bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase equilibria and crystal chemistry in the Y2O3–Al2O3–SiO2 system
Authors: Kolitsch U. , Seifert H. J. , Ludwig T. , Aldinger F.
Published: March 2008

In order to clarify inconsistencies in the literature and to verify assumed ternary solubilities, the phase equilibria in the Y2O3–Al2O3 –SiO2 system at 1600, 1400, and 1300 °C were experimentally determined using x-ray diffraction (XRD), scanning electron microscope with attached energy-dispersive detector system (SEM-EDX), and electron probe microanalyzer (EPMA). Six quasibinary phases were observed: Y4Al2O9 (YAM), YAlO3 (YAP), Y3Al5O12 (YAG), Y2SiO5, Y2Si2O7 (C and D modifications), and ˜3Al2O3· 2SiO2 (mullite). Y4Al2O9 forms an extended ternary solid solution with the formula Y4Al2(1-x)Si2xO9+x (x = 0 2 ˜0.31). The lowest ternary eutectic temperature was determined at 1371 ± 5 °C by high-temperature differential scanning calorimetry (DSC). The results were compared with previous data available for the Y2O3–Al2O3 –SiO2 system and with data for other RE2O3–Al2O3 –SiO2 (RE = rare earth element) systems.
Phenomenological analysis of α′L-to-β martensitic transformation in phosphorus-bearing dicalcium silicate
Authors: Fukuda K.
Published: March 2008

Crystals of (Ca1.95□0.05) (Si0.9P0.1)O4, where □ denotes a vacancy, composed of both the α′L and β phases, were prepared and examined by the precession method. The β phase was exclusively twinned on (100)β, and the relative volumes of the twin-related variants were almost identical with each other. On the basis of the lattice correspondence between the two phases and their cell parameters, the phenomenological crystallographic theory was applied to determine the habit planes and the shape deformations upon α′L-to-β martensitic transformation. The habit planes, which define the coherent interphase boundaries between α′L and β, were nearly parallel to either (100)α′L or (010)α′L·. The alternate shape deformations that produce the former habit planes resulted in the actual (100) twin structure of the β phase. The total displacement was along [100]α′L with the magnitude of 0.008. Because the transformation involved a very small volumetric shrinkage of 0.6%, the strain accommodation would be almost completed. The coherency at the interface boundaries between the two phases and the effective strain accommodation probably caused the thermoelasticity of the Ca2SiO4 solid solutions.
Commonalties of the influence of lower valent A-site and B-site modifications on lead zirconate titanate ferroelectrics and antiferroelectrics
Authors: Tan Qi , Xu Z. , Viehland Dwight
Published: March 2008

Studies of the structure-property relations of lead zirconate titanate (PZT) modified with lower valent substitutions on the A- and B-sites have been performed as a function of substituent concentration. These investigations have yielded common changes induced by these substitutions on ferroelectric phases. The commonalties are the presence of fine domains and polarization pinning effects. Differences in domain morphologies were observed between the rhombohedral and tetragonal ferroelectric phases. Rhombohedral ferroelectrics were found to exhibit “wavy” domain patterns with increasing dopant concentrations, whereas a lenticular domain shape was preserved as the domain size was decreased for tetragonal ferroelectrics. These differences were explained in terms of different pinning mechanisms based on the differences in local elastic strain accommodations. Investigations of high Zr-content PZT have revealed that the ferroelectric rhombohedral phase becomes stabilized over the antiferroelectric orthorhombic with increasing concentrations of lower valent modifications. This change was explained in terms of the enhanced coupling between oxygen octahedra due to the bonding of oxygen-vacancy dipoles.
Low temperature sintering and elongated grain growth of 6H-SiC powder with AlB2 and C additives
Authors: Tanaka Hidehiko , Zhou You
Published: March 2008

6H(α)-SiC fine powder was sintered at normal pressure with additives of between 0.67 to 2.7 wt.% of AlB2 and 2 wt.% of C. The powder could be densified at 1850 °C. This sintering temperature was lower than that for SiC with B and C additives by 150–300 °C. During sintering, 6H-SiC partially transformed into 4H-SiC, and the transformation caused grain to grow and develop a nonspherical shape. The fracture toughness of sintered SiC increased with increases in the amount of AlB2 additive, the mean grain size, and the mean aspect ratio of grain shape. AlB2 and C additives are believed to have formed an Al8B4C7 compound which melted below 1800 °C and enhanced sintering and grain growth.
High-temperature creep of polycrystalline BaTiO3
Authors: Park E. T. , Nash P. , Wolfenstine J. , Goretta K. C. , Routbort J. L.
Published: March 2008

Compressive creep of dense BaTiO3 having linear-intercept grain sizes of 19.3–52.4 μm was investigated at 1200–1300 °C by varying the oxygen partial pressure from 102 to 105 Pa in both constant-stress and constant-crosshead-velocity modes. Microstructures of the deformed materials were examined by scanning and transmission electron microscopy. The stress exponent was ≈1, the grain-size dependence was ≈1/d2, and the activation energy was ≈720 kJ/mole. These parameters, combined with the microstructural observations (particularly grain displacement and absence of deformation-induced dislocations), indicated that the dominant deformation mechanism was grain-boundary sliding accommodated by lattice cation diffusion. Because of the absence of an oxygen partial pressure dependence, diffusion was probably controlled extrinsically.
Preparation of microcrystalline diamond in a low pressure inductively coupled plasma
Authors: Okada Katsuyuki , Komatsu Shojiro , Matsumoto Seiichiro
Published: March 2008

