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Commercially available polycrystalline nickel (grain size: 30 μm) and electrodeposited nanocrystalline nickel (grain size: 30 nm) were analyzed for the effect of stress-induced heat generation during plastic deformation at room temperature. Tensile coupons in conformance to ASTM E8 standard were tested at a strain rate of 10 -1/s to record the amount heat dissipated using a high resolution infrared detector. The maximum temperature increases recorded for nanocrystalline and polycrystalline nickel close to sample fracture were 58° and 70°, respectively. Grain growth in nanocrystalline nickel due to stress-induced heat generation is unlikely since the maximum temperature during deformation is below the previously reported onset temperature for grain growth in nanocrystalline nickel. © (2012) Trans Tech Publications, Switzerland., 7th International Conference on Processing and Manufacturing of Advanced Materials, THERMEC'2011, 1 August 2011 through 5 August 2011, Quebec City, QC

Present study endeavors to establish the physical basis of an unprecedented trend in scatter, observed in nonlinear ultrasonic (NLU) parameter, associated with varying degree of crystallographic orientation change across crystallites in a polycrystalline material. It is shown that this scatter arises due to anisotropy in harmonics generation as a result of orientation change of slip systems in polycrystals with respect to the wave propagation direction. A near ? titanium alloy has been taken as a model alloy to demonstrate this effect of crystallographic orientation change vis-�-vis change in the orientation of slip systems. Scale of crystal orientation change is shown to have a strong correlation with the degree of scatter in NLU measurements. Further, the study establishes the dominating effect of the scale of crystalline orientation change on harmonics generation as compared to variation in other microstructural parameters such as dislocation density, interface structure etc. Frequency distribution analysis of the scatter indicates that the distribution depends on the colony size which exhibits a linear correlation with standard deviation value. The dislocation string vibration model has been extended for harmonics generation in polycrystalline aggregates to explain the trend in the scatter during measurement of NLU parameter in the material. � 2012 American Institute of Physics.

Owing to its selectivity, diffraction is a powerful tool for analysing the mechanical behaviour of polycrystalline materials at the mesoscale (phase and/or grain scale).In situneutron diffraction during tensile tests and elastoplastic self-consistent modelling were used to study slip phenomena occurring on crystallographic planes at small and large deformation. The critical resolved shear stresses in both phases of duplex stainless steel were found for samples subjected to different thermal treatments. The evolution of grain loading was also determined by showing the large differences between stress concentration for grains in ferritic and austenitic phases. It was found that, for small loads applied to the sample, linear elastic deformation occurs in both phases. When the load increases, austenite starts to deform plastically, while ferrite remains in the elastic range. Finally, both phases undergo plastic deformation until sample fracture. By using an original calibration of diffraction data, the range of the study was extended to large sample deformation. As a result, mechanical effects that can be attributed to damage processes initiated in ferrite were observed.

