined spectroscopic ellipsometry with UV/VIS and VUV spectroscopy to directly determine the optical constants of AlN in this range, thereby reducing the uncertainty in the preparation of the low-energy data extrapolation essential for Kramers–Kronig analysis of VUV reflectance. We report the complex optical properties of AlN, over the range of 1.5–42 eV, showing improved agreement with theory when contrasted with earlier results.
Microstructure and electrical properties of chemical solution deposition (Pb,La)(Zr,Ti)O3 thin films on Pt electrodes
Authors: Cross Jeffrey S. , Fujiki Mitsushi , Tsukada Mineharu , Kotaka Yasutoshi , Goto Yasuyuki
Published: March 2008

(Pb,La)(Zr,Ti)O3 (PLZT) films with thicknesses of 150 and 225 nm were prepared by the chemical solution deposition method on sputtered Pt/IrO2 coated on SiO2/Si wafers. The annealed films revealed two different microstructures: fined-grained and large-grained. The thinner film had the largest grain size and highest leakage current, whereas the thicker film had small grains and lower leakage. Atomic force microscope images showed that the thinner film had half-domed-shaped grains, which were about one-third thinner at the grain boundary triple points. These triple points also contained a nanocrystalline nonstoichiometric secondary phase, which contributed to high leakage. A model was developed showing differences in crystallization on the basis of grain growth and number of nuclei on the Pt surface. These results indicate the importance of controlling the film microstructure and its relationship to the film electrical properties.
Photoconductive Bi12MO20-type films prepared by pulsed laser deposition
Authors: Alfonso J. E. , Martín M. J. , Volkov V. , Zaldo C. , Aguiló M. , da Silva M. F. , Soares J. C.
Published: March 2008

Bi12TiO20 (BTO); Bi12GaxBi1−xO19.5 (BGaO); and Bi12(M1/3P2/3)O20, M = Cd, Zn, and Ni (BMPO) thin films were prepared by pulsed laser deposition using a KrF excimer laser on (100)Y-stabilized zirconia (YSZ), (100)Bi12GeO20 (BGO), and (110)Bi12SiO20 (BSO) crystalline substrates. All these films have a sillenite structure. On (100)YSZ the sillenite is oriented as {310} with the 〈130〉 direction parallel to the 〈021〉YSZ directions (〈130〉{310}BTO〈021〉{100}YSZ). On (100)BGO and (110)BSO the sillenite film reproduces the substrate orientation, and the films formed are able to channel He+ particles. The optimum deposition temperatures for BTO and BGaO are 600 and 550 °C, respectively. Higher temperatures must be avoided to minimize the nucleation of Bi-deficient phases due to the diffusion of Bi into the YSZ substrates. BMPO films are polycrystalline. The lattice parameters of these films were determined. The crystalline films support guided optical modes. The refractive indices obtained for the films are close to those measured in bulk crystals, being slightly larger for films deposited on isomorphous sillenite substrates. The crystalline films deposited on YSZ are photoconductors when excited in the green and blue spectral regions.
Hydrazine-controlled hydrothermal synthesis of Co9S8 from a homogeneous solution
Authors: Zhan J. H. , Yang X. G. , Xie Y. , Wang D. W. , Qian Y. T. , Liu X. M.
Published: March 2008

Single-phase nanocrystalline Co9S8 was prepared by hydrothermal treatment of Co(Ac)2 and NH2CSNH2 in hydrazine solution at 170 °C. The products were characterized by x-ray powder diffraction (XRD) technique, transmission electron microscope (TEM), and wet chemical analysis. XRD indicated the product was the cubic Co9S8 phase. The relative crystallite size was 6.3 nm as determined by the Scherrer method. TEM images showed the particles were agglomerative. The electron diffraction pattern also revealed their nanocrystalline nature. In this hydrothermal formation process of Co9S8, hydrazine was a critical factor. The formation process is discussed.
Structural evolution and phase separation of CaO · Al2O3 · SiO2 glasses in an electric field
Authors: Liu W. , Gu X. M. , Zheng Y. K. , Liang K. M.
Published: March 2008

