Selected Area Diffraction Patterns Research Articles

HRTEM Observation of the Age Hardening Precipitates in Mg-Gd-Sc Alloy

High resolution transmission electron microscope (HRTEM) observation was carried out to investigate the precipitates in Mg-Gd-Sc alloy. In the specimen aged at 473K, the hardness increased gradually with increasing aging time, started to increase rapidly after 16h and the peak hardness was obtained at 128h. In the as-quenched specimen, the diffuse spots considering to the some ordering were observed between 0000 transmitted spot and 1100 magnesium matrix spots in the selected area diffraction pattern. The diffraction spots corresponding to D0 19 type structure (a=0.64nm, c=0.521nm) were observed in the early stage of aging at 473K. The contrast of the precipitates similar to the B' phase based on base centered orthorhombic structure in Mg-Gd alloy were observed predominantly in the specimen after aging for 32h. It was revealed that the precipitates in Mg-Gd-Sc alloy were similar to that of Mg-Gd alloy.

Development of Environmental Cell for Gas Reaction of Nano-Size Particles

“Environmental cell” microscopy was applied for surveying gas reaction of hydrides in magnesium base alloys, which are candidates for hydrogen storage materials in advanced hydrogen energy systems. In order to clarify the mechanism of hydrogenation process, in-situ experiment has been carried out by using a 200 kV transmission electron microscope (TEM) equipped with a newly developed environmental cell, which is capable to 0.1 MPa in the temperature range between R.T. and 200°C. When hydrogen gas reacted with magnesium powders, straightening of surface steps (60~70 nm in height) was observed, indicating that volume expansion occurred. In addition, the formation of MgH2 was indicated in selected-area-diffraction patterns (SADP). The precise study on this in-situ experiment, as well as its improvement, will be continued, with using transparent films.

Space group analysis of Sr1−xCaxTiO3 ceramics with x = 0.20, 0.27 and 0.30 through electron diffraction

The space groups of Sr1−xCaxTiO3 inthe composition range 0.20≤x≤0.30 have been investigated using powder x-ray diffraction (XRD) and electron diffractiontechniques. Electron diffraction has been used in selected area diffraction (SAD),convergent beam electron diffraction (CBED) and micro-diffraction modes to recordzero-order Laue zone (ZOLZ) and higher-order Laue zone (HOLZ) patterns. For the0.20≤x≤0.30 composition range there is still controversy regarding the correct space group:P 21/m,Pnma,Imma or I4/mcm. By invoking Rietveld refinement, detailed analysis of CBED patterns containingA2-type GM-lines and comparison between simulated ZOLZ/FOLZ andexperimentally observed SAD patterns, we have established that forSr1−xCaxTiO3 (0.20≤x≤0.30) two types of phase coexist at room temperature. These are thePnma and P 21212 orthorhombic phases, coexisting with volume fractions of about 40% and 60%respectively.

Synthesis of Iron Oxide Nanowires by Heating Iron Foils

We have fabricated the iron oxide nanowires directly from iron foils through the simple heating in N2 ambient. We have characterized the samples by means of scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray (EDX) spectroscopy, and selected area diffraction pattern. The EDX spectrum revealed that the nanowires contained elements of Fe and O. The iron oxide nanowires were crystalline with diameters in the range of 30-200 nm. We have discussed the possible growth mechanisms.

Hollow Amorphous Formation via Oxidation of Al Nanoparticles at Low Temperatures

Formation of hollow structure through oxidation of Al nanoparticles was studied by applying transmission electron microscopy. Al nanoparticles 6~8 nm in diameter were observed to become hollow particles after having been exposed to air at 295 K for a few minutes. An analysis of the Debye-Sherrer rings in the selected area diffraction patterns before and after oxidation showed that hollow oxide nanoparticles are amorphous. The formation mechanisms of hollow oxide are discussed based on the low-temperature oxidation mechanism of Al and on the comparison with our previous results of hollow ZnO formation via oxidation of Zn nanoparticles.