A 13.56 MHz low pressure inductively coupled plasma (ICP) has been applied to prepare diamond films. The Faraday shield drastically suppressed the electrostatic coupling, which frequently causes contamination due to the etching of the quartz tube. The characterizations of the obtained deposits by scanning electron microscopy (SEM), transmission electron diffraction (TED), and reflection high energy electron diffraction (RHEED) revealed that the deposits are composed of microcrystalline diamond and disordered microcrystalline graphite. The CO additive to a CH4/H2 plasma brought about the morphological change from a scale-like deposit to a particle one. Besides, the number of encountered particles was increased with an increase of CO additive. The TED and RHEED observations showed that non-diamond carbon was effectively removed with an increase of CO additive. These results indicate that oxygen-contained radicals produced by the addition of CO play an effective role in the removal of non-diamond carbon in the diamond growth conditions and that the CO additive makes the supersaturation degree of carbon large.
Dense and smooth epitaxial BaTiO3 thin films by the dipping-pyrolysis process
Authors: Kim S. , Fujimoto T. , Manabe T. , Yamaguchi I. , Kumagai T. , Mizuta S.
Published: March 2008

Dense and smooth BaTiO3 thin films were prepared on SrTiO3 (100) substrates by the dipping-pyrolysis process using a mixed precursor solution of barium and titanium naphthenates. Combination effects of prefiring [at 150–450 °C in air or low oxygen partial pressure, p(O2)[ and final heat treatment [at 850 °C in air or low p(O2)[ on preparation of BaTiO3 thin films were examined. An epitaxial BaTiO3 thin film with a dense and smooth surface consisting of nanosized grains about 70 nm was prepared by prefiring under low p(O2) at 250 °C and final heat treatment under low p (O2) at 850 °C.
Fracture of fused silica with 351 nm laser-generated surface cracks
Authors: Dahmani F. , Lambropoulos J. C. , Schmid A. W. , Papernov S. , Burns S. J.
Published: March 2008

Laser-induced-surface-flaw experiments on fused silica at 351 nm and 500 ps pulse duration are reported here. Specimens with surface flaws produced at a measured exit-surface damage threshold fluence of Fexit/th = 10 J/cm2 were irradiated at a constant fluence of FL = 1.8 × Fexit/th by different numbers of laser pulses, N = 110 to 520. Micrograph observations show that (i) the produced cracks have a semielliptical shape and (ii) the material strength predictions based on the radial crack depth (normal to the surface) instead of the crack surface length (parallel to the surface) are in good agreement with measured strengths obtained using a four-point bending fixture. The underlying basis of conventional crack analysis is first examined critically and is argued to be deficient in the way the failure strength for the cracks is related to the characteristic parameters of crack geometry. In general, it is necessary to incorporate a residual term into the failure strength formulation. The crack depth and the failure strength are found to increase and decrease with the number of laser pulses, respectively.
Coherent vibrations in percolative oil-resin systems: A Böse condensation effect observed by the technique of thermostimulated currents
Authors: Pagès O. , Grimau M. , Lamure A. , Zaoui A. , Legendre B.
Published: March 2008

The analysis of thermostimulated currents by the fractional polarization procedure is used to understand percolative behaviors in conductor-insulator-like oil-resin mixtures. On the fundamental side oil-poor systems are particularly attractive. They offer for the first time the opportunity to apply a pure Debye-like dielectric treatment of the quasi-elastic dipolar relaxation since the involved dipoles are independent, associated with spatially separated bounded clusters. An unusual compensation phenomenon is observed in the sense that first it does not describe hierarchically correlated motions and secondly it is related to the conducting phase but exhibits characteristics of the insulating phase. This compensation phenomenon is interpreted within the framework of Fröhlich's approach of relaxation processes in biological materials, as significative of a coherent vibration resulting from Böse condensation effects. On the practical side, the surveillance of this compensation phenomenon appears to be a new way to follow the coalescence of conducting bounded clusters with aging.
High corrosion resistant ZrC films synthesized by ion-beamassisted deposition
Authors: He Xiao-Ming , Shu Li , Li Hai-Bo , Weng Duan
Published: March 2008

ZrC films with high hardness were deposited on A3 steel by ion-beam-assisted deposition and had a corrosion rate more than two orders less and a corrosion potential 0.19 V greater than those of the bare A3 steel. The corrosion current of ZrC films was 10 times less and the polarization resistance at least 7.82 times higher than those of both Teflon and ZrN films, respectively. The experimental results confirmed that ZrC films notably enhanced the corrosion resistance of steels.
Temperature and time dependence of phase formation of HgBa2Can−1CunO2(n+1)+δ superconductors
Authors: Yamamoto Ayako , Itoh Makoto , Fukuoka Atsushi , Adachi Seiji , Yamauchi Hisao , Tanabe Keiichi
Published: March 2008

We systematically studied the temperature and time dependence of phase formation of HgBa2Can−1CunO2(n+1)+δ [Hg-12(n − 1)n, n = 1, 2, 3, 4] superconductors by a single step firing method. All samples were synthesized from high-purity HgO, BaO, CaO, and CuO in a sealed quartz tube. The phase formation of Hg-12(n − 1)n was examined by both x-ray diffraction (XRD) analysis and dc susceptibility measurement. A single-phase HgBa2CuO4+δ (Hg-1201) was obtained in a relatively wide temperature range (600–850 °C), while single-phase HgBa2CaCu2O6+8 (Hg-1212) and HgBa2Ca2Cu3O8+δ (Hg-1223) were obtained only in narrow temperature and time ranges for the synthesis. The optimum temperatures for Hg-1212 and Hg-1223 were found to be 665 and 710 °C, respectively, when the sintering time was fixed for about 50 h. The HgBa2Ca3Cu4O10+δ (Hg-1234) phase was obtained as a mixture with Hg-1223.
Thermal instability of (Bi,Pb)2Sr2Ca2Cu3Ox in contact with silver
Authors: Moon Robert J. , Trumble Kevin P. , Bowman Keith J.
Published: March 2008