In the present paper, the process of phase separation in calcium aluminosilicate glasses (CAS glasses) containing TiO2 as a nucleating agent is studied. A static electric field promotes the process of phase separation even when the time of heat treatment is short. The effect of electric field on phase separation acts through the higher polarizability of Ti ions. Alkali ions, when present, will diffuse toward the cathode, which may generate different micromorphology at the parts of samples near the cathode and the anode. X-ray photoelectron spectroscopy and Raman spectra analysis confirm the conclusion that the electric field has promoted phase separation in CAS glasses.
Multicomponent metastable phase formed by crystallization of Ti–Ni–Cu–Sn–Zr amorphous alloy
Authors: Louzguine Dmitri V. , Inoue Akihisa
Published: March 2008

Crystallization of the Ti45Ni20Cu25Sn5Zr5alloy has been studied by means of scanning differential calorimetry, x-ray diffraction, and conventional and high-resolution transmission electron microscopy. The first stage at about 750–800 K is related to the primary crystallization of the Ti8Ni3Cu3SnZr metastable phase having Im3m body-centered-cubic structure with a lattice parameter ofa= 0.3069 nm followed by precipitation of the secondary dotlike phase precipitates on its boundaries. The activation energy for the first exothermic reaction determined by Kissinger analysis was found to be 310 kJ/mol. CuTi, Ni2TiZr, and an unknown phase are formed during long-term annealing at high (more than 850 K) temperature.
Raman spectroscopic characterization of submicron vapor-grown carbon fibers and carbon nanofibers obtained by pyrolyzing hydrocarbons
Authors: Endo M. , Nishimura K. , Kim Y. A. , Hakamada K. , Matushita T. , Dresselhaus M. S. , Dresselhaus G.
Published: March 2008

Variations of the properties of submicron vapor-grown carbon fibers (VGCFs) and nanofibers, with diameters around 0.1–0.2 μm and 80–100 nm, respectively, are observed by Raman spectroscopy as a function of heat-treatment temperature. The microstructural evolution strongly depends on the original properties of the material, such that the main transition temperatures associated with the onset for establishing two-dimensional graphene ordering are defined below 1500 °C for the nanofibers and 2000 °C for the submicron VGCFs, respectively. The relative intensities (ID/IG) of the as-grown phase for submicron VGCFs and nanofibers are 3.44 and 1.35, while those for the corresponding graphitized samples are 0.393 and 0.497, respectively.
Stability of Tl–Ba–Ca–Cu–O superconducting thin films
Authors: Siegal M. P. , Overmyer D. L. , Venturini E. L. , Padilla R. R. , Provencio P. N.
Published: March 2008

We report the stability of TlBa2CaCu2O7 and Tl2Ba2CaCu2O8 on LaAlO3(100) epitaxial thin films, under a variety of conditions. All films are stable in acetone and methanol and with repeated thermal cycling to cryogenic temperatures. Moisture, especially vapor, degrades film quality rapidly. These materials are stable to high temperatures in either N2 or O2 ambients. While total degradation, resulting from Tl depletion, occurs at the same temperatures for both phases, 600 °C in N2 and 700 °C in O2, the onset of degradation occurs at somewhat lower temperatures for TlBa2CaCu2O7 than for Tl2Ba2CaCu2O8.
Intrinsic stress effects on the growth of planar SiO2 films
Authors: Delph T. J. , Lin M-T.
Published: March 2008

We report here on the results of a numerical study on the effects of intrinsic stress on the growth of SiO2 thin films. In accordance with a widely accepted model of stress effects upon silicon oxidation, we assume that the intrinsic stress affects only the oxidant diffusion rate. We examine several different models of stress-assisted diffusion. In the first of these models, the diffusivity is taken to be an exponential function of the stress, whereas in the second, the stress gradient appears as an additional term in the standard diffusion equation. Intrinsic stress effects result in deviations of up to 18% in expected layer thickness, depending upon the mode of oxidation and the diffusion model adopted. The implications of these results for the measurement of diffusion coefficients in SiO2 films are discussed.
Preparation of Cu(In,Ga)Se2 thin films from In–Ga–Se precursors for high-efficiency solar cells
Authors: Nishiwaki S. , Satoh T. , Hayashi S. , Hashimoto Y. , Negami T. , Wada T.
Published: March 2008

