bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructural characterization and solidification behavior of atomized Al–Fe powders
Authors: Zhou Y. , Juarez-Islas J. A. , Alvarez-Fregoso O. , Yoon W. Y. , Lavernia E. J.
Published: March 2008

The effect of solidification history on the resultant microstructure in atomized Al–2.56 wt% Fe and Al–6.0 wt% Fe powders was studied, with particular emphasis on droplet size, undercooling, and phase stability. The atomized Al–Fe powders exhibited four microstructural features, i.e., Al3Fe phase (now known as Al13Fe4), Al + Al6Fe, α–Al dendrite, and a predendritic microstructure. The presence of these phases was noted to depend on alloy composition and a kinetic phase competitive growth mechanism due to the initial undercooling experienced by the powders. The occurrence of structures of the predendritic, cellular, and/or dendritic type was properly predicted by the theory of dendrite growth into undercooled alloy melts for the case of large undercoolings.
Corrosion of martensitic and austenitic steels in liquid gallium
Authors: Barbier F. , Blanc J.
Published: March 2008

The compatibility of 1.4914 martensitic steel and 316 L austenitic stainless steel has been studied in the presence of static liquid gallium. It was shown that the materials are severely attacked by the liquid metal. The corrosion is characterized by the formation of a reaction layer identified as FeGa3. Depending on the steel, the growth kinetics and the morphology of the layer are found to be different. In the case of 1.4914 steel, the growth law is linear, which implies an interface controlled regime. Moreover, the layer formed from an initially rectangular substrate exhibits a typical cruciform pattern. In the case of 316 L steel, a parabolic growth is found after a transient period, indicating a process mainly controlled by diffusion. Contrary to the martensitic steel, the morphology of the layer occurring during the solid-liquid interaction leads to complete coverage of the 316 L substrate, with rounded edges.
Soft x-ray absorption spectroscopy study of electrochemically formed passive layers on AISI 304 and 316L stainless steels
Authors: López M. F. , Gutiérrez A. , Torres C. L. , Bastidas J. M.
Published: March 2008

The structure and composition of passive films electrochemically formed on AISI 304 and 316L stainless steels in a chloride-containing solution have been studied by soft x-ray absorption spectroscopy. Soft x-ray absorption spectra were taken at the oxygen 1s edge and at the transition metals (Cr, Fe, Ni) 2p edges, making it possible to determine the main contributions to the passive film's composition. The soft x-ray absorption spectra at the Cr 2p edges indicate that in all cases the passive film is mainly formed by Cr2O3. Spectra at the Fe and Ni 2p edges exhibit no significant contribution of Ni and Fe oxides to the passive layer composition. However, differences in spectral shape with respect to metallic Ni and Fe suggest the presence of a small amount of hydroxides, which is maximum for the AISI 304 stainless steel polarized at the lowest scan rate. The spectra at the O 1s edges confirm the results obtained at the transition metal edges.
The kinetics of indium/amorphous-selenium multilayer thin film reactions
Authors: Lu K. , Sui M. L. , Perepezko J. H. , Lanning B.
Published: March 2008

The reaction kinetics in vapor-deposited indium/amorphous-selenium (a-Se) multilayer thin films were studied using differential scanning calorimetry (DSC), x-ray diffraction (XRD), and transmission electron microscopy (TEM). A number of reactions were observed upon heating with characteristic temperatures which were found to be independent of the multilayer modulation wavelength. The initial interface reaction between In and a-Se is the formation of an In2Se phase. Kinetic analyses of the In2Se formation process combined with TEM observations indicated that interface reaction is characterized by the two-dimensional growth of pre-existing In2Se regions formed during deposition to impingement in the plane of the original In/a-Se interface. The change of the density of In2Se grains with temperature was analyzed in terms of the derived kinetic parameters, which is consistent with TEM observations and the heat release measurements.
Phase transformation and thermal expansion of Cu/ZrW2O8 metal matrix composites
Authors: Holzer Hermann , Dunand David C.
Published: March 2008

Powder metallurgy was used to fabricate fully dense, unreacted composites consisting of a copper matrix containing 50–60 vol% ZrW2O8 particles with negative thermal expansion. Upon cycling between 25 and 300 °C, the composites showed coefficients of thermal expansion varying rapidly with temperature and significantly larger than predicted from theory. The anomalously large expansion on heating and contraction on cooling are attributed to the volume change associated with the allotropic transformation of ZrW2O8 between its high-pressure γ-phase and its low-pressure α- or β-phases. Based on calorimetry and diffraction experiments and on simple stress estimations, this allotropic transformation is shown to result from the hydrostatic thermal stresses in the particles due to the thermal expansion mismatch between matrix and reinforcement.
Particle-shape control and formation mechanisms of hydrothermally derived lead titanate
Authors: Moon Jooho , Carasso Melanie L. , Krarup Henrik G. , Kerchner Jeffrey A. , Adair James H.
Published: March 2008

