bluuebunny/crossref_metadata_2025 huggingface dataset:
Minimum Grain Size in Nanocrystalline Metal Powders
Authors: Eckert J. , Abe Y. R. , Fu Z. , Johnson W. L.
Published: March 2011

Nanocrystalline metal powders can be synthesized by mechanical attrition in a highenergy ball mill. A general relation determining the grain size of these materials is inferred. The ultimate grain size of nanocrystalline metals (typically 6 − 22 nm) is governed by the competition between the severe plastic deformation introduced during ball milling and the recovery behavior of the material. The lower bound grain size achievable by mechanical attrition is given by the minimum distance between two dislocations in a pile-up within a grain for all pure metals. Foar binary alloys the ultimate grain size depends on the composition of the material. Varying the composition changes the grain size reversibly. This can be explained by introducing solid solution hardening effects in the general relation for the lower bound grain size in pure metals. Thus, the proposed model for the ultimate grain size achievable by ball milling seems to be. applicable to all metals and alloys subjected to heavy mechanical deformation. However, reversible grain size changes are not restricted to mechanical attrition, but have also been observed for nanocrystalline Pd-H solid solutions produced by hydriding at constant pressure. Solid solutions prepared at different compositions, i.e. samples with different compositions, exhibit different grain sizes. Cycling between different temperatures/compositions changes the grain size reversibly. This cannot be explained by a model based on plastic deformation as in the case of ball-milled metal powders. The results are compared with data for ball-milled powders and samples prepared by inert gas condensation. The grain size changes are discussed with respect to the compositional changes and the grain boundary energy of the material.
The Effect of Fatigue Loading on the Interfacial Shear Properties of SCS-6/Ti-Based MMCS
Authors: Kantzos Pete , Eldridge J. , Koss D. A. , Ghosn L. J.
Published: March 2011

Fractographic analysis of SCS-6/Ti-24Al-11 Nb(a/o) (Ti-24-11 hereafter) and SCS-6/Ti-1 5V- 3Cr-3Al-3Sn(w/o) (Ti-15-3 hereafter) composites subjected to fatigue crack growth conditions indicates that the interface is prone to wear damage as a result of fiber/matrix sliding. In this study, the effect of fatigue loading on the integrity of the Interface was studied by using fiber pushout testing to compare the interfacial shear strength of composite specimens in the asreceived condition with specimens that were previously subjected to fatigue loading. Fatigue loading was also simulated by pushing fibers back and forth (multiple reverse pushouts). It was concluded that interfacial sliding during fatigue loading results in interfacial damage and degradation of the interfacial shear strength. Tensile testing of extracted fibers exposed to fatigue-induced interfacial damage was also performed to determine the effect of interface damage on the fiber strength. Interfacial damage also resulted in decreased fiber strength of the SCS-6 fiber. Fracture and wear of the outer carbon coatings on the SCS-6 fiber is the main contributing factor in the deterioration of these interfaces.
Mechanical evaluation of FP alumina reinforced NiAl Composites
Authors: Anton D. L. , Shah D. M.
Published: March 2011

NiAl is well known for its low density, superb oxidation resistance and low ductile to brittle transition temperature. It is equally renowned for its low room temperature fracture strength and poor high temperature creep strength. A compositing approach has been used to introduce chopped and aligned FP Al2O3 into a matrix of fine grain NiAl via a powder metallurgical approach. This resulted in composites with approximately 40 vol. per cent undamaged alumina reinforcement. Fiber orientation effects on strength have also been characterized. Room temperature tests resulted in yield strength increases of 425% for chopped FP reinforcements and 800% for aligned composites. Elevated temperature tests conducted at 1200°C were even more dramatic in their strength increment with 200% and 3600% increases respectively. Fractographic results show matrix ductility, fiber-matrix decohesion and minimal fiber pull-out.
Characterization of Fiber/Matrix Interfaces by Transmission Electron Microscopy in Titanium Aluminide/Sic Composites
Authors: Rhodes Cecil G.
Published: March 2011

This paper presents examples of the use of transmission electron microscopy to characterize matrix/reinforcement interaction in titanium aluminide matrix composites reinforced with continuous SCS-6 type SiC. As a result of the high temperature required for consolidating this type composite, reaction products form in the interface. Using diffraction and x-ray energy dispersive spectroscopy techniques, reaction products in Ti3Al and Ti2AINb alloy matrix composites have been identified. TiC1 –xand Ti5Si3compounds are common in these composites, with AlTi3C also present depending on consolidation temperature and matrix composition. Residual stress calculations indicate that these reaction products may be subject to cracking during cooling from consolidationtemperatures.
Fatigue of Extruded Steel/Nial Composites
Authors: Bannister M. K. , Spearing S. M. , Löfvander J. P. A. , Graef M. De
Published: March 2011

Fatigue tests were performed on a novel, extruded, stainless steel/NiAl composite having good impact and tensile properties. A high fatigue limit was observed to occur at approximately 67% of the σUTS. The fracture surface showed a distinct change in morphology between the fatigued and fast fracture areas and the formation and growth of microcracks was postulated as the initial fatigue mechanism. The microcrack development was monitored by intermittent measurement of the elastic modulus and associated hysteresis. Microstructural characterization by means of SEM, TEM and EDS revealed the existence of approximately 100nm diameter Al2O3 particles decorating the interface between the NiAl and the stainless steel tubes.
Oxidation of Powder Processed Nial and Nial/Tib2 Composites
Authors: Korinko P. S. , Alman D. E. , Stoloff N. S. , Duquette D. J.
Published: March 2011