1차원 InN 단결정 나노선의 구조특성에 대한 고찰

High-Quality 1-Dimensional InN single crystalline have been grown by Halide Vapor-Phase Epitaxy on the Au catalyst coated Si substrate using the vapor-liquid-solid growth mechanism. We have been grown 1-dimension InN nanowires having controlled the growth conditions for substrate temperature and gases flow rate. The grown InN nanowire of characteristics for morphologies, crystal structure, and element analysis were carried out by SEM, HR-TEM, and EDS respectively. And the defects of InN crystalline were analyzed by indexing of selective area diffraction pattern with attached HR-TEM. We have successfully obtained the defect-free 1-dimensional InN single crystalline nanowire at the atmosphere pressure.

Fabrication and magnetic properties of ordered Fe 60Pb 40 nanowire arrays electrodeposited in AAO templates

Ordered ferromagnetic–nonmagnetic heterogeneous Fe 60Pb 40 nanowire arrays were successfully fabricated by alternating current (AC) electrodeposition into nanoporous alumina templates. Transmission electron microscopy (TEM) image and selected-area diffraction (SAED) pattern analysis showed that the Fe 60Pb 40 nanowires are polycrystalline with an average diameter of 22 nm and lengths up to several micrometers. X-ray diffraction (XRD) observations indicated that α -Fe and fcc Pb phase coexist and do not form metastable alloy phase. The as-deposited samples were annealed at 200, 300, 400 and 500 ∘C, respectively. Magnetic measurements showed that nanowires have high magnetic anisotropy with their easy axis parallel to the nanowire arrays, and the coercivity of the samples increased with the annealing temperature up to 400 ∘C and reached a maximum (2650 Oe). The change of magnetic properties associated with the microstructure was discussed.

Phase transformation of plasma-sprayed hydroxyapatite coating with preferred crystalline orientation

Highly oriented hydroxyapatite coatings (HACs) were obtained on titanium substrates through a radio-frequency thermal plasma spraying (TPS) method. XRD patterns showed that the HACs had crystallites with [0 0 l] preferred orientation vertical to the coating's surface. XRD results also indicated that tetracalcium phosphate crystallites in the as-sprayed HAC were oriented in the (1 0 0) direction. XRD peaks corresponding to tetracalcium phosphate, tricalcium phosphate and calcium oxide were absent after heat and hydrothermal treatment. The orientation degree of the HAC was influenced little by such post-heat treatments. Considering the crystallographic relationship between the tetracalcium phosphate in the as-sprayed HAC and the HA crystallites formed in the heat-treated HAC, these XRD results indicate that the tetracalcium phosphate in the as-prepared coatings transformed topotaxially into HA during the post-heat treatment. TEM and SEM analyses of the highly oriented HAC were conducted. The characteristic lamellar structure of TPS deposits was observed in cross-sections of the HAC. A prismatic texture was also observed in magnified SEM images. TEM observation showed that 200–800-nm-wide prismatic crystallites were formed in HA splats, and their longitudinal axis was oriented vertically to the coating's surface. SAD patterns showed that the longitudinal axis of the prismatic crystallites corresponded to the [0 0 1] zone axis of the HA crystal.

Formation of Intermetallic Compounds in Friction Bonding of Al Alloys to Steel

The microstructure of the friction-bonded interface of Al alloys to low C steel has been investigated by TEM observations to reveal the controlling factor of the formation and growth of the IMC (Intermetallic Compound) layer, which caused the premature fracture at the interface even when its thickness was less than 1 μm, as reported in a previous paper. The thickness of the IMC layer observed at the interfaces of Al-Mg alloy/steel and pure-aluminum/steel joints increased almost in proportion to the friction time, but did not obey the parabolic law a characteristic kinetics of the diffusion-controlled process. Analyses of SAD patterns from the IMC layer indicate that it consisted of Fe2Al5, Fe4Al13, (Fe, Mn)Al6 and FeAl2, depending on the alloying elements. These IMCs were granular and distributed almost randomly within the IMC layer, suggesting that mechanical mixing of the steel with the Al alloy occurred at the interface. In the low C steel adjacent to the IMC layer, a zone of much finer grains than those of the base metal was observed. Its width increased with friction time and pressure, and with the growth of the IMC layer, as well. These results suggest that the superficial region of the steel underwent a heavy plastic deformation during the friction process and it had a close relation with the growth of the IMC layer.