Phase-pure perovskite lead titanate with various morphologies has been synthesized by a hydrothermal method at 150 °C. Particle shapes include cubic, tabular, and aggregated platelike shapes. The feedstock concentration greatly influences particle morphology of the hydrothermally derived PbTiO3. At a concentration of 0.05 M, the tabular particles form while cubic particles are produced at 0.1 M. Aggregated plateletlike particles are synthesized at 0.125 M. It was observed that both tabular and cubic particles directly precipitate from the coprecipitated precursor gel. In contrast, the plateletlike shaped intermediate phase appears during the initial stage of reaction at 0.125 M and in situ transforms into perovskite PbTiO3 during further hydrothermal treatment. The intermediate phase preserves its particle shape during transformation and, acting as a template, gives rise to the final tabular PbTiO3 particles. It is demonstrated that only base reagents such KOH and NaOH, which provide a highly basic condition (i.e., pH > 14), promote transformation of the coprecipitated gel into the perovskite PbTiO3. A Hancock and Sharp kinetic analysis in conjunction with microstructural evidence suggests that the formation mechanism is dissolution and recrystallization in which the degree of supersaturation plays an important role in dictating the crystallographic particle phase and morphology of the particles. An experimentally constructed solubility diagram indicates that an excess lead condition is necessary to compensate for loss of lead species and to increase supersaturation to expedite precipitation of PbTiO3 at highly alkaline conditions.
Combustion synthesis of α–Si3N4 whiskers
Authors: Cao Yong-Ge , Ge Chang-Chun , Zhou Zhang-Jian , Li Jiang-Tao
Published: March 2008

α–Si3N4 whiskers were fabricated first through combustion synthesis (CS) technology. The as-synthesized crystals with [001] as the elongated axis contain a large amount of linear defects including (a + b)-type, (a + b + c)-type, and c-type of dislocations. The growth of α–Si3N4 whiskers is mainly controlled by vapor-condensation (VC) mechanism. Special additive plays an important role in promoting the growth of α–Si3N4 whiskers and suppressing the phase transformation of α–Si3N4 to β–Si3N4.
Synthesis and sintering of rare-earth-doped ceria powder by the oxalate coprecipitation method
Authors: Higashi Kenji , Sonoda Kazutoshi , Ono Hiroshi , Sameshima Soichiro , Hirata Yoshihiro
Published: March 2008

Doped ceria, which has a higher oxygen ion conductivity than yttria-stabilized zirconia, is one of the possible electrolytes for solid oxide fuel cell at low temperatures. This study concerns powder preparation and densification of rare-earth-doped ceria. Rare-earth-doped ceria powders with a composition of Ce0.8R0.2O1.9(R = Yb, Y, Gd, Sm, Nd, and La) were prepared by heating the oxalate coprecipitate when a mixed rare earth/cerium nitrate solution was added to an oxalic solution. The oxalate and derived-oxide powders were characterized by x-ray diffraction (XRD), thermogravimetry differential thermal analysis (TG-DTA), particle size analyzer with laser diffraction, inductively coupled plasma (ICP), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). This method provided the oxalate solid solutions containing Ce and R, which were calcined to form the oxide solid solutions at 600 °C in air. The lattice parameter of oxide powders increased linearly with increasing ionic radius of doped rare earth. The size of platelike particles of oxalates and oxides depended on the concentration of oxalic acid and showed a minimum at 0.4 M oxalic acid. Dry milling of oxide powder with α–Al2O3ball was effective in reducing the size and aspect ratios of particles with little contamination of Al2O3. These rare-earth-doped ceria powders with various sizes were formed by uniaxial pressing (49 MPa) followed by cold isostatic pressing (294 MPa), and sintered at 900–1600 °C in air for 4 h. The micrometer-sized-doped CeO2 powders were densified above 95% of the theoretical density at 1200 °C. The grain size of rare-earth-doped ceria after sintering at 1600 °C was larger in the samples with the larger rare-earth element.
Absolute total energy of small copper clusters in an all-electron mixed-basis approach with the generalized-gradient approximation
Authors: Shiga Keiichiro , Ohno Kaoru , Kawazoe Yoshiyuki , Fu Rong-Tang , Maruyama Yutaka
Published: March 2008

In order to investigate the absolute value for the total and exchange-correlation energies of small transition metal clusters, an all-electron mixed-basis approach with the generalized gradient approximation (Perdew–Wang's GGA-1) is applied for the first time to small Cu clusters. We find that the GGA significantly deepens (2.57–2.59 a.u. per atom) both the total and exchange-correlation energies obtained with the local density approximation. A better agreement is obtained with experiments for the binding energy of Cu2 when the spin-dependent calculation is used for an isolated Cu atom.
The effect of RuO2/Pt hybrid bottom electrode structure on the leakage and fatigue properties of chemical solution derived Pb(ZrxTi1−x)O3 thin films
Authors: Kim Seung-Hyun , Hong J. G. , Streiffer S. K. , Kingon Angus I.
Published: March 2008

We have investigated the effect of RuO2 (10, 30, 50 nm)/Pt layered hybrid bottom electrode structure and film composition on the leakage and fatigue properties of chemical solution derived Pb(ZrxTi1−x)O3 (PZT) thin films. It was observed that the use of high Ti content (Zr: Ti = 30: 70) films with control of excess PbO at the thin RuO2 (10 nm)/Pt bottom electrode surface reduced leakage current and showed good fatigue properties with high remanent polarization compared to the use of high Zr films (Zr: Ti = 50: 50) or thicker RuO2 (30, 50 nm)/Pt bottom electrodes. Typical P-E hysteresis behavior of PZT films was observed even at an applied voltage of 3 V, demonstrating greatly improved remanence and coercivity. Fatigue and breakdown characteristics of these modified PZT thin films (Zr: Ti = 30: 70) on RuO2 (10 nm)/Pt, measured at 5 V, showed stable behavior, and less than 15% fatigue degradation was observed up to 1010 cycles.
Reduction of intrinsic stresses during the chemical vapor deposition of diamond
Authors: Nijhawan Sumit , Jankovsky Susan M. , Sheldon Brian W. , Walden Barbara L.
Published: March 2008