NiAl and NiAl/TiB2 composites were tested in air at 800, 1000, and 1200°C. The oxidation resistance of the composites depends on the fabrication route, and subsequently on the reinforcement phase morphology and distribution. The oxidation resistance of NiAl reinforced with large TiB2 particles was found to decrease with increasing TiB2 content. NiAl reinforced with large TiB2 particles was completely oxidized at 1200°C after a 100 hour exposure.
The Structure and Properties of MoSi2-Mo5Si3 Composites
Authors: Kung H. , Mason D. P. , Basu A. , Chang H. , Aken D. C. Van , Ghosh A. K. , Gibala R.
Published: March 2011

The addition of Mo5Si3 as a reinforcing second phase in a MoSi2 matrix has been investigated for possible high temperature strengthening effects. MoSi2 with up to 45 vol % Mo5Si3 was fabricated using powder metallurgy (PM) and arc-casting (AC) techniques. Effects of processing routes, which result in different microstructures, on their mechanical properties are given. PM composites, which have an equiaxed microstructure, exhibit a limited increase in hardness. Higher hardnesses are observed in script-structured AC eutectics and Er-modifiedeutectics throughout the temperatures studied (25–1300°C). Crack propagation paths induced by indentation show long transphase cracks in the AC materials vs short intergranular and interphase cracks in the PM composites at high temperatures.

Transmission electron microscopy discloses that the interface in the AC composites has a low-index orientation relationship between the two phases and shows regularly faceted interfacial structures, while planar interfaces are found in the PM composites. These observations suggest the interface is stronger and lower in energy in the AC composites, which is consistent with the higher hardness values and long transphase cracks observed.

Dislocation analysis shows the presence of ordinary dislocations (<100>, <110> and 1/2<111>) in MoSi2 in the as-fabricated composites. These types of dislocation are also responsible for the high temperature plastic deformation in compression in both the monolithic MoSi2 and the composites. <331> types of dislocation are only found in MoSi2 either near the interface of the AC composites or in materials deformed below 1000°C.
Electron Microscopy Studies Of Mo5Si3-MOSi2 Eutectic Composites Modified By Erbium Additions
Authors: Mason D. P. , Aken D. C. Van , Mansfield J. F.
Published: March 2011

Erbium additions to MO5Si3-MoSi2 eutectic composites have been investigated in an effort to reduce oxygen impurity levels found in the MoSi2 starting powders. Additions of 0.35 atomic percent Er were found to refine the script lamellar microstructure and increase the hardness of the composite as compared with the unmodified material. This increase in hardness was maintained over the temperature range 25°C to 1300°C. Oxygen rich Er particles have been observed in the Er-modified material suggesting that Er has acted as a gettering agent for oxygen. An intermetallic phase Er2Mo3Si4was also observed in the Er-treated material. The character of this phase was determined by convergent beam electron diffraction (CBED), wavelength dispersive spectroscopy (WDS) and X-ray dispersive spectroscopy (XEDS). The particles of Er2Mo3Si4 were found to be heavily faulted which caused a reduction in the experimental diffraction symmetries. Thus, ambiguities arose during CBED analysis. Therefore, a standard sample of Er2Mo3Si4 was prepared and used to aid in the identification of the faulted particles.
Interfacial Shear Behavior of Two Titanium-Based SCS-6 Model Composites
Authors: Roman I. , Jero P. D.
Published: March 2011

Single fiber push-out and push-back tests combined with acoustic response monitoring were used to examine the interfacial behavior in two titanium alloy-SiC fiber composites. Distinctly different behaviors were observed in the two systems. The differences were attributed to the formation of a substantial interfacial reaction layer in one of the composites which changed the interfacial chemistry and the resulting debond topography. The reaction layer caused an increase in the interfacial bond strength and in the roughness of the debonded interface. The latter resulted in substantially increased sliding friction. Although both composite interfaces exhibited some roughness, only one showed a seating drop during fiber push-back. This is related to the fact that the reaction layer which formed in one of the composites was severely degraded during fiber pushout. Although this interface was still rough, the roughness correspondence between fiber and matrix was destroyed during sliding, such that seating was no longer possible.
Consolidation of Continuous Fiber, Intermetallic-Matrix Composites
Authors: Semiatin S. L. , Goetz R. L. , Kerr W. R.
Published: March 2011

Processing routes for fabrication of continuous fiber, intermetallic-matrix composites are reviewed. These methods include conventional and isostatic hot pressing of layups of matrix material (e.g. foil or powder cloth) and fiber mats; consolidation of monotapes made by techniques such as arc, plasma, vapor, or electron beam deposition or tape casting; and liquid metal infiltration-base methods. The advantages and disadvantages of the various methods are discussed. Particular attention is focussed on HIP consolidation via foil-fiber-foil techniques. Process modeling techniques to assess the effects of pressure, temperature, and time on consolidation behavior are described. By this means, maps to delineate the interaction of process variables in such methods can be developed and applied for process optimization.
Process Modeling for Titanium Aluminide Matrix Composites
Authors: Bampton C. C. , Graves J. A. , Newell K. J. , Lorenz R. H.
Published: March 2011

Consolidation of continuous fiber-reinforced titanium aluminide matrix composites (TMC) by the foil/fiber/foil method has traditionally taken an empirical approach utilizing processing cycles derived by simple trial and error. In an effort to reduce the empirical nature of producing TMC, a simple but effective analytical approach is employed. This approach analyzes the effect of fiber and foil geometries on consolidation parameters by combining a physical constitutive creep model with computational methods of interpreting raw materials characterization data. Examples of SCS-6/super a2(Ti-25Al-10Nb-3Mo-lV) and Saphikon/γ-TiAl composites consolidation are discussed by comparing the model predictions with equivalent validation specimen microstructures.
In-Situ Synthesis of Intermetallic Matrix Composites
Authors: Shah Dilip M. , Anton Donald L.
Published: March 2011

