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Journal of materials science & technology 102, 89 - 96 (2022). doi:10.1016/j.jmst.2021.06.041, In modern ��-solidified TiAl alloys, the decomposition of ��$_2$ phase is frequently observed during heat treatment or high-temperature deformation of the alloys. In this study, high-temperature deformation and decomposition mechanisms of ��$_2$ phase in a Ti-45Al-8.5Nb-0.2B-0.2W-0.02Y alloy are investigated. In a sample deformed at 800 ��C, the precipitation of ��$_o$(��$_o$) phase is observed within the equiaxed ��$_2$ phase. The nucleation of ��$_o$ particles within the ��$_o$ matrix indicates the ��$_2$ ��� ��$_o$ ��� ��$_o$ transformation. In addition, numerous �� phase precipitates form within the ��$_o$(��) areas. The ��$_2$ lamellae decompose into ultrafine (��$_2$+��) lamellae and coarsened �� lamellae via ��$_2$ ��� ��$_2$ + �� and ��$_2$ ��� �� transformation, respectively. Moreover, the ��$_o$ phase nucleates within the ultrafine lamellae via ��$_2$ ��� ��$_o$ transformation. However, in a sample deformed at 1000 ��C, the nucleation of ��$_o$ particles is sluggish, which is caused by the efficient release of the internal stress via dynamic recrystallization (DRX). These results indicate that complex phase transformations can be introduced by the decomposition of ��$_2$ phase in TiAl alloys with a high amount of ��-stabilizing elements., Published by Ed. Board, Journal of Materials Science & Technology, Shenyang

The transformations between the phases α2 (Ti3Al) and ωo were investigated in a lamellar multiphase titanium aluminide alloy based on γ (TiAl). The paper complements an earlier investigation performed on the same material in which the importance of deformation-induced twin structures for the α2→ωo transformation was demonstrated. The present study shows that the reverse transformation ωo→α2 can also occur during high-temperature deformation. The transformation is probably triggered by constraint stresses, which exist between the different constituents due to the crystalline mismatch. The combined operation of mechanical twinning of the α2 phase and the reversible transformation fully converts the α2 lamellae into a mixture of α2 and ωo. This conversion greatly reduces the mechanical anisotropy existing in former α2 lamellae. Regarding the technical use of the alloy, the stability of the converted structure with respect to further annealing was also examined. The reported processes occur at the nano-meter and sub nano-meter scale, thus, advanced characterization techniques were applied, such as high-resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT).

(Na0.5Bi0.5)0.4Sr0.6Ti1-xZrxO3 relaxor ferroelectric ceramic were prepared by a traditional ceramic preparation process introducing Zr4+ at the B-site. It was observed that introducing an appropriate amount of Zr4+ ions into the NBST matrix can improve the energy storage efficiency. (Na0.5Bi0.5)0.4Sr0.6Ti0.5Zr0.5O3 shows excellent energy storage density up to 2.83 J/cm3, and excellent efficiency (83.90 %) at 220 kV/cm. A single layer ceramic capacitor (SLCC) was also prepared by the tape casting technique for multilayer ceramic capacitors (MLCCs) to further enhance the energy storage performance. The recoverable energy storage capacity is increased to 4.52 J/cm3 and the efficiency is 70.02 % at 460 kV/cm. Moreover, it still has a relatively stable energy storage performance after 105 cycles of charge and discharge. This sample has exhibited outstanding energy storage performance, fatigue resistance, and charge/discharge performance and has great potential value in practical applications.

Owing to their importance in applications related to textured ceramics engineering, two-dimensional perovskite single-crystal microplates are highly desirable. In this work, (001)-oriented perovskite-structured BaTiO3 (BT) single-crystal microplatelets were fabricated from an Aurivillius-structured BaBi4Ti4O15 precursor via topochemical transformation. XRD, SEM, DTA, and TEM characterizations were performed to investigate the crystallization behavior and morphology evolution of the product at different reaction stages, with a focus on the formation mechanism of BT single crystalline microplatelets. Our results indicate that secondary recrystallization repaired the significant micro-structural/crystalline damage that was caused, thereby preserving the single-crystal structure during structural conversion. The subsequent epitaxial growth and replenishment through Ostwald ripening resulted in more regular shapes and narrower distributions of BT microplatelets. This study not only suggests suitable BT template candidates for the application of textured ceramics, but also provides new insights into a simple topochemical transformation strategy for manufacturing two-dimensional perovskite microcrystals.

High-entropy alloys (HEAs) contain multiple principal alloying elements, but usually with simple crystal structures. Quasicrystals are structurally complex phases, but are generally dominated by only one element. However, near-equiatomic high-entropy quasicrystals have rarely been reported because they are difficult to prepare experimentally and predict theoretically. Therefore, the preparation and crystal structures of near-equiatomic high-entropy quasicrystals have drawn much interest. We report a quinary decagonal quasicrystal (DQC) with near-equiatomic alloying elements in Al20Si20Mn20Fe20Ga20 melt-spun ribbons, which is the first to our knowledge. Meanwhile, the structural features of the DQC are characterized in detail. The configurational entropy of both the alloy and DQC satisfies the entropy-based criterion for HEAs, suggesting a high-entropy DQC. Our findings provide a new strategy to develop high-entropy quasicrystals.

