Search

B′ is a common type of metastable precipitate in over-aged Al-Mg-Si alloys, which is long regarded as a variation of the Q precipitate in Al-Mg-Si-Cu alloys due to the similarity between their lattice parameters. Atomic-resolution high angle annular dark field scanning transmission electron microscopy and energy dispersive X-ray elemental mapping at low beam damage conditions, as well as first-principles calculations were used to explore the atomistic structure of B′. It has a hexagonal unit cell with a space group P 6 ¯ and lattice parameters a = 10.3(1) Å, c = 4.05 Å. The M sites in B′, which are analogous to Cu sites in the Q structure, were inferred with 50% Si atoms and 50% vacancies. The chemical nature of other sites agrees well with the model predicted by Ravi et al. The determined model Al 3 Mg 9 Si 8 has the lowest formation enthalpy and the smallest lattice misfit with the Al matrix along the [0001] growth direction. Step-like boundaries with alternately arranged Mg-Si-Mg-Si atoms were observed at the coherent interfaces (10 1 ¯ 0) B′ // (5 ¯ 10) Al. A layer of defect structures sandwiched in the B′ precipitate was found geometrically necessary to allow both (5 ¯ 10) Al interfaces to arrange coherently in 3 dimensions and thus to relieve the strain of the surrounding matrix. The transformation from U1 → U2 → B′ was evidenced and the reverse transformation B′ → U2 nucleating at the incoherent B′/Al interfaces (150) Al is also likely. These results will provide new insight into the aging precipitation and compositional design of Al-Mg-Si(-Cu) alloys. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Nanoscale intergrowth is a ubiquitous phenomenon in layered manganites, and the interaction with the host material results in structural reconstruction around the interface, which plays an important role in the physical properties, similar to the interface effect happening in oxide heterostructures. In this work, by combining the aberration-corrected scanning transmission electron microscopy and density functional theory calculations, the oxygen octahedral coupling at the interface was directly visualized and quantified at atomic scale, and the role of oxygen octahedral coupling in the microstructure and electronic structure of bilayered Ca 3 Mn 2 O 7 were studied. The intergrowth induced interfacial phases show different octahedral tilting angles which depend on the form of nanoscale intergrowth, and thus are structurally and electronically different from bulk materials. These findings can well explain the observed mixture of tetragonal and orthorhombic phases in Ca 3 Mn 2 O 7 at room temperature, and also offers great insights into understanding of peculiar magnetism induced by the presence of intergrowth. Since the tilting angle of these intergrowth induced phases can be controlled by the thickness and density of the intergrowth, the latter could have the potential to be used to tune the physical properties. [ABSTRACT FROM AUTHOR]

Ceramic capacitors are widely used devices due to their excellent characteristics, such as rapid charge and discharge rates and high power density. However, simultaneously attaining exceptional energy storage performance and outstanding cycling stability in ceramic-based energy storage capacitors remains a considerable challenge. In this work, a multi-scale synergistic optimization strategy was proposed to enhance the energy storage performance and cycling stability of K 0.5 Na 0.5 NbO 3 ceramics, accomplished through grain refinement, introducing polar nanoregions (PNRs), and inducing weakly polar pseudo-cubic phases. As a result, ultrafine grains (∼110 nm), excellent energy storage performance [energy storage density (W rec) ∼ 3.16 J/cm3, energy storage efficiency (η) ∼ 65%], and incredible cycling stability (W rec variation: ∼0.09%, η variation: ∼0.28%) are concurrently realized in the 0.93K 0.5 Na 0.5 NbO 3 -0.07(Sr 0.7 La 0.2)(Mg 1/3 Nb 2/3)O 3 relaxation ferroelectric ceramic. This work investigates the microscopic origins of the improved energy storage performance of KNN-based ceramics and presents a synergistic optimization strategy to achieve exceptional energy storage performance and incredible cycling stability. [ABSTRACT FROM AUTHOR]