In pursuing the development of intermetallics as high temperature structural materials, a composite approach is considered necessary for achieving room temperature toughness. If not further qualified, the term “composite” generally implies the application of mechanical processes by which a strong reinforcing phase is dispersed in the matrix, often as aligned continuous fibers. While this approach appears simple and promising in principle, in practice it is limited by the availability of compatible fibers, controlled processing, and microstructural homogeneity and reproducibility. Alternatively, the composite microstructures may be created in-situ either synthetically or naturally. In synthetically derived composites, the desired phases may be deposited layer by layer using such techniques as chemical vapor deposition (CVD), and potentially a variety of lithographic techniques may be employed to control the microstructure. However, such techniques are currently rate limited and not well developed for the large dimensions required for structural composites. In contrast, the in-situ composites, which rely on phase separation by either eutectic solidification or solid state precipitation, are economical and especially well suited for generating naturally compatible ductile phase toughened composites with uniform fine scale microstructures. This paper attempts to classify these approaches in perspective, discuss the benefit of in-situ composites relying on the natural phase separation mechanisms, and review the current activities with emphasis on the concept of ductile phase toughening.
Evaluation of Various Intermetallic Matrix - Ceramic Particle Systems for Melt Processing of Metal Matrix Composites
Authors: Sen S. , Dhindaw B. K. , Stefanescu D. M.
Published: March 2011

The possibility of incorporating SiC or TiC particulate reinforcements in a Ni3Al matrix through the melt processing route was examined. Interface bonding and thermal stability of SiC and surface treated SiC in Ni3Al has been investigated through sessile drop and DTA experiments. Feasibility of various processing techniques such as the mechanical mixing method and the vacuum infiltration method was also explored.
Microstructural Characterization of Al2O3/Gamma Titanium Aluminide Composites
Authors: Das G. , Krishnamurthy S.
Published: March 2011

Alumina (A12O3) fibers were incorporated into gamma titanium aluminide(TiAl) based powders by hot isostatic pressing (HIP'ing). The microstructure of as-HIP'd and heat treated composite specimens were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM studies reveal the presence of an amorphous reaction zone at the fiber/matrix interface. Numerous dislocations, dipoles and loops as well as twins are observed in A12O3fibers. In addition, it is determined that the fiber/matrix interface stability is significantly affected by the matrix microstructure.
Epitaxial Buffer Layers on (012) Sapphire and (100) SrTiO3 for the Integration of YBa2Cu3Ox in Microwave Devices and Squids
Authors: Schmidt H. , Vollnhals G. , Gieres G. , Wersing W. , Kinder H.
Published: March 2011

The epitaxial growth of YBa2Cu3Ox films on sapphire for microwave applications requires epitaxial buffer layers hindering interdiffusion. Therefore the epitaxial growth of YSZ, the layer sequence Y2O3/YSZ, and Y2O3 on (012) sapphire was examined. In addition the growth of MgO and srTiO3 on sapphire substrates and the growth of MgO and CeO2 on SrTiO3 substrates was studied by X-ray diffraction, X-ray pole figure measurement and RBS-ion channeling. With a combination of these buffer layers bi-epitaxial grain boundaries in YBa2Cu3Ox films can be fabricated in future.
Space Group and Fundamental Vibrations of the (RElBa2Cu3O7)m (RE2Ba2Cu3O7)n Superlattices
Authors: Mirovitskii V. Yu.
Published: March 2011

The (RE1Ba2Cu3O7)m (RE2Ba2Cu3O7)n superlattices (SL) with the superporiod d along [100]. [010] and [001] have been considered as a single crystals with primitive cells formally multiplied duo to ordering of rare earth atoms in an initial hypothetical mixed system (RE1pRE21-p)Ba2Cu3O7 By means of symmetry methods it is found that the suporporiodicity in those SL, unlike Ge/Si or GaAs/AlAs. keeps the initial space group Pmmm at any m and n. On the contrary, the obtained Table of the SL atoms distribution over Wyckoff positions indicates that the type, multiplicity and the number of the positions essentially depend on d and Cm.nD. Those data are used for group thoorotical classification of the fundamental vibrations of SL's. The analysis of spectrum changes under transformation from the initial compound to SL is performed. In particular, it is found out that already at the lowest m and n the oven vibrations of RE, Cul and Ol, occupying only one-fold positions in the initial structure, occur. Also for each d the typo of spectrum is shown to depend on both m+n and the fact if the pair (m.n) is even-oven, odd-odd or oven-odd.
New Perovskite Based Structures in the Bi-Sr-O System
Authors: Bokhimi  , Portilla M.
Published: March 2011

We report one amorphous and four new crystalline phases in the Bi-Sr-0 system. The structure of three of the crystalline phases was identified. The Br10Bi6O24-y phase, which is cubic with space group Fm3m and cell parameter a = 0.8471(1) nm. The SreBi10O27-y phase, which is tetragonal with the space group I/mmm, and cell parameters a = 0.6007(1), c = 0.8376(1) nm. The SreBi10O27-y phase, which is tetragonal with space group I/mmm and cell parameters a = 1.3221(1), c = 0.4249(1) nm. We show that in the crystalline structures Sr and Bi occupy equivalent sites.
Properties of Hot Isostatically Pressed Bi2Sr1.7CaCu2Ox
Authors: Nash A. S. , Goretta K. C. , Miller D. J. , Biondo A. C. , Shi Donglu , Sengupta S. , Poeppel R. B.
Published: March 2011