Growth of Cu(In,Ga)Se2 (CIGS) films from In–Ga–Se precursors was characterized by scanning Auger electron spectroscopy (SAES), secondary ion mass spectroscopy (SIMS), x-ray diffraction, scanning electron microscopy, and transmission electron microscopy (TEM). In–Ga–Se precursor layers were deposited on Mo-coated soda-lime glass, and then the layers were exposed to Cu and Se fluxes to form CIGS films. The SIMS and SAES analyses showed a homogeneous distribution of Cu throughout the CIGS films during the deposition of Cu and Se. The phase changes observed in the CIGS films during the deposition of Cu and Se on the In–Ga–Se precursor films were as follows: (In,Ga)2Se3 →[Cu(In,Ga)5Se8] →Cu(In,Ga)3Se5 →Cu(In,Ga)Se2. The grain size increased from the submicron grains of the (In,Ga)2Se3 precursor film to several micrometers in the stoichiometric Cu(In,Ga)Se2 film. A growth model of CIGS crystals is introduced on the basis of the results of TEM observations. CIGS crystals are mainly grown under (In,Ga)-rich conditions in the preparation from In–Ga–Se precursor films.
Residual stresses in spray-formed A2 tool steel
Authors: Hu H. M. , Lavernia E. J. , Lee Z. H. , White D. R.
Published: March 2008

The objective of this work was to investigate the fundamental factors that govern the formation and magnitude of residual stresses in A2 tool steel fabricated using spray-forming techniques. To that effect, a finite-element method (FEM) was performed by using a commercial code, ABAQUS, to solve for the temperature and displacement fields. Moreover, the residual stresses in the spray-formed materials were measured using x-ray diffraction to compare the FEM results with experimentation. Two types of substrate material, copper and Rescor™ 780 cer-cast ceramic, were used to investigate the influence of heat conduction on residual stress in the preforms. Relatively good agreement was found between experimentation and theory. The results show that the residual stress varies greatly with the position in deposited preform and that heat-transfer coefficient at the interface of spray-formed material/substrate affects the distribution and magnitude of the residual stresses significantly.
Phase segregation in binary SiO2/TiO2 and SiO2/Fe2O3 nanoparticle aerosols formed in a premixed flame
Authors: Ehrman Sheryl H. , Friedlander Sheldon K. , Zachariah Michael R.
Published: March 2008

Binary SiO2/TiO2 and SiO2/Fe2O3 nanoparticle (diameter < 100 nm) aerosols of varying mole ratios of Ti or Fe to Si were generated in a premixed Bunsen-type aerosol flame reactor. The distribution of species within the particles was investigated using transmission electron microscopy, electron energy loss spectrometry, x-ray diffraction, and Fourier transform infrared spectroscopy. Phase segregation was observed to varying degrees in qualitative agreement with segregation expected from binary phase diagrams for the bulk systems. Differences between the SiO2/TiO2 and SiO2/Fe2O3 systems can be explained by considering the variation in the thermodynamically stable liquid-phase solubility and differences in the ability of iron and titanium ions to substitute for silicon ions in the network structure.
Study of the structure and dielectric relaxation behavior of Pb(Mg1/3Nb2/3)O3–PbTiO3 ferroelectric ceramics
Authors: Zhang Xiaowen , Fang Fei
Published: March 2008

(1–x)PMN–xPT[PMN, Pb(Mg1/3Nb2/3)O3; PT, PbTiO3] system ferroelectric ceramics with x = 0.30, 0.33, 0.35, and 0.38 were synthesized by the columbite precursor method. Their structure and dielectric behavior were investigated. X-ray diffraction results demonstrate that no two-phase region is presented, but a quasi-cubic to tetragonal phase boundary lies between x = 0.30 and 0.33. Examination of the dielectric behavior reveals that the transformation from relaxor to normal ferroelectric behavior across the morphotropic phase boundary (MPB) is successive and continuous. It is suggested that x 4 0.30 to 0.33 is the composition of MPB for the PMN–PT system. The MPB is also a boundary for the PMN–PT system to transform from relaxor to normal ferroelectrics.
Role of zirconia addition in pore development and grain growth in alumina compacts
Authors: Pan Yi-Ming , Page Richard A. , Long Gabrielle G. , Krueger Susan
Published: March 2008