Quasicrystals, which have long-range orientational order without translational symmetry, are incompatible with the theory of conventional crystals, which are characterized by periodic lattices and uniformly repeated unit cells. Reported here is a novel quasicrystal-related solid state observed in two Al–Cr–Fe–Si alloys, which can be described as a mosaic of aperiodically distributed unit tiles in translationally periodic structural blocks. This new type of material possesses the opposing features of both conventional crystals and quasicrystals, which might trigger wide interest in theory, experiments and the potential applications of this type of material.

Strain glass is a frozen disordered strain state with local strain order manifested by nano-sized strain domains, which is formed as a result of doping sufficient point defects into the normal martensitic system. Exploration of the transition between strain glass and long-range strain-ordered martensite is of both great fundamental importance and practical interest. However, it remains a mystery whether magnetic field can induce a transition from strain glass to martensite. Here, we report for the first time the magnetic-field-induced strain-glass-to-martensite transition, in a model system Fe-Mn-Ga. It was found that the martensitic transformation temperature of the Fe43-xMn28Ga29+x alloys decreases rapidly with increasing x and the martensitic transformation disappears when x reaches the critical value xc = 2.0. Strain glass transition occurs in the alloy with x = 2.0 (Fe41Mn28Ga31), which is confirmed by the invariance of the average structure during cooling, the frequency dispersion of the ac storage modulus and internal friction following the Vogel–Fulcher relation, and the formation of nanodomains. The magnetic-field-induced transition from strain glass to non-modulated tetragonal martensite in Fe41Mn28Ga31 was indicated by the abrupt magnetization jump on the M(H) curve and directly evidenced by the crystal structure evolution with magnetic field change revealed by in-situ neutron diffraction experiments. The microscopic mechanism for this magnetic-field-induced strain-glass-to-martensite transition is discussed. The present study may not only help establish the unified theory for strain-glass-to-martensite transition under external fields but also open a new avenue for designing advanced materials with novel functional properties.

Barium titanate (BaTiO 3 )-based lead-free relaxor ferroelectric ceramic Ba 0.65 Sr 0.245 Bi 0.07 TiO 3 was developed via a traditional electrocremic processing technique to obtain Pb-free dielectric bulk ceramics with enhanced energy storage performance that can be potentially used in pulsed power devices. The added CuO can broaden the phase transition peak, and move it to lower temperature, reinforcing the dielectric relaxor behavior. The microstructure evolution of the sample was investigated via Piezoforce microscopy, and the corresponding mechanism regarding the electric breakdown strength was studied. The solubility of solid CuO in the Ba 0.65 Sr 0.245 Bi 0.07 TiO 3 is approximately 0.02 mol. The ceramic sample with 0.005 mol CuO possesses 160 kV/cm electrical breakdown strength and an energy storage efficiency higher than 76%, which yields 1.28 J/cm 3 energy storage density. Moreover, the ceramic specimen with 0.005 CuO exhibits relatively good temperature stability, good frequency stability from 1 Hz to 200 Hz, and also good fatigue resistance up to 10 5 cycles, and can be a potential candidate for future energy storage applications.

Recently, ferroelectric ceramics with high maximum polarization, low remnant polarization and high electric breakdown strength (BDS) have attracted much attention due to their potential applications in energy storage capacitors. In this work, we show a novel kind of (Ba,Sr)TiO3 (BST)-based lead-free ferroelectric ceramics, i.e., (1-x)Ba0.9Sr0.1TiO3-xBi(Zn0.5Zr0.5)O3 (BST-xBZZ) solid solutions, which were fabricated by the traditional solid-state reaction process. By introducing the BZZ into BST with a content from 0.05 to 0.20, purely pseudocubic perovskite phases and highly dense structures are obtained. The increase of the BZZ content not only shifts the TC toward to lower temperature, but also induces strong relaxor behaviors with diffuse phase transition characteristics, thus improving the temperature stability of dielectric properties. Of special interest is the improved energy storage properties, which were systematically evaluated by measuring the polarization-electric field (P-E) hysteresis loops as a function of electric field, frequency and loading cycle. It is found that BT-0.15BZZ ceramic achieves a maximum energy density of 1.11 J/cm3, which is attributed to the improvement of BDS. In addition, relatively good frequency stability and fatigue resistance of this composition suggest its potential application in energy storage devices.

A spintronic device based on the spin-dependent Hall effect has attracted great interest because of its great potential applications in the multivalue storage and logic gate, which is a promising candidate to break the bottleneck of the information industry in the big data period. It is a technological challenge to implant spintronic devices into semiconductor integrated circuits. The anomalous Hall angle (θ), defined as the deviation of the electron flow from the current direction, is the key parameter to evaluate the capacity of Hall device compatibility. However, the bottleneck for the device is low θ (less than 5%) at room temperature (RT), making it difficult to directly complement with the semiconductor circuit which limits its potential application. Here, we report a simple perpendicular multilayered structure with θ up to 5.1% at RT. Wide working temperature (250-350 K) across RT for our samples will accelerate the potential applications in spintronic memory. A giant Hall angle at RT originates from the enhanced side-jump scattering at the atomic-scale-modified interfacial structure. The high θ at RT together with wide working temperature is practically significant and may provide the way for further 3D spintronic devices based on the spin-dependent Hall effect with ultrahigh storage density and ultralow power consumption.

