bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of yttria content on the preparation of nanocrystalline yttria-doped zirconia
Authors: Huang Dai , Venkatachari K.R. , Stangle Gregory C.
Published: September 2007

Nanocrystalline zirconia doped with 0–10 mol % Y2O3 has been prepared by a combustion synthesis process, followed by a rapid densification process. The concentration of Y2O3 in the as-reacted zirconia appeared to have a significant influence on the reduction of the crystallite size, in the combustion temperature range studied (450 °C–550 °C), as well as on the stabilization of the tetragonal and/or cubic phases. The green compacts were densified by a fast-firing process. During fast-firing, the dwell temperature significantly affected the final average grain size and the final density of the article. On the other hand, the ranges of heating rates and dwell times that were used in this study were shown to have a much less significant effect on the article's final density and final average grain size. The yttria content had the largest influence on the final density and final average grain size. The densification took place much more rapidly in the 4 mol % Y2O3-ZrO2 samples than in the 10 mol % Y2O3-ZrO2 samples. In particular, the difference in densification rates between the samples with different Y2O3 content was attributed to the influence and magnitude of the associated grain-growth process. It was determined, however, that a high final density (>99% ρth) and a very fine final average grain size (<200 nm) could be simultaneously achieved with each of three different heating rates for the 4 mol% Y2O3-ZrO2 articles.
The influence of Pt and SrTiO3interlayers on the microstructure of PbTiO3thin films deposited by laser ablation on (001) MgO
Authors: Stemmer S. , Streiffer S.K. , Hsu W-Y. , Ernst F. , Raj R. , Rühle M.
Published: September 2007

We have used conventional and high-resolution transmission electron microscopy to investigate the microstruture of epitaxial, ferroelectric PbTiO3films grown by pulsed laser ablation on (001) MgO single crystals, and on MgO covered with epitaxial Pt or SrTiO3. Pronounced variations are found in the widths and lengths ofa-axis-oriented domains in these films, although the volume fraction ofa-axis-oriented material varies only weakly for the different types of samples. In addition, the films deposited onto Pt-coated MgO have a larger grain size than those deposited onto bare MgO or SrTiO3/MgO. Possible reasons for the variations in the distribution ofa-axis-oriented material in these samples include differences in the elastic properties and electrical conductivities of the different substrate combinations.
Scanning tunneling microscope/scanning tunneling spectroscopy investigation of the structural modulation on the surface of cleaved Bi2Sr2CaCu2Oy, single crystal
Authors: Ting Wu , Itti R. , Ishimaru Y. , Gu G. , Enomoto Y. , Koshizuka N. , Tanaka S.
Published: September 2007

The surface of cleaved Bi2Sr2 CaCu2O3 (Bi2212) single crystals has been studied by means of scanning tunneling microscope (STM) and scanning tunneling spectroscopy (STS) at room temperature in ultrahigh vacuum. We obtain atomic images of the BiO surface using logarithmic current mode and conventional mode. It is demonstrated that the Bi atoms in the BiO plane are not missing. Some Bi atoms are depressed down below the BiO surface. STS obtained at different places of the surface shows more or less the same feature, indicating that local electronic density of states does not change much due to the depression or the well-known structural modulation. The possible origins of the variation in the period of the structural modulation in the BiO plane of cleaved Bi2212 single crystals extracted from STM images are also studied.
The microstructural evolution of a silver-containing spray deposited 1223 Tl–Ca–Ba–Cu oxide superconductor
Authors: Briant C.L. , DeLuca J.A. , Karas P.L. , Garbauskas M.F. , Sutliff J.A. , Goyal A. , Kroeger D.
Published: September 2007

This paper reports a study of the microstructural evolution of Ag-containing 1223 Tl-Ca-Ba-Cu oxide superconductors in spray-deposited films. The films were formed by spray depositing nitrates of Ca, Ba, Cu, and Ag onto a polycrystalline yttria-stabilized zirconia substrate. These deposits were then converted to a mixture of oxides (calcia, calcium-copper oxide, and barium cuprate) and metallic silver by heating in oxygen. When thallium oxide vapor was passed over the film, the thallium was incorporated into the film and the 1223 phase was formed. The evidence strongly suggests that the development of the 1223 superconductor involves the formation of a liquid phase. Our analysis suggests that the initial phase to form a liquid is CaO which contains thallium, barium, copper, and silver. Once this initial liquid is formed, it incorporates more thallium which, in turn, allows it to dissolve other types of oxides present in the film. In this way the liquid spreads across the surface. The equilibrium 1223 phase precipitates from it.
Size dependent hardness of silver single crystals
Authors: Ma Qing , Clarke David R.
Published: September 2007

The hardness of thick, high-purity, epitaxially grown silver on sodium chloride is found to be dependent on the size of the indentation for sizes below ≃10 μm. The measurement of the size effect has been made in two ways. In one, the hardness has been calculated from the load-displacement curve obtained from an instrumented microhardness testing machine and assuming a geometric self-similarity in the indenter shape. In the other measurement, the hardness was obtained from the load exerted by the microhardness tester divided by the indentation impression area as measured by atomic force microscopy. The observed variation in microhardness with indentation size is consistent with a simplified strain gradient plasticity model in which the densities of the geometrically necessary and statistically stored dislocations are fitting parameters. An equally good fit can also be made with a simple geometric scaling relationship. Transmission electron microscopy observations of a thin (≃50 nm) epitaxial gold film embedded in the silver layers revealed that the deformation was primarily restricted to the sharp edges of the indentation. In addition, deformation twinning within the indentation impression was observed on the {1H} planes.
Homogeneous precipitation of doped zinc sulfide nanocrystals for photonic applications
Authors: Gallagher D. , Héady W.E. , Racz J.M. , Bhargava R.N.
Published: September 2007