The paper describes a level set framework for the finite-element modelling of recrystallization in polycrystalline materials, including the nucleation, primary recrystallization and grain growth stages. A set of convection- reinitialization-diffusion equations is implemented within a finite-element formulation to describe boundary motion, according to a kinetic law relating the velocity of the boundary to a thermodynamic driving force. Different theoretical test cases illustrate the potential of the method for simulations of recrystallization and grain growth following large plastic deformation and/or considering complex microstructures. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In this study we investigate the effect of imperfect (not perfectly bonded) interfaces on the stiffness and strength of hierarchical polycrystalline materials. As a case study we consider a honeycomb cellular polycrystal used for drilling and cutting tools. The conclusions of the analysis are, however, general and applicable to any material with structural hierarchy. Regarding the stiffness, generalized expressions for the Voigt and Reuss estimates of the bounds to the effective elastic modulus of heterogeneous materials are derived. The generalizations regard two aspects that are not included in the standard Reuss and Voigt estimates. The first novelty consists in considering finite thickness interfaces between the constituents undergoing damage up to final debonding. The second generalization consists of interfaces not perpendicular or parallel to the loading direction, i.e., when isostress or isostrain conditions are not satisfied. In this case, approximate expressions for the effective elastic modulus are obtained by performing a computational homogenization approach. In the second part of the paper, the homogenized response of a representative volume element (RVE) of the honeycomb cellular polycrystalline material with one or two levels of hierarchy is numerically investigated. This is put forward by using the cohesive zone model (CZM) for finite thickness interfaces recently proposed by the authors and implemented in the finite element program FEAP. From tensile tests we find that the interface nonlinearity significantly contributes to the deformability of the material. Increasing the number of hierarchical levels, the deformability increases. The RVE is tested in two different directions and, due to different orientations of the interfaces and Mixed Mode deformation, anisotropy in stiffness and strength is observed. Stiffness anisotropy is amplified by increasing the number of hierarchical levels. Finally, the interaction between interfaces at different hierarchical levels is numerically characterized. A condition for scale separation, which corresponds to the independence of the material tensile strength from the properties of the interfaces in the second level, is established. When this condition is fulfilled, the material microstructure at the second level can be efficiently replaced by an effective homogeneous continuum with a homogenized stress–strain response. From the engineering point of view, the proposed criterion of scale separation suggests how to design the optimal microstructure of a hierarchical level to maximize the material tensile strength. An interpretation of this phenomenon according to the concept of flaw tolerance is finally presented.

In this paper, the phenomenon of intergranular fracture in polycrystalline materials is investigated using a nonlinear fracture mechanics approach. The nonlocal cohesive zone model (CZM) for finite thickness interfaces recently proposed by the present authors is used to describe the phenomenon of grain boundary separation. From the modelling point of view, considering the dependency of the grain boundary thickness on the grain size observed in polycrystals, a distribution of interface thicknesses is obtained. Since the shape and the parameters of the nonlocal CZM depend on the interface thickness, a distribution of interface fracture energies is obtained as a consequence of the randomness of the material microstructure. Using these data, fracture mechanics simulations are performed and the homogenized stress-strain curves of 2D representative volume elements (RVEs) are computed. Failure is the result of a diffuse microcrack pattern leading to a main macroscopic crack after coalescence, in good agreement with the experimental observation. Finally, testing microstructures characterized by different average grain sizes, the computed peak stresses are found to be dependent on the grain size, in agreement with the trend expected according to the Hall-Petch law.

A micromechanically motivated model is proposed to capture nonlinear effects and switching phenomena present in ferroelectric polycrystalline materials. The changing remnant state of the ferroelectric crystal is accounted for by means of so-called back fields-such as back stresses-to resist or assist further switching processes in the crystal depending on the local loading history. To model intergranular effects present in ferroelectric polycrystals, the computational model elaborated is embedded into a mixed polygonal finite element approach, whereby an individual ferroelectric grain is represented by one single irregular polygonal finite element. This computationally efficient coupled simulation framework is shown to reproduce the specific characteristics of the responses of ferroelectric polycrystals under complex electromechanical loading conditions in good agreement with experimental observations. � 2011 Springer-Verlag.

Numerical aspects of the nonlocal cohesive zone model (CZM) presented in Part I are discussed in this companion paper. They include the FE implementation of the proposed nonlocal CZM in the framework of zero-thickness interface elements and the numerical treatment of the related nonlocality. In particular, a Newton–Raphson method, combined with a series expansion to obtain tentative values for the cohesive tractions, is used to efficiently compute the tangent stiffness matrix and the residual vector of the interface elements. Then, numerical applications to polycrystalline materials are proposed, focusing on the constitutive modelling of the finite thickness interfaces between the grains. It will be shown that the parameters of the nonlocal CZM (shape, peak stress, fracture energy) depend on the thickness of the interface. The CZM is able to produce statistical distributions of Mode I fracture energies consistent with those assumed a priori in stochastic fracture mechanics studies. The statistical variability of fracture parameters, originating from the natural variability of the interface thicknesses, has an important influence on the crack patterns observed from simulated tensile tests. Finally, we show that the relation between interface thickness and grain size can be used to explain the grain-size effects on the material tensile strength. In particular, considering a sublinear relation between the interface thickness and the grain diameter at the microscale, the nonlocal CZM is able to recover the Hall–Petch law. Therefore, the proposed model suggests that an inverse relation between the interface thickness and the grain size would lead to an inversion of the Hall–Petch law as well. This new interpretation seems to be confirmed by experimental data at the nanoscale, where the inversion of the Hall–Petch law coincides with the anomalous increase of the interface thickness by reducing the grain size.

