Search

As negative electrode materials with high capacity and long cycle lives for advanced Li-ion batteries, Si-based alloy films have been prepared on Cu-foil substrate by use of electron beam deposition method or magnetron-sputtering method at room temperature. In this study, nano-structures of the Si-based alloy films have been investigated by conventional and analytical transmission electron microscopy. Experimental results are summarized as follows: (1) Si-based alloy films consist of a number of nano-fibers of 5 nm in diameter. Electron diffraction patterns from the films show halo. Crystallites are seldom found in high resolution images. (2) One-dimensional modulations of the constituents are formed in the range of 3.6 to 11 nm in the films. These nano-structures of the Si-based alloy films could relax the volume expansion of the Si during Li-insertion, causing the longer cycle lives than that of the Si film as the negative electrodes.

In order to improve the hydrogen absorption properties of the layer structure appearing at the nickel rich side of La-Mg-Ni alloy, appropriate amounts of Ni were replaced by some elemental atoms, Mn, Co and Al. The La0:8Mg0:2Ni3:4� xCo0:3(MnAl)x (0 < x < 0:4) alloy system was synthesized and crystal structures were investigated by electron microscopy. The atomic concentration ratio of (LaMg) to the other atoms was 3.7 in this system. The Pr5Co19-type structure (5:19H-structure) and the Ce5Co19-type structure (5:19R-structure) were found in this alloy system. Electron micrographs of these structures are presented in this paper. Structure analysis of the complex layer structure is demonstrated by careful observation of the electron diffraction pattern. [doi:10.2320/matertrans.MBW200631]

Amorphous Cr-silicide films are prepared by electron-beam-deposition on a Cu-substrate at room temperature. The microstructures of as-grown films are investigated using transmission and analytical electron microscopy. The morphology of the amorphous films is dendritic. In addition, one-dimensional concentration modulations are observed. The modulated structure is revealed not only by TEM imaging but also by a series of satellite spots at the centre of the diffraction pattern. This concentration modulation is confirmed by analytical electron microscopy.

Microstructures of graphite mechanically milled under a hydrogen gas or an argon gas atmosphere using zirconia balls as well as chromium steel balls were investigated. Using transmission electron microscopes, high-resolution transmission electron microscopy (HREM), selected area electron diffraction (SAD), electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis (EDS) were carried out to compare the microstructures. Hydrogen concentration reaches up to 7.4 mass% after 80 h milling under a hydrogen gas atmosphere using chromium steel balls and homogeneous distribution of iron nano crystals was observed. No significant difference was observed in microstructures of 80 h milled graphite under the different gas atmosphere using the balls of different materials. This suggests that the significant absorption of hydrogen into the mechanically milled graphite strongly relates to the iron nano crystals included there.

We examined hydrogen absorption/desorption behaviors in graphite mechanically milled under hydrogen pressures ranging from 0.3 to 6.0 MPa. Experimental results indicated that the chemisorbed hydrogen concentration during 80 h milling decreased from 6.1 to 4.1 wt.% with increasing milling hydrogen pressure, while the physisorption-like hydrogen concentration increased with increasing milling hydrogen pressure and reached more than 0.5 wt.% at 6 MPa. Moreover, higher pressure hydrogen suppressed the fracture rate of the milled graphite more effectively, suggesting that the hydrogen atoms trapped at the edges of the graphene sheets and between the graphene layers near the surface are responsible for preserving the lamellar nanocrystalline structure, which may be the host for physisorption-like hydrogen absorption.

The ternary alloy, MgYNi 4 , was synthesized by mechanical alloying (MA). Its microscopic structures and hydriding properties were studied. The annealing of the alloy at 773 K was also studied. The alloy consists of nanocrystals of less than 10 nm in diameter. The capacity of the hydrogen atoms in the alloy increases with the increasing size of the nanocrystals. The crystal structure was found to be the C15 type Laves phase structure for the MA-treated alloy, while crystal structure of the as annealed alloy was the ordered C15 type structure which is conventionally called C15b type and is formally called AuBe 5 type structure. The hydrogen capacity in the alloy might have a strong relation to the atomic arrangement of this alloy.