The chemical and microstructural evolution of particulate (Bi,Pb)2223 in contact with pure bulk silver at 830 to 905 °C under flowing air and Ar−5% O2 atmospheres has been studied. Specimens annealed under PO2 and temperature conditions for which the (Bi,Pb)2223 phase itself is stable, based on a critical assessment of the literature, revealed a silver/(Bi,Pb)2223 interface-limited reaction, producing both solid and liquid decomposition phases. The (Bi,Pb)2223 not in direct contact with silver exhibited no reaction under the same conditions. Solid silver dissolves into the (Bi,Pb)2223 incongruent liquid, facilitating the incongruent melting reaction. On cooling, equiaxed metallic silver particles precipitated uniformly throughout bulk specimens partially melted on a silver substrate.
Fabrication and properties of arrays of superconducting nanowires
Authors: Dubois S. , Michel A. , Eymery J. P. , Duvail J. L. , Piraux L.
Published: March 2008

We report on the fabrication and structural characterization of arrays of superconducting nanowires by electroplating lead into the nanopores of track-etched polymer membranes. The diameters of the lead nanowires range from 400 down to 70 nm, whereas their length is about 20 μm. Large enhancement of the critical field has been observed in good agreement with the Ginsburg–Landau–Silin theory. By comparing the predicted critical field enhancement for thin cylinders with experimental results, we have extracted the effective penetration depth. The dependence of the effective penetration depth and electron mean free path on the wire diameter is also discussed.
Large grain polycrystalline silicon via chemical vapor deposition
Authors: Beckloff Bruce N. , Lackey W. Jack , Pickering Elliott M.
Published: March 2008

Large grain polycrystalline Si films were grown by chemical vapor deposition (CVD) onto TiB2 substrates using the SiCl4–H2 reagent system. A statistically designed processing study was used to correlate the film growth rate, crystallographic orientation, and grain size with deposition temperature, the SiCl4 : H2 ratio, and the level of B doping. Each process variable influenced grain size with temperature having the dominant effect. Grains as large as 15 to 20 μm were achieved for a coating thickness of about 50 μm.
Relating mechanical testing and microstructural features of polysilicon thin films
Authors: Jayaraman S. , Edwards R. L. , Hemker K. J.
Published: March 2008

Polycrystalline silicon thin films (polysilicon) have been deposited on single crystalline silicon substrates, and square and rectangular windows have been etched into these substrates using standard micromachining techniques. Pressure-displacement curves of the resulting polysilicon membranes have been obtained for these geometries, and this data has been used to determine the elastic constants E and v. The microstructural features of the films have been investigated by transmission electron microscopy (TEM) and x-ray diffraction. The grains were observed to be columnar and were found to have a 〈011〉 out-of-plane texture and a random in-plane grain orientation. A probabilistic model of the texture has been used to calculate the bounds of the elastic constants in the thin films. The results obtained from bulge testing (E = 162 ± 4 GPa and v = 0.20 ± 0.03) fall in the wide range of values previously reported for polysilicon and are in good agreement with the microsample tensile measurements conducted on films deposited in the same run as the present study (168 ± 2 GPa and 0.22 ± 0.01) and the calculated values of the in-plane moduli for 〈1103〉 textured films (E = 163.0–165.5 GPa and v = 0.221–0.239).
Phase transformation in ball-milled iron-rich Sm–Fe(–C) powders
Authors: Mao O. , Altounian Z. , Ström-Olsen J. O. , Yang Jun
Published: March 2008

Two intermetallic phases, R2Fe17 carbide and R2Fe14C, which are promising candidates for permanent magnets, are formed in the iron-rich R–Fe–C ternary alloy system (R = rare earths). Using x-ray diffraction and thermomagnetometry the phase formation, transformation, and thermodynamic relations between the two structures, prepared by high energy ball milling, are studied quantitatively for R = Sm. The results lead to a free energy diagram for the pseudobinary system of Sm2Fe17 and C. A maximum equilibrium carbon content, xc, has been established for the carbide Sm2Fe17Cx and its temperature dependence determined. Beyond the equilibrium concentration, Sm2Fe17Cx transforms into a mixture of Sm2Fe17Cxc, Sm2Fe14C, and α–Fe. Although not thermodynamically stable, Sm2Fe17Cx can still be formed through nonequilibrium processes by being kinetically favored over the stable phase(s). This feature is important for the production of Sm–Fe–C-based permanent magnets.
Restructuring of alumina particles using a plasma torch
Authors: Shim H. , Phillips J. , Silva I. S.
Published: March 2008

A method to modify ceramics using a low power microwave plasma torch is described. The size, shape, surface area, and phase of alumina particles were dramatically modified by passage through an atmospheric pressure argon plasma, operated at 1 kW or less power. Specifically, irregularly shaped particles of γ-alumina with an average diameter of 11 μm were converted to smaller (ca. 4 μm) spherical particles primarily consisting of δ- and α- (corundum) phases. Also notable was the finding that modifications of the particles, such as changes in surface area, correlate to applied plasma energy. The plasma torch was operated with an argon flow rate of 5 slpm, power of between 400 and 1000 W, and average particle residence time in the plasma of 0.1 s.
Crystal growth of layered perovskite Sr2Nb2O7 and Sr2Ta2O7 film by the sol-gel technique
Authors: Okuwada Kumi , Nakamura Shin-ichi , Nozawa Hiroshi
Published: March 2008