Проведено численное исследование формирования деформационного рельефа на свободной поверхности трехмерных поликристаллов с периодической структурой в условиях одноосного растяжения. Проанализировано влияние условий нагружения мезообъемов и размера зерна на характеристики рельефных образований. С целью последующей оптимизации численного анализа исследовано влияние толщины трехмерного модельного образца на формирующиеся деформационные складки. Показано, что основное влияние на деформационный рельеф оказывает микроструктура приповерхностных слоев, лежащая в пределах 3-4 зеренных диаметров., The formation of a deformation-induced relief on the free surface of 3D polycrystals with a periodic microstructure under uniaxial tension was studied in numerical simulation. The effect of loading conditions and grain size on the characteristics of relief was analyzed. For subsequent optimization of the numerical analysis, the influence of the thickness of a 3D model specimen on arising deformation folds was investigated. It is shown that the microstructure of subsurface layers lying within three-four grain diameters makes a major contribution to the deformation-induced relief.

Development of textured crystalline silicon from amorphous silicon film using a pulsed Nd3+:YAG laser is reported. The technique involved is laser annealing and subsequent laser nano texturing by over lapping the laser spot by 50% and 90% of the diameter. Experimental investigations were performed using third (355 nm), second (532 nm) and fundamental harmonics (1064 nm) of the pulsed Nd3+:YAG laser. To investigate the texturization AFM measurement was performed. Absorbance and photoconductivity measurements were performed to analyze the photovoltaic properties of thin films. The process was theoretically analyzed using a 3-D heat transformation model in FEMLAB software. 355 nm laser assisted nano-texturing with 90% overlap showed an improvement in crystalline property and improved textured surface with a higher absorbance as compared to that of 50% overlap.

Two different approaches to intergranular crack propagation in brittle polycrystals are contrasted. Crack paths resulting from a method that allows a detailed description of the stress field within a polycrystal are compared to cracks dictated by topological considerations. In the first approach, a fracture path is determined with a Generalized Finite Element Method for polycrystals considering isotropic elastic grains. In the second approach a fracture path is generated using Dijkstra’s shortest path algorithm. This algorithm yields minimum fracture energy crack paths. A series of simulations is performed to assess the influence of the method of analysis on the crack path.

Two different approaches to intergranular crack propagation in brittle polycrystals are contrasted. Crack paths resulting from a method that allows a detailed description of the stress field within a polycrystal are compared to cracks dictated by topological considerations. In the first approach, a fracture path is determined with a Generalized Finite Element Method for polycrystals considering isotropic elastic grains. In the second approach a fracture path is generated using Dijkstra’s shortest path algorithm. This algorithm yields minimum fracture energy crack paths. A series of simulations is performed to assess the influence of the method of analysis on the crack path.

The paper describes a robust finite element model of interface motion in media with multiple domains and junctions, as is the case in polycrystalline materials. The adopted level set framework describes each domain (grain) with a single level set function, while avoiding the creation of overlap or vacuum between these domains. The finite element mesh provides information on stored energies, calculated from a previous deformation step. Nucleation and growth of new grains are modelled by inserting additional level set functions around chosen nodes of the mesh. The kinetics and topological evolutions induced by primary recrystallization are discussed from simple test cases to more complex configurations and compared with the Johnson-Mehl-Avrami-Kolmogorov theory. © 2009 IOP Publishing Ltd.