Microstructural and microanalytical investigations were carried out for traditional Japanese clay ceramics called Sekishu-kawara. In this study, optical microscopy as well as scanning- and transmission-electron microscopy were employed. Specimens under investigation are (A) the original wet materials dried in air for several days, (B) the materials dried at 773 K, and (C) the same materials fired and sintered at 1493 K in a tunnel kiln. Not only some clear SEM images but also the TEM images, which were taken for the first time by us, for the clay ceramics are presented. TEM mi-crographs of specimen C show that mullite crystals, grown in the firing and sintering process, are in the shape of strip, 5 nm×50 nm×500 nm in largest, and are dispersed, in the amorphous glass. SEM micrographs of specimen C, on the other hand, show that the clay ceramics are porous and contain considerable amount of tunnel-shaped open spaces called continuous pores. The continuous pores are constructed by a complicated, three dimensional shape of amorphous glass, in which the mullite strips exist.

In order to clarify the β → ω phase transformation mechanism in β-titanium alloys, an investigation of the atomic structure of Ti-Mo alloys at early stages of aging was carried out using high resolution electron microscopy (HREM), in situ HREM, and image-processing methods. The initial structure of ω-phase crystals was observed as a line structure of bright spots in the 〈111〉 directions with 0.28 nm spacing. The formation of the line structure was also observed with in-situ HREM. The appearance of the line structure was confirmed by an image contrast simulation method.

The alloys Mg-x at.%Ni (x = 33, 38, 43 and 50) with different nanometer-scale structures were successively synthesized by mechanical grinding of Mg2Ni mixed with various amounts of additional Ni, and the relations between their structural and hydriding properties were investigated in detail. The total hydrogen contents in these alloys increase from 1.7 mass% for x = 33 to 2.2 mass% for x = 43 and 50. This result is explainable by estimating both the volume fractions and the maximum hydrogen contents of three regions in each alloy; the intra-grain region of nanostructured Mg2Ni, its inter-grain region, and the amorphous MgNi region. The dehydriding temperature lowers down to 373 K in the alloy composed of only the amorphous MgNi region, while the dehydriding kinetics of the alloy composed of the above three regions are faster than those of only the amorphous MgNi region.

The alloys Mg−x at.% Ni (x=33, 38, 43 and 50) with nanometer-scale structures were successively synthesized by mechanical grinding of Mg2Ni mixed with various amounts of additional Ni. The total hydrogen contents in these alloys increases from 1.7 mass% for x=33 to 2.2 mass% for x=43 and 50, while the dehydriding temperatures gradually lower from 440 K to 373 K with increasing of the Ni amounts. The value of the total hydrogen content in each alloy is reasonably explained by taking into account the hydrogen contents of the following three regions; the intra-grain region of nanostructured Mg2Ni, its inter-grain region, and the amorphous MgNi region. The maximum hydrogen content in the amorphous MgNi region, 2.2 mass%, might imply a specific interatomic occupation of hydrogen atoms in this region.

A new material containing 1.6 wt.% of hydrogen (Mg2NiH1.8) was synthesized by reactive mechanical grinding under hydrogen atmosphere by Orimo and Fujii [Orimo, S. and Fujii, H., J. Alloys and Compounds, 1996, 232, L16]. The microstructures of this alloy, Mg2NiH1.8, was investigated by high resolution transmission electron microscopy (HRTEM). It has been found from the HRTEM images that the texture mainly consists of nanocrystals of Mg2NiHx (x ≤ 0.3) with an average size of approximately 15 nm, and also found that heavily distorted regions exist around or between nanocrystals. The width or the thickness of these regions is thought to be approximately 1–2 nm. These results are consistent with the results deduced from the peak broadening of the X-ray diffraction pattern and magnetic analysis [Orimo S., Fujii, H. and Ikeda, K. Acta Metallurgica, accepted]. It is plausible to assume that these regions can contain an unexpected number of hydrogen atoms. © 1997 Elsevier Science Limited. All rights reserved.