This paper presents the synthesis of multifunctional ceramics, represented as Sr 2- x Sm x Ag 0.2 Na 0.8 Nb 5- x Ti x O 15 , through the solid-state reaction method. Smaller ions in both A and B sites were co-substituted, resulting in a notable relaxation behavior, which was analyzed to determine the contributing factors for underlying structural mechanisms. Introducing Sm3+ and Ti4+ not only transformed the structure from Im 2 a to Bbm 2 symmetry and then eventually to paraelectric P 4/ mbm phase, but also induced the evolution of incommensurate structure and the formation of nano-domains to modulate relaxation behavior. Notably, the enhanced energy storage properties (W rec ∼ 3.38 J/cm3, η ∼ 84.5 %) and desirable red-orange emission performance (λ em = 610 nm) were obtained for Sr 1.7 Sm 0.3 Ag 0.2 Na 0.8 Nb 4.7 Ti 0.3 O 15 ceramics. Moreover, the multifunctional ceramics exhibited high power and current densities (P D ∼ 116.38 MW/cm3, C D ∼ 1026.43 A/cm2) together with a prolonged decay life (745 μs). Therefore, the proposed materials may be suitable for potential applications in optoelectronic devices. [ABSTRACT FROM AUTHOR]

A series of (1- x)K 0.5 Na 0.5 NbO 3 - x Ba(Zn 1/3 Nb 2/3)O 3 ((1- x)KNN- x BZN) nanostructural ceramics was successfully synthesised via solid-state reactions. These nanostructural ceramics exhibited high energy storage density compared with pure KNN ceramics. Further analysis of their dielectric/ferroelectric properties and structures revealed that the addition of BZN alloy disrupted the long-range order of the ferroelectric lattice of pure KNN and favoured the formation of ferroelectric islands and/or polar nano-regions. Consequently, the nanostructured ceramic with x = 0.05 exhibited ultrahigh energy storage density, W , of approximately 9.14 J/cm3 and recoverable energy storage density, W rec , of approximately 4.87 J/cm3 under a fairly low applied electrical field (220 kV/cm). These values exceed the highest values ever reported for KNN-based bulk ceramics. In addition, both excellent fatigue endurance (105 cycles) and temperature stability (Δ ε' / ε 100°C < 15 % in the range 30–390 °C) were realised with the 0.97KNN-0.03BZN ceramic. Their excellent energy storage properties render KNN-based ceramics potential candidates for application in pulsed-power systems. [ABSTRACT FROM AUTHOR]

A series of unfilled tungsten bronze Ca 0.5 (Sr 0.5 Ba 0.5) 2 Nb 5- x Sb x O 15 (CSBNS x) ceramics were synthesized by traditional solid-phase method to investigate the relationship between energy storage performances (ESPs) and structural changes including the lattice distortion and structural modulation. The Sb5+ substitution prompted the crystal structure to evolve from tetragonal P 4 bm to orthorhombic Ama 2 and then to tetragonal P 4/ mbm symmetry. The appearance of incommensurate Ama 2 structure and the polar nanoregions were the main factors for the stronger relaxation behavior. Moreover, the effectively enhanced bulk and grain boundary resistivity were conducive to the increase of breakdown field E b. The P - E loops become more elongated and the T c peak moved towards lower temperatures. Ultimately, an excellent recoverable energy density (W rec , 2.38 J/cm3), energy storage efficiency (η , 85%), power density (P D , 200.9 MW/cm3) and current density (C D , 1545.6 A/cm2) were achieved simultaneously for CSBNS 0.2 ceramics. The excellent ESPs make the CSBNS 0.2 show considerable potential in high-power capacitor applications. [ABSTRACT FROM AUTHOR]