Porous Al63Cu25Fe12 quasicrystal alloys with the surfaces and the wall of pores covered with abundant (Al11.5Fe13.9Cu19.7)O54.9 nanosheets were successfully fabricated through the combination of powder metallurgy and dealloying in NaOH solutions. Their compositions, microscopic morphology, and crystal structures were investigated using energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. We found that the composite of porous Al63Cu25Fe12 quasicrystal alloys and (Al11.5Fe13.9Cu19.7)O54.9 nanosheets shows high catalytic performances in hydrogen production by methanol steam reforming at relatively low temperatures. X-ray photoelectron spectroscopy was used to analyze the catalytic mechanisms, and Cu was found to be the key element in this catalytic reaction.

To solve the sensitivity of soft magnetic properties of Fe-B-P-C-Cu alloy system without transition metal addition on heat treatment process parameters, the effect of P content on the heat treatment process parameters and soft magnetic properties of Fe83B12-xPxC4Cu1 (x = 3, 5 and 7) alloys have been investigated. It is found that increasing P can effectively reduce the sensitivity of microstructure and soft magnetic properties on the annealing holding time (th). The th of Fe83B7P5C4Cu1 and Fe83B5P7C4Cu1 alloys can be extended to 60 min compared to the th of 6 min for Fe83B9P3C4Cu1 alloy to obtain a low coercivity (Hc) below 8.5 A/m. However, too high P content will reduce the stability of residual amorphous phase and shorten the optimal th. The results indicate that increase of P can also reduce the sensitivity of microstructure and soft magnetic properties on the heating rate (β). The β of Fe83B7P5C4Cu1 and Fe83B5P7C4Cu1 alloys can be as low as 40 K/min and 20 K/min to obtain high saturation magnetic flux density (Bs) of 1.80 T and 1.73 T, and low Hc of 8.4 A/m and 8.1 A/m, respectively.

Seldom could metals and alloys maintain excellent properties in cryogenic condition, such as the ductility, owing to the restrained dislocation motion. However, a face-centered-cubic (FCC) CoCrFeNi high-entropy alloy (HEA) with great ductility is investigated under the cryogenic environment. The tensile strength of this alloy can reach a maximum at 1,251±10 MPa, and the strain to failure can stay at as large as 62% at the liquid helium temperature. We ascribe the high strength and ductility to the low stacking fault energy at extremely low temperatures, which facilitates the activation of deformation twinning. Moreover, the FCC→HCP (hexagonal close-packed) transition and serration lead to the sudden decline of ductility below 77 K. The dynamical modeling and analysis of serrations at 4.2 and 20 K verify the unstable state due to the FCC→HCP transition. The deformation twinning together with phase transformation at liquid helium temperature produces an adequate strain-hardening rate that sustains the stable plastic flow at high stresses, resulting in the serration feature.

The decagonal diffraction symmetry of a decagonal quasicrystal (DQC) results from its particular autocorrelation (Patterson) function. Structural subunits (‘clusters’) with decagonal symmetry may exist but do not need to exist. By atomic resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), we observed the so far largest tenfold symmetric structural subunits in decagonal Al59Cr21Fe10Si10 scaling up to 5.2 nm. This amazing result provides direct experimental evidence how the local tenfold symmetry of DQCs is expanded to a larger size.

Due to the lack of independent slip systems and the difficulty in mechanical twinning, D019 ordered α2-Ti3Al phase is known to be of substantial mechanical anisotropy, which partly accounts for the low ductility of two-phase (α2+γ) TiAl alloys. However, recent studies have shown that in Al-rich α2 phase compression deformation twins can be activated, which could be beneficial for the ductility of the alloys. In the present study, for the first time, we have revealed a novel internal twinning mechanism of α2 phase in a TiAl alloy deformed at high temperature. Three twin generations of a common type {20 2 ¯ 1} 1 ¯ 014> were revealed: Secondary twins formed within the primary twin, and tertiary twins formed in the secondary twin. It is important to note that this internal twin structure can only be observed in the 1 ¯ 1 ¯ 6> direction but not the commonly used 2 ¯ 0> direction. The shear plane P of all twin variants is of type {1 2 ¯ 10}. Due to the variation of the twinning elements between the twin variants, the twinning shear is blunted. The interfaces between the twin variants are characterized by high-resolution electron microscopy. Special attention was paid to the structure of the coherent and incoherent twin boundaries. The effect of chemical ordering is discussed. Our results also shed light on the complex twinning mechanisms in hexagonal structures.

Twin boundaries (TBs) of decagonal quasicrystal approximants generally exhibit structural characteristics that are peculiar compared with traditional crystals with small lattice parameters. Herein, the TBs of the orthorhombic (3/2, 2/1) 2 decagonal approximant in the quaternary Al 60 Cr 20 Fe 10 Si 10 alloy were investigated, and four types of (101) TBs were found using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy. The structural features of these TBs at the atomic level were revealed and the corresponding projected structural models along the pseudo-tenfold axis were proposed and discussed. These results demonstrate that the diversifications of the TBs of decagonal approximants are closely related to the rich combinations of substructural blocks, and this may trigger further interest in the planar defects present in other decagonal approximants.