The microstructure of the cubic transition metal Laves phase ZrFe 2 with boron additions of 0, 1 and 5 at% has been investigated. Samples were obtained in the form of thin films by the melt-quenching method. All films obtained had a homogeneous distribution of the constituent atoms and consisted of grains of Laves phase crystallites. The thin films with 5 at% boron showed a trace of ZrB 2 crystals. After annealing at 1173 K for 24 h, the excess Fe atoms reacted with ZrFe 2 forming a small amount of ZrFe 3 crystals. No difference could be detected in the microstructure or brittleness of specimens with and without boron atoms. A considerable number of the crystal grains contained many stacking faults. An electron microscope in situ tensile test at room temperature suggested that the dislocations as well as the grain boundaries do not move in the Laves phase alloy of this system, independent of boron addition.

A coincidence site lattice (CSL) model is applied t o analyse the boundary structures of Laves phase alloys, Mg (Al0.5 Cu0.5) 2 and Mg (Cu1-x Znx) 2.All the origins in every layer are adopted as lattice points to draw interpenetrating lattices. Due to this extention, the interpenetrating lattices give characteristic CSL-patterns which predict not only detailed ordered structures inside a period appearing at the boundary but also predict smaller DSC-vectors which are Burgers vectors of boundary dislocations. The CSL-patterns as well as the DSC (displacement - shift - complete) - lattices are demonstrated for various layer structures, in order to interpret high resolution electron micrographs of the boundaries of the Laves phase alloys.

Microstructures of the Laves phase alloy, (Ti0.95 V0.05) Co2, were studied by high resolution electron microscopy and electron diffraction. In this alloy system, coexistence of several kinds of layered structures was observed. Among these structures, a new stacking variant was found and was analyzed to be ABCAB'A'C'BCA'C'B'. This structure belongs to the trigonal system of the space group P3m1 (no. 164). The lattice parameters presented in the hexagonal system are a = 0.4727 +/- 0.0009 nm and c = 4.628 +/- 0.008 nm. This structure is called 12T in the Ramsdell notation and 4323 in the Zhdanov symbol, and is classified into hP3m1-(6i)5(3f)(3e)(2d)12(2c)6 using the Wyckoff notation.

We report on the thermal expansion coefficient α of La2−x Sr x CuO4 (x=0.14) single crystals between 5 and 300 K measured by both a capacitive method and a strain-gauge method. We have observed anomalies in α at the tetragonal-orthorhombic structural phase transition (T d1=200 K) and at the superconducting transition (T c=34 K). A thermodynamic analysis using the Ehrenfest relation shows that the pressure effects of both T d1 and T c observed in hydrostatic-pressure experiments are actually determined by the sum of compensating in-plane and c-axis uniaxial pressure coefficients with opposite signs. Using additional results obtained by X-ray diffraction at low temperatures, we will also discuss how to obtain nearly untwinned crystals below T d1.

not Available.

A series of micrometer-scale Si thin films were fabricated by electron-beam deposition on the Cu substrate with specially treated concave-convex surface. The combined analyses involving scanning and transmission electron microscopy, selected area electron diffraction, and X-ray diffraction revealed that the deposited Si layer possessed good adhesion to the substrate and a discontinuous amorphous microstructure in which there existed large amounts of interface regions. The surface changes of the Si thin-film electrodes during Li insertion and extraction were investigated by glow discharge optical emission spectroscopy. The half-cell tests showed that these thicker films had higher capacity and more impressive cycleability relative to those reported in the literature; their cycleability could be substantially improved by limiting Li insertion depth. The full-cell tests indicated that Si films thicker than 4 μm could provide sufficient capacity to match the standard LiCoO 2 cathode with a ∼70-μm-thick coating layer. Such cells demonstrated small self-discharge rate as well as good cycling stability and efficiency in the long run, suggesting feasibility for potential practical applications.

