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In the present study we have synthesized polycrystalline sample of (Nd1/2Li1/2)(Fe1/2V1/2)O3 ceramic by a standard high-temperature solid-state reaction technique. Studies of dielectric and electrical properties of the compound have been carried out in a wide range of temperature (RT - 400 °C) and frequency (1kHz - 1MHz) using complex impedance spectroscopic technique. The imaginary vs. real component of the complex impedance plot ( Nyquist plot) of the prepared sample exhibits the existence of grain, grain boundary contributions in the complex electrical parameters and negative temperature coefficient of resistance (NTCR) type behavior like semiconductor. Details study of ac conductivity plot reveals that the material obeys universal Jonscher's power law. [ABSTRACT FROM AUTHOR]

Submicrocrystalline structure of 99.99% pure copper produced by equal channel angular pressing was under investigation. After deformation the samples were subjected to low-temperature annealing. Grain and subgrain structure was studied by scanning tunnel microscopy. Internal interface energy was estimated using the method based on measurement of dihedral angles (ψ) of the boundary grooves formed by electrochemical etching. Analysis of the differential and cumulative distribution functions for relative grain boundary energy enabled to qualitatively evaluate energy redistribution between the boundaries of different types and internal bulk crystallites and to study evolution of submicrocrystalline structure under low-temperature annealing. [ABSTRACT FROM AUTHOR]

The results of study the phenomenon, discovered by author (1971), of the phase transition of grain boundary by the formation of two-dimensional liquid or quasi-liquid films have been done. The described phenomena of the first order phase transition (two-dimensional melting) at temperatures 0.6 - 0.9 TS0 (of the solid state melting point) is a fundamental property of solid crystalline materials, which has allowed to revise radically scientific representations about a solid state of substance. Using the mathematical tools of the film thermodynamics it has been obtained the generalized equation of Clausius - Clapeyron type for two-dimensional phase transition. The generalized equation has been used for calculating grain boundary phase transition temperature TSf of any metal, which value lies in the range of (0.55...0.86) TS0. Based on these works conclusions the develop strategies for effective forming of coatings (by thermo-chemical processing) on surface layers of functional alloys and hard metals have been made. The short overview of the results of some graded alloys characterization has been done. [ABSTRACT FROM AUTHOR]

The article discusses research which examined the origin of high temperature embrittlement of 625L expansion bellows in a fluid catalyst cracking (FCC) unit exposed to higher their intended service temperature. Topics discussed include a summary of the major problems of expansion joint systems and use of the optical microscopy to determine the mode of crack propagation.

We report here the coercivity (Hc) enhancement by way of surface diffusing Dy into the sintered Nd-Fe-B magnets, employing a novel and simple vapor deposition method. The beneficial effect on coercivity and the ominous effect on remanence were both studied and correlated with the time dependent Dy diffusion. The coercivity of Nd-Fe-B magnet is improved by partial substitution of Dy for Nd and described here is the surface diffusion method adopted to infiltrate Dy in to the sintered Nd-Fe-B magnet and the consequential effect on the microstructure and the magnetic properties. An 80% improvement in Hc occurred for four hours of Dy diffusion, while encountering a fall of about 11% in remanence. The SEM-EDS analysis brought out that Dy partition to a higher degree in to the Nd-rich grain boundary phase than the matrix Nd2Fe14B. [ABSTRACT FROM AUTHOR]

The magneto-dielectric properties of ferromagnetic-ferroelectric (FM-FE) composites synthesized by using Mn-Zn ferrite and BaTiO3 (BTO) nanoparticles are reported in this work. The X-ray diffraction analysis of the composites show the existence of FM and FE phases. The field emission scanning electron micrographs (FESEM) studies show two types of inter grain connectivity. Two types of ionic relaxations in the dielectric properties at the low frequency region are observed. In this frequency range, the short-range mobility of conduction phenomena is explained using electric modulus analysis. The hopping mechanism of electrical conduction is verified. The high coercivity in the magnetization data indicates the formation of Ba hexaferrite (hard ferrimagnetic). The variation of magnetization is related to the variation in grain size of FE inclusions in the composites. [ABSTRACT FROM AUTHOR]