Big-data analysis of phase-formation rules of high-entropy alloys ( HEAs) was conducted and a phase formation rule from a dynamic view was deduced. It was indicated in literatures that cooling rate has a strong influence on the phase formation of HEAs. Higher cooling rate may promote the generation of amorphous phase, and accordingly suppress the formation of intermetallics. Meanwhile, it was also shown that cooling rate had little impact on the formation of solid-solution phase. To demonstrate this rule, a series of FeCoNi(AlSiB)x HEAs ribbons were fabricated by a melt-spinning technique, and the microstructure, mechanical, and magnetic properties were also investigated. The results show that all ribbons exhibit disordered solid-solution structure. The addition of boron changes the alloy from ductility to brittleness, but without evident change of magnetic properties. The alloy in the nominal composition of FeCoNi(AlSi)0.2 has the best combination of mechanical and magnetic properties. A distinct feature of HEAs in magnetization was noticed and explained.

A shield-like tile (SLT) consisting of one star tile and two hexagon tiles was used as one structural block to describe the tilings of quasicrystal approximants in our previous work [J. All. Compds. 647 (2015) 797–801.] because of its merits compared with the hexagon-boat-star model. In this paper, we aim to elucidate the rules of connection and the orientations of SLTs. Two examples of high-angle annular dark-field scanning transmission electron microscopy images are provided to support these rules. The SLT orientation mapping of the quasicrystal-related structures along the pseudo-tenfold axis was achieved, and the structural characterizations were revealed intuitively. Furthermore, some new quasicrystal approximants were discussed based on the changeable rows of SLTs.

Hexagonal Si (2H polytype) has attracted great interest because of its unique physical properties and wide range of potential applications. For example, it might be used in heterojunctions based on hexagonal and cubic Si. Although hexagonal Si has been reported in Si nanowires, its existence is doubted because structural defects of diamond cubic Si can produce structural signals similar to those attributed to hexagonal Si. Here, through the use of atomic resolution high-angle annular dark-field scanning transmission electron microscopy imaging, we unambiguously report the coherent intergrowth of diamond cubic (3C polytype) and 2H hexagonal Si in Si nanowires grown by chemical vapor deposition. A model describing the intergrowth of 3C and 2H Si is proposed and the reasons for the generation of 2H Si are discussed in detail.

In this work, Fe83+x(B4P8C4)16-xCu1 (x = 0, 1, 1.5 and 2 at. %) alloy system with amorphous/α-Fe hierarchic structures in as-cast state were artificially designed. The microstructure, crystallization kinetics, nanocrystalline structure, and magnetic properties of the alloys were systematically investigated. And the structural mechanism for the magnetic properties of these alloys was discussed. It is shown that the structure is evolved from full amorphous to amorphous/α-Fe dual-phase microstructure in the free surface side, and/or roller side layer with Fe content increasing. The formation of hierarchic structure decreases the activation energies of onset and peak crystallization of α-Fe phase, and increases the size of nanocrystalline grains, and subsequently is beneficial to improve the Bs of alloys. The Hc of alloys increases due to the formation of hierarchic structure, whereas this effect is gradually eliminated by the annealing process at the suitable crystallization annealing temperature (Ta). Typically, Fe85B3.5P7C3.5Cu1 nanocrystalline alloy exhibit the Bs of 1.86T and Hc of 5.7 A/m after annealing at 723 K. High Fe bearing alloys have lath domain structure with stronger orientation preference in as-cast state, and transformed into labyrinth packing with thinner spacing after structural relaxation annealing, demonstrating that hierarchic structure leads to the high magnetic anisotropy in the alloys.

The electrostrictive effect has some advantages over the piezoelectric effect, including temperature stability and hysteresis-free character. In the present work, we report the diffuse phase transitions and electrostrictive properties in lead-free Fe3+-doped 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-0.5BCT) ferroelectric ceramics. The doping concentration was set from 0.25 to 2 mol %. It is found that by introducing Fe3+ ion into BZT-0.5BCT, the temperature corresponding to permittivity maximum Tm was shifted toward lower temperature monotonically by 37 °C per mol % Fe3+ ion. Simultaneously, the phase transitions gradually changed from classical ferroelectric-to-paraelectric phase transitions into diffuse phase transitions with a weak relaxor characteristic. Purely electrostrictive responses with giant electrostrictive coefficient Q33 between 0.04 and 0.05 m4/C2 are observed from 25 to 100 °C for the compositions doped with 1–2 mol % Fe3+ ion. The Q33 of Fe3+-doped BZT-0.5BCT ceramics is almost twice t...

