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Alloying is an effective method for modulating metal nanoclusters to enrich their structural diversity and physicochemical properties. Recent investigations have demonstrated that polyoxometalates (POMs) can act as effective multidentate ligands for silver (Ag) nanoclusters to endow them with synergistic properties, reactivity, catalytic properties, and stability. However, the application of POMs as ligands has been confined predominantly to monometallic nanoclusters. Herein, we report a synthetic method for fabricating surface‐exposed gold (Au)−Ag alloy nanoclusters within a ring‐shaped POM ([P8W48O184]40−). Reacting an Ag nanocluster stabilized by the ring‐shaped POM with Au ions (Au+) was found to substitute several Ag atoms at the core of the nanocluster with Au atoms. The resultant {Au8Ag26} alloy nanocluster demonstrated superior photocatalytic activity and stability compared to the pristine Ag nanocluster in the aerobic oxidation of α‐terpinene under visible‐light irradiation. These findings provide fundamental insights into the formation and catalytic properties of POM‐stabilized alloy nanoclusters and advance exploration into the synthesis and applications of diverse metal nanoclusters. [ABSTRACT FROM AUTHOR]

SnGe4N4O4 was synthesized at high pressure (16 and 20 GPa) and high temperature (1200 and 1500°C) in a large‐volume press. Powder X‐ray diffraction experiments using synchrotron radiation indicate that the derived samples are mixtures of known and unknown phases. However, the powder X‐ray diffraction patterns are not sufficient for structural characterization. Transmission electron microscopy studies reveal crystals of several hundreds of nanometres in size with different chemical composition. Among them, crystals of a previously unknown phase with stoichiometry SnGe4N4O4 were detected and investigated using automated diffraction tomography (ADT), a three‐dimensional electron diffraction method. Via ADT, the crystal structure could be determined from single nanocrystals in space group P63mc, exhibiting a nolanite‐type structure. This was confirmed by density functional theory calculations and atomic resolution scanning transmission electron microscopy images. In one of the syntheses runs a rhombohedral 6R polytype of SnGe4N4O4 could be found together with the nolanite‐type SnGe4N4O4. The structure of this polymorph was solved as well using ADT. [ABSTRACT FROM AUTHOR]

Controlling nanoscale heat generation, dissipation, and transport is crucial for miniaturizing electronic devices and for designing highly efficient thermoelectric materials. However, it has been challenging to directly measure thermal properties at individual atom level. Herein, direct atomic‐resolution column‐by‐column imaging of the rattling motion of Ba atoms in a clathrate compound Ba8Ga16Ge30 using atomic‐resolution scanning transmission electron microscopy with a segmented detector is shown. The directional anisotropy of the rattling motion is clearly visualized in real space and its amplitude and anisotropy are quantitatively evaluated by Bayesian analysis of the thermal diffuse scattering distribution. These results open a new possibility for directly characterizing nanoscale thermal properties in materials and devices, even those containing heavy elements such as thermoelectric materials. [ABSTRACT FROM AUTHOR]

Grain boundary (GB) migration is one of the most important phenomena in materials science, which plays a key role in modifying the microstructures and properties of polycrystalline ceramic materials. Understanding how GB migrates is thus a fundamental and critical issue for future ceramic material design. While the understanding of GB atomic structures has evolved significantly over the past several decades due to the progress of atomic‐resolution electron microscopy and atomistic simulation, the understanding of the atomistic grain boundary migration is still lacking. The present article briefly reviews our recent progress on the direct observation of atomistic GB migration in ceramic material by atomic‐resolution scanning transmission electron microscopy (STEM). Using Al2O3 as a model material, we found that the atomistic GB migration proceeds with atom shuffling accompanied by GB structural change and/or nucleation of disconnection, which is highly dependent on the GB atomic structures. [ABSTRACT FROM AUTHOR]

Transition‐metal‐doped silicon nitride ceramics have attracted much attention as gate materials for semiconductors because of their electrical properties as well as chemical and thermal stability. The present study aims to clarify the defect structures of Hf‐doped β‐Si3N4 by theoretical calculations and scanning transmission electron microscopy (STEM). First‐principles calculations based on a hybrid functional method were performed. It was found that Hf dopants are mainly substituted for the Si sites and can be occasionally located at interstitial sites in the lattice of β‐Si3N4. The substitution sites of Hf dopants predicted by the first‐principles calculations were also confirmed by the high‐resolution STEM images. [ABSTRACT FROM AUTHOR]

