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We present the structural and photovoltaic properties of Sr-doped polycrystalline BiFeO3 thin films prepared by sol-gel method. The result shows that all the BiFeO3 thin films doped with 0 ∼ 20 at....

Magnetoelectric multiferroic fluids composed of BaTiO3@CoFe2O4 composite nanoparticles dispersed in a highly insulating nonpolar oleic acid/silicone oil mixture have been developed. The effects of the particle volume fraction and a magnetic field, as well as an electric field, on the ferroelectric and magnetic properties, as well as the magnetoelectric coupling effect, have been systematically studied and discussed in this paper. Magnetic characterization shows an approximation to superparamagnetism, and both the remanent magnetization (Mr) and the coercive field (Hc) increase with increases in the volume fraction and applied electric field. Similarly, a superparaelectric state has been observed in the multiferroic fluids, in which both the remanent polarization (Pr) and the coercive field (Ec) are near zero, whereas they increase with increases in the applied magnetic field and volume fraction. High converse and direct magnetoelectric coupling coefficients are estimated to be αH = 8.16 × 10−4 (Oe cm) V−1 and αE = 1.58 × 104 V (cm Oe)−1, respectively. Further analysis indicates that the composite particles can be aligned under an external magnetic/electric field so that their magnetic/electric moments can be parallel to the external field, which in turn results in changes in the magnetization/polarization directions. These results imply that besides magnetoelectric fluids that consist of core/shell-structured nanoparticles, conventional multiferroic fluids based on composite particles may provide an opportunity to gain electrical control of magnetization and vice versa, which implies potential applications.

Ba0.8Sr0.2TiO3 (BST) and Cu0.5Co0.5Fe2O4 (CCFO) nanopowders were prepared by hydrothermal method and chemical coprecipitation, respectively. Barium strontium titanate nanopowder–nano mixed oxides containing copper, cobalt, and iron (BST-CCFO) multiferroic fluids with different mass ratios (mBST/mCCFO = 1:2, 1:1, and 2:1) were prepared by using dimethyl silicone oil and silane coupling agent. Effect of mass ratio on the magnetoelectric performance was comparatively investigated. X-ray diffraction (XRD) showed that the BST and CCFO powders had no secondary phases, which are tetragonal perovskite structure and cubic spinel structure, respectively. Scanning electron microscopy (SEM) showed that the average grain size of BST and CCFO was 26.34 nm and 26.82 nm, respectively. The agglomeration of BST nanopowder was serious. Under the external magnetic field, the BST-CCFO multiferroic fluid will form a chain structure due to the directional movement of magnetic particles, thus enhancing the dielectric properties and ferroelectric properties of multiferroic fluid. The chain structure under the action of magnetic field will change the motion of ferroelectric particles, so that the magnetoelectric coupling effect of multiferroic fluid is significantly enhanced, which is much higher than that of the same type of magnetoelectric composite ceramics. This study is expected to provide a new way to improve the magnetoelectric coupling effect of multiferroic materials.

The (1-x)BiFeO3-xBaTiO3 (short for (1-x)BFO-xBTO, x = 0.2–0.4) ceramics were prepared by solid-state reaction with microwave sintering (MWS) and conventional sintering (CS) methods. The crystal structure, microstructures, dielectric properties, ferroelectric properties, and magnetic properties of BFO-BTO ceramics sintered by MWS and CS were systematically investigated. It is found that the MWS can effectively decrease the grain size and enhance the compactness of BFO-BTO ceramics. The X-ray diffraction (XRD) results confirm that all ceramics exhibit a single perovskite structure, and the phase transforms from rhombohedral in BiFeO3-rich compositions to pseudo-cubic phase gradually as x increases. Introducing BTO into BFO can strengthen its dielectric relaxation behavior. Compared with CS, the MWS samples have a lower remanent polarization (Pr) and a smaller coercive field (Ec) under the same electric field. Therefore, MWS contributes to the decrease of dielectric loss. Addition of BTO can contribute to the reduction of the coercive force (Hc) of BFO-based ceramic, and so decrease the hysteresis loss. At the same time, its remanent magnetization (Mr) value can be decreased by introducing BTO into BFO and using MWS method. The present research provides a route for decreasing the dielectric loss and hysteresis loss of BiFeO3-based ceramics using the MWS method.