The ZnO nanoparticles in a uniformed size have been applied as the photocatalysts over the reduction of Cr(VI). The morphologies of the ZnO nanoparticles are decided by the cluster type of mother sample Zn-MOFs, which are prepared with the same bi-ligands 1,3,5-benzenetricarboxylic acid (H3BTC) and phenanthroline (phen) in the presence of Zn ions. The SEM, TEM, infrared spectroscopy, thermogravimetric analysis and UV–vis study reveal the physical properties and structural information of ZnO nanoparticles. The reduction rate of Cr(VI) under the UV light irradiation indicates that the ZnO nanoparticles have higher activities with promoting reduction rate comparing with the related Zn-MOFs. The test of photocurrent approves the reduction ability of each sample.

Twins or multiple twins occur frequently in the orthorhombic Al20Cu2Mn3 approximant of decagonal quasi crystal (DQC). Due to the specific structural units, the twins in the Al20Cu2Mn3 approximant usually exhibit the glide-reflection characteristics. Using aberration-corrected transmission electron microscope at the atomic scale, we have observed not only glide-reflection twins but also simple mirror-reflection twins in the Al20Cu2Mn3 approximant. The two twinning modes are found to coexist in the present sample. These twins exhibit variant configurations at the twin boundaries where the tessellations of local subunits are imaged at an atomic scale. At the twin boundaries, diversified tiles such as star-like (S), bowtie-shaped and boat-shaped (B) are observed. The diversified tiles stacking with various manners allow the coexistence of the DQC and the approximant. Furthermore, the variants of B and S tiles are also found.

The age hardening responses of the Al-5.2Mg-0.45Cu alloy with Zn addition have been investigated in this study. It is found that the age hardening process of the Zn-containing Al-5.2Mg-0.45Cu alloys can be divided into four stages, namely the initial jump(Ⅰ), the linear increase (Ⅱ), the accelerated increase to the peak (Ⅲ) and the overage (Ⅳ). The addition of Zn to the Al-5.2Mg-0.45Cu alloy leads to an enhanced and accelerated age-hardening response in two aspects: firstly introducing the T-[Mg 32 (Al, Zn) 49 ] phase resulting from the high Mg/Zn ratio and relatively high aging temperature; secondly stimulating the precipitation of the Guinier-Preston-Bagaryatsky (GPB) zones by increasing the supersaturation upon quenching, and accelerating the precipitation of S-Al 2 MgCu phase by increasing Cu/Mg ratio in the matrix due to the formation of the T phase. The peak hardness is from the synergetic effects of the S and T phases. The clustering and partitioning behaviors of solutes after 1 h aging treatment have been investigated in detail using atom probe tomography (APT) and high resolution transmission electron microscopy (HRTEM). It is shown that the formation of Mg-Cu clusters (precursor of the S phase) precedes that of Mg-Zn clusters (precursor of T phase), and the Mg-Cu clusters are responsible for the age hardening during the first two age hardening stages in the Cu-bearing alloys.

Microwave sintering was successfully applied to prepare (Zn, Nb) co-doped BT ceramics in short soaking time. Tetragonal BT was detected as the major phase for all the samples. With increasing ZnNb2O6 addition, Ba2Ti5O12 was detected as the second phase. ZnNb2O6 formed a solid solution with BaTiO3, which is effective to inhibit grain growth. The co-doping with Nb and Zn induced core–shell inhomogeneous structures, resulting in broadened permittivity peaks shifting to lower temperature. The introduction of ZnNb2O6 (less than 4.5%) was not only useful to enhance the densification, but also helpful to decrease the dielectric loss.

Designing high-performance Al-based alloys based on the entropy concept offers a promising strategy for next-generation advanced structural materials. The main idea of entropy increasing is to increase the content of alloying elements. For traditional high-strength Al–Zn–Mg–Cu alloy, however, significantly increasing the content of alloying elements, especially when the Zn content is increased to above 10 at.% (atomic percent), leads to poor deformability and poor tensile property. Here, we overcome this trend by designing a quinary alloy based on the idea of high-entropy alloys. We fabricate a high-Zn-content Al80Zn14Li2Mg2Cu2 alloy with the Zn content above 10 at.%. It shows Zn, and Al–Zn precipitates in the as-cast state, and it is observed that Al3(Li, Mg), MgZn2, and Zn nano-precipitates form after rolling. The precipitation transformation contributes to high strength and high deformability. Our present findings provide not only a fundamental understanding of precipitation transformation in the high-Zn-content Al alloys but valuable guidance for the development of lightweight alloys as well.

BaTiO3 (BT)-based lead-free ceramics are regarded as one kind of prospective candidates for next generation pulsed power capacitors due to their environmentally friendly and relatively high energy storage properties. Nevertheless, BT-based ceramics are still suffering from their small recoverable energy storage density (Wrec 410 kV cm−1) and a large Wrec (3.54 J cm−3) are achieved in Sr0.7Bi0.2TiO3 and Li2CO3 modified BT ceramic simultaneously. High Wrec (>2.5 J cm−3 at 300 kV cm−1) with small variation is maintained over a wide temperature range (30–150 °C) and frequency range (0.1–100 Hz), demonstrating very excellent temperature and frequency stability. The recorded ultrahigh BDS with high Wrec achieved in this work indicates that our combined strategy is effective to elevate the electric energy storage performances of BT-based dielectric ceramics and could be further generalized to other ceramic materials for the applications of advanced pulsed power capacitors.