International audience; Procedures for synthesizing digital polycrystalline microstructures are illustrated, either from 2D statistical data or from 3D deterministic data. Finite element meshes representing the digital microstructures are generated using anisotropic and adaptive mesh refinement close to the grain boundaries. Digital mechanical testing based on crystal plasticity theory provides an estimate of the spatial distribution of strain energy within the polycrystalline aggregate. The latter quantity is used as an input for modelling subsequent static recrystallization, grain boundary motion being described within a level set framework. The kinetic law for interface motion accounts for both the stored strain energy and the grain boundary energy. The possibility to include nucleation events within the level set framework is illustrated, as well as the evolving topology of the grain boundary network. The recrystallization model is tested in different configurations and compared to the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory.

Two different approaches to intergranular crack propagation in brittle polycrystals are contrasted. Crack paths resulting from a method that allows a detailed description of the stress field within a polycrystal are compared to cracks dictated by topological considerations. In the first approach, a fracture path is determined with a Generalized Finite Element Method for polycrystals considering isotropic elastic grains. In the second approach a fracture path is generated using Dijkstra's shortest path algorithm. This algorithm yields minimum fracture energy crack paths. A series of simulations is performed to assess the influence of the method of analysis on the crack path.

Two different approaches to intergranular crack propagation in brittle polycrystals are contrasted. Crack paths resulting from a method that allows a detailed description of the stress field within a polycrystal are compared to cracks dictated by topological considerations. In the first approach, a fracture path is determined with a Generalized Finite Element Method for polycrystals considering isotropic elastic grains. In the second approach a fracture path is generated using Dijkstra's shortest path algorithm. This algorithm yields minimum fracture energy crack paths. A series of simulations is performed to assess the influence of the method of analysis on the crack path.

Thèse préparée au sein du laboratoire:European Synchrotron Radiation Facility (ESRF), Grenoble; Inelastic X-ray scattering (IXS) is a tool to determine the phonon dispersion along high symmetry directions in single crystals. However, novel materials and crystals under extreme conditions are often only available in form of polycrystalline samples. Thus the investigation is limited to orientationally averaged properties. To overcome these limitations, a methodology to extract the single crystal phonon dispersion from polycrystalline materials was developed. The approach consists of recording IXS spectra over a large momentum transfer region and confront them with a Born–von Kármán model calculation. A least-square refinement of the model IXS spectra then provides the single crystal dispersion scheme. In this work the method is developed on the test case Be. Further studies were performed on more and more complex systems, in order to explore the limitations. This novel application of IXS promises to be a valuable tool in cases where single crystalline materials are not available.; La diffusion inélastique de rayons X (IXS) est un outil pour la détermination de la dispersion des phonons dans les systèmes mono-cristallines. Cependant, les nouveaux matériaux ou les cristaux dans des conditions extrême ne sont souvent disponible que sous forme polycristalline. Il n'est ainsi possible d'en extraire que des propriétés moyennées. Pour surmonter ces limitations, nous avons développé une méthode qui permet d'extraire la dispersion du système mono-cristallin à partir de données obtenues sur un échantillon polycristallin. Dans cette nouvelle approche, nous enregistrons des spectres IXS pour une large gamme de moments transférés que nous confrontons à un calcul modèle (Born – von Kármán). Un ajustement de ce calcul par la méthode des moindre carrés nous permet alors de remonter à la dispersion du mono-cristal. Des expériences sur des systèmes de plus en plus complexes ont été realisées afin de développer la méthode et d'éprouver les limites de la méthode.

This letter describes a level set framework for the numerical modelling of primary static recrystallization in a polycrystalline material. The topological evolution of the grain structure is simulated in two and three dimensions, based on a kinetic law relating the velocity of the boundary to the thermodynamic driving force. The adopted finite element approach is described, discussed and tested from simple to more complex configurations. The possibility to accurately describe nucleation and growth is illustrated in three dimensions. © 2008 Acta Materialia Inc.