BiFeO3 (BFO) thin films with different layers were deposited on Pt/Ti/SiO2/Si substrates via the sol–gel method, and the effect of nonuniform electric field formed by asymmetry electrodes on the photovoltaic properties has been investigated through experimental approaches. The Au/BFO/Pt heterostructures show 1.3 V open-circuit voltages and ∼0.242% photovoltaic power conversion efficiency when illuminated under sunlight (AM 1.5), this high efficiency is at least one order of magnitude larger than many other values thus far reported for BFO-based devices prepared by the spin coated method. The film layer dependence of the photovoltaic effect suggests that the large open-circuit voltage and high efficiency are contributed by both the ferroelectric polarization and the asymmetric structures formed by top and bottom electrodes. Theoretical analysis indicates that the efficiency may be further significantly improved by increasing the number of film layers and the nonuniform depolarization field, implying potential applications.

This is the first systematic report on the preparation and thermoelectric properties of n-type Pb1–x Fe x Te alloys. Iodine-doped n-type Pb0.85Fe0.15Te polycrystalline was prepared by melting and hot-pressing techniques. The morphology and phase structure of the prepared materials were analyzed by scanning electron microscopy and x-ray diffraction, which indicated that the samples possessed a rock-salt crystal structure and showed a biphase structure. The major phase was the polycrystalline PbTe compound and the second phase was the FeTe compound. The FeTe nano-/micro-precipitates were homogeneously distributed in the PbTe matrix, which is beneficial for the reduction of the lattice thermal conductivity. The effects of the iodine content on the thermoelectric properties of I-doped Pb0.85Fe0.15Te have been investigated. The measurement results of electrical resistivity, carrier concentration, Seebeck coefficient, and thermal conductivity in the temperature range of 300–850 K indicate that the thermoelectric transport properties of the obtained samples are sensitive to the iodine content. When the concentration of iodine is about 0.6 at.%, the maximum dimensionless figure-of-merit value of ∼0.65 at 800 K was obtained.

Effects of electric field training on the transport properties and photovoltaic properties of oxygen-deficient La 0.8 Sr 0.2 MnO 3− δ films have been investigated. Oxygen-deficient films annealed in vacuum show obvious increase of resistance and photovoltaic effect, a direct correlation between the magnitude of the photovoltage and training electric field has been observed. The photovoltaic effect was remarkably enhanced by increasing the electrical pulse voltages, that is, it exhibits field-enhanced photovoltaic effect. The formation of Schottky like barrier at the Pt/La 0.8 Sr 0.2 MnO 3− δ interface induced by oxygen vacancies accumulation is believed to be responsible for the increase of photovoltaic effect. These results may be important for practical applications in photoelectric devices.

Effects of oxygen vacancies on the electrical transport properties of oxygen stoichiometric La0.8Sr0.2MnO3 and oxygen-deficient La0.8Sr0.2MnO3−δ films have been investigated. The result presents that the oxygen-deficient films annealed in vacuum show obvious increase of resistance and lattice parameter. With the sweeping voltage or temperature increasing, the resistance exhibits obvious bipolar switching effect, no forming process was needed. Oxygen deficiency in the annealed film leads to the formation of a structural disorder in the Mn–O–Mn conduction channel due to the accumulation of oxygen vacancies under high external electric field or temperatures and hence is believed to be responsible for the bipolar resistance switching effect and the enhanced resistivity compared with oxygen stoichiometric La0.8Sr0.2MnO3 film. These results may be important for practical applications in photoelectric or storage devices and point to a useful direction for other oxidizing materials.