Dense Bi2Sr1.7CaCu2Ox (2212) superconductor pellets were made by hot isostatic pressing in an inert atmosphere. The pellets exhibited a small amount of preferred orientation of the grains. The transport critical current density (Jc) values were very low for all specimens. Dislocations, planar faults, and intergrowths of the Bi2Sr2CuOx phase, which were produced during the pressing, caused the intragranular Jc to increase substantially.
Anomalous Low-Field Magnetic Behaviour of High-TC Superconductors
Authors: Tai M. F. , Wang H. J. , Lin C. C. , Wang H. L.
Published: March 2011

We report on the studies of low-field magnetic properties in the well-characteristic superconducting LaCaBaCu3Oy, YBa2Cu3Oy, YaBa4Cu8Oy, (La1–85Sr0–15)CuO4-y, (Tl0–5Pb0–5)Ca2Sr2Cu3Oy and (Bi2−xPbx)Ca2Sr2Cu3Oy oxides. The studies of magnetic properties include ac zero-field cooled (ZFC), field-cooled (FC), and ac susceptibilities, and their dependences on the applied magnetic field and temperature. As the applied dc magnetic field is low enough, the FC susceptibility varies flat with the increasing of temperature from low temperature, but the diamagnetic signal becomes increasing at some temperature and reaches to the maximum values, and then continously decreases with temperature, at last the diamagnetism rapidly transfers to paramagnetism with temperature going to above Tc. The magnetization reduction at low temperature significantly appears at the low dc magnetic field and exists within a lot of single-phase high-Tc superconductors. However, this phenomenon is not observed in the measurements of low-frequency ac complex susceptibility for the ac applied fields from 0.001 G to 10 G and disappears for higher dc applied field. But, there exists a two-step drop in ac and ZFC susceptibilities curve and the drop correlates with the de FC magnetization dip. The magnetic field range of the dip occurrence is dependent on specimens. The strange magnetic property may be regard with superconducting coupling link in grain boundaries and interpreted by the grain-cluster model associated with Josephson effect.
Thickness Dependence of Vortex Pinning in Epitaxial Tl-Ca-Ba-Cu-O Thin Films
Authors: Venturing E. L. , Lee W. Y. , Morosin B. , Ginley D. S.
Published: March 2011

The critical current density inferred from magnetization hysteresis for epitaxial Tl2Ca2Ba2Cu3O10 films on LaAlO3 exhibits a pronounced increase with film thickness in the high-field, high-current regime. This thickness dependence does not extend to comparatively “thick” single crystals, however, suggesting that the grain boundaries play a major role in collective vortex pinning for Tl-based superconducting thin films.
Sensitive Method of Measuring Microwave Surface Impedance of Superconducting Films
Authors: Jiang H. , How H. , Widom A. , Vittoria C.
Published: March 2011

We used a microwave technique in which a small strip of YBCO film is induced to self-resonant in order to measure the surface impedance at 21 GHz. Both the amplitude and phase of the transmission coefficient, S21, as a function of frequency was measured at different temperatures. The surface resistance, Rs, was obtained from at resonant frequency, where Z0is the waveguide impedance. The surface reactance, Xa was obtained from the measurement of frequency shift with temperature. We found that Ra changed about 3 orders of magnitude as T decreased from 90K to 80K reaching a low value of 4.9 × 10−4μ. From Ra and Xa we deduced the London penetration depth to be λ ∼ 1800Å at 4K and 8000Å at 86.5K.
Hole Concentration and Tc in the TI2-x-zBa2+xCa2+xCu3O10-y System
Authors: Paranthaman M. , Foldeaki M. , NaziriPour A. , Hermann A. M.
Published: March 2011

Single phase Tl-2223 samples were prepared in the TI2-x-zBa2Ca2+xCu3O10-y (z represent Tl vacancies in the range 0.22 – 0.27 and y represent oxygen vacancies in the range 0.17 – 0.33) system with x between 0 and 0.4. A small impurity phase was found at x = 0.6. All samples were found to be tetragonal. The Tc varied between 112 and 118 K for the “as-synthesized” samples. After post-annealing in a sealed quartz tube under vacuum at 750*deg;C for 10 days, the Tc increased from 116 to 122 K for x = 0.3 and from 118 to 120 K for x = 0,4 samples. Although x = 0.3 sample had small impurity phases after post-annealing, a large amount of impurity phases were found for x = 0.4 sample after post-annealing. Wet chemical analysis showed that all samples were both Tl and oxygen deficient. The Tc was found to increase with increasing hole concentration. The origin of the holes for all these samples is due to Ca2+ substitution on the TI3+ sites and overlap of Tl-6s band with the conduction band of the CuO2 sheets.
In-Situ Growth of C-Axis Oriented YBa2Cu3O7−x on Silicon with Composite Buffer Layers by Plasma Enhanced Metalorganic Chemical Vapor Deposition
Authors: Zhang Jiming , Gardiner Robin , Kirlin Peter S.
Published: March 2011

YBa2Cu3O7−x thin films have been grown in-situ on Si (100) with a composite buffer layer of Pt/Ta/ONO (ONO stands for a S1O2 / Si3N4 /SiO2 trilayer) by plasma enhanced metal organic chemical vapor deposition (PE-MOCVD). X-ray diffraction measurements indicate that c-axis oriented YBa2Cu3O7−x films are formed in-situ at substrate temperatures as low as 650 °C on Pt/Ta/ONO/Si. The composite P/Ta/ONO provided an adherent metallic interlayer and effectively prevented the interaction between YBa2Cu3O7−x and Si. Four probe resistivity measurements indicate the onset of superconductivity at 92 K and achieved zero resistance at 65 K.
Heteroepitaxial Bi2Sr2CaCu2Ox Superconducting thin films Deposited on LaA1O3 by Solid Phase Epitaxy and OMCVD
Authors: Chen J. , Lu H. A. , DiMeo F. , Wessels B. W. , Schulz D. L. , Marks T. J. , Schindler J. L. , Kannewurf C. R.
Published: March 2011