The role of 12.4 vol% ZrO2 addition in the microstructure evolution of alumina compacts during the intermediate and final stages of sintering was investigated by means of small-angle neutron scattering measurements and stereological analysis. Both the pore-size evolution results and the grain-growth data indicate a narrowly defined onset density for the transition to the final sintering stage. The presence of ZrO2 as a second phase apparently maintains the stability of the intermediate sintering stage out to significantly higher density than in single-phase alumina and plays an important role in inhibiting grain growth and in preventing pore–grain boundary separation. The influence of the ZrO2 second phase on pore evolution, grain growth, and sinterability of the alumina–zirconia composite is discussed and compared to the behavior of single-phase alumina. The samples were prepared from commercially available powders, with naturally occurring porosity distributions, rather than from artifact(model) pore compacts prepared from nominally pure research-grade materials. The goal was to gain an improved understanding of microstructure development in real materials.
Microstructure of a bearing-grade silicon nitride
Authors: Liu Mingqi , Nemat-Nasser Sia
Published: March 2008

The microstructure of a bearing-grade silicon nitride, prepared by pressureless sintering with Y2O3, AlN, and TiO2 additives and then hot-isostatically pressed, is examined with high-resolution transmission electron microscopy, scanning electron microscopy, and x-ray diffraction. The material consists of large acicular β–Si3N4 grains and small equiaxial α–Si3N4 grains. An amorphous phase containing the sintering aids is observed at the two-grain boundaries and at the grain pockets. No crystalline boundary phase is identified. The α-to-β and β-to-β grain boundaries appear straight and well defined. The dominant crystalline planes observed at the β-grain boundaries are (1010) and (1120). The intergranular spacing of the two-grain boundaries (α-to-β and β-to-β) is 1.0 nm when a high-contrast boundary phase is present, and it is 0.8 nm when a low-contrast boundary phase is present, confirming that the film thickness is strongly dependent on the boundary-phase composition. The α-to-α boundaries are often curved, and the thickness of the amorphous film at these boundaries varies from 0.7 to 1.1 nm. Evidence of near-intimate contact between β-grains is also observed.
Effect of heat treatment on elastic properties of separated thermal barrier coatings
Authors: Basu D. , Funke C. , Steinbrech R. W.
Published: March 2008

Elastic response behavior of four different plasma-sprayed deposits has been investigated using depth-sensing micro-indentation technique. Due to the high degree of porosity and inhomogeneity of the coatings, the characteristic elastic moduli were found to be in the range of 20–75% of that of the dense bulk material (200 GPa). Considering the wide variation of properties, 150 data points were generated with five different indentation loads for each coating, and statistical tools were employed to represent the scatter of the data. The characteristic elastic moduli of all the coatings were observed to be almost doubled when the magnitude of indentation load was reduced from the highest (1000 mN) to the lowest (30 mN). The coatings were subsequently heat treated at 1100 °C, the operational temperature of a gas turbine, for 2, 25, and 100 h, and in all the coating grades the corresponding elastic moduli increased significantly. However, the stiffening effect was not uniform in two grades and was more pronounced for the smaller indentation loads. The increase in elastic modulus is attributed to elimination of fine porosity and sintering neck formation, an assumption also supported by the results of mercury porosimetry.
Diffused phase transition in fine-grained bismuth vanadate ceramics
Authors: Shantha K. , Varma K. B. R.
Published: March 2008

Nanocrystalline powders of ferroelectric bismuth vanadate, Bi4V2O11 (n-BiV), with crystallite size less than 50 nm, were obtained by mechanical milling of a stoichiometric mixture of bismuth oxide and vanadium pentoxide. The n-BiV powders on sintering yielded high-density, fine-grained ceramics with improved dielectric and polar characteristics. Dielectric studies on samples obtained from milled powders indicated that the ferroelectric-to-paraelectric phase transition temperature is strongly frequency dependent. The Curie–Weiss law is found to be valid only at a temperature away from the transition temperature, confirming the diffused nature of the transition, which is attributed to the presence of compositional inhomogeneity, because of partial reduction of vanadium.
Effect of film composition on the orientation of (Ba,Sr)TiO3 grains in (Ba,Sr)yTiO2+ythin films
Authors: Kaiser Debra L. , Vaudin Mark D. , Rotter Lawrence D. , Bonevich John E. , Levin Igor , Armstrong John T. , Roytburd Alexander L. , Schlom Darrell G.
Published: March 2008