Intrinsic stresses which arise during the chemical vapor deposition (CVD) of diamond were controlled by multistep processing. Film stresses (thermal and intrinsic) were measured with the bending plate method. The thermal stresses are compressive and arise due to the mismatch in thermal expansion coefficient between the film and substrate. The dominant intrinsic stresses are tensile and evolve during the deposition process. These stresses increase with deposition time. An intermediate step consisting of annealing the film when the diamond crystallites are only partially coalesced reduces the intrinsic stress by more than 50%. Annealing at longer growth times (i.e., after complete coalescence) does not produce large reductions in intrinsic stress. Our results are consistent with stress generation due to the formation of nonequilibrium grain boundary structures. The intermediate annealing step does not produce a large, direct stress reduction; instead, it alters the film microstructure in some subtle way which reduces stress generation during subsequent growth.
Atomic force microscopy study of small-size nanotubular polymer thin films
Authors: Zhu C. F. , Lee I. , Li J. W. , Wang C. , Cao X. Y. , Xu H. , Zhang R. B.
Published: March 2008

In this paper, we report atomic force microscopy (AFM) images of a tubular polymer and its supermolecular polymer thin films, operated in contact mode at room temperature in air. The configuration models are also calculated using molecular dynamics. The diameter of the polymer nanotube is about 0.7 nm, the smallest size a tube can have. The results of calculation agree with the experimental results.
Optical properties of heat-treated polyparaphenylene
Authors: Matthews M. J. , Brown S. D. M. , Dresselhaus M. S. , Endo M. , Takamuku T. , Karaki T.
Published: March 2008

The optical properties of heat-treated polyparaphenylene (PPP) were investigated by means of Raman and photoluminescence (PL) spectroscopy. Special attention is given to PPP heat-treated to temperatures (THT) near the carbonizing temperature region (THT ≈ 700°C) since polymer-based carbonaceous compounds with low-THT (<1000 °C) have been found to exhibit electrochemical properties that strongly contrast both the as-prepared polymer and fully carbonized samples. The Raman spectra show that for THT in the range 650–725°C, several Raman bands near 1300 cm−1 can be correlated with both ground-state benzenoid and excited-state quinoid PPP Ag modes. An increase in quinoid character is observed with increasing THT, which is consistent with the theoretically predicted stabilization of the quinoid form in the presence of a high density of defects. The smaller energy bandgap for π – π* transitions in the quinoid conformation relative to that for the benzenoid form allows for a resonance condition to be present for laser excitation wavelengths (λexc) near the visible (∼1–2 eV). We also report a small dispersion effect in the observed quinoid breathing mode band which can be compared to dispersion effects previously reported for the case of trans-PA. The decrease in bandgap for the defect-induced quinoid form is also evidenced in the PL spectra of samples heat-treated up to 650°C, which show vibronic structure in the blue-green emission data in the energy range 2.4–3.0 eV, with well-resolved peaks separated by quinoid phonon energies of 0.165 eV. Franck–Condon analysis shows an increase in the Huang–Rhys parameter (S) with increasing THT which can be related to changes in the electron-phonon coupling of valence and conduction band states.
Computer simulation of grain growth kinetics with solute drag
Authors: Fan D. , Chen S. P. , Chen Long-Qing
Published: March 2008

The effects of solute drag on grain growth kinetics were studied in two-dimensional (2D) computer simulations by using a diffuse-interface field model. It is shown that, in the low velocity/low driving force regime, the velocity of a grain boundary motion departs from a linear relation with driving force (curvature) with solute drag. The nonlinear relation of migration velocity and driving force comes from the dependence of grain boundary energy and width on the curvature. The growth exponent m of power growth law for a polycrystalline system is affected by the segregation of solutes to grain boundaries. With the solute drag, the growth exponent m can take any value between 2 and 3, depending on the ratio of lattice diffusion to grain boundary mobility. The grain size and topological distributions are unaffected by solute drag, which are the same as those in a pure system.
Synthesis and characterization of B–C–N compounds on molybdenum
Authors: Yu Jie , Wang E. G. , Xu Guichang
Published: March 2008

B–C–N compounds were prepared on molybdenum by means of bias-assisted hot filament chemical vapor deposition (HFCVD). Effect of the substrate temperature (Ts) on the growth of B–C–N films has been investigated systematically by x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) based on the detailed analysis and calculation of the XPS. The substrate temperature plays a key role in the formation of the bonding states, the composition, and the surface morphology. Boron carbonitride is the main phase at all depositing temperatures, and the obtained compounds are as follows: B0.83C0.17 + B0.39C0.35N0.26 at 873 K, B0.30C0.34N0.36 at 973 K, B0.64C0.36 + B0.51C0.23N0.26 at 1073 K, B0.51C0.31N0.18 at 1173 K, and B0.37C0.54N0.09 at 1273 K.
Characterization of GaN Grown on SiC on Si/SiO2/Si by Metalorganic Chemical Vapor Deposition
Authors: Zhou W. L. , Namavar F. , Colter P. C. , Yoganathan M. , Leksono M. W. , Pankove J. I.
Published: March 2008

SiC (3C-SiC) was grown on the top Si layer of SIMOX (Si/SiO2/Si) by carbonization followed by chemical vapor deposition (CVD). Subsequently, GaN was deposited on the SiC by metalorganic (MO) CVD to produce a GaN/SiC/Si/SiO2/Si multilayer structure. This multilayer film was investigated by conventional transmission electron microscopy (TEM) and high-resolution (HR) TEM from cross-sectional view. The GaN layer was found to consist of predominately hexagonal gallium nitride (h-GaN), and a small fraction of cubic GaN (c-GaN) crystallites. The orientation relationship between most of the h-GaN grains and SiC (3C-SiC) was found to be (0001)Ga N||s(111)SiC; [1120]GaN||[110]SiC, while most of the c-GaN grains had an orientation relationship (001)GaN||(001)SiC; [110]GaN||[110]SiC with respect to 3C-SiC substrate. The hexagonal grains of GaN were found to grow as two variants. The defects in both h-GaN and c-GaN are also discussed.
Nanostructure of GaN and SiC Nanowires Based on Carbon Nanotubes
Authors: Zhu Jing , Fan Shoushan
Published: March 2008