High dielectric and low loss capacitor thin films of Sr2Nb2O7 (SN), Sr2Ta2O7 (ST), and their solid solution Sr2(Nbx, Ta1−x)2O7 (SNT) were investigated using the sol-gel technique. The SN film grows with the (0n0) orientation in the case of heating at over 700 °C. Heat treatment at a lower temperature results in the polycrystal ST-type structure. The SNT at x < 50% also resulted in the ST type. The dielectric constant for the SN film was 45, within 10% variation at ±0.5 MV/cm. Dielectric loss (tan δ) was 0.3–0.5%. The small variation in dielectric constant and the paraelectricity with low loss are suitable for capacitor applications.
Grain boundary impedance of doped Mn–Zn ferrites
Authors: Arcos D. , Vázquez M. , Valenzuela R. , Vallet-Regí M.
Published: March 2008

The electrical properties of Mn–Zn ferrites undoped and doped with Nb2O5 and V2O5 were investigated by impedance spectroscopy. The observed impedance response corresponded to that of a highly resistive grain boundary component in series with a less resistive bulk component. The presence of Nb5+ and V5+ led to an enhancement in the electrical resistance, especially in grain boundaries, as well as a greater difference in the electrical behavior between bulk and grain boundary components. The different dopant performance of these two components is discussed on the basis of grain boundary structure and chemical data, electrical conductivity, and dielectric dispersion.
Microstructure and ambient properties of a Sialon composite prepared by hot pressing and reactive sintering of β–Si3N4 coated with Al2O3
Authors: Ghosh G. , Vaynman S. , Fine M. E. , Hsu S. M.
Published: March 2008

A composite microstructure, consisting of β-Sialon, O-Sialon, and X-Sialon phases was produced by coating β–Si3N4 particles with amorphous alumina followed by hot pressing and reactive sintering at 1923 K. The particle coating procedure was selected over conventional powder blending in order to promote heterogeneous nucleation of β-Sialon grains on β–Si3N4 particles uniformly. The microstructure, chemistry of the phases, and interphase interfaces of this ceramic were characterized by transmission electron microscopy (TEM) and high-resolution analytical electron microscopy (AEM). Both electron energy-loss spectroscopy (EELS) and energy-dispersive spectroscopy (EDS) x-ray microanalysis in AEM revealed that b-Sialon grains had varying aluminum and oxygen contents. High-resolution electron microscopy (HREM) examination of several interphase interfaces and triple junctions suggests that the amount of glassy phase in the produced ceramic is substantially lower compared to those reported in the literature. This is of importance of high temperature properties. The fracture toughness and wear properties were evaluated at room temperature. Available data indicate that the fracture toughness and wear of β-Sialon composite can be significantly improved by the powder coating technique compared to the conventional powder blending technique.
Effects of PbO excess in Pb(Mg1/3Nb2/3)O3–PbTiO3 ceramics: Part II. Microstructure development
Authors: Villegas M. , Fernáandez J. F. , Caballero A. C. , Samardija Z. , Drazic G. , Kosec M.
Published: March 2008

The microstructure evolution of Pb(Mg1/3Nb2/3)O3 –PbTiO3 (PMN-PT) based ceramics has been investigated to determine the influence of the presence of PbO content in excess of stoichiometric values. The microstructure of the different materials showed a different evolution of secondary phases (free PbO and pyrochlore type) related to the PbO excess. The pyrochlore phase appeared in a layer near the top surface of the specimens. The thickness of the layer and the grain size of this secondary phase increased with the amount of PbO excess. A transmission electron microscopy (TEM) study of the sintered specimens revealed a core-shell structure in more than 30% of grains. The shell of these grains was Ti-rich PMN, and it is related to the presence of a liquid-phase-assisted sintering mechanism.
Synthesis and sintering of SiC under high pressure and high temperature
Authors: Bhaumik S. K. , Divakar C. , Devi S. Usha , Singh A. K.
Published: March 2008

Starting from elemental powders, simultaneous synthesis and compaction of SiC were conducted at 3 GPa pressure and temperatures in the range 2100–2900 K. The sintered compacts were characterized by x-ray diffraction, microhardness measurements, and microscopic studies. The efficiency of formation of SiC was dependent on the particle size of the silicon powder, crystallinity of the reactant carbon, molar ratio of silicon and carbon, and synthesis temperature and time. Carbon in excess of the stoichiometric amount was required to obtain compacts free from residual silicon. The SiC samples, with a Si: C molar ratio 1: 1.05, prepared at 2100 K for 300 s had a density and hardness of 3.21 g/cm3 (98.8% of theoretical density) and 22 GPa, respectively. The crystal structure of the SiC depended on the synthesis temperature. Pure β–SiC in the temperature range 2100–2500 K, and a mixture of α– and β–SiC above 2500 K were obtained. The β–SiC was highly crystalline and nearly defect-free.
Bulk thermal expansion for tungstate and molybdates of the type A2M3O12
Authors: Mary T. A. , Sleight A. W.
Published: March 2008

Bulk thermal expansion properties of 19 members of the A2M3O12 family of tungstates and molybdates were determined from room temperature to 800 °C. The observed behavior ranges from strong negative thermal expansion (α = −11 × 10−6 K−1) in Sc2W3O12 to near zero thermal expansion in Al1.68Sc0.02In0.30W3O12.
Reaction synthesis of mullite-zirconia from mixtures of alumina, silica, and 3 mol% yttria-zirconia powders
Authors: Lin Yung-Jen
Published: March 2008