-Heteroepitaxial superconducting Bi,Sr2CaCu2Ox (BSCCO 2212) thin films have been formed by solid phase epitaxy from amorphous films deposited on (100) LaA1O3 single crystal substrates by organometallic chemical vapor deposition. The epitaxial structure of the film is confirmed by x-ray diffraction including θ/2θ and Φ (in plane rotation) scans. Cross-sectional high resolution transmission electron microscopy indicates that the film-substrate interface is nearly atomically abrupt. Improvements in superconducting properties of the epitaxial thin films are noted in comparison to highly textured films deposited on MgO.
Destruction of Scalino Law for Flux Pinning in Layered Structures
Authors: Lykov A. N. , Zdravkov V. I.
Published: March 2011

The multilayers based on Nb/NbO (S-I-S) were investigated in external magnetic fields at various temperatures. It was found that the shear deformation of the solid vortex lattice de-termenes critical current density in the case of large period structures and high parallel fields. The solid vortex lattice can be destroyed by decreasing of both the period and the upper critical field. The qualitative change of the magnetic field dependence of the volume pinning force was observed as temperature was increasing. It reveals structural transitioon from elasti-cally deformed flux line lattice to plastically deformed one. Thus the scaling low is destructed for these structures. We have determened the volume pinning force by direct summing of elementary pinning forces in oxide layers in this case.
Power-Law Scaling Behaviors and Kosterlitz-Thouless Transition in the Resistive State of Ultra-Thin High-Tc Superconducting Films
Authors: Onogi T. , Sugano R. , Murayama Y.
Published: March 2011

By means of a Langevin dynamic simulation we studied the current-voltage characteristics of a two-dimensional (2D) Josephson-coupled lattice as a model high-Tc superconducting film. The result illustrates qualitative features of non-Ohmic power-law scaling behaviors observed in transport measurements, including striking effects of applied magnetic fields. We thereby suggest that the Kosterlitz-Thouless transition associated with 2D vortex-antivortex pairs may dominate over the resistive transition in weak magnetic fields H/Hc2 ≪C 1. Through a simple theoretical estimate, we also show that the KT model illustrates the thickness-dependence of resistive transition temperature and electric field effect in ultra-thin YBa2Cu3O7−x films.
Relation of Constituents with Superconducting Characteristics in Low-Temperature-Preheated YBCO Ceramics
Authors: Nishino Junya , Nishikawa Hiroaki , Ayabe Muneo , Ikegami Yuji
Published: March 2011

YBCO bulk ceramics pre-heated at low temperature before sintering were studied on the structure and superconducting properties mainly by varying the concentration of Ba/Y ratio.

At 15.8–16.2wt% of the oxygen content Oc calcurated from the compositions of yttrium, barium and copper on the assumption that the valence of copper is 2, (123) phase is main and critical temperature(Tc) and critical current density(Jc) reach to 88–90K and about 103A/cm2, respectively.

It is presumed that there is a possibility of the exixtence of oxygen deficient and disordered phase in addition to (123) and (211) phases and BaCuO2.
Superconducting Properties of Ultrathin YBa2CU3O7 Films
Authors: Terashima T. , Shimura K. , Daitoh Y. , Yano Y. , Bando Y. , Matsuda Y. , Komiyama S.
Published: March 2011

Ultrathin YBa2CU3O7 (YBCO) films were epitaxially grown on non-superconducting PrBa2CU3O7 (PrBCO) buffer layer by reactive evaporation, in which the crystal growth was controlled through the monitoring of reflection high energy electron diffraction (RHEED) specular intensity oscillations. Atomic force microscope (AFM) observation reveals that the steps in the surface of ultrathin YBCO films (∼100Aå) have one-unit-cell height, implying a unit cell-by-unit cell growth manner. One-unit-cell thick (1-UCT) YBCO layer exhibits superconductivity when charge reservoir layers of BaO-CuO-BaO are located above and below the CuO2 bilayer interposed with an Y layer. Essential transport properties of the normal state in bulk YBCO, such as T-linear dependence of resistivity and T-1 dependence Of Hall resistivity, are found to be inherent in the individual CuO2 bilayer. Study of diagonal and Hall resistivities provides evidence of Kosterlitz-Thouless transition to be occurred in 1-UCT YBCO.
Influence of Nickel on Magnetic and Electric Properties of Melt-Processed YBa2Cu3Oy/Ni Superconducting Composites
Authors: Kozllwski G. , Oberly C. E. , Maartense I. , Cao X. W. , Ho J. C.
Published: March 2011

To assess a Ni-clad melt-processed YBa2Cu3Oy (YBCO) conductor approach, a systematic study was made on commercially available YBCO powder mixed and co-sintered with nickel oxide (NiO). Our research effort has focused on the effect of nickel on the critical current density in the YBCO/Ni composites. Four series of YBCO samples mixed with 0.3, 0.7, 1, 1.3, 2 and 3 wt% of high purity NiO were prepared, and optimized conditions for the melt process were established. These samples were characterized by resistivity, AC susceptibility and DC magnetization measurements. The highest magnetization critical current density (Jcm∼3×105 A/cm2 at T=4.2K and H=0 was observed in melt-processed samples with ∼ 1 wt% Ni (or -1.3 wt% NiO) subjected to a cooling rate of 2°C/hr from 1040°C to 980°C. This Jcm was found near the middle of the Ni-solubility range (about 2 wt% Ni is the solubility limit of Ni in YBCO) which may be attributed to the local Ni/Cu compositional fluctuation leading to an increased pinning force density in these composites.
High TC Superconducting Switch
Authors: Kalkur T. S. , Ward Dave
Published: March 2011