The nanostructure of GaN and SiC nanowires produced by carbon nanotube confined reaction has been studied by means of high-resolution electron microscopy, microanalysis, and microdiffraction. The GaN nanowire is a single crystal with fewer defects and the SiC nanowire is a β–SiC crystal with heavy layer sequence faults. Considering experimental results, a possible reaction path for making GaN is suggested.
Local and Electronic Structure of Siloxene
Authors: Kurmaev Ernst Z. , Shamin Sergei N. , Ederer David L. , Dettlaff-Weglikowska Ursula , Weber Jörg
Published: March 2008

Silicon L2,3 x-ray emission spectra (XES) of siloxene powder samples prepared according to Wöohler and Kautsky (Wöhler and Kautsky siloxene) are presented. The results are compared with the Si L2,3 spectra of the reference compounds a-Si, c-Si, SiO2, and SiOx. A close similarity of the electronic structure of Wöhler siloxene to that of a-SiO0.43: H and of Kautsky siloxene to that of a-SiO0.87: H is found. We determine the number of oxygen atoms per Si atom at ~0.5 in Wöhler siloxene and ~0.8 in Kautsky siloxene. The relative concentrations are in good agreement with the results of infrared absorption measurements on the same samples.
Changes in Preferred Orientation of Pt Thin Films Deposited by dc Magnetron Sputtering Using Ar/O2 Gas Mixtures
Authors: Kim Min Hong , Park Tae-Soon , Yoon Euijoon , Lee Dong-Su , Park Dong-Yeon , Woo Hyun-Jung , Chun Dong-Il , Ha Jowoong
Published: March 2008

(200)-oriented Pt thin films were deposited on SiO2/Si substrates by dc magnetron sputtering using Ar/O2 gas mixtures. Oxygen incorporation into Pt films changed deposition rate, resistivity, stress, and preferred orientation of the films. Increase in film resistivity and decrease in tensile stress were presumed to be the results of the incorporated oxygen into grain boundaries, while the change of preferred orientation resulted from the oxygen incorporation into the Pt lattice. The preferential growth of (200) planes with less total strain energy from the incorporated oxygen resulted in strong (200) preferred orientation in Pt films.
The Role of Ni in the Formation of Low Resistance Ni–Ge–Au Ohmic Contacts to n+ GaAs Heterostructures
Authors: Lumpkin Nancy E. , Lumpkin Gregory R. , Blackford Mark G.
Published: March 2008

Nickel is a commonly used wetting agent in alloyed Au–Ge ohmic contacts to n-GaAs, resulting in uniformity improvements to the morphology and contact resistance. In order to study the role of Ni in Ni–Ge–Au alloys, we have fabricated samples with varying Ni content and characterized them using electron microbeam techniques. Our data indicate the amount of Ni in the alloy affects the microstructure and composition, the morphology of the metal/GaAs interface, and the amount of GaAs consumed during the alloy reaction. Also, the dopant distribution into the GaAs is heterogeneous depending on the alloy microstructure.
Effect of Ti Substitution on the Microstructure and Properties of Zr–Mn–V–Ni AB2 Type Hydride Electrode Alloys
Authors: Song Xueyan , Zhang Ze , Zhang Xiaobin , Lei Yongquan , Wang Qidong
Published: March 2008

The electrochemical capacity, hydrogen absorbed/desorbed activation properties of alloy Zr(Mn0.1V0.3Ni0.6)2 were improved after Ti substitution for the Zr. The microstructure of Zr1xTix (Mn0.1V0.3Ni0.6)2 (x = 0, 0.5) alloys was analyzed by x-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive spectrum (EDS) analysis. A systematic structural analysis shows that there are two phases in the Ti-substituted alloy of Zr0.5Ti0.5(Mn0.1V0.3Ni0.6)2: C14 Laves phase and Ti-containing “premartensite” R phase of Ti0.8Zr0.2Ni. The improvement of electrochemical properties of alloy Zr(Mn0.1V0.3Ni0.6)2 after Ti substitution can be attributed to the Ti substitution for Zr sites in C14 Laves phase, the formation of Ti0.8Zr0.2Ni R-phase, and disappearance of Zr–Ni binaries.
Mechanical Stress, Grain-boundary Relaxation, and Oxidation of Sputtered CuNi(Mn) Films
Authors: Brückner W. , Pitschke W. , Baunack S. , Thomas J.
Published: March 2008

This paper focuses on understanding stress development in CuNi42Mn1 thin films during annealing in Ar. In addition to stress-temperature measurements, resistance-temperature investigations and chemical and microstructural characterization by Auger electron spectroscopy, scanning and transmission electron microscopy, x-ray diffraction, and atomic force microscopy were also carried out. The films are polycrystalline with a grain size of 20 nm up to 450 °C. To explain the stress evolution above 120 °C, atomic rearrangement (excess-vacancy annihilation, grain-boundary relaxation, and shrinkage of grain-boundary voids) and oxidation were considered. Grain-boundary relaxation was found to be the dominating process up to 250–300 °C. A sharp transition from compressive to tensile stress between 300 and 380 °C is explained by the formation of a NiO surface layer due to reaction with the remaining oxygen in the Ar atmosphere. This oxidation is masking the inherent structural relaxation above 300 °C.
Some Physicochemical Studies on Organic Eutectics and Molecular Complex: Urea – p-nitrophenol System
Authors: Rai U. S. , Rai R. N.
Published: March 2008