A process was developed to prepare nanocrystalline and quantum-confined particles of manganese-doped zinc sulfide. By the reaction of diethylzinc with solubilized hydrogen sulfide, particle sizes of 30–36 Å were achieved by control of reactant concentration, and size appeared to vary with the thermodynamic considerations indicative of homogeneous precipitation. Managanese doping required the development of an in situ chemical reaction compatible with the homogeneous precipitation reaction. To that end, ethylmagnesium chloride was reacted with manganese chloride to form the metastable diethylmanganese which acted as the dopant source. Quantum confinement of the particles was accomplished by using methacrylic acid and poly(methyl methacrylate) polymer of low molecular weights. These surfactants were transparent to the ultraviolet wavclcngths of light which allowed luminescent excitation of the material and provided surface passivation which enhanced phosphor brightness. The surfactant adsorption and effect of ultraviolet curing of the surfactant on the luminescent efficiency of the doped nanocrystals was investigated by infrared spectroscopy. These results indicate that the chemisorption of the surfactants to the nanoparticle surface and oxidation followed by crosslinking during curing are responsible for the improvement in luminescent efficiency.
Hyperfine structure changes in iron-base amorphous alloys produced by high current density electropulsing
Authors: Lai Z.H. , Chao Y.S. , Conrad H. , Chu K.
Published: September 2007

The effects of high current density electropulsing on the hyperfine structure of amorphous alloys Fe73Si9.5B17.5, Fe75Si10B15, and Fe79Si7B14 were investigated by Mössbauer spectroscopy. Electropulsing influenced the microstructure at a temperature well below the bulk crystallization temperature. In the alloy having least boron (or highest concentration of Fe), α-Fe particles ≃3 nm in size precipitated from the amorphous matrix, giving a change in internal magnetic field.
Characterization of W/Si multilayers by ultrasoft x-ray emission spectroscopy
Authors: Kurmaev E.Z. , Shamin S.N. , Galakhov V.R. , Wiech G. , Majkova E. , Luby S.
Published: September 2007

The SiL2.3 emission spectra of amorphous W/Si multilayers were measured. For the as-deposited samples the SiL2,3 emission spectra have been found to be very close to that of amorphous Si. The formation of WSi2 phase during annealing of W/Si multilayers at a temperature ≥50 °C was detected. From the SiL2,3 emission spectra of as-deposited and annealed samples, the amount of W/Si2 phase was estimated. It is shown that this technique can be used for quantitative estimation of the ratio of amorphous Si and WSi2 phases in W/Si multilayers.
Low temperature synthesis and some physical properties of barium-substituted lanthanum manganite (La1−x BaxMnO3)
Authors: Chakraborty Amitava , Sujatha Dévi P. , Maiti H.S.
Published: September 2007

Barium-substituted lanthanum manganite (La1−xBaxMnO3) powders have been synthesized by a novel autoignition technique, and the effect of barium content on the autoignition characteristics, stability of the compound, and the powder characteristics have been investigated. X-ray examinations show that the material exists as a single phase having perovskite structure up to 40 at. % substitution of Ba for La, beyond which mixed phases of LaMnO3 and BaMnO3 are formed at least up to the highest limit of substitution (50 at. %) and calcination temperature (1350 °C) investigated. Electrical conductivity and thermal expansion behavior of the material have been studied for plausible use as cathode material in solid oxide fuel cells.
Dielectric and electrostrictive properties of (1 – x) Pb(Mg1/3Nb2/3)O3−xPb(Mn2/3W1/3)O3 ceramics
Authors: Yoon Ki Hyun , Kim Seung Yun , Karig Dong Heon
Published: September 2007

The dielectric and electrostrictive properties of (1 - x) PMN−xPMW (x ⋚ 0.2) using chloride salts were investigated as a function of x. When the PMN-PMW powders were calcined at 700 °C for 1 h, the perovskite phase formed was 92%–97% at any given PMW composition (x ⋚ 0.2). With the increase of PMW content up to 0.2, the relative density of the specimens increased slightly, and the electrostrictive coefficient Q11 of the 0.8 PMN−0.2 PMW specimen increased about 6 × 10−2 m4/C2. However, the dielectric constant and electrostrictive strain of the specimens decreased despite the improved sinterability.
Role of excess PbO on the microstructure and dielectric properties of lead magnesium niobate
Authors: Gupta S.M. , Kulkarni A.R.
Published: September 2007

Stoichiometric and 2 wt. % excess lead oxide containing lead magnesium niobate (PMN) ceramics have been prepared by partial oxalate route. Dielectric measurements with frequency showed a typical relaxor behavior for stoichiometric PMN, while PMN with excess PbO shows a scatter in the dielectric curves at all temperatures above Tc. Under the same processing conditions, the dielectric constant (Kmax) decreases drastically from 16,300 to 9500 at 1 KHz for PMN without and with excess PbO, respectively. Microstructure studies revealed a second phase (unreacted PbO) segregated in the grain boundaries for excess PbO samples. A careful analysis of the data on dielectric properties and phases present coupled with microstructural detail indicate that the second phase in the grain boundary has a pronounced effect on the dielectric properties and not the pyrochlore phase.
Ion-beam induced disordering and onset of amorphization in spinel by defect accumulation
Authors: Bordes N. , Wang L.M. , Ewing R.C. , Sickafus K.E.
Published: September 2007