Wide bandgap III‐nitrides, such as cubic boron nitride and wurtzite‐type aluminum nitride, are promising systems for optoelectronics. To extend their luminescent properties, we doped single Ce atoms into III‐nitride single crystals using reactive flux with a temperature gradient method at high‐pressure and high‐temperature conditions. To fully understand such properties in a large size‐mismatch system, it is critically important to determine the point‐defect structures of single dopants, their spatial distribution in three dimensions, and their atomistic dynamics at an atomic level. This review discusses point defect structures and their dynamics in III‐nitrides using single‐atom‐sensitive scanning transmission electron microscopy, and the recent progress in the related field of electron microscopy. [ABSTRACT FROM AUTHOR]

In order to fabricate tetragonal yttria stabilized zirconia samples with large grain size, 3 mol% Y2O3 doped zirconia thin films were grown on (0001) α‐Al2O3 substrate by pulsed laser deposition (PLD) followed by subsequent high temperature annealing. The thin film samples were annealed at 1200°C, 1250°C, 1300°C, and 1350°C in order to obtain larger grain size without Y segregation. The microstructure and chemical composition of these annealed films were analyzed using atomic force microscopy, scanning transmission electron microscopy, and energy‐dispersive X‐ray spectroscopy. The as‐grown thin film was found to be composed of [111]‐oriented grains of ∼100 nm connected with small‐angle tilt boundaries. Based on analysis of annealed thin films, it was revealed that grain growth of tetragonal zirconia occurred anisotropically. Cross section scanning transmission electron microscopy observations revealed that such grain growth behavior is affected by the step‐terrace structures of the sapphire substrate. Energy‐dispersive X‐ray spectroscopy showed that Y was found to distribute almost uniformly below 1300°C but to segregate at the grain boundaries at 1350°C. As a conclusion, the 1300°C‐annealed sample shows the largest grain size with homogeneous Y distributions. [ABSTRACT FROM AUTHOR]

Introducing artificial strain in epitaxial thin films is an effective strategy to alter electronic structures of transition metal oxides (TMOs) and to induce novel phenomena and functionalities not realized in bulk crystals. This study reports a breaking of the conventional trade‐off relation in thermopower (S)–conductivity (σ) and demonstrates a 2 orders of magnitude enhancement of power factor (PF) in compressively strained LaTiO3 (LTO) films. By varying substrates and reducing film thickness down to 4 nm, the out‐of‐plane to the in‐plane lattice parameter ratio is controlled from 0.992 (tensile strain) to 1.034 (compressive strain). This tuning induces the electronic structure change from a Mott insulator to a metal and leads to a 103‐fold increase in σ up to 2920 S cm−1. Concomitantly, the sign of S inverts from positive to negative, and both σ and S increase and break the trade‐off relation between them in the n‐type region. As a result, the PF (=S2σ) is significantly enhanced to 300 µW m−1K−2, which is 102 times larger than that of bulk LTO. Present results propose epitaxial strain as a means to finely tune strongly correlated TMOs close to their Mott transition, and thus to harness the hidden large thermoelectric PF. [ABSTRACT FROM AUTHOR]

Electron‐doped SrTiO3 has been attracting attention as oxide thermoelectric materials, which can convert wasted heat into electricity. The power factor of the electron‐doped SrTiO3, including SrTiO3‐LaTiO3 and SrTiO3‐SrNbO3 solid solutions, has been clarified. However, their thermal conductivity (κ) has not been clearly identified thus far. Only a high κ (>12 W m−1 K−1) has been assumed from the electron contribution based on Wiedemann–Franz law. Here, we show that the κ of the electron‐doped SrTiO3 is lower than the assumed κ, and its highest ZT exceeded 0.1 at room temperature. The κ slightly decreased with the carrier concentration (n) when n is below 4 × 1021 cm−3. In the case of SrTiO3‐SrNbO3 solid solutions, an upturn in κ was observed when n exceeds 4 × 1021 cm−3 due to the contribution of conduction electron to the κ. On the other hand, κ decreased in the case of SrTiO3‐LaTiO3 solid solutions probably due to the lattice distortion, which scatters both electrons and phonons. The highest ZT was 0.11 around n = 1 × 1021 cm−3. These findings would be useful for the future design of electron‐doped SrTiO3‐based thermoelectric materials. [ABSTRACT FROM AUTHOR]