The phase diagram of urea–p-nitrophenol system, in the form of a temperature-composition curve, shows the formation of a 1: 1 molecular complex surrounded by two eutectics containing 0.216 and 0.777 mole fraction of p-nitrophenol. Data on growth velocity (v), obtained by measuring the rate of movement of the interface at different undercoolings (ΔT), suggest that they obey the Hillig–Turnbull equation, i.e., v = u (ΔT)n, where u and n are constants depending on the nature of materials involved. From the heat of fusion values, determined by the differential scanning calorimetry (DSC) method, heat of mixing, entropy of fusion, roughness parameter, interfacial energy, radius of the critical nucleus, and the excess thermodynamic functions were calculated. While the x-ray diffraction data show that the eutectics are not mechanical mixtures of the components under investigation, the microstructural investigations give their characteristic features.
Crack-bridging Processes and Fracture Resistance of a Discontinuous Fiber-reinforced Brittle Matrix Composite
Authors: Akatsu Takashi , Tanabe Yasuhiro , Yasuda Eiichi
Published: March 2008

A simple bridging model is proposed for the toughening of a discontinuous fiber-reinforced brittle matrix composite, in which the frictional bridging of fibers during, as well as after, the interfacial debonding is considered. The R-curve behavior and the work-of-fracture of the composite can be theoretically predicted by the computation of the bridging model applying material parameters, such as fiber volume fraction, size and shape of fibers, fiber tensile strength, elastic moduli of fibers and matrix, fracture toughness and work-of-fracture of matrix, and frictional shear stress at interface. The experimental result obtained from a SiC-whisker-reinforced Al2O3 composite confirms the theoretical predictions of the present bridging model. Through the model calculation, the R-curve, crack profile, and bridging stresses of the composite can be estimated correspondingly to the bridging processes.
Structural Properties of Yttria-stabilized Zirconia Thin Films Grown by Pulsed Laser Deposition
Authors: Dai J. Y. , Ong H. C. , Chang R. P. H.
Published: March 2008

Yttria-stabilized zirconia (YSZ) thin films grown by the pulsed laser deposition method on (0001) sapphire substrates have been studied by x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM). It was found that the crystal orientation of the YSZ films changes as a function of oxygen pressure during deposition. At low oxygen pressure (50 mTorr), well-defined (111) oriented YSZ films are grown. High oxygen pressure favors the nucleation of (001) oriented YSZ grains. A model to explain the preferred growth direction of (001) YSZ is presented. Utilizing the experimental data, we have developed a two-step process to epitaxially grow high-quality (001) oriented YSZ on (0001) sapphire substrate.
Processing Magnetoresistive Thin Films Via Chemical Solution Deposition
Authors: Polli A. D. , Lange F. F. , Ahlskog M. , Menon Reghu , Cheetham A. K.
Published: March 2008

A chemical solution deposition (CSD) procedure was used to prepare epitaxial lanthanum calcium manganese oxide (LCMO) thin films on (100) SrTiO3 single-crystal substrates. The colossal magnetoresistance (CMR) properties of the films were found to be comparable to those processed with vacuum deposition techniques and to bulk samples. The (200) LCMO d-spacing and insulator-metal transition temperature (TIM) were measured for films heat-treated at different temperatures, partial pressures of O2, and different times. The variations observed suggest a direct link between lattice parameter and TIM, as can be understood through their mutual dependence on the Mn4+/Mn3+ ratio. The measurements also suggest that film and powder samples crystallize Mn41-rich with respect to the Ca-substitution level, consistent with the larger lattice parameter and higher TIM observed following short heat treatments at high temperatures or long treatments at lower temperatures. Films refired in reducing conditions had the largest (200) d-spacing and slightly lower TIM, as expected from the 30% Ca-substitution level and consistent with the LCMO electronic/magnetic phase diagram constructed for bulk samples.
Structure and Thermal Stability of Nanostructured Iron-doped Zirconia Prepared by High-energy Ball Milling
Authors: Jiang J. Z. , Poulsen F. W. , Mørup S.
Published: March 2008

Fully stabilized cubic zirconia doped with iron oxide has been synthesized by high-energy ball milling from powder mixtures of monoclinic zirconia and hematite. It is found that the iron ions dissolved in cubic ZrO2are in substitutional positions with a maximum solubility of approximately 18.5 mol% α–Fe2O3. The unit-cell volume of the cubic ZrO2phase decreases with increasing iron content. During heating the cubic-to-tetragonal transition occurs at approximately 827 °C and the tetragonal-to-monoclinic transition seems to be absent at temperatures below 950 °C. During cooling the tetragonal-to-monoclinic transition occurs at 900–1100 °C.
Imprint and Fatigue Properties of Chemical Solution Derived Pb1–-xLax(ZryTi1–y)1–x/4O3 Thin Films
Authors: Kim Seung-Hyun , Kim Dong-Joo , Hong JoonGoo , Streiffer S. K. , Kingon A. I.
Published: March 2008