Ion-irradiation induces amorphization in many intermetallics and ceramics, but spinel (MgAl2O4) is considered a “radiation resistant” ceramic. Spinel was irradiated with 1.5 MeV Kr+ at 20 K and observed in situ by transmission electron microscopy (TEM). The spinel remained crystalline to a high dose of 1 × 1016 ions/cm2, without any evidence of amorphization. Another spinel was preimplanted with Ne (400 keV and 50 keV). The microstructure revealed a still crystalline material with 8 nm interstitial loops. After irradiation with 1.5 MeV Kr+ (20 K), amorphization, a result of cation disordering, initiated at a dose of 1.7 × 1015 ions/cm2. At a dose of 1 × 1016 ions/cm2, the spinel was partially amorphous and the remaining crystalline domains disordered. These results show that spinel can be disordered and that amorphization can be triggered by the introduction of stable defects, followed by ion irradiation at low temperature.
Auger electron spectroscopy analysis of SiC-whisker surfaces and SiC-whisker/alumina interfaces
Authors: Braski D.N. , Alexander K.B.
Published: September 2007

Auger Electron Spectroscopy (AES) has been used to examine as-received and oxidized silicon carbide whiskers and their respective whisker/matrix interfaces after fabrication into SiC-whisker-reinforced alumina composites. As-received whisker surfaces exhibited a 2–3 nm-thick near-surface region that was C-rich. Oxygen was detected at the outer surface, but diminished to near zero within 25 nm of the surface. Oxidized whiskers had 60 nm-thick SiO2 surface layers, which was in agreement with the transmission electron microscopy observations. The whisker/matrix interfaces in both composites consisted of thin (<0.5 nm) layers of a C-Si-O noncrystalline material. The thick SiO2 layers on the oxidized whiskers were ejected from the interfaces during hot-pressing. It was concluded that (i) the higher toughness of the composite fabricated with as-received SiC whiskers may be related to the higher C and lower O in its SiCw/Al2O3 interfaces, and (ii) interface composition cannot be reliably predicted using the surface composition of free whiskers prior to fabrication.
Structural changes from polyimide films to graphite: Part IV. Novax and PPT
Authors: Bourgerette C. , Oberlin A. , Inagaki M.
Published: September 2007

Various polyimide films (Kapton, Upilex, Novax, and PPT) were carbonized and graphitized up to 3000 °C. They were studied by optical and electron microscopies. All films retaining oxygen as a cross linker over 1000 °C, i.e., Kapton, Upilex, and Novax, graphitize as anthracites (high rank coals) do. They get a long range statistical orientation parallel to the film plane with a nanotexture of flattened pores. Graphitization is both sudden and perfect above 2100 °C when the pore walls break. Since oxygen is released at 1000 °C, the film PPT behaves as a compact nonporous graphitizing carbon (orientation parallel to the film plane). Thermal graphitization is progressive and begins at a higher temperature.
Compressive behavior of materials: Part II. High performance fibers
Authors: Kozey Victor V. , Jiang Hao , Mehta Vinay R. , Kumar Satish
Published: September 2007

The primary focus of this paper is on the axial compression behavior of high performance polymeric and carbon fibers. Seven test methods used for determining the compressive strength of single fibers have been reviewed. Various micromechanical models proposed in the literature to understand the compressive failure in single filaments and in other anisotropic systems have been discussed and analyzed. The results of various approaches to influence the compressive strength of polymeric fibers have been summarized. Possible reasons for the variation in the compressive strength of pitch and PAN-based carbon fibers have also been addressed.
Erratum
Authors: Brusso J.A. , Mikkola D.E.
Published: September 2007

“Effects of boron on the deformation behavior of Ni3Al” [J. Mater. Res. 9, 1742–1754 (1994)]
Influence of the annealing atmosphere on the formation of Al–Cu–Fe quasicrystals
Authors: Kang Song-Seng , Dubois Jean-Marie
Published: September 2007

Icosahedral samples of nominal composition Al63.5Cu24Fe12.5, which normally grow a rhombohedral approximant crystal, were submitted to heat treatments of various durations. The atmosphere in contact with the surface of the specimens was either dry air or secondary vacuum in order to test whether the formation of the icosahedral phase is sensitive or not to the nature of the atmosphere. Materials annealed in air showed a very thin surface layer of oxide which contained hydrogen. Beneath this oxide layer, small quantities of oxygen and hydrogen were also detected within the underlying lattice. This contamination was sufficient to shift the composition of the samples out of the stability domain of the icosahedral phase and has induced formation of a significant amount of the cubic phase. In contrast, the rhombohedral compound no longer appeared. This behavior goes along with the great sensitivity of the icosahedral phase stability to a sharply denfined electron to atom ratio.
Oxygen interaction with ternary chalcogenide: an electron spectroscopy for chemical analysis study of AgInTe2
Authors: Badrinarayanan S. , Mandale A.B.
Published: September 2007

X-ray photoelectron spectroscopic measurements of oxidation of the AglnTe2 surface at different temperatures are reported. The results are analyzed quantitatively. The oxidized surface was shown to have TeO2, Te, and In2O3. The presence of In2O is also identified. The experimental results are explained on the basis of the heat of formation.
Deposition of epitaxial β–SiC films on porous Si(100) from MTS in a hot wall LPCVD reactor
Authors: Chiu Chien C. , Desu Seshu B. , Chen Gang , Tsai Ching Yi , Reynolds William T.
Published: September 2007