Resistive switching devices are considered as one of the most promising candidates for the next generation memories and nonvolatile logic applications. In this paper, we report an anomalous resistive switching effect in BiFeO 3 based hetero-structures. Different from conventional resistive switching devices made of metal oxides, no forming process is needed to obtain a stable resistive switching effect in the ferroelectric resistive switching devices. Both positive and negative current peaks are observed under forward bias and reverse bias, respectively, suggesting that flexible Schottky-like barriers and conductive channels form at the top and bottom interfaces, which play important roles in the resistive switching of Ag/Bi 0.9 La 0.1 FeO 3 /La 0.3 Sr 0.7 MnO 3 sandwiched structures. These flexible Schottky-like barriers may come from the migration of charged oxygen vacancies/ions under the electric field of sweeping bias and the redistribution of carriers with ferroelectric switching, while the conductive channel resulted from charged oxygen vacancies/ions. These results demonstrate promising prospects for application of the ferroelectric resistive switching effect at interfaces to nonvolatile memory.

The photovoltaic effects in Bi0.9La0.1FeO3 thin films are found to be strongly dependent on the oxygen concentration which can be manipulated by cooling oxygen pressure. Switchable photovoltaic effects can be observed without any electric field applied in low oxygen pressure cooled samples, however, it is hard to detect with high oxygen pressure cooled samples, until the occurrence of polarization flipping by applied electric field. This switchable photovoltaic effects can be explained well by the variation of the Schottky barrier at the metal–Bi0.9La0.1FeO3 interface resulting from the combination of oxygen vacancies and polarization. The sign of photocurrent could be independent of the direction of polarization when the modulation of the energy band induced by oxygen vacancies is large enough to offset that induced by polarization. The photo-current induced by the electro migration of oxygen vacancies is variable due to the diffusion of defects such as oxygen vacancies or the recombination of oxygen vacancies with hopping electrons. Our work provides new ideas for tuning the photovoltaic effect in ferroelectric materials.

Magnetic properties and magnetocaloric effect (MCE) of HoNi0.9Cu0.1Al have been investigated. The compound experienced two phase transitions at about 5.7 K and 11.8 K which was assumed as the combination and competence between the ferromagnetic and antiferromagnetic ordering components. “Table-like” magnetic entropy changes were found under low field changes. The maximum values of ΔS were –10.3 and –23.5 J/kg K with corresponding RC as 98 J/kg and 330 J/kg for field changes of 0–20 kOe and 0–50 kOe, respectively. The “table-like” ΔS, large RC, low ordering temperatures and no hysteresis loss enabled it a potential material for commercial utilization in the future.

The magnetic properties and magnetocaloric effect (MCE) of the compound NdSi have been studied. The magnetic ground state of this compound is determined to be ferromagnetic and a second-order phase transition occurs at the Curie temperature T C =46 K. Large magnetic-entropy changes (Δ S ) with no hysteresis loss are found with field variation. Maximum values of Δ S −6.8 J/kg K and −12.4 J/kg K are found for field changes of 0–20 kOe and 0–50 kOe, respectively. With the merits of the large Δ S and without hysteresis loss, NdSi can be considered as a competitive candidate magnetic refrigerant.

A scientific question vitally important to the materials community is whether there exist “self-assembled” nanoclusters that are thermodynamically stable at elevated temperatures. Using in situ neutron scattering, we have characterized the structure and thermal stability of a nano-structured ferritic alloy. Nanometer sized nanoclusters were found to persist up to ∼1400 °C, providing direct evidence of a thermodynamically stable alloying state for the nanoclusters. High-temperature neutron diffraction measurements show a stable ferritic matrix, with little evidence of recrystallization or grain growth at temperatures up to 1300 °C. This result suggests that thermally stable nanoclusters and the oxygen-vacancy interaction limit the diffusion of Fe atoms and hence the mobility of grain boundaries, stabilizing the microstructure of the ferritic matrix at high temperatures.