Heat conduction in ceramics is attributed to phonon propagation, which can be strongly suppressed at boundaries. Usually, polycrystals show lower thermal conductivity (κ) than single crystals, as polycrystals contain many grain boundaries. For functional applications in thermal management technologies, ceramics with low thermal conductivity are required. While grain boundary engineering is effective for reducing κ, its utilization is limited by the fact that other functional properties are often damaged. Here it is shown that single‐crystalline oxide of InGaO3(ZnO)m with a natural superlattice structure exhibits anomalously lower κ than polycrystals. Single‐crystalline films of InGaO3(ZnO)m (m = integer), which has a superlattice structure of InO2−/GaO(ZnO)m+ stacking along the c‐axis with a controllable layer thickness of m, are fabricated. It is found that the κ perpendicular to the superlattices decreases with decreasing m‐value, and the minimum κ is 1.1 W m−1 K−1 (m = 4, 5), which is lower than randomly oriented polycrystalline InGaO3(ZnO)m. On the other hand, the κ parallel to the superlattices have similar values with those of polycrystalline. The present finding suggests that layer boundaries between different components inside single crystal can also function as thermal resistance, which will be useful for the material design of thermal management technologies. [ABSTRACT FROM AUTHOR]

Tetragonal yttria‐stabilized zirconia thin film was successfully fabricated by a pulsed laser deposition method. The thin film grew heteroepitaxially with the orientation relationship of (111)[110]ZrO2‖(0001)[11¯00]Al2O3. Energy dispersive X‐ray spectroscopy mapping revealed that Y3+ ions were distributed homogeneously without local segregations. X‐ray and electron‐diffraction analysis confirmed a single crystalline structural feature of the film. On the other hand, high‐resolution scanning transmission electron microscopy observations show that this film contains small‐angle tilt grain boundaries, which is composed of the periodic array of dislocations with the Burgers vector b=a/2[11¯0]. [ABSTRACT FROM AUTHOR]

Doping is a fundamental technique to control sintering of α‐Al2O3, and many types of elements have been used to control grain growth and material properties. Such dopants tend to be concentrated at the grain boundaries and modify grain boundary properties. It is therefore important to investigate the variation of grain boundary atomic structures induced by additives. However, in the sintering process it is difficult to prevent small amounts of unintentional impurity (such as Si), and the potential influence of additives and impurities on the grain boundary structure should be taken into account. Here we show that two types of grain boundary atomic structures are formed in a Ti‐doped Σ13 [12¯10]/(101¯4) α‐Al2O3, which has been determined by atomic‐resolution scanning transmission electron microscopy. Combining with atomic‐scale spectroscopic analyses, we elucidate that the local concentration of Si impurities significantly alters the grain boundary atomic structures and the valence state of Ti additives. The present results suggest that the subtle change in concentrations of both additives and impurity should have a strong impact on sintering processes and resultant properties in α‐Al2O3. [ABSTRACT FROM AUTHOR]

Encapsulating metal nanoclusters into zeolites combines the superior catalytic activity of the nanoclusters with high stability and unique shape selectivity of the crystalline microporous materials. The preparation of such bifunctional catalysts, however, is often restricted by the mismatching in time scale between the fast formation of nanoclusters and the slow crystallization of zeolites. We herein demonstrate a novel strategy to overcome the mismatching issue, in which the crystallization of zeolites is expedited so as to synchronize it with the rapid formation of nanoclusters. The concept was demonstrated by confining Pt and Sn nanoclusters into a ZSM‐5 (MFI) zeolite in the course of its crystallization, leading to an ultrafast, in situ encapsulation within just 5 min. The Pt/Sn‐ZSM‐5 exhibited exceptional activity and selectivity with stability in the dehydrogenation of propane to propene. This method of ultrafast encapsulation opens up a new avenue for designing and synthesizing composite zeolitic materials with structural and compositional complexity. [ABSTRACT FROM AUTHOR]

Abstract: Based on a previously constructed intergranular glassy film (IGF) model for bulk silicon nitride, a large periodic model of 3864 atoms containing 2 grains of different orientations from the main bulk β‐Si3N4 and 2 IGFs was fully relaxed using the ab initio density‐functional theory package VASP. The relaxed structure was then used to calculate the electronic structure, density of states, interatomic bonding, partial charge distribution, and electron localization using the OLCAO method. Analysis of the data focuses on the interfacial regions between bulk β‐Si3N4 and the Si‐O‐N glass layer with different orientations. The total bond order density (TBOD) is evaluated in different interfacial and bulk regions. We show minor differences in the internal cohesion between crystalline grains of different facets. However, the overall charges in the bulk crystal grains and in the glassy regions are electropositive which are balanced by the negatively charged interfacial region between the two. The presence of a less rigid glassy layer is the reason for structural flexibility in ceramics without a huge penalty in the steric energy. The optimization of the interfacial structure and bonding via the creation of defective sites is the atomic origin for the existence of the IGF in silicon nitride. The insights obtained from this detailed quantum mechanical analysis of a realistic IGF model are discussed including implications on the strength, fracture toughness, and processing methods. We also discuss the potential applications of our method to other complex materials systems. [ABSTRACT FROM AUTHOR]