Mullite-zirconia composites were synthesized by reaction-sintering powder mixtures of α-alumina, amorphous silica, and 3 mol% yttria-stabilized zirconia. It is found that the addition of 3 mol% yttria-zirconia improves sintering and lowers the mullitization temperature. It also suppresses the cristobalite formation and enhances zircon formation between 1300 and 1400 °C. Results further suggest that these effects are consequences of modification of the silicate glass by yttria. Samples containing ≥20 vol% of 3 mol% yttria-zirconia could be sintered at 1500 °C for 2 h to obtain dense composites consisting of mullite and tetragonal zirconia. The microstructural investigations of the sintered samples support the viewpoint that mullite formation is via nucleation and growth from aluminosilicate glass. They also reveal that zirconia can hinder the grain growth of mullite and that the coalescence of zirconia grains is accomplished by grain boundary diffusion.
Field-activated pressure-assisted combustion synthesis of polycrystalline Ti3SiC2
Authors: Feng Aiguo , Orling Tim , Munir Z. A.
Published: March 2008

The simultaneous synthesis and densification of the ternary Ti3SiC2 was investigated by the field-activated, pressure-assisted combustion method. Depending on temperature and time at temperature, relatively pure and nearly fully dense materials can be synthesized by this approach. The optimum conditions to produce this phase were a reaction temperature of 1525 °C and a time at temperature of 2 h. The product contained TiC as a second phase at a level of ≤2 mol%. The resulting ternary phase has typically elongated grains which were about 25 μm in size. Within a range of applied force of 1–4 N, the microhardness of the product was relatively constant, ranging from 6 to 7 GPa. Investigations on the thermal and chemical stabilities of the ternary were also conducted. Vacuum annealing at temperatures of 1600 and 2000 °C resulted in the formation of a surface layer of TiC, while the air annealing at 1000 °C resulted in the formation of TiO2. Oxidation studies on the prepared Ti3SiC2 were made at temperatures ranging from 800 to 1100 °C. The results suggest a two-mechanism process, one dominating in the approximate range of 800–950 °C and the other in the range 950–1100 °C with corresponding activation energies of 137.7 and 312.5 kJ·mol−1. The results are explained in terms of two proposed reactions on the basis of microprobe analyses.
Pulsed laser-ablation deposition of thin films of molybdenum silicide and its properties as a conducting barrier for ferroelectric random-access memory technology
Authors: Madhukar Sucharita , Aggarwal S. , Dhote A. M. , Ramesh R. , Samavedam S. B. , Choopun S. , Sharma R. P.
Published: March 2008

We report on the feasibility of using molybdenum silicide as a conducting barrier for integration of ferroelectric lead zirconate titanate capacitors on Si. Thin films of MoSi2 were deposited by pulsed laser-ablation deposition (PLD). The silicide films showed a structural transition from amorphous to orthorhombic to tetragonal phase as the temperature of deposition was changed from room temperature to 900 °C. The four-probe resistivity and surface roughness of the films decreased with an increase in the deposition temperature and crystallinity of the phase. Ferroelectric (La, Sr)CoO3/Pb(Nb, Zr, Ti)O3/(La, Sr)CoO3 capacitors were grown on Si/poly Si/MoSi2, and Si/poly Si/MoSi2/Pt structures. Transmission electron microscopy (TEM) studies of the MoSi2/LSCO and MoSi2/Pt/LSCO heterostructures indicated the formation of a thin layer of SiO2. In the case of Pt/MoSi2, Pt reacts with the silicide and forms PtSi, consuming the entire platinum layer and, thus, makes it unsuitable as a composite barrier. Electrical testing of the LSCO/PNZT/LSCO capacitors through capacitive coupling showed desirable ferroelectric properties on these substrates.
The influence of the external stress on the electromechanical response of electrostrictive 0.9Pb(Mg1/3Nb2/3)O3−0.1PbTiO3 in the dc electrical field-biased state
Authors: Zhao J. , Mueller Volkmar , Zhang Q. M.
Published: March 2008

The influence of uniaxial compressive stress, T3, applied parallel to the electrical field, on the electromechanical parameters of 0.9Pb(Mg1/3Nb2/3)O3−0.1PbTiO3 ceramics in the dc electrical field-biased state and at temperatures near the dielectric constant maximum Tm was investigated. It was found that T3 reduces both the dielectric constant and polarization level, which results in a reduction of the piezoelectric coefficient with stress. However, the compliance of the material does not show much change with stress. As a consequence, the coupling factor k33 is also reduced with stress. On the other hand, the existence of the local micropolar region in the material causes anomalous changes in the aforementioned properties when the material is subjected to a high electric field, which induces a macropolar state. The transformation of this macropolar state back to a micropolar state under stress involves a large volume strain and results in an enhancement of the hydrostatic piezoelectric response.
Formation and self-organization of nanometer-scale Au particles on graphite by vacuum deposition in iodine vapor
Authors: Honda Katsuya , Yamada Nobusuke , Sano Masahito , Yoshimura Susumu
Published: March 2008

Vacuum depositions of Au on highly oriented pyrolytic graphite (HOPG) and SiO2 substrates in iodine vapor of 1 × 10–4 Torr give rise to formation of dispersed nanoscale Au particles at room temperature. The iodine is physisorbed on the Au surface and prevents the Au particles from coalescing. The mean diameter of Au particles on highly oriented pyrolytic graphite (HOPG) is about 40 nm, which is larger than that on SiO2 The particles on HOPG have a narrower and more uniform size distribution than those on SiO2. Radial distribution function of the particles on HOPG showed many well-defined peaks, whereas that on SiO2 had only one peak, indicating highly structured deposition on HOPG by iodine adsorption.
Composition, oxidation, and optical properties of fluorinated silicon nitride film by inductively coupled plasma enhanced chemical vapor deposition
Authors: Jun Byung-Hyuk , Lee Joon Sung , Kim Dae-Weon , Sung Tae-Hyun , Bae Byeong-Soo , No Kwangsoo
Published: March 2008