Thin films of composition (Ba,Sr)yTiO2+y with 0.43 ≤ y ≤; 1.64, were deposited by metalorganic chemical vapor deposition on (100) MgO substrates at various growth conditions. X-ray diffraction and transmission electron microscopy studies showed that the films were composed of epitaxial Ba1–xSrxTiO3 (x ≈0.06) grains and an amorphous phase. The orientation of the tetragonal Ba1–xSrxTiO3 grains (pure a axis, pure c axis, or a mix of the two) was found to be strongly dependent upon film composition. This composition dependence is explained for the majority of the Ti-rich films by an analysis of average strains in the two-phase films, assuming a compressive strain of ≈1% in the amorphous phase.
Synthesis of α–Al2O3 platelets using sodium sulfate flux
Authors: Hashimoto Shinobu , Yamaguchi Akira
Published: March 2008

When powder mixtures of {Al2(SO4)3 + Na2SO4}or {γ–Al2O3 [obtained by heating Al2(SO4)3 at 900 °C for 3 h] + Na2SO4} were heated in an alumina crucible at 1100 °C for 1 h, α–Al2O3 platelets were formed. The powder mixture of {Al2(SO4)3 + 2Na2SO4} yielded aggregations of platelets that were less than 5 μm in size. The size of the aggregations increased in proportion to the amount of Na2SO4, and aggregations of 120 μm were obtained using a mixture of {Al2(SO4)3 + 6Na2SO4}. The powder mixture of {γ–Al2O3 + 2Na2SO4 yielded hexagonal platelets having an average diameter of 3.7 μm and an average thickness of 0.3 μm. In addition to aggregation size, the size of the hexagonal platelets also increased in proportion to the amount of Na2SO4, and platelets having an average diameter of 5 μm were obtained using a mixture of {γ–Al2O3 + 6Na2SO4}.
Mechanisms for enhanced C54–TiSi2formation in Ti–Ta alloy films on single-crystal Si
Authors: Quintero A. , Libera M. , Cabral C. , Lavoie C. , Harper J. M. E.
Published: March 2008

The mechanisms are studied for enhanced formation of C54–TiSi2at about 700 °C when rapid thermal annealing at 3 °C/s in N2is performed on 32-nm-thick codeposited Ti–5.9 at.% Ta on Si(100) single-crystal substrates. The enhancement is related to an increased C54–TiSi2nucleation rate due to the development of a multilayered microstructure. The multilayer microstructure forms at temperatures below 600 °C with the formation of an amorphous disilicide adjacent to the Si substrate and a M5Si3(M = Ti, Ta) capping layer. This amorphous disilicide crystallizes at higher temperatures to C49–TiSi2. The multilayer microstructure introduces an additional interface that increases the area available for the heterogeneous nucleation of C54. The capping layer is identified as hexagonal Ti5Si3or its isomorphous compound (Ti1–xTax)5Si3. Crystal simulations demonstrate that C54(040) has a lattice mismatch of 6–7% relative to Ti5Si3(300) suggesting that a pseudomorphic epitaxial relationship may lower the interfacial energy between these two phases and reduce the energy barrier for C54 nucleation. A C40 disilicide phase was also observed at temperatures above that required to form C54–TiSi2suggesting that, in the present experiments, the C40 phase does not play a major role in catalyzing C54 formation.
An extended x-ray absorption fine structure study of rare-earth phosphate glasses near the metaphosphate composition
Authors: Anderson R. , Brennan T. , Cole J. M. , Mountjoy G. , Pickup D. M. , Newport R. J. , Saunders G. A.
Published: March 2008