Positron annihilation and X-ray diffraction analysis have been used to study submicrocrystalline nickel samples prepared by equal channel angular pressing. In the as-prepared samples the positrons are trapped at dislocationtype defects and in vacancy clusters that can include up to 5 vacancies. The study has revealed that the main positron trap centers at the annealing temperature of Δ T= 20°C-180°C are low-angle boundaries enriched by impurities. At Δ T = 180°C-360°C' the trap centers are low-angle boundaries providing the grain growth due to recrystallization in-situ. [ABSTRACT FROM AUTHOR]

Behavior of symmetrical tilt grain boundaries under shear loading was studied in the framework of classical molecular dynamics. Grain boundaries Σ5, Σ9 and Σ11 in Ni and α-Fe were modelled. It was found that behavior of defects depends not only on the structure of boundaries, but also on the type of crystal lattice. It was shown that under external stress grain boundary behaves differently in the BCC and FCC metal. A comparison of the value of displacement of GB with the value of grain boundary slip under the condition of shear deformation was performed. These results can help to understand the features of development of plastic deformation in polycrystals under shear loading. [ABSTRACT FROM AUTHOR]

In the work study the process of self-diffusion in symmetric tilt grain boundaries (GB) with the axes misorientation [100], [110] and [111]. The research was carried out by the methods of computer simulation The objects of the research are the three GB of common and special type for each axis misorientation. The angles of misorientation of the common GB is amounted to 10°, 30° and 50°. The simulation was performed by the method of molecular dynamics in the temperature range from 600 to 1000 K, with an interval of 50 K. For research on the direction jumps atoms were built tracks the movement of atoms in the process of self-diffusion. The calculations have shown, that for all of GB is characterized by pronounced anisotropy of the jumps at low temperatures (< 700K). At temperatures near to the melting point directions of the jumps are isotropic only for three GB (Θ=30°[100], Θ=50°[100] andΣ5(013)[100]). For other GB such as [100] and [110] remains priority direction of diffusion along the nuclei GB dislocations. Arrenius curves have from one to three linear plots with different tilt. Change the tilt of Arrenius dependences testifies to the change in the mechanism of self-diffusion. The parameters of grainboundary self-diffusion were determined The activation energy of grainboundary diffusion in 4-5 times lower than the energy of activation of a volume self-diffusion of aluminum (about 200 KJ/mol). The minimum value of activation energy has GB 10° with the axis misorientation [100] (10,15 KJ/mol), maximum (104.12 Kj/mol) - a special GB 111(113). [ABSTRACT FROM AUTHOR]

Surface potential mapping of Cu(In,Ga)Se2 (CIGS) thin films using scanning Kelvin probe force microscopy (SKPFM) aims to understand the minority-carrier recombination at the grain boundaries (GBs) of this polycrystalline material by examining GB charging, which has resulted in a number of publications. However, the reported results are highly inconsistent. In this paper, we report on the potential mapping by measuring wide-bandgap or high-Ga-content films and by using a complementary atomic force microscopy-based electrical technique of scanning capacitance microscopy (SCM). The results demonstrate consistent, positively charged GBs on our high-quality films with minimal surface defects/charges. The potential image taken on a low-quality film with a 1.2-eV bandgap shows significantly degraded potential contrast on the GBs and degraded potential uniformity on grain surfaces, resulting from the surface defects/charges of the low-quality film. In contrast, the potential image on an improved high-quality film with the same wide bandgap shows significantly improved GB potential contrast and surface potential uniformity, indicating that the effect of surface defects is critical when examining GB charging using surface potential data. In addition, we discuss the effect of the SKPFM setup on the validity of potential measurement, to exclude possible artifacts due to improper SKPFM setups. The SKPFM results were corroborated by using SCM measurements on the films with a CdS buffer layer. The SCM image shows clear GB contrast, indicating different electrical impedance on the GB from the grain surface. Further, we found that the GB contrast disappeared when the CdS window layer was deposited after the CIGS film was exposed extensively to ambient, which was caused by the creation of CIGS surface defects by the ambient exposure. [ABSTRACT FROM PUBLISHER]