Nanostructured Ag-Fe-Sn/C composites were synthesized by mechanical milling Ag-Fe-Sn alloys with carbon nanotubes (CNTs). The milled composites were characterized by X-ray diffraction, high-resolution transmission electron microscopy, energy dispersive X-ray spectrometry, and selected area electron diffraction techniques. These analyses revealed that, except for residual CNTs segments protruding from the edges of the composite particles, most CNTs were converted to an amorphous structure that formed a shell around alloy particles during mechanical processing. The electrode behaviors of the synthesized materials were examined and compared with those of their unmilled counterparts as well as the original alloys. It was demonstrated that the formed amorphous carbon shell around the alloy particles significantly improved the cycling performance of the composite electrodes, though the initial irreversible capacity loss was increased. For instance, the milled Ag 3 6 . 4 Fe 1 5 . 6 Sn 4 8 /CNTs electrode provided a discharge capacity of ∼530 mAh/g in the second cycle, maintaining a rechargeable capacity of ∼420 mAh/g after 300 cycles.

The transmission electron microscope(TEM) is one of the most powerful instrument in materials characterization, and various TEM specimen preparation methods have been developed. It is known that Ar-etching method is most widely applied in the studies of high technology materials. However, it is time-consuming when a specific area is desired for examination. Because it is necessary to iterate through Ar-ion etching and TEM examination until the desired information is obtained.There is a great demand on a new specimen preparation technique that has high positional accuracy, reliability, and throughput.Focused ion beam (FIB) milling has been proposed as a solution to the above requirements. We have developed the FIB system (FB-2000) for SEM/TEM specimen preparation. An external view of the system is shown in Fig.l. The system is designed to use a compatible specimen holder (Fig.2) which allows both FIB milling and TEM observation without re-mounting the specimen. The instrument has maximum accelerating voltage of 30kV and a minimum beam diameter of lOnm. The FIB current density of 15A/cm2 is available.

The most useful and intuitive model may be a CSL-model to analyze boundary structures. In order to apply the CSL-model to layer structures, we have proposed to use ‘lattice point’ in a wide sence and to add extra lattice points to the Bravais lattice points when interpenetrating(IP)-lattices are drawn. These lattice points will be called ‘extended lattice points‘. It is well known that a layer structure is built up with (almost) identical layers stacking on the top of the others with a cirtain amount of shift in a direction perpendicular to the stacking. Each layer consists of one or more atomic planes and has almost (or exactly) the same atomic configuration. The extended lattice points can be defined as the origins in each layer in crystal. The number of such points depends upon the number of layers in a unitcell.To draw IP-lattices we have adopted all the extended lattice points in addition to the Bravais lattice points. There are three important advantages of doing this extension[ 1,2,3]. First is that the Coincidence-Sites in the IP-lattices drawn do not scatter homogeneously, but gather in a region and make a cluster. They exibit a characteristic pattern of Coincidence-Sites. This pattern is called a CSL-pattern. Second is that the DSC-lattice (Displacement Shift Complete Lattice) provides a set of basic vectors smaller than predicted before extention. Third is that reasonable models of boundaries are able to be made between two different layer structures. This is because the crystal volume attributed to one extended lattice point is exactly the same for the both adjacent crystals.