Epitaxial β-SiC thin films were grown on modified Si(100) substrates from methyltrichlorosilane (CH3SiCl3 or MTS) in a hot wall reactor by using low pressure chemical vapor deposition (LPCVD). At 1150 °C, the growth rate of the β-SiC films was 120 Å/min. Epitaxial β-SiC(100) thin films were deposited after the deposition time of 12.5 min. However, the crystallinity of the deposited films was influenced by the deposition time. For example, the occurrence of rotational β-SiC(100) crystals and polycrystalline β-SiC with a highly preferred orientation of (100) planes was obtained for the deposition time of 50 min. XRD and TEM showed the appearance of polycrystalline β-SiC films with a preferred orientation of β-SiC(111) after further increasing the deposition times (time ≥ 75 min). At 1100 °C, polycrystalline β-SiC films with poor surface morphology were observed even though the film had a preferred orientation of β-SiC(100) for short deposition time (e.g., 12.5 min). Polycrystalline β-SiC(111) film was obtained for the deposition time of 200 min at this temperature.
Catalytic properties of nanocrystalline WO3−x, Pt/WO3−x, and Pd/WO3−x particles
Authors: Lin Hong-Ming , Tung Chiun-Yen , Hsu Chi-Ming , Lee Pee-Yew
Published: September 2007

The gas-condensation technique is used to produce the nanocrystalline (NC) WO3−x, Pt/WO3−x, and Pd/WO3−x powders under different atmosphere and pressure. HRTEM images show that a coherently bonded interface exists between Pt or Pd and WO3−x. The nanocrystal WO3−x, Pt/WO3−x, and Pd/WO3−x grow into a needle shape with a plate inside when these as-evaporated powders are compacted and sintered at 900 °C for 2 h. The plate grows preferentially in {220} plane along the 〈0011〉 direction. However, the mean particle size of nanophase Pt and Pd increases only from <10 nm to 30 nm and 50 nm, respectively. The results of CO oxidation show that nanophase Pt/WO3−x powders have better catalytic effects on converting CO to CO2 than nanophase WO3−x and Pd/WO3−x powders.
Synthesis of low density carbon crystal “carbolite” by quenching of carbon gas
Authors: Tanuma Sei-ichi , Palnichenko Andrei
Published: September 2007

A new carbon crystal named carbolite has been synthesized by quenching high temperature carbon gas on a room temperature substrate. The crystal has a density as small as 1.46 g/cm3 and is transparent for visible light. The crystal structure is hexagonal, and the dimensions of the unit cell are 1.193 nm in the α-direction and 1.062 nm in the c-direction. Along the c-axis, a parallel array of carbon chains is proposed. The array is made up of a triangular lattice in which the interchain distance is 0.344 nm and the mean interatomic distance within a carbon chain is 0.133 nm. The former value is close to the van der Waals distance between the honeycomb planes of graphite, and the latter value is close to the C-C bond length in the honeycomb plane. Intercalations of potassium, sodium, and iodine atoms are performed.
Transmission electron microscopy study of Al/Al2O3 composites fabricated by reactive metal infiltration
Authors: Gao Y. , Jia J. , Loehman R.E. , Ewsuk K.G.
Published: September 2007

The microstructure of Al/α-Al2O3 composites made by infiltrating molten Al into dense mullite preforms has been characterized using transmission electron microscopy. The growth of the Al/Al2O3 composites was found to proceed through three stages. Initially, Al infiltrates into a dense mullite preform through grain boundary diffusion, and reacts with mullite at grain boundaries to form a partial reaction zone. Then, a complete reaction takes place in the reaction region between the partial reaction zone and the full reaction zone to convert the dense mullite preform to a composite of α-Al2O3 (matrix) and an Al-Si phase (thin channels). Finally, the reduced Si from the reaction diffuses out of the Al/Al2O3 composite through the metal channels, whereas Al from the molten Al pool is continuously drawn to the reaction region until the mullite preform is consumed or the sample is removed from the molten Al pool. Based on the observed microstructure, infiltration mechanisms have been discussed, and a growth model of the composites is proposed in which the process involves repeated nucleation of Al2O3 grains and grain growth.
Dynamic modeling of the interaction of gas and solid phases in multistep reactive micropyretic synthesis
Authors: Subramanian V. , Lakshmikantha M.G. , Sekhar J.A.
Published: September 2007

A mathematical model of micropyretic synthesis, including the consideration of pressure rise (due to gas evolution) in a porous compact, is developed for a multistep reaction. D'Arcy's law of gas flow, continuity equation, and gas law are combined to obtain a relationship between the pressure and temperature of gas. This equation for the gas pressure is solved along with the energy equations of gas and solid phase. The numerical analysis shows that the magnitude of pressure increase depends on the initial gas pressure, temperature, and permeability. When gas evolution is considered, the pressure increase depends on the variables that determine the kinetics of the gas evolution reaction, such as the activation energy and the pre-exponential factor. The pressure increase is maximum when the gas evolution takes place in the combustion reaction zone. The gas evolution is noted not to influence the combustion wave propagation.
Formation and characteristics of nanocrystalline composites γ–TiAl + Ti2AlN by mechanical alloying and subsequent annealing treatment
Authors: Wang K.Y. , Wang J.G. , Chen G.L.
Published: September 2007