In this work, we propose a novel low power, process tolerant, generic and reconfigurable test structure to reduce the test cost, improve diagnosability and verifiability of complex VLSI systems. The test structure contains a variety of configurable design-for-test units designed with low cost Low Temperature Polycrystalline Silicon Thin Film Transistors (LTPS TFTs) that are fabricated on a separate substrate (e.g., polymer, glass etc). The proposed test circuits do not consume any silicon area because they can be integrated on the chip using 3-D technology. This reconfigurable test paradigm eliminates the need to re-design the BIST components that may vary from one processor generation to another.

Inelastic X-ray scattering (IXS) is a tool to determine the phonon dispersion along high symmetry directions in single crystals. However, novel materials and crystals under extreme conditions are often only available in form of polycrystalline samples. Thus the investigation is limited to orientationally averaged properties. To overcome these limitations, a methodology to extract the single crystal phonon dispersion from polycrystalline materials was developed. The approach consists of recording IXS spectra over a large momentum transfer region and confront them with a Born–von Kármán model calculation. A least-square refinement of the model IXS spectra then provides the single crystal dispersion scheme. In this work the method is developed on the test case Be. Further studies were performed on more and more complex systems, in order to explore the limitations. This novel application of IXS promises to be a valuable tool in cases where single crystalline materials are not available., La diffusion inélastique de rayons X (IXS) est un outil pour la détermination de la dispersion des phonons dans les systèmes mono-cristallines. Cependant, les nouveaux matériaux ou les cristaux dans des conditions extrême ne sont souvent disponible que sous forme polycristalline. Il n'est ainsi possible d'en extraire que des propriétés moyennées. Pour surmonter ces limitations, nous avons développé une méthode qui permet d'extraire la dispersion du système mono-cristallin à partir de données obtenues sur un échantillon polycristallin. Dans cette nouvelle approche, nous enregistrons des spectres IXS pour une large gamme de moments transférés que nous confrontons à un calcul modèle (Born – von Kármán). Un ajustement de ce calcul par la méthode des moindre carrés nous permet alors de remonter à la dispersion du mono-cristal. Des expériences sur des systèmes de plus en plus complexes ont été realisées afin de développer la méthode et d'éprouver les limites de la méthode.

The paper considers the basic physical hypotheses used in constructing models for activated alloy formation by cold intensive plastic deformation. The basis for the model is a messenger mechanism of evolution for the stress pattern in plastic deformation of a polycrystalline material. Allowance is made for the vacancy fluxes as additional accommodation mode for the strain, which provides preservation of the continuity, and which enables one to describe the alloy composition redistribution on strain. Experimental data are compared with conclusions from models for activated alloy formation: a model operated on a ballistic mechanism for atomic migration and an alternative new model considered in the paper. © 2008 Springer Science+Business Media, Inc.

Heat capacity of polycrystalline R2Ti3Ge4 (R = Gd, Tb and Er) compounds (Orthorhombic, Sm5Ge4-type, Space group Pnma) has been studied in the temperature range of 1.8 K to 300 K in various applied magnetic fields. The compounds with magnetic lanthanide elements show interesting low field magnetism intrigued by possible presence of competing antiferromagnetic and ferromagnetic interactions. The magnetocaloric effect in these compounds is estimated from the field dependent heat capacity data. The magnetic entropy change and the adiabatic temperature change in the vicinity of the magnetic transition are found to be significant., 12 pages incl 3 figures, submitted to Journal of Applied Physics