We have investigated the effect of oxygen vacancies on imprint and fatigue behavior of the PLZT thin films. It is found that the compensation of oxygen vacancies with various dopant concentrations and electrode structures is an important process parameter in determining the tendency to imprint and fatigue. In the case of PLZT thin films, the voltage shifts related to imprint are attributed to the trapping of electrons at ionic defect sites such as oxygen vacancies near the film/electrode interface, the magnitude of polarization, and concentration of defect-dipole complexes involving oxygen vacancies such as V′Pb–V••o. The strong dependence of fatigue rate on electrode material for PLZT thin films is due to the effect of the ferroelectric/electrode interaction on the pinning and/or unpinning rate involving the accumulation of oxygen vacancies near the film/electrode interface during fatigue cycling. By using RuO2 as the top and/or bottom electrode instead of Pt, improved fatigue properties are obtained compared to Pt/PLZT/Pt capacitors. This is because a reduced accumulation of oxygen vacancies near the interface by the oxide electrode such as RuO2 may reduce the electronic charge trapping and, consequently, lead to less domain wall pinning.
Relation Between Coarsening and Densification in Solid-state Sintering of Ceramics: Experimental Test on Superfine Zirconia Powder Compacts
Authors: Shi J. L.
Published: March 2008

Coarsening (including grain growth and pore growth) and densification behavior of superfine Y-TZP and YSZ powder compacts in the intermediate stage were investigated. It has been found that grain growth in the compacts is basically not affected by the compaction properties, and pore growth is driven by both grain growth and densification. Grain growth alone leads to size-proportional pore growth, and densification results in pore shrinkage. The relation between grain size and density is analyzed to be linear when grain growth and densification are believed to be driven by different stresses under an identical diffusion process. Both theoretical and experimental results show that compaction properties and the heating rate do not alter this linear relation between grain size and density but influence the slope of the linear relation. Larger dihedral angle, higher green density, and narrower particle and pore size distributions are found favorable for the achievement of the grain size-density trajectory with promoted densification and minimized grain growth.
Preparation and Microstructure Characterization of Anodic Spark Deposited Barium Titanate Conversion Layers
Authors: Schreckenbach J. , Schlottig F. , Marx G. , Kriven W. M. , Popoola O. O. , Jilavi M. H. , Brown S. D.
Published: March 2008

Anodic spark deposition (ASD) is an advanced plasma-electrochemical coating process to prepare polycrystalline, ceramic-like conversion coatings on metal surfaces. As an example, polycrystalline barium titanate (BaTiO3) phases have been prepared by the anodic conversion of metal substrate and the metal ions in the electrolyte. By a combination of various characterization techniques, the configuration of the coating was elucidated. On the metal substrate a thin (~50 nm) passivating amorphous film of titania (TiO2) first forms, which subsequently changes to anatase and rutile structures. With increasing anodic potentials, a plasma-chemical conversion reaction starts, leading to the heterogeneous formation of BaTiO3layers of 2–10 μm thickness. The results of this study lead to the formulation of a model describing a polycrystalline and inhomogeneous layer configuration.
Characterization of Porosity Over Many Length Scales: Application to Colloidal Gels
Authors: Kerch Helen M. , Long Gabrielle G. , Krueger Susan , Allen Andrew J. , Gerhardt Rosario , Cosandey Frederick
Published: March 2008

Processing-microstructure relationships in a silica gel system, based on mixtures of colloidal sol and soluble potassium silicate, have been studied. Quantitative microstructural information regarding colloidal cluster sizes, size distributions, surface areas, and pore-size distribution from the nanopore range to the macropore range was determined via small-angle scattering and transmission electron microscopy. The colloid cluster size distribution varies systematically, with gels fabricated with the least colloidal fraction possessing the most polydisperse microstructure. It is shown that the porosity over the entire range can be tailored by selecting the appropriate starting chemistry; under the same pH conditions, the ratio of the two silicate ingredients controls the average size, the polydispersity of sizes, and the connectivity of the pores. A population of fine (2 nm) uniformly dispersed nanopores, which result from leaching, is responsible for large increases in surface area. The leaching process can be controlled by the surrounding macropore void size, which determines alkali transport. The product material consists of 85% large, open pores, with fine pores within the gel skeleton, making this gel an ideal candidate for controlled-porosity applications such as catalyst supports and magnetic composites.
Hydrothermal Coarsening of CeO2 Particles
Authors: Lakhwani S. , Rahaman M. N.
Published: March 2008

The effects of reaction temperature (150–300 °C), chemical composition of the starting cerium salt (cerium nitrate and cerium chloride), and doping with trivalent cations (Sc3+ and Y3+) on the coarsening of CeO2 particles in dilute suspensions under hydrothermal conditions were investigated. The particle size was measured by x-ray line broadening and by transmission electron microscopy. The particle coarsening kinetics followed a parabolic law, indicating that the interfacial reaction (dissolution) was the rate-controlling step. Furthermore, the particle size distribution data can be well-described by the Lifshitz–Slyozov–Wagner theory of Ostwald ripening controlled by the interfacial reaction. Doping with 6 at.% Y3+ produced a significant reduction in the coarsening rate but almost no change in the activation energy. At the same concentration, Sc3+ was more effective than Y3+ in reducing the coarsening rate. Particles synthesized from a starting solution of cerium(III) chloride coarsened at a markedly slower rate than that for particles synthesized from cerium(III) nitrate. The mechanisms controlling the coarsening of the particles are discussed.
Lead Zirconate Titanate Via Reaction Sintering of Hydroxide Precursors
Authors: Junmin Xue , Wang John
Published: March 2008