Amorphous fluorinated silicon nitride films have been deposited with the variation of NF3 flow rate using SiH4, N2, Ar, and NF3 gases by inductively coupled plasma enhanced chemical vapor deposition for the first time, and the absolute composition, oxidation mechanism, and optical properties were investigated. The absolute composition including hydrogen was performed by means of elastic recoil detection time of flight. It was found that the oxygen and fluorine contents in the film dramatically increased, but the hydrogen content decreased to below 4 at.% as the NF3 flow rate increased. The oxidation mechanism could be explained in terms of the incorporation of the activated residual oxygen species in the chamber into the film with unstable open structure by the fluorine-added plasma. It was shown that the density and optical properties such as refractive index, absorption coefficient, and optical energy gap depended on the film composition. The variations of the above properties for fluorinated silicon nitride film could be interpreted by the contents of fluorine and oxygen with high electronegativity.
The influence of crystallization route on the SrBi2Nb2O9 thin films
Authors: Zanetti S. M. , Leite E. R. , Longo E. , Varela J. A.
Published: March 2008

Polycrystalline SrBi2Nb2O9-layered ferroelectric thin films were synthesized on Pt/Ti/SiO2/Si substrate using the polymeric precursors solution. The dip-coated films were specular and crack-free and crystallized during firing at 700 °C. Single-, double-, and triple-layered films were obtained by several dips in the deposition solution, and the influence of crystallization between each dip was studied. Microstructure and morphological evaluation were followed by grazing incident x-ray diffraction (GIXRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Multilayered films obtained using the intermediate-crystallized layer route present a dense microstructure with spherical grains, with a preferential orientation in the 〈215〉 direction; films obtained using the intermediate-amorphous layer route are polycrystalline and present elongated grains around 250 nm in size.
Determination of shear viscosity of borosilicate glass + silica powder compacts by an optical system
Authors: Bang Jaecheol , Lu Guo-Quan , Calata Jesus Noel
Published: March 2008

The shear viscosity of borosilicate glass (BSG) + silica powder compacts was determined during isothermal sintering at temperatures between 665 and 715°C. An optical system was used to measure in situ the densification profiles of the compacts in the form of thick films constrained on a rigid substrate and in-plane stresses generated during sintering. The shear viscosity as a function of relative density was calculated from these measurements by using Scherer's viscous constitutive equations for a porous sintering body. The shear viscosity for samples with silica contents from 0 to 20 vol% generally showed a slow increase with density in the low-density regime followed by a rapid rise after some threshold density that decreased with either increasing silica powder content or decreasing sintering temperature. The dependence of shear viscosity on relative density is consistent with results from sinter-forging experiments. However, results obtained from pure BSG compacts also revealed strong dependence of shear viscosity on temperature and microstructure, which has been all but neglected in previous theoretical studies.
Synthesis and characterization of nonconventional nickel-titania glasses by sol-gel route
Authors: Kundu T. K. , Chakravorty D.
Published: March 2008

Glasses in the NiO–TiO2 system in the composition range 15 to 25 mol% of NiO have been synthesized by the sol-gel technique by heat treatment of the precursor sol at 500°C. The glass structure is built up by crosslinking of two units, namely TiO6 octahedron and NiO3 triangle. Glassy structure is confirmed at a microscopic level by scanning electron microscopy. An increase in the values of peak-to-peak width of electron paramagnetic resonance with increasing concentration of Ni2+ is attributed to an enhanced interaction between neighboring paramagnetic Ni2+ ions.
Quantitative assessment of pores in oxidized carbon spheres using scanning tunneling microscopy
Authors: Vignal V. , Morawski A. W. , Konno H. , Inagaki M.
Published: March 2008

Surface heterogeneity, particularly shape and size of pores on the surface of activated carbon spheres were studied by using scanning tunneling microscopy (STM) and field-emission type scanning electron microscopy (FE-SEM). Spheres were carbonized either in N2 or CO2 atmosphere and oxidized ones were used as samples. A new numerical method based on the determination of contour maps from STM images was proposed in order to determine the size distribution in micropores. These results were discussed with respect to the adsorption of gas and liquid molecules. A good correlation between Brunaner, Emmett, and Teller (BET) surface area determined from adsorption isotherms of N2 at 77 K and the number of pores with the size of 0.5–1.8 nm was observed, indicating that the proposed procedure to analyze the pore size distribution is effective.
Resonant Raman study of polyparaphenylene-based carbons
Authors: Marucci A. , Brown S. D. M. , Pimenta M. A. , Matthews M. J. , Dresselhaus M. S. , Nishimura K. , Endo M.
Published: March 2008

A resonant Raman study of polyparaphenylene (PPP) prepared by the Kovacic and the Yamamoto methods and heat-treated at temperatures THT between 650 and 750°C has been performed using different laser excitation energies Elaser between 1.92 and 3.05 eV. For samples treated at low THT, the Raman spectra change with Elaser, and this behavior is ascribed to the coexistence of two forms of the PPP polymer (benzenoid and quinoid) as well as a disordered carbon material. For higher THT samples, only a dispersion of the position of the Raman band as a function of Elaser is observed, and this is explained as due to the carbonization of the original polymer. The transition temperature between these two regions of resonance behavior is lower for the Yamamoto-PPP samples than for the Kovacic-PPP samples.
Quantitative evaluation of adhesion of diamond coatings
Authors: Fan Qi Hua , Fernandes A. , Pereira E. , Grácio J.
Published: March 2008