A switch has been developed which uses a thin film of Y-Ba-Cu-O as a switching element. The two important process parameters in the fabrication of the switch - contact resistance between a metal and a superconductor and the passivation of the superconducting films by SiO2 have been studied. The thin film of superconductor is patterned into a narrow line (gate) crossed by a metal control line with a deposited SiO2 as an insulation layer between them. When the control line carries current large enough to switch the gate into the normal state the gate is in the ‘off’ state. When no current is present, the gate is superconducting and it is in the ‘on’ state. The operation of the device was verified by testing at 77 K. Applications of the device include amplifiers, digital logic circuits, and microwave switches.
The Fabrication of High-TC Superconducting Wires, Tapes and Bulk Conductors
Authors: Briggs A , Denton I E , Hooper A , Lee J A , Jmattingley N
Published: March 2011

The results of a UK-based industrial consortium, aimed at the development of high-Tcsuperconducting wires, tapes and bulk conductors, are reviewed. The powder-in-tube method has been used to fabricate 10's of metre lengths of bismuth-based, Ag-clad, single and multi-filamentary wires. Performance highlights include current densities of 23,000Acm-2 [7A] at 77K; (zero field) for 2223 bismuth-based wire and greater than 105Acm-2 [25A] and 104cm-2 at 4.2K, zero field and 15T, respectively, for 2212-based wire. Ag-backed, 2212, tape-cast conductors have carried currents of over 60A [80,000Acnrr-2] at 4.2K; (zero field). Bulk ceramic processing techniques, sol-gel chemistry and plasma-spraying have also been used to fabricate a range of YBCO and bismuth-based components. Currents in excess of 100A have been carried in bulk 2223 bismuth-based samples at 77K.
Superconducting Multilayer Structures Grown by All-Mbe
Authors: Bozovic I. , Eckstein J. N. , Klausmeier-Brown M. E. , Virshup G. F. , Rails K. S.
Published: March 2011

Thin films of various Bi-Sr-Ca-Cu-O (2201, 2212,…, 2–2–11–12) compounds have been synthesized using atomic-layer-by-layer molecular beam epitaxy (ALL-MBE). Single-crystal films with excellent transport properties, smooth surfaces and atomically sharp interfaces in multilayer structures have been obtained. That made it possible to deposit virtually perfect ultrathin layers and superlattices, and fabricate hysteretic Josephson junctions from SIS multilayers.
Magnetic Anomaly in the YBa2Cu3O7 System at Low External Magnetic Fields
Authors: Bokhimi
Published: March 2011

Magnetization curves for low external magnetic fields of field-cooled superconducting YBa2Cu3O7 samples show an increase in the diamagnetic signal when the sample temperature is near the transition to the normal state. The Increase of the diamagnetic signal depends on the external magnetic field (H ≤ 13.5 Oe). The effect is observed when the samples are field-cooled, but not when they are zero-field-cooled, that means that it is related with the behavior of the vortex lattice.
A Thin Barrier Technology for the Integration of YBa2Cu3O7−x Thin Films to Semiconductors
Authors: Mesarwi A. , Wu N. J. , Fredricksen H. , Ignatiev A.
Published: March 2011

Ultra-thin SiO2 barriers have been developed for application to the integration of thin films of YBa2Cu3O7−x (YBCO) superconductors to silicon. The SiO2 barriers are formed by the selective oxidation of Si with 2–5 ML yttrium overlayers. The Y-promoted SiO2, barrier formed by this technique is highly stoichiometric and is an effective buffer which prevents YBCO/substrate interdiffusion. The technique has been applied to YBCO on Si and has resulted in a YBCO transition temperature of TC=78°K for a 70Å Y-promoted SiO2 barrier.

This technique has also been applied to the growth of multilayer YBCO films and fabrication of SIS junctions. For this purpose, a Y-promoted SiO2 barrier was prepared by the selective oxidation of a Y/Si/Y sandwich layer grown on thin fdm YBCO deposited on MgO by standard laser deposition. This resulted in a 20–40Å SiO2/Y2O3-, high quality barrier. Following barrier preparation, a second YBCO thin layer was deposited on the barrier yielding a YBa2Cu3O7−x-SiO2-YBa2Cu3O7−x (SIS) structure which was then patterned to yield 100μm diameter SIS junctions. Voltage-current measurements across the SIS junction have shown Joseph son junction behavior.
Pulsed Laser Deposition and Characterization of Superconducting Ba1−xKxBiO3 Thin Films
Authors: Platt C. E. , Teepe M. R. , Ciofl C. , Zhang H. , Dravid V. P. , Schweinfurth R. A. , Van Harlingen D. J. , Eades J. A. , Lin C. H. , Strother D. , Hammond R.
Published: March 2011

We report on high quality Ba1−xKxBiO3 (BKBO) thin films grown by pulsed laser deposition. The best films exhibit resistive and magnetic transition temperatures of 28 K, with a transition width of 0.4 K and critical current densities above 106 A/cm2 measured at 5 K. Surface impedance is measured to be 1 mΩ. Films are single phase and highly oriented in the (100) direction and electron diffraction shows no other phases. Analysis using Moire' fringes shows films to consist of 100 nm size dislocation-free regions which show a high degree of in-plane epitaxy.
Processing and Properties of Silver-Clad Tl-Ba-Ca-Cu-O Wires and Tapes
Authors: Goretta K. C. , Wu C. -T. , Lanagan M. T. , Boling M. A. , Shi Donglu , Miller D. J. , Chen Nan , Hanewald W. G. , Sengupta S. , Wang Z. , Poeppel R. B. , Foong F. , Liou S. H.
Published: March 2011