A variable-temperature (79, 145, and 293 K) extended x-ray absorption fine structure study, using rare-earth LIII absorption edges, is reported for phosphate glasses doped with rare-earth elements (R, where R = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er) with compositions close to metaphosphate, R(PO3)3. The results yield nearest-neighbor R–O distances that demonstrate the lanthanide contraction in a glassy matrix and an R–O coordination intermediate between 6 and 7 for rare-earth ions with smaller atomic number (Z) and 6 for rare-earth ions with largerZ. Thermal parameters show no significant changes in R–O distances or coordination numbers between 293 and 79 K. There is evidence of an R–P correlation between 3.3 and 3.6 Å and the beginning of a second R–O correlation at approximately 4 Å. No R–R correlations up to a distance of approximately 4 Å were observed.
Hydroxyapatite coatings grown by pulsed laser deposition with a beam of 355 nm wavelength
Authors: Fernández-Pradas J. M. , Clèries L. , Sardin G. , Morenza J. L.
Published: March 2008

Calcium phosphate coatings, obtained at different deposition rates by pulsed laser deposition with a Nd:YAG laser beam of 355 nm wavelength, were studied. The deposition rate was changed from 0.043 to 1.16 Å/shot by modification of only the ablated area, maintaining the local fluence constant to perform the ablation process in similar local conditions. Characterization of the coatings was performed by scanning electron microscopy, x-ray diffractometry, and infrared, micro-Raman, and x-ray photoelectron spectroscopy. The coatings showed a compact surface morphology formed by glassy grains with some droplets on them. Only hydroxyapatite (HA) and alpha-tricalcium phosphate (α–TCP) peaks were found in the x-ray diffractograms. The relative content of (α–TCP diminished with decreasing deposition rates, and only HA peaks were found for the lowest rate. The origin of (α–TCP is discussed.
Highly (200)-oriented Pt films on SiO2/Si substrates by seed selection through amorphization and controlled grain growth
Authors: Kim Min Hong , Park Tae-Soon , Lee Dong-Su , Yoon Euijoon , Park Dong-Yeon , Woo Hyun-Jung , Chun Dong-Il , Ha Jowoong
Published: March 2008

Highly (200)-oriented Pt films on SiO2/Si substrates were successfully prepared by a combination of a dc magnetron sputtering using Ar/O2 gas mixtures and subsequent controlled annealing. The intensity ratio of (200) to (111) planes (I200/I111) was over 200. The (200)-oriented Pt microcrystallites were less susceptible to amorphization due to their lower strain energy with oxygen incorporation than (111)-oriented ones. The controlled grain growth from the selected (200)-oriented seed microcrystallites during subsequent annealing provided a kinetic pathway where grain growth of the seed microcrystallites was predominant, while suppressing the nucleation of surface energy-driven, (111)-oriented seed microcrystallites and subsequent (111) preferred orientation.
Epitaxial growth of semiconducting LaVO3 thin films
Authors: Choi Woong , Sands Timothy , Kim Kwang-Young
Published: March 2008

Epitaxial thin films of LaVO3 were grown on (001) LaAlO3 substrates by pulsed laser deposition from a LaVO4 target in a vacuum ambient at substrate temperatures ≥500 °C. X-ray diffraction studies showed that epitaxial LaVO3 films consist of mixed domains of [110] and [001] orientations. Thermoprobe and four-probe conductivity measurements demonstrated the p-type semiconducting behavior of the epitaxial LaVO3 films. The temperature dependence of the conductivity is consistent with a thermally activated hopping mechanism with an activation barrier of 0.16 eV.
Phase selection during solidification of undercooled bulk Bi95Sb5 melts
Authors: Zhou Z. , Zhao J. , Wang W.
Published: March 2008

Relationships between melt heat treatment and undercooling of alloy melts were clarified with Bi95Sb5 through four-factor, three-level orthogonal experiments. The results show that the cooling rate plays the most important role in the undercooling of Bi95Sb5 alloy melts. Undercooling as large as 121 K was obtained in the bulk Bi95Sb5 alloy melt. It is presently the highest undercooling of this alloy system. A metastable phase with tetragonal structure was found in the Bi95Sb5 alloy with undercooling of 121 K.
Fabrication and characterization of large Nd–Ba–Cu–O grains prepared under low oxygen pressure
Authors: Lo W. , Babu N. Hari , Cardwell D. A. , Shi Y. , Astill D. M.
Published: March 2008