In the making process of supercapacitors, the conductive agent carbon black is used for improving the conductivity of the electrodes and decreasing the resistance of interaction. Is it useful for porous activated carbon? In this research, partly graphitized activated carbon materials are obtained by boron and nitrogen catalysis with renewable fallen leaves as carbon source in a one-step method. The symmetric supercapacitors are fabricated in a conductive agent-free system. The fabrication process is time saving and simple with mixing of activated carbon and binder. Ion adsorption can achieve equilibrium within 2.22 s in the absence of carbon black (CB). The energy density and the power density reach to 48.6 W h kg−1 and 3600 W kg−1 at the potential window of 1.5 V.

Diamond particles dispersed Zr-alloyed Cu matrix composites were produced by a gas pressure infiltration route. The thermal conductivity first increased and then decreased with increasing Zr content in the range of 0.0–1.0 wt.%, yielding a maximum thermal conductivity of 930 W/mK at 0.5 wt.% Zr. The high thermal conductivity is attributed to the optimized thickness of interfacial ZrC layer formed between Cu and diamond. The interfacial layer thickness is crucial to the thermal conductivity enhancement in the Cu/diamond composites.

The isotope effect of hydrogen in irradiation damage plays an important role in the development of reduced activation Ferritic/Martensitic steels in nuclear reactors. The evolutions of microstructures and mechanical properties of China low active martensitic (CLAM) steel subjected to hydrogen and deuterium ions irradiation are studied comparatively. Under the same irradiation conditions, larger size and smaller density of dislocation loops are generated by deuterium ion than by hydrogen ion. Irradiation hardening occurs under the ion irradiation and the hardening induced by hydrogen ion is higher than by deuterium ion. Moreover, the coarsening of M23C6 precipitates is observed, which can be explained by the solute drag mechanisms. It turns out that the coarsening induced by deuterium ion irradiation is more distinct than by hydrogen ion irradiation. No distinct variations for the compositions of M23C6 precipitates are found by a large number of statistical data after hydrogen isotopes irradiation.

The orthorhombic (3/2, 2/1) approximant with a = 3.06 nm, b = 1.23 nm, c = 2.24 nm, and the coexisting (2/1, 3/2) approximant of decagonal quasicrystals with a = 1.90 nm, c = 3.64 nm, and β ≅ 90° are found in Al–Cr–Fe–Si alloys by aberration-corrected transmission electron microscope. The structural relationships of these two approximants are analyzed and discussed based on the high-angle annular dark-field scanning transmission electron microscopy images at atomic resolution. We find that both of their structural tiling along the [010] direction can be described by one shield-like tile, with the superiority over the previous HBS tiling model due to the clarity. Combining the shield-like tile and HBS tiling model, the domains of approximants are clearly demonstrated.

Kinking of semiconductor nanowires grown by the vapour–solid–liquid (VSL) mechanism has long been observed and studied, particularly for Si. A large variety of turning angles for kinked Si nanowires (KSiNWs) has been reported in the literature, but most authors have studied the kinking mechanism rather than the structure and corresponding geometrical features of the kinks. Here, we have investigated the relationship between the turning angles and the structure (down to atomic level) of KSiNWs grown by VSL from indium nanoparticles. By using transmission electron microscopy, we have characterized the transition regions between different segments of KSiNWs of various crystallographic orientations. We have found that most turning angles can be viewed as rich combinations of different types of {111} coherent twins that coexist within the transition regions between different segments of KSiNWs.

The early precipitation behavior of long-range-ordered (LRO) Ni 2 (Cr,Mo) strengthening phase in a Ni–21Cr–17Mo (wt%) superalloy that was subjected to a patent two-step heat treatment (705 °C/16 h/furnace cooling – 605 °C/32 h/air cooling) was revealed by means of transmission electron microscopy (TEM) and electron diffraction pattern (EDP) analysis. The coherent interfacial structure between the long-range-ordered Ni 2 (Cr,Mo) precipitate and the Ni-based matrix leads to the excellent strengthening effect of the alloy. High-spatial-resolution energy-disperse X-ray spectrum (EDX) analysis reveals that the Ni 2 (Cr,Mo) precipitates were slightly rich in Mo. The minor microstructure change after the key first-step heat treatment was especially focused on. It was found that weak streak fringes were present along 〈 311 〉 Ni - base ⁎ directions in the EDP along the [112] zone axis and the ordered nano-regions parallel to {311} Ni-base planes were distributed homogeneously in the matrix. Combined with the detailed microstructural characteristic, it is concluded that Mo atoms might enrich at every two {311} Ni-base planes during the first step of aging at high temperature (705 °C), which could increase the transition temperature of Ni 2 Cr resulting in its formation when aging at the second aging step of 605 °C. Meanwhile, Ni 2 (Cr,Mo) phase precipitates by the substitution of Mo atoms for Cr atoms every three {311} Ni-base planes in Ni 2 Cr phase with the continuous long-range diffusion of Mo atoms.