The atomic and electronic structures of inversion domain boundaries in Mn-Al dual-doped ZnO (Zn0.89Mn0.1Al0.01O) have been investigated. Using atomic-resolution scanning transmission electron microscopy, a head-to-head c-axis configuration and cation stacking sequence of αβαβ|γ|αβαβ along the c-axis were observed at the basal-plane inversion domain boundary. Energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy revealed significant localization of Mn and minor localization of Al at the basal-plane inversion domain boundary. Based on experimental findings, a Mn-doped basal-plane inversion domain boundary slab model was constructed and refined by first principles calculations. The model is in agreement with atomic-resolution images. The local electronic density of states of the slab model basal-plane inversion domain boundary shows a hybridization of the Mn d and O p states within the valence band and localized Mn d states in the conduction band. The thermoelectric properties of Zn0.99− xMn xAl0.01O ceramics have been reported in a previous work. In this work, the effects of inversion domain boundaries on the thermoelectric properties are discussed. In comparison to Zn0.99− xMn xAl0.01O ceramics with x≤0.05, inversion domain boundaries in Zn0.89Mn0.1Al0.01O caused thermal and electrical conductivity reduction due to interface scattering of phonons and electrons. The Seebeck coefficient increased, suggesting electron filtering at inversion domain boundaries. [ABSTRACT FROM AUTHOR]

Novel multiferroic materials have attracted increasing attention in recent years. Aurivillius bismuth‐layer structured Bi4Ti3O12·nBiFeO3 (BTFO: n = 1–3, 5) compounds with potential multiferroic properties are such a compound. However, the data on these BTFOs are ambigious, inconsistent, and incomplete. Therefore BTFOs were grown into single crystals for a systematic evaluation. Their crystal structures and microstructures show that intergrowth of layer structure occurs easily in this class of material. Their ferroelectric measurements show strong anisotropy and dielectric peaks at high temperature, accompanied by an abnormal loss that corresponds to their polar phase transition. At room temperature, ferroelectric hysteresis loops were successfully measured; the loops show a strong dependence in their polarization and coercive field on different values of n and anisotropy. Magnetic measurement shows that all the single crystals display magnetic transitions at high temperatures and weak ferromagnetism at room temperature. Electron spin resonance (ESR) results show the coexistence of ferromagnetic and paramagnetic signal components in all the compounds. Scanning probe microscope measurements show magnetic domains switched together with electric domains by use of an electric field. Therefore we conclude that overall spin disorder with localized order is the character of this class of material, with observed magnetoelectric (ME) coupling. This work could also point the way to novel multiferroic materials in locally magnetic ordered systems. [ABSTRACT FROM AUTHOR]

Abstract: Ultrasmall nanocrystalline manganese binary oxides with various compositions and crystal structures were synthesized by a convenient, rational low‐temperature method. These oxides were obtained in 2‐propanol‐based solutions using the organic‐solvent‐soluble MnO4− as a manganese source under controlled metal cation template hydration. Three‐dimensional spinel oxides were generated selectively by suppressing the hydration of metal cation templates. One‐dimensional tunnels and two‐dimensional layered structures predominated under adequate and high hydration, respectively. These oxides acted as efficient reusable heterogeneous catalysts for primary alcohol ammoxidation and amidation using aqueous NH3 as a nitrogen source and O2 (air) as a terminal oxidant. In particular, ultrasmall Co−Mn spinel oxide effectively catalyzed the ammoxidation of primary alcohols into their corresponding nitriles. The Li−Mn spinel oxide promoted the hydration of ammoxidation‐derived nitriles, facilitating the one‐pot conversion of primary alcohols into primary amides. [ABSTRACT FROM AUTHOR]