The nickel-rich part of the Sm-Ni system was investigated by electron microscopy and electron diffraction examination. Particular attention was paid to Sm5Ni19. Six polytype structures (2H, 3R, 4H, 6H, 9R and 12R) were found, of which the structures of the 2H and 3R types have previously been reported. The structures of the four new polytypes were analysed by electron diffraction. The space groups, lattice parameters (hexagonal axis) and stacking sequences of these polytypes are as follows: (1) 4H polytype, P63/mmc, a = 5.0 A , c = 65 A and stacking sequence [XXXA] [YYYB] [ZZZC'] [YYYB']; (2) 6H polytype, P 6 m2 , a = 5.0 A , c = 97 A and stacking sequence [XXXA] [YYYB'] [XXXA] [YYYB] [ZZZC'] [YYYB']; (3) 9R polytype, R 3 m , a = 5.0 A , c = 150 A and stacking sequence [XXXA] [YYYB] [ZZZC'] [YYYB] [ZZZC] [XXXA'] [ZZZC] [XXXA] [YYYB']; (4) 12R polytype, R 3 m , a = 5.0 A , c = 190 A and stacking sequence [XXXA'] [ZZZC'] [YYYB'] [XXXA] [YYYB'] [XXXA'] [ZZZC'] [YYYB] [ZZZC'] [YYYB'] [XXXA'] [ZZZC]. The layer symbols A and A' denote Laves phase layers and X denotes a CaCu5-type layer. B, B' and Y or C, C' and Z are obtained if A, A' and X are shifted by 1 3 or 2 3 respectively in the [110] direction.

In a series consisting of +1 and -1, a pair of the i -th and j -th elements, a( i ) and a( j ), is characterized by two integers; one is the separation m = j - i ( j > i ) and the other is the sum d of m - 1 numerals between the two elements. If the pair is denoted by [ a ( i ), a ( j ); m , d ], all pairs in a series belong to one of the following four types for given parameters m and d : [1, 1; m , d ],[1, \bar1; m , d ], [\bar1, 1; m , d ] and [\bar1, \bar1; m , d ], where 1 and \bar1 are used instead of +1 and -1. Out of these four types, it has been verified that two types of pairs [1, \bar1; m , d ] and [\bar1, 1; m , d ] appear alternately in any series and therefore the total numbers of pairs are equal to each other for these two types or are different at most by unity. This correlation is applied to a layer structure such as Laves phase, and specific relations are derived.

Two-dimensional lattice images have been obtained for the two-, four-, and nine-layer type structures of the Friauf-Laves phase, Mg(Cu0.535Al0.465)2. An intimate correlation is established between the lattice image and the crystal structure. With this relation, layer sequences of disordered stacking regions are determined. A new type of linear defect is found in the images and a structural model of the defect is proposed. The defect is always accompanied by a stacking fault, which is different from the usual stacking faults observed in close-packed structures.

SUMMARY A Mg-base Laves phase was investigated by high resolution electron microscopy (HREM). Linear defects found at terminations of stacking faults were classified into three groups. The first is a partial dislocation at a termination of a stacking fault, the second is a superposed partial dislocation which is defined as a defect produced by a superposition of terminations of two or more stacking faults lying on neighbouring layers, and the third is a combined linear defect which consists of a characteristic combination of terminations of stacking faults. In the last case the total stacking fault vector becomes equal to the translation vector in the basal plane, so that the defect needs no relaxation of the lattice. The Burgers vectors of the partial dislocations were estimated with the aid of modified Burgers circuits.

Diffuse scattering due to short range order (SRO) of the hexagonal ζ phase, Ag–Al, has been studied by X-ray and electron diffraction methods. Intensity distribution was measured in the reciprocal space at room temperature. Peculiar distribution was found such as a thin plate and a hinge shape on h 3 =0 and 1 planes in the c * direction, respectively. The maxima on these planes are shifted from 1/3, 1/3, h 3 and 2/3, 2/3, h 3 positions. SRO parameters α l m n of a single crystal of Ag–34 at.%Al alloy have been determined by the Fourier transformation of X-ray diffuse intensity. It has been found from the electron diffraction patterns that the shift of the diffuse maxima from 1/3, 1/3, h 3 decreases almost linearly with increasing Al concentration. The Fermi-surface-imaging theory seems to be appropriate to interpret the observations.