In conventional crystals, the 180° domain is generally reflected by the inversed arrangement of the orientation of unit cells in nearby domains. Herein, we report a special 180° domain related to the inverse arrangement of structural blocks in structurally complex phases in an Al60Cr20Fe10Si10 alloy. The structural features were investigated in detail by high-angle annular dark-field scanning transmission electron microscopy with atomic resolution. Furthermore, the corresponding projected structural models of the domain boundaries were proposed. Finally, the structure and the formation mechanism of the 180° domain are compared and discussed with an antiphase domain in the same alloy system.

L-shaped NaV2O5 crystals with two straight arms were controllably synthesized in a hydrothermal system with the assistance of 1,3,5-benzentricarboxylate acid (H3BTC). The arms were assembled by nanowires grown along the b-direction. By means of transmission electron microscopy, the (310) twin boundary was found to connect the nearly perpendicular arms to form the L-shaped structure. Meanwhile, the L-shaped crystallites, as the basic unit, can be further self-assembled into ┤ and + shapes.

By means of atomic-resolution high-angle annular dark-field scanning transmission electron microscopy, we found three types of giant approximants of decagonal quasicrystal in Al-Cr-Fe-Si alloys, where each type contains several structural variants possessing the same lattice parameters but different crystal structures. The projected structures of these approximants along the pseudo-tenfold direction were described using substructural blocks. Furthermore, the structural relationship and the plane crystallographic groups in the (a, c) plan of these structural variants was also discussed. The diversity of quasicrystal approximants with the same lattice parameters was shown to be closely related to the variety of shield-like tiles and their tiling patterns.

International audience; A Hot Wire assisted Chemical Vapor Deposition (HWCVD) process has been developed for producing highdensity arrays of parallel, straight and organized silicon nanowires (SiNWs) inside vertical Porous Anodic Alumina (PAA) templates, exploring temperatures ranging from 430 °C to 600 °C, and pressures varying between 2.5 and 7.5 mbar. In order to prevent parasitic amorphous silicon (a-Si) deposit and to promote the crystalline SiNWs growth, we used a tungsten hot wire to partially crack H2 into atomic hydrogen, which acts like a selective etchant regarding a-Si. Here we describe the optimization route we followed to limit the deposit of a-Si onto the surface of the porous membrane and on the walls of the pores, which led to the possibility to grow SiNWs inside the PAA membranes. Such an approach has high potentialities for device realization, like PIN junctions, FETs or electrodes for Li-ion batteries.

The fibrous PX-phase of lead titanate (PT), which can be synthesized by a hydrothermal method, has been studied to clarify its structural aspects on the atomic level. By combining synchrotron X-ray diffraction and electron microscope analysis with a first-principles calculation, a unique open-channel structure with a 5.529 angstrom diameter bore through the whole wire is determined. First-principle modeling reveals that the PX-phase structure has an indirect wide band gap and a higher formation enthalpy than the tetragonal perovskite phase. Both the frequency and symmetry of Raman-active lattice vibrational modes have been identified with polarized Raman spectra on individual monocrystalline PX-phase PT wires, showing a good match with the first-principles calculation. Furthermore, the doping of Zr in the PX-phase PT and the influence on the structure were investigated, showing a limit of 17% incorporation of Zr in the PX-phase PT.

The microstructure of ferroelectric Cd1−xZnxTe (CZT) thin films with x ≈ 0.04 grown by molecular beam epitaxy has been studied by means of cross sectional high-resolution transmission electron microscopy (HREM). High- density {1 1 1} lamellar twins are found to be the dominant defects in the films. Double-position twins with twin boundaries nearly parallel to (1 1 −2) are observed to always coexist with the (1 1 1) lamellar twins and stop the penetration of the latter. The coexistence of both kinds of twins produces complex twin structures with triple-point and quadruple-point junctions. The fact that lamellar (1 1 1) twins in the ferroelectric CZT layer are shorter than those in the Cd1−xMgxTe buffer layers is explained. The films show uniform texture direction oriented along [1 1 1] except a few regions with the habit faces of twins oblique to the surface of the films.

Keywords: electronic structure ; epitaxy ; nanostructures ; photoluminescence ; quantum dots ; Confinement ; Computation ; Gates ; Wires Reference LPN-ARTICLE-2009-008doi:10.1002/smll.200801214View record in Web of Science Record created on 2009-07-31, modified on 2017-05-12

A new kind of decagonal quasicrystal (DQC) with a periodicity of 1.23 nm was observed in the as-cast quaternary Al60Cr20Fe10Si10 alloy. The intensity distribution of some spots in the selected-area electron diffraction pattern along the tenfold zone axis was found to be different from other Al-based DQCs. High-angle annular dark-field scanning transmission electron microscopy was adopted to reveal the structural features at an atomic level. Both the tenfold symmetry and symmetry-broken decagonal (D) clusters of 1.91 nm in diameter were found, but with structural characteristics different from the corresponding D clusters in the other Al-based DQCs. The neighboring D clusters are connected by sharing one edge rather than covering, suggesting the tiling model is better than the covering model for structural description.