Formation of nanocrystalline composites γ-TiAl + Ti2AlN by mechanically alloying (MA) Ti50Al50 in a N2 atmosphere and subsequent annealing treatment are investigated. The development of the microstructure was monitored by x-ray diffraction, and differential thermal analysis and transmission electron microscopy. The amorphous phase could be obtained after milling for 30 h in a nitrogen atmosphere. The TEM results show that some nanocrystalline solid solution of Al in Ti also existed in the amorphous matrix. The results of annealing treatments at different temperatures for 0.5 h on the amorphous phase obtained by MA in N2 gas for 30 h show the formation of γ-phase (TiAl) and a nitride of titanium and aluminum (Ti2AlN). Available annealing treatments could produced nanocrystalline composites of γ-TiAl and Ti2AlN with a grain size less than 20 nm. With increasing annealing temperature, the crystalline sizes of γ-TiAl and Ti2AlN increase, but the values of microhardness increase slightly.
TiO2-Al2O3 nanocomposites
Authors: Pacheco-Malagon G. , Garcia-Borquez A. , Coster D. , Sklyarov A. , Petit S. , Fripiat J.J.
Published: September 2007

Nanosized TiO2 is synthesized in a nanosized alumina matrix by a sol-gel procedure. The results of the study of the blueshift of the TiO2 UV band edge are compared to the information obtained from transmission electron microscopy (TEM). As long as the atomic ratio Ti/Al remains smaller than 17.5%, no individualized TiO2 particles are detected by TEM, in spite of the fact that no modification of the alumina structure occurs, as revealed by 27Al MAS NMR. The shift of the UV band edge suggests the growth of homogeneous TiO2 domains in the alumina matrix. Above a critical radius, on the order of 1.2 nm, individual and crystalline TiO2 particles become visible in the TEM picture, and the porosity of the material decreases markedly.
Oxygen incorporation in aluminum nitride via extended defects: Part II. Structure of curved inversion domain boundaries and defect formation
Authors: Westwood Alistair D. , Youngman Robert A. , McCartney Martha R. , Cormack Alastair N. , Notis Michael R.
Published: September 2007

Three distinct morphologies of curved (curved, facetted, and corrugated) inversion domain boundaries (IDB's), observed in aluminum nitride, have been investigated using conventional transmission electron microscopy, convergent beam electron diffraction, high-resolution transmission electron microscopy, analytical electron microscopy, and atomistic computer simulations. The interfacial structure and chemistry of the curved and facetted defects have been studied, and based upon the experimental evidence, a single model has been proposed for the curved IDB which is consistent with all three observed morphologies. The interface model comprises a continuous nitrogen sublattice, with the aluminum sublattice being displaced across a {1011} plane, and having a displacement vector R = 0.23〈0001〉. This displacement translates the aluminum sublattice from upwardly pointing to downwardly pointing tetrahedral sites, or vice versa, in the wurtzite structure. The measured value of the displacement vector is between 0.05〈0001〉 and 0.43〈0001〉; the variation is believed to be due to local changes in chemistry. This is supported by atomistic calculations which indicate that the interface is most stable when both aluminum vacancies and oxygen ions are present at the interface, and that the interface energy is independent of displacement vector in the range of 0.05〈0001〉 to 0.35〈0001〉. The curved IDB's form as a result of nonstoichiometry within the crystal. The choice of curved IDB morphology is believed to be controlled by local changes in chemistry, nonstoichiometry at the interface, and proximity to other planar IDB's (the last reason is explained in Part III). A number of possible formation mechanisms are discussed for both planar and curved IDB's. The Burgers vector for the dislocation present at the intersection of the planar and curved IDB's was determined to be b = 1/3〈1010〉 + t〈0001〉, where tmeas = 0.157 and tcalc = 0.164.
Investigation of tetragonal distortion in the PbTiO3–BiFeO3 system by high-temperature x-ray diffraction
Authors: Sai Sunder V.V.S.S. , Halliyal A. , Umarji A.M.
Published: September 2007

Compositions in the (Pb1−xBix (Ti1−xFex)O3 solid solution system for x ⋚ 0.7 show unusually large tetragonal distortion. High-temperature x-ray diffraction was used to study the tetragonal distortion as a function of temperature (25–700 °C) for compositions (x = 0–0.7) using powders prepared by solid-state reaction in the above system. Large changes in the lattice parameters were observed over a narrow temperature range near Curie temperature (TC) for compositions near the morphotropic phase boundary (MPB) (x ≃ 0.7). Compositions near MPB showed a c/a ratio of 1.18 at room temperature. Polar plots of lattice constants at different temperatures indicated strong anisotropic thermal expansion with zero thermal expansion along the [201] direction.
Coating of uniform inorganic particles with polymers: III. Polypyrrole on different metal oxides
Authors: Huang Chin-Lin , Matijevic Egon
Published: September 2007

Five kinds of uniform metal oxide particles (α-Fe2O3, CeO2, CuO, NiO, and SiO2) were coated with polypyrrole by reacting the dispersed solids with pyrrole in a water/ethanol medium without the use of a soluble oxidant. When the process was carried out in air, all particles were coated with the polymer, although the thickness of the layer varied on different cores. In CuO dispersions, independent polypyrrole particles were produced in addition to coated spheres. While oxygen is the major oxidant that initiates the polymerization of pyrrole, some metal oxides may also affect the reaction both in terms of the amount and the composition of the shell. Thus, α-Fe2O3 and SiO2 were found to be inactive in the polymerization, while CeCh and CuO react with the adsorbed pyrrole molecules through a reductive-dissolution process, in which the monomers are oxidized, causing a release of reduced metal ions.
A microstructural study of rapidly solidified and heat-treated austenitic Fe–Mn−Al–Mo–W–Nb–C alloys
Authors: Han Kwan H. , Lee Hyun E.
Published: September 2007