For ductile metals, the process of dynamic fracture during shock loading is thought to occur through nucleation of voids, void growth, and then coalescence that leads to material failure. Particularly for high purity metals, it has been observed by numerous investigators that voids appear to heterogeneously nucleate at grain boundaries. However, for materials of engineering significance, those with inclusions, second phase particles, or chemical banding it is less clear what the role of grain boundaries versus other types of interfaces in the metal will be on nucleation of damage. To approach this problem in a step-wise fashion two materials have been investigated: high purity copper, and copper with 1% lead. These materials have been shock loaded at 1.4 GPa and soft recovered. In-situ VISAR and post mortem metallography reveals significantly less damage in the metals with no lead. The role of lead at grain boundary triple points and its behavior during shock loading will be discussed. [ABSTRACT FROM AUTHOR]

For materials at nano-scale, the influence of interfaces is amplified due to the increased fraction of atoms located at or near interfaces. The role of several kinds of defects (point vacancies, line vacancies and cracks) during the deformation of both Cu/Cu and Cu/Al interfaces, which are used as model systems of homogeneous and heterogeneous metal interfaces respectively, is explored using molecular dynamics simulations and the embedded-atom method. Some defect topologies are found to improve, instead of degrade, certain properties (e.g. fracture strain) of a bi-crystal interface system. In some cases of a defective interface, the nucleation of partial dislocations is observed. [ABSTRACT FROM AUTHOR]

The partial substitution of Si with B on the structural and magnetic properties of Co2FeSi1-xBx (x = 0-0.5) alloys was systematically investigated. X-ray and microstructural investigations show the presence of second phase at the grain boundaries which increases with increasing boron content. From thermal analysis studies, it was observed that L21-B2 ordering temperature remain constant whereas the melting point decreases with increase in boron addition and merges with ordering temperature at x=0.5. The increase in TC for the alloys x ≥ 0.25 was attributed to the increase in second phase due to boron. [ABSTRACT FROM AUTHOR]

Nanostructures of ZnO is synthesized with nanoflower like morphology by simple wet chemical method. The structural, morphological and electrical characterization have been carried out. The temperature dependent electrical characterization of ZnO pellets of thickness 1150µm is made by the application of 925MPa pressure. The morphological dependence of non-ohmic conduction beyond some arbitrary tunneling potential and grain boundary barrier thickness is compared with the commercially available bulk ZnO. Our results show the suitability of nano-flower like ZnO for the devices like sensors, rectifiers etc. [ABSTRACT FROM AUTHOR]

It is well known that changes in material properties across an interface will produce differences in the behavior of reflected and transmitted waves. On larger spatial scales, this mesoscopic behavior can result in the roughening of an initially planar shock front after interacting with grains of different orientations. We have developed an analytical model for treating stress wave scattering at grain boundaries based on crystal plasticity. Using this technique we can predict the anisotropic elastic-plastic velocity surfaces and grain boundary scattering configuration for crystalline materials undergoing deformation by slip. Following a brief description of the model we describe laser-induced shock experiments where we have measured the surface roughening due to shock-microstructure interactions. Spatial scales of the surface roughening were observed to scale approximately with the grain size of the material, which in this case was polycrystalline Be and Cu-doped Be. [ABSTRACT FROM AUTHOR]

This paper describes a series of electrical measurements and sample modifications that enabled the electrical properties of hybrid-orientation direct silicon bonded wafer interfaces to be determined. It is shown that the carrier transport across this near-surface (110)/(100) boundary is dictated by the defects present at the bond interface. These interface states are believed to pin the Fermi-level, producing a conduction barrier with a thermal activation energy Ea = 0.56 eV. The defect band has been identified by deep-level transient spectroscopy and associated with the defect states typically observed in plastically deformed silicon. The carrier transport behavior across the bonding interface, as well as the observed interface trap levels are therefore attributed to the dislocation network present at the bonding interface. [ABSTRACT FROM AUTHOR]

The paper presents results of the molecular dynamics simulation on the interaction of a shock wave with a highly-symmetric grain boundary in copper. Our calculations were done for five slopes of the boundary (110) Σ5 to the shock front and for two levels of loading: above the Hugoniot elastic limit but below the critical level at which the homogeneous dislocation production occurs and above that critical level. Shock-induced defects and their role in shear stress relaxation have been analyzed. It has been shown that there are two competing shear stress relaxation mechanisms as a result of the grain boundary shock interaction. Calculations of the temperature evolution in the vicinity of the grain boundary make evidence for the possibility of local melting far below the intersection of the Hugoniot and the melting line. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Non-local electrical properties of pulsed laser deposited La0.7Sr0.3MnO3/Bi2Sr2CaCu2O8/La0.7Sr0.3MnO3 (L-B-L) coplanar tri-layer is investigated under different wiring configurations. Long range super-current of Bi-2212 penetrating into LSMO is dependent on geometry of spin injection. From qualitative analysis of structural, magnetic and electrical data, long range super-current is suggested to pass through domain walls and/or grain boundaries of LSMO. [ABSTRACT FROM AUTHOR]