The electronic (band) structure of polycrystalline Al2O3, in particular the density of near-band edge grain-boundary localized states, plays a significant role in a host of high-temperature phenomena, including sintering, high-temperature creep, oxygen permeability in dense 'dry' Al2O3 ceramics, and Al2O3 scale formation on Al2O3 scale-forming alloys. All these phenomena involve creation or annihilation of charged point defects (vacancies and/or interstitials) at grain boundaries and interfaces, and must of necessity involve electrons and holes. Thus, the density of states associated with grain boundaries in Al2O3 assume great importance, and has been calculated using DFT for both nominally undoped and Y-doped Σ7 bi-crystal boundaries. These quantum mechanical calculations must be taken into account when considering why Y2O3 segregation to Al2O3 grain boundaries is so effective in enhancing high-temperature creep resistance of polycrystalline Al2O3, and in understanding the reactive element effect in Al2O3 scale-forming alloys. Finally, a case will be made that grain-boundary diffusion is mediated by the migration of a class of grain-boundary ledge defects called disconnections, which are characterized by a step height h and a Burgers vector b. [ABSTRACT FROM AUTHOR]

Nickel-substituted manganese spinel LiNi0.5Mn1.5O4 (LNMO) is a promising 5 V class positive electrode material for lithium-ion batteries. As micron-sized LNMO particles show high rate capability in its two-phase coexistence regions, the phase transition mechanism is of great interest in understanding the electrode behavior at high rates. Here, the phase transition dynamics of Li xNi0.5Mn1.5O4 is elucidated on high rate charging-discharging using operando time-resolved X-ray diffraction (TR-XRD). The TR-XRD results indicate the existence of intermediate states, in addition to the thermodynamically stable phases, and it is shown that the origin of such intermediate states is ascribed to the solid-solution domains at the phase transition front, as supported by the analysis using transmission electron microscopy coupled with electron energy-loss spectroscopy. The phase transition pathways dependent on the reaction rate are shown, together with possible explanation for this unique transition behavior. [ABSTRACT FROM AUTHOR]

As grain boundary ( GB) and GB segregation often have significant impact on various properties of polycrystalline materials, their atomic structures as well as the location of segregated dopant should be intensively investigated. We have thus reported several papers about segregation of Pr (praseodymium) in ZnO (zinc oxide) GBs for case study. In this study, we study the atomic structure of Pr-doped ZnO [0001]/(13 [ABSTRACT FROM AUTHOR]

One of the simplest methods for splitting water into H2 and O2 with solar energy entails the use of a particulate-type semiconductor photocatalyst. To harness solar energy efficiently, a new water-splitting photocatalyst that is active over a wider range of the visible spectrum has been developed. In particular, a complex perovskite-type oxynitride, LaMg xTa1− xO1+3 xN2−3 x ( x≥1/3), can be employed for overall water splitting at wavelengths of up to 600 nm. Two effective strategies for overall water splitting were developed. The first entails the compositional fine-tuning of a photocatalyst to adjust the bandgap energy and position by forming a series of LaMg xTa1− xO1+3 xN2−3 x solid solutions. The second method is based on the surface coating of the photocatalyst with a layer of amorphous oxyhydroxide to control the surface redox reactions. By combining these two strategies, the degradation of the photocatalyst and the reverse reaction could be prevented, resulting in successful overall water splitting. [ABSTRACT FROM AUTHOR]

The cathodic performances that can be achieved in solid oxide fuel cells (SOFCs), particularly in terms of oxygen diffusion, need to be improved so that high power densities can be produced at intermediate temperatures. Here, to improve the cathodic performance, a double columnar functional interlayer (DCFL) consisting of Sm0.2Ce0.8O2−δ (SDC) and Sm0.5Sr0.5CoO3− δ (SSC) is fabricated between a La0.9Sr0.1Ga0.8Mg0.2O3− δ electrolyte film and a SSC cathode film with pulsed laser deposition. The DCFL has a rough surface morphology consisting of nanosized grains (with diameters less than 5 nm), and it is formed of small columns that grow at an angle of ca. 45° from the substrate. Inserting the DCFL causes the electrical conductivity of the cathode to increase significantly, and the power density obtained by using it in a metal-supported SOFC is increased. Atomic resolution scanning transmission electron microscopy (TEM) images and density functional theory calculations confirm that the samarium atoms in the SDC columns and cobalt atoms in the SSC columns are located at the interfaces between SDC and SSC columns. Therefore, it is possible a SmCoO3− δ nanogradient is formed, which may cause lattice distortions. The 18O2 concentration is actually much higher in the DCFL than in either of SSC or SDC films. [ABSTRACT FROM AUTHOR]