The microstructural characteristics of melt-spun and heat-treated austenitic Fe−28Mn−8.6Al−0.5Mo−0.7W−0.5Nb−1.1C (in wt. %) alloys have been investigated by means of transmission electron microscopy. The melt-spun alloy contained fine austenitic cells and some intercelluar Nb(C, N) precipitates. Detailed observations revealed fine {100} modulations in the matrix of the cells, as well as a concomitant L′I2 atomic ordering arising from it. These observations indicate that the onset of decomposition of the initial austenite phase occurred during the rapid solidification process. Aging of the melt-spun alloy at 823–1173 K produced various microstructures, including a general precipitation of Nb(C, N) in the matrix. On isochronal annealing for 1 h, this matrix Nb(C, N) precipitation commenced at 1073 K with the formation of metastable coherent K-carbide (K′) near cell boundaries. On annealing at temperatures above 1123 K, only the Nb(C, N) precipitates were formed, on a fine scale, being accompanied by the formation of precipitate-free regions in the vicinity of cell and grain boundaries. Both intercellular and matrix Nb(C, N) precipitates obeyed a cube-to-cube orientation relationship with austenite. The general matrix precipitation of Nb(C, N) and formation of precipitate-free regions are discussed in terms of a vacancy (defect)-depletion effect. Finally, it was demonstrated that, by employing a double heat-treatment schedule of annealing at 1173 K followed by aging at 823 K, a novel microstructure consisting of fine dispersoids of Nb(C, N) carbo-nitride, distributed over the matrix of {100} modulated structure, could be produced.
Banded structures in unstable combustion synthesis
Authors: Li H.P.
Published: September 2007

Banded structures in combustion-synthesized products have been observed during unstable combustion synthesis. The formation of the banded structures is discussed in this article. It is noted that the band spacing was changed when several initial processing conditions were varied. Any change in the processing parameters that correspondingly caused more unstable combustion was observed to decrease the propagation velocity of the combustion front and increase the band spacing. The correlation of the band spacing and oscillatory frequency of the unstable oscillatory combustion with the propagation velocity was also discussed. From the results studied in this work, it is noted that the change of the band spacing can be used to infer the degree of the instability of the combustion front.
Microstructural characterization of a microwave-sintered silicon nitride based ceramic
Authors: Plucknett Kevin P. , Wilkinson David S.
Published: September 2007

The microstructure of a microwave-densified silicon nitride based ceramic has been assessed in the as-sintered, post-sinter hot-isostatically pressed (HIPed) and annealed conditions. The grain size of the as-sintered material, which is a low substitution β′-Sialon, was significantly finer than observed in conventionally processed materials of similar composition. The as-sintered ceramic exhibits a reverse porosity gradient (with the highest porosity level at the surface) due to heat dissipation to the cooler surroundings during microwave processing. This also results in a higher β′ aspect ratio close to the surface arising from an increased glass viscosity (due to heat loss) and compositional change in this region during sintering. HIPing results in removal of all porosity from the sample core; however, a reduced porosity surface layer is retained. Significant β′-Sialon grain growth is also apparent after HIPing. A fine β′ grain structure was retained after annealing, with partial devitrification of the glassy grain boundary phase to β-Y2Si2O7.
Crystalline phases of sol-gel ZrO2 in the ZrO2-SiO2 system: Differential thermal analysis and electron microscopy studies
Authors: Acosta D.R. , Novaro O. , López T. , Gómez R.
Published: September 2007

Zirconium oxide dispersed in silica was synthesized by the cogelation of tetraethoxysilane and zirconium acetate. For the gelation, acid and basic media were used. The final zirconia concentration was around 6.7 wt. %. Differential thermal analysis, thermogravimetric analysis, as well as electron microscope techniques were used for the characterization of the samples. It was found that the stabilization of the crystalline phases depends on the preparation conditions and thermal treatments. Tetragonal and monoclinic ZrO2 phases were identified in basic preparations. However, in acidic samples only low-temperature tetragonal phase was identified.
Temperature calculation for laser irradiation of sol-gel films on oxide substrates
Authors: Taylor D.J. , Birnie D.P. , Fabes B.D.
Published: September 2007

A model for estimating the temperature rise in a laser-irradiated oxide target is developed and applied to laser-firing of sol-gel films on oxide substrates. The model incorporates a continuous-wave (CW) Gaussian laser beam translated across a sol-gel film on a semi-infinite substrate. Heat effects due to phase changes are assumed to be absent. In addition, the laser energy is assumed to be absorbed primarily in the substrate material (since many sol-gel films are much thinner than the absorption depth of typical laser wavelengths). The model also takes into account the temperature dependence of the thermal properties of the substrate. The predictions from the model are compared to experimental data from various laser firing experiments. The temperatures predicted by the model are shown to agree well with experimental results.
Frequency-dependent electromechanical properties for sol-gel deposited ferroelectric lead zirconate titanate thin layers: Thickness and processing effects
Authors: Li Jie-Fang , Viehland Dwight , Lakeman C.D.E. , Payne D.A.
Published: September 2007