This paper presents a model to evaluate quantitatively the adhesion of diamond coating according to indentation tests. It is found that small indentation load causes round spallation of the coating, no matter what the shape of the indenter. An exponential sink-in deformation of the coating under the indentation is proposed [y = −a × exp(−bx)]. The deformation stress at the spallation edge is considered the coating adhesion. Using an experimentally observed relation of the indentation load versus the film spallation radius, we evaluate the adhesion of a diamond coating on copper to be about 1.921–1.956 GPa, which is in agreement with thermal quench results. The validity of this model is also verified by its self-consistence.
Enthalpy of Formation of Rare-earth Silicates Y2SiO5 and Yb2SiO5 and N-containing Silicate Y10(SiO4)6N2
Authors: Liang Jian-Jie , Navrotsky Alexandra , Ludwig Thomas , Seifert Hans J. , Aldinger Fritz
Published: March 2008

The enthalpies of formation of two rare-earth silicates (Y2SiO5 and Yb2SiO5) and a N-containing rare-earth silicate Y10(SiO4)6N2 have been determined using high-temperature drop solution calorimetry. Alkali borate (52 wt% LiBO2·48 wt% NaBO2) solvent was used at 800 °C, and oxygen gas was bubbled through the melt. The nitrogen-containing silicate was oxidized during dissolution. The standard enthalpies of formation are for Y2SiO5, Yb2SiO5, and Y10(SiO4)6N2, respectively, –22868.54 ± 5.34, –22774.75 ± 8.21, and –14145.20 ± 16.48 kJ/mol from elements, and –52.53 ± 4.83, –49.45 6 ± 8.35, and –94.53 ± 11.66 kJ/mol from oxides (Y2O3 or Yb2O3, SiO2) and nitride (Si3N4). The silicates and N-containing silicate are energetically stable with respect to binary oxides and Si3N4, but the N-containing silicate may be metastable with respect to assemblages containing Y2SiO5, Si3N4, and SiO2. A linear relationship was found between the enthalpy of formation of a series of M2SiO5 silicates from binary oxides and the ionic potential (z/r) of the metal cation.
Two- and Three-dimensional Arrays of Magnetic Microspheres
Authors: Wen Weijia , Wang Ning , Zheng D. W. , Chen C. , Tu K. N.
Published: March 2008

A novel fabrication approach for two- and three-dimensional arrays of magnetic microspheres is presented in this paper. The magnetic microsphere is made from 47 μm size Al2O3 spheres onto which a 2–3 μm thick nickel layer is coated through electroless plating. After proper anneal, the outer nickel layer is converted to exhibit a crystalline structure. As an example for utilizing such magnetic microspheres, a two-dimensional, anisotropically conductive matrix is made by transferring the magnetic microsphere array from a template to a transparent adhesive tape using a magnetic attractive force. In addition, a three-dimensional array has also successfully been constructed on a metal plate. The two-dimensional conductor array may be useful for high-density circuit packaging applications in the semiconductor industry, and the three-dimensional array may open up a possibility for constructing three-dimensional photonic crystals.
Epitaxial Growth of Patterned SrBi2Ta2O9 Lines by Channel Stamping
Authors: Kim Jin Hyeok , Lange Frederick F. , Cheon Chae-Il
Published: March 2008

Patterned epitaxial SrBi2Ta2O9 (SBT) lines with (00l) out-of-plane orientation were grown on a (001) SrTiO3 substrate by the novel “channel stamping” method. Parallel channels in a poly(dimethylsiloxane) stamp were filled with a metalorganic precursor solution by spin coating. After solvent evaporation, the solid precursor within the channels was transferred to the substrate by stamping. Stamped precursor lines were pyrolyzed at 350 °C/1 h and then heated to 850 °C/1 h. It was shown by x-ray diffraction and scanning electron microscopy that patterned SBT lines were epitaxial, had a smooth surface with c-axis out-of-plane orientation, and a single in-plane orientation.
Thin Film Microstructure Control Using Glancing Angle Deposition by Sputtering
Authors: Sit J. C. , Vick D. , Robbie K. , Brett M. J.
Published: March 2008

Thin films with microstructures controlled on a nanometer scale have been fabricated using a recently developed process called glancing angle deposition (GLAD) which combines oblique angle evaporation with controlled substrate motion. Critical to the production of GLAD thin films is the requirement for a narrow angular flux distribution centered at an oblique incidence angle. We report here recent work with low-pressure, long-throw sputter deposition with which we have succeeded in fabricating porous titanium thin films possessing “zig-zag,” helical, and “pillar” microstructures, demonstrating microstructural control on a level consistent with evaporated GLAD. The use of sputtering for GLAD simplifies process control and should enable deposition of a broader range of thin film materials.
Speeding up Film Deposition Rate: Its Effects on Microstructures of YBa2Cu3Oy Superconducting Thick Films
Authors: Zhang X. F. , Kung H. H. , Foltyn S. R. , Jia Q. X. , Peterson E. J. , Peterson D. E.
Published: March 2008

Two very different pulsed laser deposition rates, 192 and 6 Å/s, were used to produce 1 μm thick superconducting YBa2Cu3Ox (YBCO) films on (001) SrTiO3 single-crystal substrates at 790 °C. Transmission electron microscopy (TEM) was used to characterize and compare microstructures between the two films. It has been found that the high deposition rate led to a slight deviation from the expected epitaxial orientations, and extra stress was induced in the films by increased lattice mismatch between the films and the substrates. In addition, misoriented YBCO grains were formed in the high-rate films after a thickness of about 150 nm. Postannealing in oxygen had no visible influence on these defects, although superconducting properties were improved significantly. In contrast to the high-rate films, overall epitaxial orientations have been formed in the low-rate films, and no misoriented YBCO grains were found. However, variations in lattice parameters and columnar voids were observed, although their existence apparently does not have considerable influence on superconducting current density (Jc). Cation disorder was observed in both films. A two-step film growth mechanism is concluded which is responsible for the formation of some defects in the high-deposition rate films.
Effects of the Heating Rate on Conversion of the Precursor Powders Used for Melt Processes into YBa2Cu3O7−y
Authors: Kim Chan-Joong , Kim Ki-Baik , Jee Young A. , Kuk Il-Hyun , Hong Gye-Won
Published: March 2008