Microstructural study of nano hydroxyapatite coating obtained by pulse electrodeposition process on Ti–6Al–4V

Hydroxyapatite and other calcium phosphates are one of the important biomaterials used as a coating on biometals for implants and dental prostheses. Nanosized hydroxyapatite coatings have remarkable properties which improve their workability. The coating applied by cathodic electrodeposition and the variation of electrochemical parameters such as voltage, current density and pulse conditions caused a marked change in the microstructure of the deposit. Nanosize particles were obtained using pulse deposition in which ton and toff were 60 and 90 s. Transmission electron microscopy and X-ray diffraction studies showed the presence of three phases of calcium phosphates. Selected area diffraction pattern of the deposits were indexed and confirmed the presence of those three calcium phosphate phases which are biocompatible.

Preliminary Results for a Methanol Fuelled SOFC Tubular Stack with Nanocrystalline 8YSZ Electrolyte

This paper presents preliminary result from characterization, development and testing of a nanocrystalline structured 8mol% yttrium stabilized zircona (8YSZ) electrolyte. Bright field TEM images showed a range of particle sizes, upwards of 40 nm. The selected area diffraction pattern indicated the presence of a very fine nanostructure. The crystal structure of the nanocrystalline electrolyte powder was characterized using XRD and was shown to be cubic. Initial electrochemical testing was performed using pellet fuel cells, 31 mm dia by 5 mm, in a custom designed testing rig. This allowed a comparison between standard 8YSZ electrolyte and nano crystalline structured 8YSZ. The initial nano crystalline structured 8YSZ was shown to have a 10% increase in power density at 800 degree C compared to the standard 8YSZ.

MeV heavy ion induced recrystallization of buried silicon nitride layer: Role of energy loss processes

We report on MeV heavy ion beam induced epitaxial crystallization of a buried silicon nitride layer. Transmission electron micrographs and selected area diffraction patterns are used to study the recrystallization of an ion beam synthesized layer. We observe complete recrystallization of the silicon nitride layer having good quality interfaces with the top and substrate Si. Recrystallization is achieved at significantly lower temperatures of 100, 150, and 200°C for oxygen, silicon, and silver ions, respectively. The fact that recrystallization is achieved at the lowest temperature for the oxygen ions is discussed on the basis of the energy loss processes.

Encapsluation of Co and Pd multi-metal nanowires inside multiwalled carbon nanotubes by microwave plasma chemical vapor deposition

We report the synthesis of multiwalled carbon nanotubes (MWCNTs) encapsulated with Co/Pd magnetic and nonmagnetic multi-metal nanowires using Co and Pd thin-layers deposited on Si substrate by microwave plasma enhanced chemical vapor deposition using a bias-enhanced growth method. Detailed structural and compositional investigations of these metal nanowires inside MWCNTs were carried out by scanning electron microscopy and transmission electron microscopy to elucidate the growth mechanisms. Energy dispersive X-ray spectroscopy revealed that MWCNTs were encapsulated with Co and Pd nanowires, separately, at the tube top and the bottom of Co nanowire, respectively. The face-centered-cubic (fcc) structure of Co nanowires was confirmed by a selected area diffraction pattern. We proposed a fruitful description for the encapsulating mechanisms of both Co and Pd multi-metal nanowires.