A large, single-grain Nd–Ba–Cu–O (NdBCO) composite consisting of superconducting NdBa2Cu3O7-δ containing nonsuperconducting Nd4Ba2Cu2O10 phase inclusions was fabricated up to 2 cm in diameter using a top-seeded melt-textured growth technique. A MgO single-crystal seed was used to provide a heterogeneous nucleation site at the center of a presintered pellet heated above its peritectic temperature and cooled continuously in a conventional tube furnace in reduced oxygen partial pressure. This process produces individual grains with the c axis oriented at ≈10° to the seed surface which, from vibrating-sample magnetization measurements, exhibit a pronounced peak effect in their magnetic moment over a wide temperature range (50–90 K) when the supercurrent flows in the a-b planes. A very high irreversibility field (>9 T at 77 K) is also observed in these grains for field applied both perpendicular and parallel to the crystallographic c axis which is significantly greater than that observed in good-quality melt-processed Y–Ba–Cu–O. These results underline the potential of NdBCO for high-field engineering applications.
Lattice parameters and thermal expansion of GaN
Authors: Reeber Robert R. , Wang Kai
Published: March 2008

Neutron powder diffraction methods with Rietveld analysis are utilized to determine GaN lattice parameters from 15 to 298.1 K. Using these measurements and literature data, we calculated the thermal expansion of gallium nitride (GaN) and predicted its higher temperature thermal expansion. The results are compared with available experimental data and earlier work.
X-ray diffraction and transmission electron microscopy analysis of ordering and structure in Al1−xInxAs thin films
Authors: Forrest R. L. , Kulik J. , Golding T. D. , Moss S. C.
Published: March 2008

This paper presents an x-ray diffraction and transmission electron microscopy analysis of Al1−xInxAs grown by molecular beam epitaxy. Two samples grown on (001) InP at temperatures of 370 and 400 °C are characterized. The first, which contains a high density of twin lamellae, exhibits triple-period short-range ordering with a rather short correlation range normal to the (111) planes. Within these (individual) planes, the concentration, however, is uniform over a considerably greater distance, leading to a highly anisotropic scattering. This is the first observation of triple-period short-range ordering in a sample that exhibits 2 × 1 surface reconstruction. The second sample exhibits CuPt-type short-range ordering with scattering that is significantly streaked, suggestive of lamellar-shaped ordered domains. Both samples contain high densities of stacking faults leading to additional sharp streaking along symmetry-allowed 〈111〉 directions.
Icosahedral nanophases in the Al–Mn–Ce system
Authors: Manaila R. , Popescu R. , Jianu A. , Constantin M. , Devenyi A.
Published: March 2008

Nano-icosahedral phases were prepared by melt-spinning in the AlMnCe system (Al ≥ 89 at.%). Ce-induced structure alterations are reported by x-ray diffraction for the icosahedral (i) AlMnCe phase. They comprise apparition of superstructure diffraction lines, due to chemical ordering in the 6-dimensional icosahedral lattice, which gradually changes from a simple to a face-centered (FCI) type. Also, strong anomalies of diffracted intensities, with reference to model FCI phases, support Ce preferential location on a special set of sites. Microstructure investigations show a nanodispersion of i-AlMnCe in an Al-rich matrix, suggesting a low nucleation barrier of this metastable phase in the melt.
Micropyretic synthesis of NiAl containing Ti and B
Authors: Dey G. K. , Arya A. , Sekhar J. A.
Published: March 2008

The effect of alloying additions of Ti and B on the process of micropyretic synthesis on NiAl and on the microstructure of the synthesized alloy was examined. It was observed that the combustibility of the quaternary alloy is good despite the presence of the alloying elements because of an additional combustion reaction between Ti and B. The microstructure of the quaternary alloy was found to consist primarily of the NiAl and Ti boride phases. The effect of preheating of the specimen prior to synthesis on the process of synthesis was also examined. It was observed that preheating not only can change the morphology of the phases but also influence the nature of the phases present in the alloy. The mechanism of the formation of the two phase microstructure during the synthesis from the elemental powders was established by stopping the combustion front and by carrying out a detailed microstructural characterization of regions around the stopped combustion front.