By means of transmission electron microscopy, four crystalline phases with compositions close to (Al,Si)(4)Cr have been found in Al-Cr-Si alloys. The hexagonal mu'-(Al4Si)(4)Cr has the same space group P6(3)/mmc as mu-(Al,Si)(4)Cr, but its c parameter is only one half of c mu. On the other hand, the orthorhombic epsilon-Al4Cr, epsilon'- and epsilon"-(Al,Si)(4)Cr have about the same lattice parameters but different space groups: Bbmm (or Cmcm), Pbnm and P2(1)2(1)2(1), respectively. The lattice parameters of these phases are closely related: a(epsilon,epsilon ',epsilon '') = root 3a(mu,mu ') congruent to 3.46 nm; = b(epsilon,epsilon ',epsilon '') = a(mu,mu ') = 2.00 nm; c(epsilon,epsilon ',epsilon '') = 1/2c(mu) = c(mu ') congruent to 1.24 nm. The symmetry of space group decreases from mu(mu '), epsilon, epsilon ' to epsilon '' and the space groups of any two neighboring phases have the minimal supergroup and the maximal subgroup relationship. Strong diffraction spots of all these phases exhibit pseudo icosahedral symmetry. In the (001) plane, icodahedra are linked by mutual penetration along the five-fold axis forming icosahedral chains in three directions at 120 degrees apart. These four (Al,Si)(4)Cr phases together with the epsilon-Al4Cr are not only structurally close related, but also are approximants of quasicrystals. (c) 2006 Elsevier B.V. All rights reserved.

A new unit cell with a = 2.0595 nm, b = 0.7574 nm, c = 1.0949 nm and beta = 107.34 degrees is proposed for the monoclinic Al45Cr7 in which icosahedra form chains in the monoclinic direction as well as triangular chains on (111). The main building block in the monoclinic Al45Cr7, the orthorhombic epsilon-Al4Cr, and the hexagonal mu-Al4Cr is the 2I3 cluster consisting of 2 vertex-linked I3 clusters which in turn consists of 3 vertex-connected icosahedra. The arrangement of 2 such clusters is similar in the former two phases but slightly different in the third. (c) 2005 Elsevier B.V. All rights reserved.

We report on a new nonlinear optical phenomenon during laser ablation on transparent dielectrics, coined as ciliary white light. It is universally observed on 14 different dielectrics with femtosecond pulses at 800 nm and 1.8 mu m.

International audience; The low temperature catalytic growth of multiwall carbon nanotubes (MWCNTs) rests on the continuous nucleation and growth of graphene layers at the surface of crystalline catalystparticles. Here, we study the atomic mechanisms at work in this phenomenon, by observing the growth of such layers in situ in the transmission electron microscope, in the case of iron-based catalysts. Graphene layers, parallel to the catalyst surface, appear by a mechanism of step flow, where the atomic layers of catalyst are "replaced" by graphene planes. Quite remarkably, catalyst facets systematically develop while this mechanism is at work. We discuss the origin of faceting in terms of equilibrium particle shape and graphene layer nucleation. Step bunching due to impeded step migration, in certain growth conditions, yields characteristic catalyst nail-head shapes. Mastering themechanisms of faceting and step bunching could open up the way to tailoring the structure of low temperature-grown MWCNTs, e.g. with highly parallel carbon walls and, ultimately, with controlled structure and chirality.

International audience; Y- and comb-type carbon nanotrees formed from branched carbon nanofibres grown by plasma-enhanced chemical vapour deposition were studied by transmission electron microscopy. Different growth mechanisms are proposed for the two types of nanotrees based on the observed and reconstituted dynamic transformations of the catalyst particles during synthesis. However, the splitting of the larger catalyst particles is required for both kinds of nanotrees, whatever the involved growth mechanism. The carbon nanotrees are well crystallized and connections of the branches are continuous, which may be interesting for future applications in nanoelectronic devices and also composite materials.

We report on the formation of laser-induced periodic annular surface structures on fused silica irradiated with multiple femtosecond laser pulses. This surface morphology emerges after the disappearance of the conventional laser induced periodic surface structures, under successive laser pulse irradiation. It is independent of the laser polarization and universally observed for different focusing geometries. We interpret its formation in terms of the interference between the reflected laser field on the surface of the damage crater and the incident laser pulse. (C) 2013 AIP Publishing LLC.

We compare, by in situ annealing of carbon nanofibres (CNFs) in the TEM, the catalytic activities of Ni and Fe for the nucleation of graphene layers. Graphene planes that are at an angle with the metal are dissolved in the case of Ni, while new graphene layers are generated parallel to the surface. In the case of Fe, we see no evolution of the particle in the same conditions, unless we start from an amorphized CNF. In that case, the amorphous carbon is easily dissolved into the Fe. These dissolved carbon atoms get out of the particle in the form of a new nanotube, where nucleation takes place - partly at least - perpendicular to the Fe surface.

Intense laser pulses impinged on the surface of solid dielectrics lead to ablation, massive material removal from the surface. With femtosecond laser pulses, many interesting phenomena have been observed during this process, such as surface periodic fringe with period much less than the laser wavelength (0.1λ~0.5λ), formation of arrays of nanometer-scale rods, etc. So far, little attention has been given to the evolution of the laser pulse itself during the ablation process. Here we present the first experimental investigation on the spatial and spectral evolution of femtosecond laser pulse during laser ablation of transparent materials. A universal new phenomenon, coined as ciliary white-light was observed, which also provides a real time in-situ observation of laser ablation on transparent materials.