Size, number density and volume fraction of nano-precipitates are important microstructural parameters controlling the strengthening of materials. In this work a widely accessible, convenient, moderately time efficient method with acceptable accuracy and precision has been provided for measurement of volume fraction of nano-precipitates in crystalline materials. The method is based on the traditional but highly accurate technique of measuring foil thickness via convergent beam electron diffraction. A new equation is proposed and verified with the aid of 3-dimensional atom probe (3DAP) analysis, to compensate for the additional error resulted from the hardly distinguishable contrast of too short incomplete precipitates cut by the foil surface. The method can be performed on a regular foil specimen with a modern LaB 6 or field-emission-gun transmission electron microscope. Precisions around ± 16% have been obtained for precipitate volume fractions of needle-like β″/C and Q precipitates in an aged Al-Mg-Si-Cu alloy. The measured number density is close to that directly obtained using 3DAP analysis by a misfit of 4.5%, and the estimated precision for number density measurement is about ± 11%. The limitations of the method are also discussed. [ABSTRACT FROM AUTHOR]

Lead-free (Na 0 .5 Bi 0.5 ) 0.95 Ba 0.05 TiO 3 (0.95NBT–0.05BT) thin films were deposited on polycrystalline Ni substrates by using the RF high-pressure sputtering system. Microstructural studies by high resolution X-ray diffraction reveal that the as-deposited 0.95NBT–0.05BT thin films are polycrystalline structures. The piezoelectric property measurements by a piezoresponse force microscopy exhibit that the polycrystalline 0.95NBT–0.05BT thin films have an excellent piezoelectric response. It is indicated that the as-grown 0.95NBT–0.05BT thin films have the potential for the development of the structural health monitoring systems and related device applications. [ABSTRACT FROM AUTHOR]

• NiO-MOF with three-dimensional polyhedral structure is synthesized by hydrothermal method. • For the first time, polyhedral NiO-MOF material for ultra-short pulse generation. • This is the first time NiO-MOF has been applied to realize harmonic mod-locking at the fs level of more than 400 MHz. As a member of organic porous crystal structure, metal organic frameworks (MOFs) material has more unique properties due to its large specific surface area, high porosity, diversified structure and functions, it has been successfully applied in new energy, microelectronics, chemical reaction medical science and other fields. However, no study about NiO-MOF for the ultrafast optics application has been reported till now. In this paper, NiO-MOF polyhedral particles is prepared by hydrothermal method and successfully applied to ultrafast photonics. The modulation depth of NiO-MOF is 18.98 % through a dual-balance detection system. Most importantly, the 109th harmonic solitons are realized for the first time based on NiO-MOF in a compact mode-locked fiber laser at 1.55 μm, the fiber laser has pulse duration of 766 fs and repetition frequency of 413 MHz. As far as we know, this is the first time NiO-MOF has been applied to realize harmonic mode-locking at the fs level of more than 400 MHz. Due to the rich variability of MOFs structure, this study successfully provides support for the application of MOFs material in advanced photonics. [ABSTRACT FROM AUTHOR]

• Random strain fields in core-shell ZnO nanowires are directly imaged by the STEM techniques. • Origin of the strain contrast is discussed based on measured and simulated STEM images. • Strain contrast strongly depends on sample thickness and collection angles of the ADF detector. • Optimum experimental parameters for imaging random strain fields is proposed for different samples. Imaging strain fields at the nanoscale is crucial for understanding the physical properties as well as the performance of oxide heterostructures and electronic devices. Based on scanning transmission electron microscopy (STEM) techniques, we successfully imaged the random strain field at the interface of core-shell ZnO nanowires. Combining experimental observations and image simulations, we find that the strain contrast originates from dechanneling of electrons and increased diffuse scattering induced by static atomic displacements. For a thin sample with a random strain field, a positive strain contrast appears in the low-angle annular dark-field (LAADF) image and a negative contrast in the high-angle annular dark-field (HAADF) image, but for a thick sample (> 120 nm), the positive contrast always occurs in both the LAADF and HAADF images. Through the analysis of the relationship between strain contrast and various parameters, we also discuss the optimum experimental condition for imaging random strain fields. [ABSTRACT FROM AUTHOR]