Electron Irradiation Induced Crystal-to-Amorphous-to-Crystal Transition in Some Metallic Glasses

Electron irradiation induced crystal-to-amorphous-to-crystal (C-A-C) transition in metallic glasses was investigated in various metallic glasses among binary Zr-based, ternary Fe-Nd-B and Fe-Zr-B alloys. In situ observation of the TEM microstructures and corresponding SAD patterns was performed by ultra high-voltage electron microscope (UHVEM). The origin of amorphization, crystallization and C-A-C transition was discussed based on the temperature-Gibbs free energy diagram.

Characterization of oxide film formed on NiTi by laser oxidation

NiTi was surface treated by laser oxidation for improving corrosion resistance. While the corrosion behavior of laser oxidized NiTi is reported elsewhere, the present study aims at characterizing the oxide film formed in laser oxidation by means of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and selected-area diffraction (SAD). The naturally formed (NF) oxide film on a mechanically polished substrate is included in the study for comparison with the laser formed (LF) oxide film. The LF oxide film on NiTi carries a golden-yellowish interference color, and has a thickness of about 25 nm versus a thickness of 5 nm for the NF film, as determined by TEM or estimated from XPS depth profiling. The average surface roughness R a increases from 1.02 nm for the NF oxide film to 13.1 nm for the LF oxide film. XPS analysis shows a surface Ni/Ti atomic ratio of 0.17 for laser oxidized samples, which is lower than that of 0.30 for mechanically polished samples. Depth profiling of composition by XPS reveals that the LF oxide film contains mainly titanium oxides, together with a small amount of Ni in oxidized and metallic states. The oxidation state of Ti changes from Ti 4+ (corresponding to TiO 2) in the top layer of the LF oxide film to lower oxidation states Ti 3+ and Ti 2+ (corresponding to Ti 2O 3 and TiO). The LF film is composed of nanocrystallites, as evidenced from SAD patterns. High-resolution TEM image shows that the crystallite size in the LF oxide film is about 10 nm. These findings show clearly that laser oxidation significantly changes the characteristics of the oxide film on NiTi and also provide an explanation for the improvement in surface properties due to laser oxidation.

〈111〉 Rotation Twins in an Orthorhombic LaGaO3 Perovskite

Phase‐transformation‐induced twins in pressureless‐sintered lanthanum gallate (LaGaO3) ceramics have been analyzed using transmission electron microscopy. Twins are induced by solid‐state phase transformation upon cooling from rhombohedral (r, R3c) to orthorhombic (o, Pnma) symmetry at 145°C. Domains with a 150°–60°–150° configuration were frequently detected when viewed along [210]. This observation representing the co‐existence of the {121} and {123} twins is suggested by analyzing corresponding selected area diffraction patterns across the domain boundaries. The former, with the twin plane lying on {121}, is the reflection type whose twin variants are related by mirror plane symmetry. The latter, although its nature was confirmed by tilting experiments along an unsplit row of reflections, exhibits characteristic crystallographic orientation relationships that are distinctive from those of the {121} twins. The twin laws represented in the matrix form are also derived accordingly from corresponding orientation relationships. Crystallographic analysis indicates that these domains commonly possess an orientation relationship that can be described by the twofold rotation axis about 〈111〉 lost upon the rhombohedral→orthorhombic phase transition. They are therefore the 180° parallel‐rotation twin, with the twin axis 〈111〉 lying in {123}. Twins generated by the r→o phase transition between crystals of non‐group–subgroup relations are discussed in terms of an intermediate metastable cubic phase of the lowest common supergroup symmetry.