The aim of this paper is to study rate-dependent switching in ferroelastic materials. More specifically, a micro-mechanically motivated model is embedded into an iterative three-dimensional and electromechanically coupled finite-element framework. An established energy-based criterion serves for the initiation of domain switching processes as based on reduction in (local) Gibbs free energy. Subsequent nucleation and propagation of domain walls is captured via a linear kinetics theory with rate-dependent effects being incorporated in terms of a deformation-dependent limit-time parameter. With this basic model in hand, two different switching formulations are elaborated in this work: on the one hand, a straightforward volume-fraction ansatz is applied with the volume-fraction value depending on the limit-time parameter; on the other hand, a reorientation-transformation formulation is proposed, whereby the orientation tensor itself is assumed to depend on the limit-time parameter. Macroscopic behaviour such as stress versus strain curves or stress versus electrical displacement graphs are obtained by applying straightforward volume-averaging techniques to the three-dimensional finite-element-based simulation results which provides important insights into the rate-dependent response of the investigated ferroelastic materials. � IOP Publishing Ltd.

Polycrystalline samples of VOMoO4 are prepared by a solid-state reaction method and their electrochemical properties are examined in the voltage window 0.005-3 V versus lithium. The reaction mechanism of a VOMoO4 electrode for Li insertion/extraction is followed by ex situ X-ray diffraction analysis. During initial discharge, a large capacity (1280 mAh g-1) is observed and corresponds to the reaction of ?10.3 Li. The ex situ XRD patterns indicate the formation of the crystalline phase Li4MoO5 during the initial stages of discharge, which transforms irreversibly to amorphous phases on further discharge to 0.005 V. On cycling, the reversible capacity is due to the extraction/insertion of lithium from the amorphous phases. A discharge capacity of 320 mAh g-1 is obtained after 80 cycles when cycling is performed at a current density of 120 mA g-1. � 2007 Elsevier B.V. All rights reserved.

ZnO is a unique material that offers about a dozen different application possibilities. In spite of the fact that the ZnO lattice is amenable to metal ion doping (3d and 4f), the physics of doping in ZnO is not completely understood. This paper presents a review of previous research works on ZnO and also highlights results of our research activities on ZnO. The review pertains to the work on Al and Mg doping for conductivity and band gap tuning in ZnO followed by a report on transition metal (TM) ion doped ZnO. This review also highlights the work on the transport and optical studies of TM ion doped ZnO, nanostructured growth (ZnO polycrystalline and thin films) by different methods and the formation of unique nano- and microstructures obtained by pulsed laser deposition and chemical methods. This is followed by results on ZnO encapsulated Fe3O4 nanoparticles that show promising trends suitable for various applications. We have also reviewed the non-linear characteristic studies of ZnO based heterostructures followed by an analysis on the work carried out on ZnO based phosphors, which include mainly the nanocrystalline ZnO encapsulated SiO2 ,an ew class of phosphor that is suitable for white light emission. (Some figures in this article are in colour only in the electronic version)

Electrical resistivity studies on mischmetal-substituted, C15 type AB 2 alloy (Mm0.2Tb0.8Co2) hydrides with varied hydrogen interstitial concentrations have been carried out in the temperature range 80-300 K. Hydrogen concentration-dependent metal-semiconductor-like transition has been observed and explained based on the charge transfer between hydrogen and the 3d band and the reduction in 6S component of the electron density. Polycrystalline thin film of the alloy capped with palladium has been obtained by electron beam evaporation technique on clean glass substrates. Switching properties from reflecting to a transparent state by electrochemical polarization in an alkaline electrolyte of pH 13 at room temperature have been investigated. In addition, the cyclic durability of the films has been studied and compared with that of rare-earth-based switchable mirror films. Preferential interstitial site occupancy for the hydrogen atoms has been analyzed based on the curent voltage characteristics of alloy thin film. � 2007 American Chemical Society.

The polycrystalline Sm1-xNdxFe1.93 (x=0, 0.08, 0.12, 0.16, 0.2, 0.24, 0.32, and 0.36) compounds are found to stabilize in MgCu2-type C15 cubic Laves phase structure. The compound x=0.12 is found to exhibit giant magnetostriction value of -1572 � 10-6 due to the anisotropy compensation between Sm3+ and Nd3+ ions. The easy direction of magnetization (EMD) is observed towards ?111? for the 0?x?0.20 compounds, accompanied by a rhombohedral distortion. For the x=0.32 compound, an orthorhombic distortion, with a support that the EMD is towards (110), is observed. � 2007 American Institute of Physics.