To obtain the high dielectric constant, the effect of sintering process on the electrical properties of Ba0.70Sr0.30(Fe0.5Nb0.5)O3 ceramics were investigated. X-ray diffraction pattern of the samples at room temperature shows a monoclinic structure. Microstructure analysis shows well-grown and dense microstructure in all the samples. We found giant dielectric constant (~3.59 X 105) with low dielectric loss (~0.49) at room temperature for 2 hr sintered sample at 1250 °C. The extrinsic phenomena like interfacial polarization due to space charge accumulation at grain boundaries are discussed. [ABSTRACT FROM AUTHOR]

We investigate local electronic properties of CdTe solar cells using electron beam to excite electron-hole pairs and evaluate spatially resolved photocurrent characteristics. Standard semiconductor processes were used to fabricate Ohmic metal contacts on the surface of p-type CdTe / n-type CdS device extracted from a commercial solar panel. An ion milling process was used to prepare cross-sections of the devices. Local injection of carriers was controlled by an acceleration voltage of electron beam (1 kV to 30 kV) in a scanning electron microscope, and the results were correlated with the local morphology, microstructure, and chemical composition of the devices. [ABSTRACT FROM PUBLISHER]

Nano-crystalline spinel ferrites of composition MnxZn1-xFe2O4 (x=0.25 and 0.5) were synthesized using chemical coprecipitation approach. The Rietveld analysis of the XRD pattern showed single phase spinel structure with space group Fd-3m. The nano-grains were observed in FE-SEM micrographs. Impedance spectra were analyzed in the frequency range of 40 Hz to 1 MHz at room temperature. Cole-Cole plots are well fitted assuming the presence of double relaxation mechanism. The equivalent circuit model confirmed the presence of grain and grain boundary relaxation in the nano-crystalline system. This reveals that the impedance response is a competition between the bulk and grain boundary behavior. [ABSTRACT FROM AUTHOR]

A recently developed precession electron diffraction (PED) technique in transmission electron microscopy (TEM) was employed to characterize the grain orientation and grain boundaries for Cu interconnects of the 45 nm node. The results showed a strong &#60;111gt; and &#60;110gt; textures along the width and the thickness of the line, respectively and a low fraction of coherent twin boundaries. The microstructure characteristics were applied to evaluate the grain structure effect on electromigration (EM) reliability. We first extracted the interfacial diffusivity components for (111), (110), and (100) surfaces and the averaged grain boundary diffusivity by analyzing the resistance traces observed in EM tests. Then the flux divergence at the triple points of grain boundary intersecting the interface was calculated to identify potential voiding sites. Similar analysis was extended to via/line regions to evaluate the flux divergence for slit void formation and to assess the probability of EM early failure. [ABSTRACT FROM PUBLISHER]

Grain boundary (GB) microstructural defects in polycrystalline high-? dielectric thin films may cause localized non-random trap generation during the percolation breakdown (BD) process. We study the effect of this non-random trap generation on the reliability statistics of the metal gate (MG) - high-κ (HK) stack. For the first time, we propose a fundamental physics-based Kinetic Monte Carlo (KMC) model considering the thermodynamics and kinetics of bond breaking, generation of oxygen vacancy traps and simulating the trap evolution process in a dual-layer HK - interfacial layer (IL) gate stack. Our simulation model helps explain the non-Weibull distribution trends for time dependent dielectric breakdown data (TDDB) and also determine the sequence of BD which is found to be independent of the thickness ratio of (tHK : tIL) and gate voltage (Vg). Results show that the IL layer is always more susceptible to early percolation and circuit level failure may only be caused by multiple soft BD (SBD) events in the IL layer. The possibility of a sequential IL → HK breakdown is very unlikely for operating voltage conditions of Vop = 1V. [ABSTRACT FROM PUBLISHER]