Lead zirconate titanate (PZT) has been successfully fabricated via a unique one-step sintering processing route, which is simpler than the traditional precursor-calcinationmilling- pelleting-sintering route and is able to deliver an enhanced sintered density at a much reduced sintering temperature. The hydroxide precursor was prepared by coprecipitation from a mixed nitrate solution containing Pb2+, Zr4+, and Ti4+ ions, and it was then compacted into pellets without being calcined at a low temperature. The precursor pellets were dehydrated at 400, 500, and 600 °C for 4 h, respectively, followed by an isostatic pressing at 350 MPa, prior to being sintered at a high temperature. Dehydration temperature has a large impact on the sintering behavior of these hydroxide-derived PZT ceramics. The PZT dehydrated at 400 °C was seriously cracked when sintered at temperatures ranging from 950 to 1150 °C, due to the incomplete dehydration. A sintered density of 99.2% theoretical density was obtained at 1050 °C for 2 h for the powder pellet dehydrated at 500 °C for 4 h. It exhibits a dielectric constant of 1024 and a dielectric loss of 2.1% at a frequency of 1 kHz at room temperature. A calcination at a too-high temperature, e.g., 600 °C, results in a reduction in the sinterability of the precipitate-derived PZT ceramic.
Sol-gel Lithium Borophosphates
Authors: Ali A. F. , Mustarelli P. , Quartarone E. , Tomasi C. , Baldini P. , Magistris A.
Published: March 2008

In this paper we present sol-gel synthesis and thermal and structural characterization of some lithium borophosphates. The as-prepared samples are mostly partially crystalline, and densification heat treatments at 500 °C cause samples to crystallize. In the phosphorus-rich part of the composition triangle we have lithium excess with respect to the nominal composition, which is likely due to the low reactivity of the phosphorus precursor. On the boron-rich side, in contrast, lithium losses are found which probably occur during syneresis.
Effect of Gravity on Titanium Carbide Foams by Self-propagation High-temperature Synthesis
Authors: Tanabe Yasuhiro , Sakamoto Takashi , Okada Nobuko , Akatsu Takashi , Yasuda Eiichi , Takasu Seiichi , Sabato Takayuki
Published: March 2008

Titanium carbide foams are synthesized by a self-propagation high-temperature synthesis technique using carbon black, which generates gases during the synthesis. The synthesis is performed under terrestrial and microgravity conditions. The effects of gravity on the synthesis are evaluated in this study. The foaming is mainly caused by H2O and CO gases from the carbon black. The elongation of the products increases with decreasing environmental pressure and increasing amount of generated gases. Since the gas flows out along the direction of the combustion wave propagation, the products expand only along this direction. The propagation velocity of the combustion wave increases with increasing amount of generated gases and environmental pressure, which is due to the amount of molten Ti transporting into the reaction/preheat zone. Under higher environmental pressures, thermal convection of the environmental gases mainly affects the propagation velocity. However, at lower pressures, the behavior of the molten Ti has a great effect compared with the gases surrounding the specimens.
Nanostructured Yttria Powders Via Gel Combustion
Authors: Roy Sukumar , Sigmund Wolfgang , Aldinger Fritz
Published: March 2008

Nanostructured yttria powders were prepared by a gel combustion technique. The technique involves exothermic decomposition of an aqueous citrate-nitrate gel. The decomposition is based on a thermally induced anionic redox reaction. A variety of yttria powders with different agglomerate structures can be made by altering the citrate-nitrate ratio γ. The gel with γ = 0.098 in situ yields nanostructured yttria powder at 258 °C that is porous and agglomerated with an average of 25 nm primary particles. Its specific surface area is 55 m2/g. The decomposition of the gels was investigated by simultaneous thermogravimetry analysis (TGA) and differential thermal analysis (DTA) experiments. The produced ashes and calcined powders are characterized by x-ray diffraction (XRD), ir spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer, Emmett, and Teller (BET) analysis.
Repeated Loading, Residual Stresses, Shakedown, and Tribology
Authors: Williams J. A. , Dyson I. N. , Kapoor A.
Published: March 2008

Protective residual stresses may be developed in the near surface layers of tribological contacts which enable loads sufficiently large to cause initial plastic deformation to be accommodated purely elastically in the longer term. This is the process of shakedown and, although the underlying principles can be demonstrated by reference to relatively simple stress systems, the situation is complex under a moving Hertzian pressure distribution. Bounding theorems can be used to generate appropriate load or shakedown limits not only for uniform half-spaces but also those with plastic and/or elastic properties which vary with depth. In this way, shakedown maps, which delineate the boundaries between potentially safe and unsafe operating conditions, can be generated for both hardened and coated surfaces.
Seeded Epitaxial Growth of PbTiO3 Thin Films on (001) LaAlO3 using the Chemical Solution Deposition Method
Authors: Kim J. H. , Lange F. F.
Published: March 2008

Epitaxial PbTiO3 (PTO) thin films were grown on (001) LaAlO3 (LAO) substrates by a preseeded, two-step process via spin coating a Pb–Ti double alkoxide precursor solution. In the first step, a substrate was preseeded with epitaxial islands of PTO by coating the substrate with a very thin layer of the precursor solution and heat treating to 800 °C for 1 h. The isolated islands had an epitaxial orientation relationship of [100] (001)PTO || [100] (001)LAO. In the second step, another PTO thin film was deposited by spin coating to produce an epitaxial film via grain growth from the seeded islands. The sequence of epitaxy during heating between 400 and 800 °C was characterized by x-ray diffraction, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy (TEM). This sequence was compared to the case where the LAO substrate was not seeded. Regardless of whether the substrate was seeded or not, perovskite PTO grains nucleated and grew within the pyrolyzed, amorphous film. Films grown on the unseeded substrates were, at best, only highly textured, polycrystalline films. TEM observations showed that only a low number of epitaxial nuclei formed at the substrate/film interface due, apparently, to the large strain energy associated with the large lattice mismatch (~4%) between PTO and LAO. Other, unoriented, PTO grains that nucleated within the amorphous film were not consumed as the epitaxial grains grew larger with increasing temperature. On the other hand, good epitaxial films could be produced when the number density of epitaxial nuclei was increased by first forming a seeded substrate.
A Novel Organic Complex Thin Film for Rewritable Optical Storage
Authors: Hou S. M. , Ouyang M. , Lin L. , Xue Z. Q. , Yang W. J. , Chen H. Y. , Zhang H. X.
Published: March 2008