Calculated local diesel-water two phases flow in a tube with elbow were compared with experimental data. The well-known volume of fluid (VOF) model combined with continuum surface tension (CSF) model and an interface geometric reconstruction method was used to simulate the flow phenomena by a computational fluid dynamics (CFD) approach. The simulated flow pattern, critical oil superficial velocity and water average velocity are in good agreement with the experiments, and reveal why severe internal corrosion occurs in some spots of pipelines. Hence, the water deposited in pipeline could be flushed out only when the oil flow rate exceeds the critical value. KEYWORD: CFD; VOF; Local two-phase flow; Water displacement International Conference on Industrial Technology and Management Science (ITMS 2015) © 2015. The authors Published by Atlantis Press 1273

DLC films ranging from 5 to 180 nm in thickness have been prepared by plasma-based ion implantation (PBII) with C on Si. The structures of the films were studied with XPS and Raman spectroscopy. The nanohardness and the intrinsic stress of the films were measured. Dry sliding wear experiments have been carried out, using a ball-on-disc tester, to investigate the tribological properties of DLC films against alumina balls, employing various normal applied loads and reciprocating frequencies. For comparison, DLC films prepared by plasma-assisted chemical vapor deposition (PACVD) on Si were also investigated. The results show that the films prepared by PBII exhibit more significant improvement in tribological properties than the films prepared by PACVD because the former present higher sp 3 /sp 2 ratio, higher hardness and lower stress than the latter. The effects of the film thickness, the applied loads and the reciprocating frequencies on the tribological properties are also presented.

It is shown within the framework of the ab initio statistical mechanics that the triple defect formation is not the dominant thermal excitation in stoichiometric B2–FeAl, at least at low temperatures. Therefore the customary type of analysis of magnetic susceptibility measurements exclusively in terms of triple defects may yield erroneous results for the concentration of Fe vacancies.

Taking Mo-Si compounds as model systems, we show that the coefficients of thermal expansion (CTEs) of complex structures can be calculated precisely from first principles by incorporating the Debye model for acoustic response. Specifically, we obtain a nearly isotropic CTE in MoSi2 but a highly anisotropic CTE in Mo5Si3. The CTE anisotropy in Mo5Si3 is due to an elastically more rigid basal plane and a higher anharmonicity along the c axis. As the structure of 5-3 compounds is modified from D8m to D8l by boron substitutions (Mo5SiB2), we predict a significant decrease in the CTE anisotropy, which is confirmed by experiments.

The relationships between the crystal structure modification, due to the doping element of Sn, and the critical temperature Tc of Sn-doped YBa2Cu3-x SnxO7- , with x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, have been investigated by means of the peak shift and the peak broadening of the powder x-ray diffraction pattern. The profiles of x-ray diffraction peaks, due to crystal planes (006), (020), (021) and (200), were studied using the multi-peak fitting technique which is based on the Gaussian distribution function. It is interesting to note that the Sn-doped atoms effectively occupy the Cu2 sites in the CuO2 layer. The critical temperature of the Y-123 phase depends more sensitively on the lattice parameters a and b, rather than on the c-axis parameter c. The samples used for this investigation underwent the same treatment to ensure the requirement for maintaining the same oxygen content, particle size and residual stress. In this way, we can make sure that the Sn doping basically causes the peak shift and the peak broadening. Based on our results, we conclude that Sn doping in YBCO leads to an increase of the lattice constants a and b. The greater the expansion in a and b, the lower the critical temperature that results.

Ba0.6Sr0.4TiO3 (BST) thin films deposited on Pt/Ti/SiO2/Si substrates by radio frequency magnetron sputtering and crystallized by rapid thermal annealing (RTA) exhibit much thinner BST/Pt interfacial transition layer and higher dielectric properties than the films crystallized by conventional thermal annealing (CTA). HRTEM observations show that the transition layer is 2-3nm thick for RTA and 4-5nm thick for CTA. XPS investigations display that the transition layer is composed of perovskited BST phase and non-perovskited BST phase, and RTA corresponds to much less non-perovskited BST phase than CTA. The reason for non-perovskited BST phase and the dielectric properties of BST films are also presented.