Investigation on microstructural characterization of in situ TiB/Al metal matrix composite by laser cladding

The aluminum matrix composite (AMC) coating reinforced with TiB was prepared utilizing in situ synthesized technique by laser cladding. Microstructural characterization and dry sliding wear behavior of in situ TiB/Al metal matrix composite were studied by SEM, XRD, TEM and Pin-on-disc friction and wear tester. The phase structure of the composite coating consists of α-Al, TiB, Al 3Ti and Al 3Fe. It has been found that the shape of in situ synthesized TiB is mainly taken on micro-magnitude lump and nano-magnitude whisker. Owing to B27 structure of TiB, the TiB has an anisotropy axis of growth, which results in the TiB strip and whisker preferring grown along [0 1 0] direction. It is worth to notice that the novel microstructure inside of TiB is particle and strip Al 5Fe 2 phase and definite crystallographic relationship between the Al 5Fe 2 phase and TiB has been determined by selected area diffraction pattern. The wear tests results show that the composite coatings can only improve wear resistance at the lower applied load (below 26.7 N), but at higher applied load (26.7–35.6 N) the wear resistance behavior of the coating is worsened due to the fracture and pullout of reinforcement phase.

Novel Phase Transition in BaPr 2Mn 2O 7

The rare earth manganite BaLn 2Mn 2O 7(Ln = rare earth element) has a Sr 3Ti 2O 7-type layered perovskite structure with double-block oxygen octahedra belonging to the Ruddlesden-Popper-type homologous series AO(ABO 3) 2. In Premanganite, a novel phase transition was first observed in situ at 1040 K by a thermal transmission electron microscope. At 1040 K, reflections began to split along the c-direction in the selected area diffraction pattern. This indicates that a new phase appears in the original phase matrix; the c length of the new phase is 1.5% longer than that of the original phase. After about 5 min, the original phase disappears. No change in the crystal symmetry (space group I41/ mmm) is observed above 1040 K.

Two types of S phase precipitates in Al–Cu–Mg alloys

Transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) have been used to study S phase precipitation in an Al–4.2 Cu–1.5 Mg–0.6 Mn–0.5 Si (AA2024) and an Al–4.2 Cu–1.5 Mg–0.6 Mn–0.08 Si (AA2324) (wt.%) alloy. In DSC experiments on as solution treated samples two distinct exothermic peaks are observed in the range 250–350°C, whereas only one peak is observed in solution treated and subsequently stretched or cold worked samples. Samples heated to 270 and 400°C at a rate of 10°C/min in the DSC have been studied by TEM. The selected area diffraction patterns show that S phase precipitates with the classic orientation relationship form during the lower temperature peak, and for the solution treated samples, the higher temperature peak is caused by the formation of a second type of S phase precipitates which has an orientation relationship that is rotated by ∼4° to the classic one. The effects of Si and cold work on the formation of the second type of S precipitates have been discussed.

On the crystal structure of Cr2N precipitates in high-nitrogen austenitic stainless steel. III. Neutron diffraction study on the ordered Cr2N superstructure

The ordered structure of Cr(2)N precipitates in high-nitrogen austenitic steel was investigated utilizing high-resolution neutron powder diffractometry (HRPD). On the basis of the Rietveld refinement of neutron diffraction patterns, the ordered Cr2N superstructure was confirmed to be trigonal (space group P31m), with lattice parameters a=4.800 (4) and c=4.472 (5) A, as suggested in previous transmission electron microscopy studies [Lee, Oh, Han, Lee, Kim & Takaki (2005). Acta Cryst. B61, 137-144; Lee, Kim & Takaki (2006). Acta Cryst. B62, 190-196]. The occupancies of the N atoms in four crystallographic sites [1(a), 1(b), 2(d) and 2(c) Wyckoff sites] were determined to be 1.00 (5), 0.0, 0.74 (9) and 0.12 (3), respectively, reflecting a partial disordering of N atoms along the c axis. The position of the metal atom was specified to be x=0.346 (8) and z=0.244 (6), corresponding to a deviation from the ideal position (x=0.333 and z=0.250). This deviation caused the ((1/3 1/3)(0))-type superlattice reflection to appear. A comparison between the ideal and measured crystal structures of Cr2N was performed using a computer simulation of selected-area diffraction patterns.