Effects of the heating rate (100−6000 °C/h) to a peritectic temperature (Tp – 1015 °C) on conversion of Y2O3−BaCuO2−CuO and Y2BaCuO5−BaCuO2−CuO precursor powders into YBa2Cu3O7−y (Y123) were studied. Both precursor powders were rapidly converted into the Y123 phase. A volume fraction of the Y123 phase was more than 50%, even at a relatively fast heating rate of 3000 °C/h. At about 100−200 °C/h, which correspond to the rates of the first heating cycles of practical melt processes, almost 100% of the precursor powders were converted into a Y123 phase. Microstructures were studied in respect to Y2BaCuO5 (Y211) particle size, distribution, gas evolution, and nucleation mechanism of Y211 particles.
Electrochemical Synthesis and Characterization of La2CuO4+δ Single Crystals
Authors: Scarfe D. P. , Xiong X. , Zhu W. J. , Hor P. H. , Moss S. C. , Jacobson A. J.
Published: March 2008

An electrochemical oxidation technique was used to obtain bulk oxidized La2CuO4+δ single crystals from the as-grown crystals. Samples were prepared by galvanostatic oxidation with currents in the range 5–10 μA and with different charging times. Some samples were annealed at 110 °C in flowing oxygen. Small high-quality crystals were obtained from electrochemically oxidized larger crystals that contained microcracks. Transmission x-ray Laue photography and rocking curve measurements for several fundamental diffraction peaks were used to confirm the crystal quality. The Tc and bulk magnetic properties of samples at different stages in the oxidation process are reported. After annealing at 110 °C, a 15 K transition was observed.
Photoluminescence Spectral Lines Identification in Ho3+-, Er3+-, and Tm3+-doped MgxZn1–xSe Single Crystals
Authors: Kim Young-Geun , Song Ho-Jun , Oh Seok-Kyun , Kim Wha-Tek , Park Kwang-Ho , Kim Duck-Tae , Jin Moon-Seog , Kim Chang-Dae , Yoon Chang-Sun
Published: March 2008

MgxZn1-xSi: Ho3+, MgxZn1-xSe: Er3+, and MgxZn1-xSe: Tm3+ single crystals were grown by the closed-tube sublimation method. The single crystals crystallized into a zincblende structure at the composition x = 0.11 and a wurtzite structure at the composition x = 0.25, 0.32, and 0.41. The trivalent ions (Ho3+, Er3+, and Tm3+) of the rare-earth elements Ho, Er, and Tm site in Td and C3v symmetries in the single crystals with zincblende and wurtzite structures, respectively. Sharp emission peaks appeared in the photoluminescence spectra of the single crystals. These emission peaks are identified to originate from the radiation recombination between the energy levels of the trivalent ions sited in Td and C3v symmetries.
Nanoscale Heterogeneities in Amorphous Semiconductorxmetal1–x Alloys: A Small-angle X-ray Scattering Study
Authors: Rigden J. S. , Newport R. J.
Published: March 2008

A series of small-angle x-ray scattering (SAXS) experiments has been conducted in order to probe further the X-ray absorption fine structure (EXAFS)-derived nanoscale structure of amorphous hydrogenated siliconxtin1–x, hydrogenated siliconxnickel1x, and germaniumxgold1–x materials as a function of metal content. The SAXS results reveal information on cluster formation within these reactively radio-frequency–sputtered amorphous thin films. The data are considered within the context of EXAFS data and lend support to a model in which the degree and nature of the heterogeneities depend primarily on the metal species, with the level of metal content inducing additional effects. In particular, the results support a percolation model for the metal: nonmetal transition in amorphous semiconductorxtransition metal1–x alloys, the conducting volume elements comprising metal or metal compound-rich regions within the amorphous tetrahedral host network.
Ultrasonic Linear and Nonlinear Behavior of Fatigued Ti–6Al–4V
Authors: Frouin Jerome , Sathish Shamachary , Matikas Theodore E. , Na Jeong K.
Published: March 2008

The change in ultrasonic nonlinear property of a titanium alloy subjected to cyclic loading has been studied, with an objective to develop a new characterization methodology for quantifying the level of damage in the material undergoing fatigue. In order to determine the degree of nonlinearity, the ultrasonic second harmonic generation technique has been used. The second harmonic signal was monitored during the fatigue process, and a substantial increase in the second harmonic amplitude (180% increase in nonlinear factor) was observed. This indicates that the second harmonic signal is very sensitive to the microstructural changes in the material caused by fatigue.
Constrained Cavitation and Fast Fracture at Metal-ceramic Interfaces at Elevated Temperatures
Authors: Kennefick C. M.
Published: March 2008

Processes that constrain or promote cavity growth and fast fracture at elevated temperatures are examined. Solutions are given for the stress caused by inhomogeneous deposition of matter in metal-ceramic and alumina grain boundaries and for the tensile stress near the top of a hemispherical pore during pore growth. Velocities of dislocation climb that could promote fast fracture are calculated for elastic stresses acting upon dislocations arising from both a crack tip and interface repulsion. The rates for the atomic diffusive processes and the magnitudes of stresses resulting from them are found to agree well with experimental rate of pore growth, and new data on pore growth and fracture at an aluminum-sapphire interface are presented.