The electromechanical properties of sol-gel-derived ferroelectric Pb(Zr0.53Ti0.47)O3 (PZT 53/47) thin layers deposited on silicon were determined as a function of field strength, measurement frequency, and total thickness. Both electrically induced strains (∊) and piezoelectric properties (d33) were characterized by interferometry. Dielectric spectroscopy and polarization switching (P-E) measurements were determined for comparative purposes. An asymmetry between forward and the reverse bias conditions in the ∊-E displacements was found for both five-layer deposited and nine-layer deposited structures. However, no asymmetry was observed in the P-E hysteresis characteristics. In addition, the electrically induced strains and the piezoelectric response were found to be dependent on measurement frequency. No significant frequency dependence was observed in the polarization or dielectric responses. The results are discussed in terms of a possible clamping effect on polarization switching.
Evidence for glide and rotation defects observed in well-ordered graphite fibers
Authors: Endo M. , Oshida K. , Kobori K. , Takeuchi K. , Takahashi K. , Dresselhaus M.S.
Published: September 2007

New structural features observed in heat-treated vapor-grown carbon fibers (VGCF's), produced by the thermal decomposition of hydrocarbon vapor, are reported using image analysis of the lattice plane structure observed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The TEM lattice image of well-ordered graphite fibers (heat-treated VGCF's at 2800 °C) was treated by a two-dimensional fast Fourier transform, showing sharp bright spots associated with the 002 and 100 lattice planes. The heat-treated VGCF's consist of a polygonally shaped shell, and the long and short fringe structures in the TEM lattice image reflect the 002 and 100 lattice planes, respectively. From this analysis, new facts about the lattice structure are obtained visually and quantitatively. The 002 lattice planes remain and are highly parallel to each other along the fiber axis, maintaining a uniform interlayer spacing of 3.36 Å. The 100 lattice planes are observed to make several inclined angles with the 002 lattice planes relative to the plane normals, caused by the gliding of adjacent graphene layers. This work visually demonstrates coexistence of the graphitic stacking, as well as the gliding of the adjacent graphene layers, with a gliding angle of about 3–20°. These glide planes are one of the dominant stacking defects in heat-treated VGCF's. On the other hand, turbostratic structural evidence was suggested by AFM observations. The structural model of coexisting graphitic, glide, and turbostratic structures is proposed as a transitional stage to perfect three-dimensional stacking in the graphitization process. These structural features could also occur in common carbons and in carbon nanotubes.
Composites based on thermally hyper-conductive vapor grown carbon fiber
Authors: Ting Jyh-Ming , Lake Max L. , Duffy David R.
Published: September 2007

Aluminum matrix composites and carbon/carbon composites based on vapor grown carbon fiber (VGCF) were fabricated for analysis of thermophysical properties. Due to the highly graphitic nature of VGCF, the resulting composites exhibit values of thermal conductivity that have not been achieved by using any other carbon fibers, and thus represent new materials for thermal management in applications such as packaging for high-power, high-density electronic devices. In the aluminum matrix VGCF composites, a thermal conductivity of 642 W/m-K was obtained by using a VGCF loading of only 36.5 vol.%. For VGCF/C composites, thermal conductivity of 910 W/m-K has been observed, a value which is more than a factor of two higher than that of copper. Based on the observed thermal conductivity of VGCF/Al composites and VGCF/C composites, the room temperature thermal conductivity of VGCF in the composite was calculated to be 1460 W/m-K and 1600 W/m-K, respectively.
Surface chemical states of barium titanate: Influence of sample processing
Authors: Mukhopadhyay Sharmila M. , Chen Tim C.S.
Published: September 2007

The composition and chemistry of the near-surface region of BaTiO3 have been studied using x-ray photoelectron spectroscopy (XPS). It is found that the Ba3d photoclectron peak shows two chemical states, one of which is attributed to the bulk perovskite and the other to a special surface state unrelated to contamination. The bulk component is reduced and the surface component increases when the material is annealed at high temperatures (either in reducing or oxidizing atmosphere). Both the components are unaltered if the sample is exposed to air, solvents, or water: processes that lead to adsorption of impurities. The surface peak, therefore, attributed to a relaxation related and not contamination-related state, has been compared with those in other Ba-containing oxides. The oxygen photoelectron peak consists of a normal perovskite peak typical of most titanates and a higher energy component clearly related to surface contamination. Annealing in reducing atmosphere results in drastically different optical and electrical properties, and in chemical reduction of some Ti4+ ions to Ti3+. The overall stoichiometry, however, does not change with annealing atmosphere. These results have been discussed in light of our current understanding of this and other related oxides.
Pt/Ti/SiO2/Si substrates
Authors: Fox G.R. , Trolier-McKinstry S. , Krupanidhi S.B. , Casas L.M.
Published: September 2007

Pt/Ti/SiO2/Si structures have been studied to investigate the structural, chemical, and microstructural changes that occur during annealing. Grain growth of the as-deposited Pt columns was observed after annealing at 650 °C, and extensive changes in the Pt microstructure were apparent following a 750 °C anneal for 20 min. In addition, two types of defects were identified on the surfaces of annealed substrates. Defect formation was retarded when the surface was covered with a ferroelectric film. Concurrent with the annealing-induced Pt microstructure changes, Ti from the adhesion layer between the Pt and the SiO2 migrated into the Pt layer and oxidized. It was shown with spectroscopic ellipsometry and Auger electron spectroscopy that for long annealing times, the titanium oxide layer can reach the Pt surface. Consequently, at the processing temperatures utilized in preparing many ferroelectric thin films, the substrate is not completely inert or immobile. The changes associated with Ti migration could be especially problematic in techniques that require the substrate to be heated prior to film deposition.
Plan-view microstructures of Co/Ru bilayers
Authors: Pan G.Z. , Michel A. , Pierron-Bohnes V. , Vennéguès P. , Cadeville M.C.
Published: September 2007