Tin-doped samples were synthesized in sealed silica tubes by a solid-state reaction method. The dominant phase involved in the sample is a superconducting phase of (Hg(Sn)-1223), which is a solid solution of Sn in the compound . An impurity phase also exists together with the dominant phase. The results of thermogravity analysis and XRD analysis show that the impurity phase and superconducting phase Hg(Sn)-1223 have different decomposition temperatures in flowing He gas and in flowing gas atmosphere. The onset decomposition temperatures of these two phases measured in flowing He gas are 560 and respectively. They increase to 576 and respectively in flowing gas. Studies of the effect of annealing temperature on by resistance measurement for this sample show that the superconductivity is reversible in flowing gas below the decomposition temperature of the superconducting phase Hg(Sn)-1223, namely . The quality of the superconductor, including the critical temperature and the sharpness of the transition, can be improved by removing the impurity phase from the sample using a high-temperature annealing process under flowing gas.

The displacement of domain walls in the film of (BiTm) 3 (FeGa) 5 O 12 has been studied experimentally under the conditions of increasing applied magnetic field with change rates of R = d H d t = 0, 67, 358 and 401 (A/m −1 )s −1 . The relationship between the displacement ΔX and the magnetic field H was established using the experimental data obtained by the photographic technique. On the other hand, the experimental results are interpreted based on the fundamental equation that describes the motion of domain wall under a magnetic force. We note that the damping coefficient α for our sample was shown to be very small ( α ≈ 10 −6 ). It increases with increasing the change rate of the magnetic field R . It is also shown that the equivalent resistant field, H r , for our sample is relatively large. Furthermore, we note that for the case of zero change rate, i.e. R = 0, the applied field that corresponds to the Faraday's rotation angle for the saturation state is approximately determined by the value of the magnetic field at which the turning point in the ΔX vs H curve occurs.

The ideal Griffith energies and the critical stress intensity factors for three cleavage modes are determined from the calculated elastic constants and surface energies. The propensity for crack tip deformation is estimated on the basis of the calculated antiphase boundary (APD), complex stacking fault and superlattice intrinsic stacking fault energies and the anisotropic coupling effect on dislocation mobility, i.e. non-Schmid effects. It is shown that while the calculated Griffith energy of Ni3 Si is larger than that of Ni3Al, dislocation emission from a crack tip is easier and dislocation mobility is higher in Ni3Al than in Ni3Si. When a crack is loaded in a mixed mode (KI + KIII), emission of a super-Shockley partial from the crack trailing extended SISF is predicted and confirmed by in situ straining transmission electron microscopy observations of Ni3Al.

Recent advances in our understanding of the fundamental mechanisms of strength and ductility in ordered intermetallic alloys are summarized. State of the art experimental techniques and innovative computational advances have together stimulated the current activity in this field and opened new opportunities for research. The current status and scientific issues in the area of bulk and defect properties, deformation and strengthening mechanisms, and fracture and toughening mechanisms are assessed. Future research areas of major importance for understanding of deformation and fracture behavior in intermetallic compounds are identified.

First-principles quantum mechanical calculations based on the local-density-functional theory have been used together with the anisotropic elasticity theory of dislocations to study the electronic and mechanical properties of transition-metal aluminides. The bonding mechanism can be described by the combination of Al-to-transition metal charge transfer and strong p-d bonding hybridization effects. Point defect self-energies, elastic constants, various shear fault energies and cleavage energies are determined from first-principles for the L1 2 (Ni 3 Al and trialuminides), B2 (FeAl and NiAl) and L1 0 (TiAl) structure-base intermetallics. A comprehensive understanding of the bonding mechanism, point defect structure, yield strength anomaly and brittle fracture behavior forms the basis for a better assessment of extrinsic effects on the strength and ductility of aluminides (e.g., hydrogen in FeAl, and boron in Ni 3 Al).