We have studied the ultrafast optical response of highly implanted and highly annealed polycrystalline silicon films using 400 nm ultrashort amplified pulses with fluence ranging between 8 mJ cm-2 to 56 mJ cm -2. Transient reflection measurements reveal differences both in the short and long temporal behaviour between the implanted non-annealed and annealed samples. Important contributing factors to the dynamics of the non-annealed sample are the carrier recombination centres and traps induced by ion implantation. In contrast to the non-annealed sample, the Auger recombination process is a key factor in the dynamics in the first few picoseconds for the sample annealed at 1100 °C. A model based on two coupled differential equations has been employed to investigate in detail the carrier dynamics in these systems. Parameters including carrier trapping times, diffusion coefficients and the Auger coefficient have been extracted. © 2006 IOP Publishing Ltd. 21 8 1041 1046 Cited By :3

Strong demand exists for an experimental facility enabling new experimental investigations on condensed matter systems based on epithermal neutron scattering at high energy and low momentum transfers. This need will be met by the very low angle detector (VLAD) bank, to be installed on the VESUVIO spectrometer at the ISIS spallation neutron source. The equipment will operate in the scattering angular range 1 degrees < 2 theta < 5 degrees. Scattering measurements from a polycrystalline ice sample using a VLAD prototype demonstrates the effectiveness of the detection technique adopted for the construction of the full detector array. The resulting density of states in ice is 9 +/- 2 atoms/cell, in agreement with previous measurements.

Polycrystalline, Dy0.5Gd4.5Si2Ge 2 compound (monoclinic, space group P21/a) has been synthesized and characterized. This compound orders ferromagnetically at ?210 K (T C) followed by an antiferromagnetic-like transition at ?21 K (TN). The electrical resistivity, ?, follows T2 law in the ferromagnetically ordered state indicating the presence of dominant single magnon scattering. There is a pronounced increase of resistivity in the vicinity of antiferromagnetic transition. Thermoelectric power, S, indicates a slope change near TC and has T3 dependence at low temperatures. � 2005 Elsevier B.V. All rights reserved.

Carbonados are porous polycrystalline diamonds of uncertain origin, which are found at locations in Bahia (NE Brazil) and in the Central African Republic. Their combination of extreme hardness and toughness is ideal for drilling and cutting tools. A variety of elements including Fe, Ni, Cu and Ag are associated with the diamonds. Following a suggestion that Mn-doped diamond may be intrinsically ferromagnetic, we have analysed six samples from Brazil which show ferromagnetic moments of up to 3 A m2 kg-1, which is reduced by acid leaching. X-ray diffraction on the crushed powder showed a cubic diamond structure, with no secondary phases visible. Scanning electron microscopy shows an inhomogeneous distribution of heavy metals and M?ssbauer spectroscopy indicates that iron is present as native iron. We find no evidence from the carbonados for the existence of transition-metal doped ferromagnetic carbon. The intrinsic diamagnetic susceptibility of carbonados is -4.5?10-9 m3 kg-1, similar to the accepted value for diamond,-5?10-9 m3 kg -1. © 2005 Elsevier B.V. All rights reserved. Journal of Magnetism and Magnetic Materials

Structure analysis of polycrystalline BaMg1/3Ta 1/3Nb1/3O3 ceramics has been carried out using the Rietveld technique, wherein the B cations (Mg, Ta, and Nb) have the same occupancy with a size difference and charge imbalance. The compound has an ordered trigonal structure as well as a disordered cubic phase depending on the preparation temperature. The weight percentage of the ordered phase is found to increase with a rise in the calcination temperature. � Pleiades Publishing, Inc., 2006.