SUMMARY Nb3Ge-films synthesized on Mo-substrates by the co-evaporation method show a characteristic fabric with a quasi-twelvefold symmetry around the [001]-axis of the A15-type cubic structure. Among approximate +30°- and ±60°-rotation boundaries, grain boundaries having rotation angles between 28° and 29° are observed most frequently in the Nb3Ge-films. Using the high resolution electron micrographs, a Σ17-boundary having an ideal rotation angle of 28.07° is analysed and plausible boundary models on the atomic level are proposed.

Electrical resistivities, Hall coefficients and magnetoresistances have been measured on γ-Mo 4 O 11 -type crystals grown by chemical vapour reaction from two different starting mixtures MoO 2 :MoO 3 = 1:3 and MoS 2 : MoO 3 = 1:9. A deep-bluish crystal of MoO 2.74 S 0.12 synthesized from the latter mixture has nearly the same structural and electrical properties as those of γ-Mo 4 O 11 grown from the former mixture. These crystals show charge density wave instabilities at T c = 90–110 K . The isothermal annealing of γ-Mo 4 O 11 in sulphur vapour is also studied.

The lattice image of the FeCr σ-phase was observed by high-resolution electron microscopy with the c axis of the tetragonal cell parallel to the incident beam. It was found that bright dots of the observed image correspond to the positions of atoms in the z = ± 1 4 planes of the σ-phase structure. Sequence faults were found in the irregular part of the lattice image. The analysis of the faults shows that an extra plane of 1 2 a 0 width is inserted into the regular structure and one side of the fault is slightly shifted parallel to the fault plane with respect to the other side, which is consistent with the model proposed by Frank and Kasper. A unit cell step of the sequence faults was found and a model of the step was proposed.

A high‐speed rotor which is characterized by a mechanical precession eliminator and by a magnetic suspension has been constructed. In this instrument, a cylindrical rotor 2 cm (0.02 m) in diameter and 20 cm (0.2 m) long was made of aluminum. The moment of inertia of this rotor was approximately 86 g cm2 (8.6×10−6 kg m2) about the long axis. A stable rotation of 120 000 rpm was obtained in air as well as in vacuum. The rotor was suspended vertically by a set of suspension magnets at the top of the rotor and a set at the bottom. In addition, the bottom of the rotor is flexibly supported by a ruby bearing which moves smoothly on a plate but is constrained by friction. When precession of the rotor begins, the frictional force eliminates the precession intrinsically. Measurements of slowing rate for the revolution were made at several different air pressures. There is good agreement with the theory.

Mise en evidence par microscopie electronique a haute resolution des defauts lineaires appeles disinclinaisons dans l'alliage MgCd. Ces disinclinaisons apparaissent le long des lignes d'intersections des joints de mâcles dues aux deformations spontanees de reseau a la temperature de transition de phases. La disinclinaison «en etoile» compense le champ de deformation des disinclinaisons. Observation de dipoles, tripoles, quadripoles et multipoles des disinclinaisons

Diffuse scattering from TiNi alloys of near equi-atomic composition is investigated by electron diffraction, and several high-resolution images produced by diffuse scattering together with some Bragg reflections are presented. Three characteristic features of diffuse scattering are as follows. (1) The maxima of the diffuse scattering are located near n/7, 2n/7, 3n/7 (n an integer) and equivalent positions. The positions can be understood if eight variants of the X-phase Ti11 Ni14 exist in a parent phase (cubic B2) at the same time. (2) A ring-type diffuse scattering observed in the h0l reciprocal plane reversibly transforms at a low temperature (∼120K) into a particular pattern which has diffuse maxima near n/3, 0, n/3 (n an integer), where the rhombohedral phase shows the superstructure reflections. (3) All the diffuse scattering disappears in the electron diffraction pattern when the electron beam is incident parallel to the direction. From high-resolution images it is concluded that the ...