Fundamental aspects of cleavage fracture behavior of ordered intermetallic alloys are analyzed on the basis of first-principles total energy calculations of cleavage strength (and energy) and anisotropic elasticity modeling of crack tip slip (and twinning). Intrinsic brittleness of Al 3 Sc and NiAl is rationalized from the comparative analyses with Ni 3 Al and FeAl, respectively. The cleavage habit planes of (110) for NiAl and (100) for FeAl are correctly predicted in terms of the anisotropy of cleavage energies and elastic properties of dislocations. Boron strengthening in Ni 3 Al and hydrogen embrittlement in FeAl are discussed in view of the calculated results.

In this paper first-principles calculation of the elastic constants, shear fault energies, cleavage strength, and bonding charge density of Ni Al and FeAl are presented. For NiAl, we find that the dissociation of {l angle}111{r angle} superdislocations into partial dislocations is unlikely, because of a high antiphase boundary (APB) energy and a weak repulsive elastic force between partial dislocations. The APB energy of FeAl is found to be highly anisotropic with respect to different slip planes. FeAl has a high ideal cleavage strength as a result of the directional d-bond formation at the Fe sites. The strong ordering behavior of NoAl is explained in terms of the repulsive interaction between Al atoms as a result of the Al-to-Ni charge transfer and the atomic size difference of Ni and Al. The active slip plane of {l brace}112{r brace} in FeAl at low temperatures is predicted on the basis of the anisotropic elastic coupling effect of non-glide stresses. The spontaneous glide decomposition of the {l angle}111{r angle} superdislocation in NiAl, which can be a source of {l angle}100{r angle} slip, is also discussed.

Previously we have reported that with the addition of Te, ceramics with nominal composition YTe x Ba 4 Cu 6 O y contain at least two phases: YTe x 1 Ba 2 Cu 3 O y and YTe x 2 Ba 4 Cu 5 O y . A mo analysis reveals in this investigation that yet two more phases exist in the YTe x -146 sample. These two phases, one superconducting, called the Y-111 ' , and the other, non-superconducting, called Y-NSC, are found in samples prepared using the same heating processes and with the predetermined composition YTe 0.1 Ba 1.1 Cu 1.2 O y . The various volume fractions of the above stated four constituent phases are calculated quantitatively employing our X-ray diffraction data for samples with various amounts of Te. These volume fractions appear to be sensitive to the amount of Te contained in the sample. The lattice constants of the crystals for various phases are determined for different Te amounts.

A first principles study of various relevant energetics for Co films deposited on Cu(111) is presented. The tendency of Cu diffusion to the surface is explained in terms of a lower surface energy of Cu than that of Co. In the low Co coverage regime, the growth of the fcc stacking is found to be predominantly determined by the following considerations: (1) the diffusing Cu atoms prefer fcc sites when they are present on the Cu(111) substrate; (2) both a Cu overlayer (i.e., in the case of Cu atoms locally forming a capped overlayer) and a Co overlayer on Cu(111) prefer fcc stacking. On the other hand, Co adatoms on fcc-Co(111) substrate strongly prefer hcp sites, suggesting that the layer stacking sequence becomes pure hcp as the diffusion of Cu atoms to the surface diminishes. Energetically, Co and Cu atoms are found not to mix with each other on the surface. Since Cu has an fcc preference, a coexistence of fcc- and hcp-type domains is expected in the intermediate Co coverage regime.