Plan-view microstructures of two Co/Ru bilayers with a composition of [Co12ÅRu45Å]2 and [Co40ÅRu35Å]2 have been studied by conventional and high resolution electron microscopy. Large differences in electron diffraction and image contrast between the two bilayers were observed, which are recognized as the microstructural variations during the relaxation of large coherent planar strains when the Co layers wet coherently or semicoherently the Ru layers. For the [Co12ÅRu45Å]2 bilayer, the Co layers are unrelaxed from the Ru layers; only one set of electron diffraction patterns was observed, and the image consists of three types of contrasts which are closely related with either the generation and movement of misfit dislocations or large coherent strains. For the [Co40ÅRu35Å]2 bilayer, the Co layers are relaxed basically from the Ru layers; two sets of electron diffraction patterns with double diffraction spots were observed, and the image consists of small irregular areas with moiré fringe dots.
X-ray diffraction and high-resolution transmission electron microscopy study on A-site ordering of lanthanum-modified lead zirconate titanate relaxor
Authors: Fang Fei , Zhang Xiaowen
Published: September 2007

The ordering behavior of La-modified lead zirconate titanate relaxor (PLZT 9/65/35) was investigated by use of an x-ray diffractometer (XRD) and high-resolution transmission electron microscopy (HRTEM). It was shown that a {h + 1/2, k + 1/2, 0}-type superlattice exists both in the x-ray diffraction pattern and selected area electron diffraction (SAED) image. High-resolution electron micrographs further demonstrated the existence of the superlattice and exposed the ordered and disordered regions in the lattice level. A model referring to an A-site body-centered pseudo-cubic superstructure was proposed.
Electron emission from chemical vapor deposited diamond and amorphous carbon films observed with a simple field emission device
Authors: Feng Z. , Brown I.G. , Ager J.W.
Published: September 2007

Electron emission from chemical vapor deposited (CVD) diamond and amorphous carbon (a-C) films was observed with a simple field emission device (FED). Both diamond and a-C films were prepared with microwave plasma-enhanced CVD techniques. Electron emission in the ficld strength range + 10 to −10 MVm−1 was studied, and the field emission source was confirmed by a diode characteristic of the I-V curve, a straight line in the Fowler-Nordheim (F-N) plot, and direct observation of light emission from a fluorescent screen. The turn-on field strength was ∼5 MVm−1, which was similar for both kinds of carbon films. The highest current density for diamond films, observed at a field strength of 10 MVm−1, was ∼15 μA cm−2. Diamond films yielded a higher emission current than a-C films. The reasons for the observed field emission are discussed.
Growth rate estimation of YBa2Cu3Ox single crystal grown by crystal pulling
Authors: Yamada Yasuji , Krauns Christian , Nakamura Masaru , Tagami Minoru , Shiohara Yuh
Published: September 2007

We have estimated the growth rate of the YBa2Cu3Ox crystal grown from the solution by crystal pulling, in terms of solute diffusion in the liquid with convection. The maximum growth rate deduced from the solute diffusion rate is roughly estimated to be about one order larger than the typical measured value. This implies that the driving force for the surface reaction is significantly larger when compared to the total driving force for the growth of YBa2Cu3Ox crystal in our method.
Silver-palladium alloy particle production by spray pyrolysis
Authors: Pluym Tammy C. , Kodas Toivo T. , Wang Lu-Min , Glicksman Howard D.
Published: September 2007

Spray pyrolysis was used to produce submicron Ag-Pd metal alloy particles for applications in electronic component fabrication. The particles were prepared in nitrogen carrier gas from metal nitrate precursor solutions with various compositions. The Ag-Pd alloy was the predominant phase for reactor temperatures of 700 °C and above for all compositions. The 70-30 Ag-Pd partcles were fully dense at 700 °C, but an increased reaction temperature was necessary to produce dense particles at higher Pd to Ag ratios. The extent of palladium oxidation was suppressed with increased amounts of Ag. Single-crystal particles could be produced at sufficiently high temperatures. These results show that particle phase composition, size, oxidation behavior, and morphology can be controlled by the Ag-Pd ratio in the precursor solution and by the reaction temperature.
Mechanical properties and microtructure of sputter-deposited Nb5Si3/Nb microlaminates
Authors: Rawal S.P. , Swanson G.M. , Moshier W.C.
Published: September 2007

Crystalline Nb5Si3/Nb microlaminates were fabricated to a thickness of 20 μm by depositing the materials onto elevated temperature (750 °C) substrates. Modulation wavelengths of the microlaminates were varied (λ = 40 and 200 nm) while holding their silicide volume fraction constant to assess the effect of layer thickness on the composite properties. X-ray and selected area diffraction confirmed that both the metal and silicide layers exhibited a polycrystalline structure in the as-deposited microlaminates. Nanoindentation measurements of both microlaminates indicated that calculated elastic modulus values were similar to the values obtained by the rule-of-mixtures (ROM). Nanohardness values of the microlaminates increased with decreasing wavelength in a manner described by the Hall-Petch relationship. Vickers hardness (Hv) measurements were also found to be a function of the modulation wavelength, decreasing from 7.32 GPa at λ = 40 nm to 3.04 GPa at λ = 200 nm. Even with a Nb volume fraction of 50%, the λ = 40 nm microlaminate and the monolithic Nb5Si3 film exhibited similar Vickers hardness values of 7.5 GPa. These results show the significant role of modulation wavelength on the hardness, compressive strength, and toughness characteristics of a microlaminate composite.