Polycrystalline silicon thin film samples implanted and annealed at various temperatures have been studied using ultrafast laser pulse excitation. Nondegenerate pump-probe technique has been utilized to investigate carrier dynamics in the highly implanted samples at a relatively small fluence. A model based on two coupled differential equations has been used to fit the experimental data, giving a simple but adequate picture of the dynamics of this system. Basic sample parameters such as carrier trapping times, diffusion coefficient, and penetration depths have been extracted, providing a dependence on the annealing temperature for the samples under investigation. © 2006 American Institute of Physics. 88 18 Cited By :7

A study of arsenic ion-implanted polycrystalline silicon films before and after annealing at various temperatures has been performed using spectroscopic ellipsometry in the ultraviolet to the visible spectral region. Using the Bruggeman effective medium approximation, an optical/structural model is presented for all the annealed samples explaining the measurements. Ellipsometric measurements reveal important structural changes as a function of annealing temperature which provide an interesting inside into the annealing kinetics of ion-implanted polycrystalline silicon films. This work also demonstrates the importance of spectroscopic ellipsometry in determining non-destructively the dielectric functions in materials that have undergone complex processing. © 2005 Elsevier B.V. All rights reserved. 496 2 253 258 Cited By :22

The interfacial behavior of thallium ions on polycrystalline silver electrodes is analyzed using cyclic voltammetric and chronocoulometric and impedance studies. The specificity associated with bromide ions leading to the anion-induced adsorption of the thallium complex is pointed out and the stoichiometry of the thallium complex is deduced. ? 2004 Elsevier Inc. All rights reserved.

CuIn3Se5 thin films were grown by stepwise flash evaporation from the polycrystalline powder source. Bulk CuIn3Se 5 was synthesized by melt-quench technique, starting from the stoichiometric mixture of constituent elements. Phase purity of the synthesized material was confirmed by powder X-ray diffraction. Structural investigations by transmission electron microscopy (TEM) show that the films grown at 370 K and above were polycrystalline in nature. Compositional analysis by Rutherford backscattering spectrometry (RBS) revealed that the films have near stoichiometric composition. Analysis of optical transmittarice data yielded a band gap value of ? 1.26 �0.02 eV. ? 2004 Elsevier B.V. All rights reserved.

CuInSe2 and CuIn3Se5 films were grown by stepwise flash evaporation onto glass and Si substrates held at different temperatures. Transmission electron microscopy (TEM) studies revealed that the films grown above 370 K were polycrystalline, with CuInSe2 films exhibiting larger average grain size than CuIn3Se5. Optical absorption studies yielded band gaps of 0.97�0.02 and 1.26�0.02 eV for CuInSe2 and CuIn3Se5, respectively. Rutherford backscattering spectrometry (RBS) study of the films on Si showed that CuInSe2/Si structures included an inhomogeneous interface region consisting of Cu and Si, whereas CuIn3Se 5/Si structures presented sharp interface. ? 2004 Elsevier B.V. All rights reserved.

The estimation of electrochemical quartz crystal microbalance (EQCM) frequencies from a given cyclic voltammetric data is analysed using underpotential deposition (UPD) of metals as an illustrative process. The crucial role played by the surface roughness of electrodes and electrosorption valency of the depositing species is pointed out. The computed EQCM frequency shifts for the UPD of Cd and Tl on polycrystalline Ag electrodes are in satisfactory agreement with the experimental data. ? Springer-Verlag 2005.

Transmission electron microscopy (TEM) and ion beam techniques were used to study the DC reactively sputtered In2O3 films on Si substrates. TEM studies showed that the films are single-phase and polycrystalline. Particle induced X-ray emission (PIXE) enabled trace analysis of the films. Rutherford backscattering spectrometry (RBS) investigations suggested the formation of 20 nm thick inhomogeneous interface region between In2O3 film and Si. Secondary ion mass spectrometry (SIMS) depth profiling and current-voltage measurements confirmed the presence of the interface region. ? 2004 Elsevier B.V. All rights reserved.