TlBA2Cu3Ox and Tl2Ca2Cu3Ox powders were synthesized, loaded into Ag tubes, and worked into wires and tapes by drawing and rolling. All processing outside of furnaces was in a dry-N2 glovebox. All heat treatments were performed in O2. The Ag-clad wires fabricated from these powders exhibited onset of superconductivity at ≈118 K and critical current densities at 77 K of 2 × 103 to 4 ×103 A/cm2.
Research on Oxide Superconducting Wire
Authors: Ikeno Y. , Doi K. , Kamisada Y. , Hayashi K. , Ogawa T.
Published: March 2011

By using the solid, liquid and vapor processes, such as doctor blade, laser pedestal growth, FZ, plasma spraying, ICB, CVD and laser ablation, wires and tapes were successfully fabricated. These experiments yielded the following results : Bi-2212 seven stranded wire with multi-layer structure by doctor blade method was prepared, and Ic of 270A (77K, OT) was achieved. Bi-2212 wires were prepared by laser pedestal growth, and Ic of 500A (77K, OT) was obtained in the case of 3mm in diameter. The a-b plane aligned Y-123 films-was deposited on Hastelloy, tape by laser ablation, and high Jc of 2.5×10 A/cm2 (77K, OT) and 2.2×10 A/cm2 (77K, 8T) were measured.
Control of a-Axis and c-AXIS Orientation of the YBa2Cu3O7−x Thin Films by Pulsed Laser Deposition
Authors: Sung Gun Yong , Suh Jeong Dae , Kang Kwang Yong , Lee Jeong Yong
Published: March 2011

We have investigated the effect of substrate temperatures ranging from 680 °C to 800 °C on the orientation of pulsed laser deposited YBa2Cu3O7−x.(YBCO) thin films on (100) LaAlO3 substrates. X-ray diffraction studies indicate that there is a progressive change in the dominant orientation of the films from c-axis oriented (c-axis perpendicular to the substrate surface) to a-axis oriented (a-axis perpendicular to the substrate surface) grown as the substrate temperature is lowered. Two YBCO bilayers, which are the a-axis oriented YBCO film on the top of c-axis oriented YBCO film (a/c) bilayer and c-axis oriented YBCO film on the top of a-axis oriented YBCO film (c/a) bilayer, have been grown by in situ two step pulsed laser deposition and were characterized by scanning electron microscopy (SEM), Rutherford backscattering (RBS) spectrum, x-ray diffraction (XRD), and Tc measurements. Through SEM and XRD studies, double layer structures of the a/c and c/a bilayers were confirmed indirectly.
The Systematics of Irreversibility in Superconducting Thallium Cuprates
Authors: Tallon J. L. , Presland M. R. , Buckley R. G. , Mawdsley A.
Published: March 2011

The irreversibility lines, Hirr(T), for the series of superconducting compoundsTlmA2CunO2+m+2n, where A is Ba or Sr, are measured between 0 and 1 tesla for m = 1,2 and n = 1,2,3 and 4 and show a marked steepening with decreasing anisotropy i.e. as m is lowered from 2 to 1. In addition, for m=2 material Hlrr(T) is observed to steepen with decreasing number of CuO2 layers. The hole dependence of the irreversibility line is also investigated in TI2Ba2CuO6+6 by changing the oxygen stoichiometry, 6. Hirr(T) progressively steepens with increasing hole concentration on the overdoped sida of Tc(max). These results are consistent with a model of flux motion arising from a crossover from 3-D vortex lines to 2-D pancake vortices which are decoupled in the c-direction, and provide guidance for materials selection and optimum doping.
Controlled Growth of Superconducting Oxide Films Using Pulsed Laser Deposition
Authors: Gupta A. , Chern M. Y. , Hussey B. W.
Published: March 2011

Reflection high-energy electron diffraction (RHEED) has been used to monitor the homoepitaxial growth of SrTiO3 buffer layer, and subsequent heteroepitaxial growth of YBa2CU3O7-δ (YBCO) films, on (100) SrTiO3 by pulsed laser deposition (PLD). The RHEED pattern during initial growth of SrTiO3 becomes sharper and increases in intensity, suggesting that the smoothness of the substrate is improved by growth of the buffer layer. On the smooth surface, the growth of SrTiO3 occurs in a layer-by-layer mode as indicated by the intensity oscillations of the specular beam. YBCO films have been subsequently grown on the buffer layer using a combination of pulsed molecular oxygen and a continuous source of atomic oxygen, with the average background pressure maintained as low as 1 mTorr. A sharp streaky pattern, and intensity oscillations are also observed during growth of YBCO. The YBCO films after cooling down in 1 atm of O2 are superconducting, with zero-resistance temperature of 80 K.
Fabrication of Silicon-Based Shape Memory Alloy Micro-Actuators
Authors: Johnson A. David , Busch J. D. , Ray Curtis A. , Sloan Charles
Published: March 2011

Thin film shape memory alloy has been integrated with silicon in a new actuation mechanism for micro-electro-mechanical systems. This paper compares nickel-titanium film with other actuators, describes recent results of chemical milling processes developed to fabricate shape memory alloy micro-actuators in silicon, and describes simple actuation mechanisms which have been fabricated and tested.
Adaptive Damping in Shape Memory TiNi during Cavitation
Authors: Jardine A. Peter
Published: March 2011

Recent studies by this author and others has demonstrated that cavitation-erosion of NiTi coatings or bulk NiTi is exceptional. Studies were undertaken to ascertain whether this property is a consequence of either the general intermetallic properties of NiTi or by an adaptive stress-dissipation mechanism of the cavitation-generated shock wave by A microstructural mechanism related to the shape memory effect.