Erasable optical storage on an organic complex thin film m-nitrobenzal malononitrile and diamine benzene (m-NBMN/DAB) has been demonstrated. High contrast pattern can be produced by 780 nm laser pulses and can be erased by heating. The static optical recording characteristics were studied by the homemade static characterizer, and the structural properties of the thin films were investigated by the high resolution scanning electron microscope (HRSEM) and transmission electron microscope (TEM).
Amorphous, Silicide, and Crystalline Fe Films Grown on Si(001) by Radio-frequency Magnetron Sputtering
Authors: Je J. H. , Kim H. K. , Noh D. Y.
Published: March 2008

The microstructure of the amorphous, silicide, and crystalline Fe films grown on Si(001) substrates by a radio-frequency (rf) magnetron sputtering was studied in synchrotron x-ray scattering experiments. During the growth, iron-silicide interlayers were always formed. The silicide interlayer became crystalline β–FeSi2 at high rf power (⩾20 W/cm2) and at the substrate temperature of 100 °C. The formation of the β–FeSi2 was also promoted by postannealing to 300 °C. The Fe films grown on top of the silicide interlayer were amorphous at low substrate temperatures (⩽100 °C). It became crystalline only at high substrate temperature (300 °C) with the low rf power of 2 W/cm2. The crystalline Fe film was nonepitaxial but had the [111] preferred orientation.
Critical undercoolings for the formation of metastable phase and its morphologies solidified from undercooled Fe–Co melts
Authors: Mingjun Li , Guangsheng Song , Gencang Yang , Yaohe Zhou
Published: March 2008

The maximum undercoolings of 304, 318, 308, and 296 K were achieved, respectively, in Fe-22, 26, 30, and 34 at.% Co alloys. The metastable bcc phase nucleated from melts when undercoolings exceeded critical ones. The critical undercoolings for the formation of metastable bcc phase from Fe-22, 26, 30, and 34 at.% Co melts were 104, 156, 204, and 248 K, respectively. The morphologies of as-obtained metastable bcc phase exhibited five typical patterns: dendrite cores with primary and second arms, well-developed second arms, and radiated, lath, and platelike structures. Based on the classical nucleation theory, the solidification behavior of the melts was analyzed with regard to the metastable phase formation when the melts were undercooled greater than critical undercoolings. The formation of various morphologies was also evaluated to consider the solidification behavior of the undercooled melts.
Lower air-crystallization temperature and nanostructured yttria-doped tetragonal zirconia polycrystals ceramics by seeding assisted chemical coprecipitation
Authors: Durán P. , Tartaj J. , Fernández J. F. , Moure C.
Published: March 2008

The crystallization temperature of yttria-doped tetragonal zirconia polycrystals (Y-TZP) amorphous precursors can be lowered 150 °C below that currently used (≥500 °C), if “seeding assisted chemical coprecipitation” is used. Completely crystallized Y-TZP nanocrystalline powder was obtained by calcining at 350 °C in air; the Y-TZP precursors seeded with 10 wt% of nanometric (∼8 nm) Y-TZP particles. The seed particles enhanced both the nucleation and the crystallization rates at lower temperatures. From such a powder, 99% dense and nanostructured (grain size, <90 n m) Y-TZP bodies can be prepared by sintering below 1050 °C.
Effect of PO2 and Ag on the phase formation of the Bi(Pb)-2223 superconductor
Authors: Wong-Ng W. , Cook L. P. , Greenwood W.
Published: March 2008

The chemical reactions and the compositional characteristics of liquids which lead to the phase formation of the Bi(Pb)-2223 [(Bi, Pb): Sr: Ca: Cu: O] superconductor have been studied for a precursor composition of Bi1.8Pb0.4Sr2Ca2.2Cu3Ox. The combined techniques of quenching, powder x-ray diffraction, differential thermal/thermogravimetric analysis (DTA/TGA), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS) were used to characterize the subsolidus phases and the presence of liquid. Samples were annealed under purified air and under a volume fraction mixture of 7.5% O2/92.5% Ar. The effects of Ag in both the pure air and the 7.5% O2/92.5% Ar experiments were also studied. Results are discussed with respect to their processing implications.
Entrapment of elongated and crystallographically aligned pores in YBa2Cu3O7−y melt-textured with BaCeO3 addition
Authors: Kim Chan-Joong , Hong Gye-Won , Kang Suk-Joong L.
Published: March 2008

Compared to entrapped spherical pores in YBa2Cu3O7−y (123) crystals melt-textured without additives, the pores entrapped within 123 crystals melt-textured with 5 wt% BaCeO3 are elongated and aligned parallel to (100), (010), and (001) growth planes of the 123 crystals. The front side of the pores that meets first the growth front of the 123 crystal is faceted but the backside is wavy. Many BaCeO3 particles are segregated at the wavy surface. The crystallographic alignment of the elongated pores and the segregation of BaCeO3 particles are discussed in terms of the contact angle of the pores on the growth front and interfacial energy relationships between the related phases.