Effects of light and electrical current on the electrical transport properties and photovoltaic properties of oxygen-stoichiometric La0.5Sr0.5CoO3 and oxygen-deficient La0.5Sr0.5CoO3??? ? films prepared by pulsed laser deposition have been investigated. Oxygen-deficient films annealed in a vacuum show an obvious increase of resistance and lattice parameter. Besides, a direct correlation between the magnitude of the photoconductivity and oxygen vacancies in La0.5Sr0.5CoO3??? ? films has been observed. The light illumination causes a resistance drop to show the photoconductivity effect. Moreover, the photoconductivity can be remarkably enhanced by increasing the electrical current, that is, it exhibits current-enhanced photoconductivity (CEPC) effect. Oxygen deficiency in the annealed film leads to the formation of a structural disorder in the Co?O?Co conduction channel due to the accumulated oxygen vacancies and hence is believed to be responsible for the increase in higher photoconductivity. These results may be important for practical applications in photoelectric devices.

The anomaly in the normal state of high-T c superconductors is related to the pseudo-gap phenomenon. For the under-doped cuprate superconductors, the relationship between the logarithmic increment in conductivity (w.r.t. the normal conductivity 1/ g 9 N (T)) and the inverse temperature exhibits some specific characters at temperatures T ∗ , T S and T F . The temperatures T ∗ and T S are respectively the opening temperature and the terminating temperature for the cross over in the pseudo-gap phenomenon, while the temperature T F is close to the onset critical temperature of the superconductor. It is shown experimentally that T ∗ , T S and T F depend linearly on the Ca-doping level, while the quantity (2 Δ PS 2 )/(2 Δ T ) − Δ T has a quadratic-polynomial dependence on the Ca-doping level.

The thermal excitation spectrum relevant to the pseudo gap phenomenon is established from the conductivity measurement results. The plot of the logarithmic deviation in the conductivity, with respect to the normal state conductivity, against the inverse temperature shows some characteristic temperatures T * and T s , at which the pseudo-gap is opened and the saturation temperature of the created quasi-particles in the pseudo gap level. There is another characteristic temperature T F , which close to the onset critical temperature of the superconductivity. There is a crossover from the strange metallic state to the pseudo-gap state within the temperature interval ΔT = T * − T s . In the temperature interval ΔT = T S − T F , the plot of ln[l/ϱ(T) − l/ϱ N (T)] vs. 1/T exhibits linear relationship. The slope of this linear relationship represents the magnitude of the pseudo-gap Δ SP /k B . The conductivity deviation can be expressed in term of the number of quasi-particles.

While sub- and grain-boundaries are the primary dislocation sources in Ll{sub 2} alloys, yield and flow stresses are strongly influenced by the multiplication and exhaustion of mobile dislocations from the secondary sources. The concept of enhanced microplasticity at grain boundaries due to chemical disordering is well supported by theoretical modeling, but no conclusive direct evidence exist for Ni{sub 3}Al bicrystals. The strong plastic anisotropy reported in TiAl PST (polysynthetically twinned) crystals is attributed in part to localized slip along lamellar interfaces, thus lowering the yield stress for soft orientations. Calculations of work of adhesion suggest that, intrinsically, interfacial cracking is more likely to initiate on {gamma}/{gamma}-type interfaces than on the {alpha}{sub 2}/{gamma} boundary. 70 refs, 5 tabs, 5 figs.

The electronic structure and magnetism of thin films of metastable bcc phase Co(001) consisting of one-, five- and nine-layers is determined by means of all-electron local spin density full potential linearized augmented plane wave (FLAPW) calculations at the lattice constant found for bcc Co stabilized on a GaAs substrate by Prinz. Band structure, surface states, density of states, charge and spin densities and contact hyperfine fields are presented. The center layer of the many-layer films yields a spin magnetic moment of 1.76μB which agrees well with results of bulk calculations for bcc Co. The surface layer has a moment (1.94μB) which is only 10% greater than the bulk value - in sharp contrast to the enhancement found for other transition metal surfaces [35% for Fe(001), 20% for Ni(001) and over 300% for Cr(001)]. Unlike these other transition metal surfaces, even the first layer below the surface layer in Co has the bulk magnetic moment - which indicates that the spin density, like the charge density, shows very short range screening of the surface-vacuum interface.