In cavitation, an oscillating pressure field causes the formation and implosion of air bubbles. As a surface easily nucleates bubbles, the subsequent implosion of the bubbles generates stresses approaching several MPa, which are large enough to ablate material, and are also high enough to generate stress-induced Martensite or Austenite, depending on whether the applied stress is tensile or compressive. The implication is that the stress wave may be partially accommodated by the stress-induced transformation, which can dissipate the energy as heat on retransformation to the materials unstressed phase.

Calculations concerning the variation of the cavitation-induced stresses and temperature distribution with depth into the TiNi coupled with the associated problems of heat transfer will be presented. It will be shown that an adaptive mechanism is plausible.
Ultimate Strain Measurement of Micromachined Membranes Using a Potentiometric Technique
Authors: Goforth R. C. , Ulrich R. K. , Leong Y. K. , Zhao G.
Published: March 2011

A potentiometric method for the measurement of ultimate strain of thin films is presented. In this method, an electric potential is applied between two electrodes located one on each side of the thin film under investigation. The electrodes are immersed in an electrolytic solution. The thin film acts as an electrical current barrier. To determine the ultimate strain, a controlled load is applied to the film. Cracking of the film causes a sharp rise in the current from an initial small leakage value. The applied load at the onset of cracking is used to calculate the ultimate strain.

we have previously demonstrated the feasibility of the method for thin silicon nitride films deposited on aluminum strips. The method is very sensitive and can detect cracks too small to be observed with a microscope. We discuss extension of the method to the measurement of the ultimate strain of micromachined membranes. The load is applied by pressurizing one side of the membrane. Micromachined structures are used to determine residual stresses.
Alternative Materials for Micro-Electro-Mechanical Device Construction
Authors: Hackeit R. H. , Larson L. E.
Published: March 2011

In order to integrate micro actuators with III-V semiconductor devices, we have devised Micro-Electro-Mechanical devices (MEM's), constructed from materials and processes common to existing III-V device processing. These processes are substantially different from silicon based processes because of the requirements for low temperature processing and the use of gold-based metallizations.

Our material choices include, vacuum deposited and plated metal films, silicon oxide and nitride dielectric layers, and polyimide layers and structures. Sacrificial layers are implemented with photoresist rather than the more common silicon dioxide. The processes available are based on the ‘lift off’ of unwanted areas of the metal films, wet plating of metals through openings in photoresist masks, and wet and plasma etching of metals and dielectrics.

This paper will discuss why we are using these materials, the process constraints imposed by the materials, the measurement of some of the material properties, and will relate some progress in applications.
Piezoelectric properties of 0-3 ceramic/polar polymer composites
Authors: Dias C. , Das-Gupta D. K.
Published: March 2011

Ferroelectric ceramics such as PZT, while exhibiting strong piezoelectric effect, have the disadvantages of a high acoustic impedance, difficulty to miniaturize and not being suitable to broad band ultrasonic applications. Polar ferroelectric polymer such as PVDF and its copolymers which can be obtained in thin film form, have low mechanical Q and low acoustical impedance although their piezoelectric coefficients are significantly lower than those of the piezoelectric ceramics. Composites of piezoelectric ceramic powders, such as PZT and Calcium modified Lead Titanate (PT) in a matrix of P(VDF/TrFE) have been fabricated in our laboratory, in order to Investigate whether these materials could have the low acoustic, broad band properties of the polymers whilst retaining the high piezoelectric coefficients of the ceramics. In the present paper the results of a study of the electromechanical coupling factor (kt), the quality factor (Qm) as well as the gh and dh piezoelectric coefficients of these 0-3 composites poled both by corona and by the conventional method are given.
Organic Charge-Transfer Complexes for High Density Storage Using a Modified Scanning Tunneling Microscope
Authors: Yamaguchi Shoji , Valenzuela Carlos A. , Potember Richard S.
Published: March 2011

We are investigating organometallic materials which exhibit a novel fieldinduced reversible switching phenomenon. Silver and copper salts of tetracyanoquinodimethane (TCNQ) and its derivatives, prepared as polycrystalline thick films and vacuum-deposited thin films, have been imaged using a scanning tunneling microscope (STM). We have recently produced images with molecular resolution of these materials. We also have demonstrated a field-induced, charge-transfer reaction driven by the electric field at the STM tip when the field generated by the STM exceeds the switching threshold of the organic charge-transfer complex. The phase transition induced by the STM tip appears as nanometer to micrometer-sized domains on the metal-TCNQ and derivatives surface. This STM-induced chemical reaction is being explored for use in a molecular-based information storage system.
Thin Film Heater on a Thermally Isolated Microstructure
Authors: Oh Seajin , Chu William , Cahill Sean
Published: March 2011

A microheater was fabricated on a thermally isolated silicon (Si) membrane and its electrical and thermomechanical properties were assessed. The sensor design was adjusted for good thermal isolation and good resistance to thermal shock. The heater was a platinum (Pt) thin-film meandering filament deposited with electron beam evaporation and patterned with lift-off methods. In order to operate the heater at high temperatures with minimum loss of Pt by evaporation, the heater was encapsulated with a ceramic film. During the heater operation, most of the heat was dissipated via conduction through the Si membrane which supported the multi-layered heater. When the Si membrane was completely etched away to suspend the heater, the power needed to heat the filament to strong incandescence (about 700–800°C) was 110 mW. Structural failure was not observed when the device was subjected to thermocycling up to approximately 500°C. The importance of the thermomechanical match of layers in a multi-layered heater structure, especially for use at high temperatures, is addressed.