Na3V2(PO4)3 is one of the most important cathode materials for sodium-ion batteries, delivering about two Na extraction/insertion from/into the unit structure. To understand the mechanism of sodium storage, a detailed structure of rhombohedral Na3V2(PO4)3 and its sodium extracted phase of NaV2(PO4)3 are investigated at the atomic scale using a variety of advanced techniques. It is found that two different Na sites (6b, M1 and 18e, M2) with different coordination environments co-exist in Na3V2(PO4)3, whereas only one Na site (6b, M1) exists in NaV2(PO4)3. When Na is extracted from Na3V2(PO4)3 to form NaV2(PO4)3, Na+ occupying the M2 site (CN = 8) is extracted and the rest of the Na remains at M1 site (CN = 6). In addition, the Na atoms are not randomly distributed, possibly with an ordered arrangement in M2 sites locally for Na3V2(PO4)3. Na+ ions at the M1 sites in Na3V2(PO4)3 tend to remain immobilized, suggesting a direct M2-to-M2 conduction pathway. Only Na occupying the M2 sites can be extracted, suggesting about two Na atoms able to be extracted from the Na3V2(PO4)3 structure. [ABSTRACT FROM AUTHOR]

Six different polytypes On (n = 1 to 6) of the conventional lithium‐ion battery cathode material LiCoO2 are examined systematically using first‐principles calculations within the framework of density functional theory. The calculations correctly predict the most stable form to be O3‐LiCoO2, and indicate that the recently synthesized O4 polytype is slightly more stable than O2‐LiCoO2, with a lattice energy per formula unit intermediate between O2‐ and O3‐LiCoO2. Extending the calculations to the as‐yet unobserved O5 polytype suggests that this is also slightly more stable than the O2 form. The potential differences of each polytype relative to lithium metal are found to decrease as the concentration of stacking faults (and volumetric mass density) increases, with a maximum of 3.89 eV for the polytype with optimum crystal packing (cubic‐close‐packing, ccp), namely O3‐ABCABC, and a minimum for the highest concentration of stacking faults, corresponding to a hexagonal close‐packed structure, i.e., O1. Other polytypes can be considered as intergrowths of these two configurations, so that for n beyond 6 the most stable form of each polytype is expected to display properties increasingly similar to those of O3 as the proportion of ccp sequences will increase. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) Part of Focus Issue on “Functional Oxides” (Eds.: T. Frauenheim, J. M. Knaup, P. Broqvist, S. Ramanathan) Different stacking configurations of close‐packed oxygen layers, with cations sandwiched in between on octahedral sites, lead to various polytypes of LiCoO2 with different energetic and electrochemical properties. A systematic comparison of these polytypes using first‐principles calculations provides new insights into their properties. The theoretical cell voltage is found to be maximum for the structure with least anisotropy and densest packing, namely the O3‐ABCABC polytype. [ABSTRACT FROM AUTHOR]

Complex oxide heterointerfaces, which play host to an incredible variety of interface physical phenomena, are of great current interest in introducing new functionalities to systems. Here, coherent super-tetragonal BiFeO3/LaAlO3 and rhombohedral BiFeO3/LaAlO3 heterointerfaces are investigated by using a combination of high-angle annular dark-field (HAADF) imaging and annular bright-field (ABF) imaging in a spherical aberration (Cs) corrected scanning transmission electron microscope (STEM), and first-principles calculations. The complicated ferroelectric polarization pinning and relaxation that occurs at both interfaces is revealed with atomic resolution, with a dramatic change in structure of BiFeO3, from cubic to super-tetragonal-like. The results enable a detailed explanation to be given of how non-bulk phase structures are stabilized in thin films of this material. [ABSTRACT FROM AUTHOR]

Zinc oxide ( ZnO) is used for a wide range of electrical applications, where its grain boundaries ( GBs) possibly influence the physical properties. It is important to determine the GB structure in atomic scale to understand GB effects on the electrical properties. In this study, the atomic structure of a ZnO GB is investigated in detail by scanning transmission electron microscopy and theoretical calculations. It is shown that the atomic structure of ZnO Σ13 [0001]/{13 [ABSTRACT FROM AUTHOR]

Atomic-resolution imaging of beam-sensitive biominerals is extremely challenging, owing to their fairly complex structures and the damage caused by electron irradiation. Herein, we overcome these difficulties by performing aberration-corrected electron microscopy with low-dose imaging techniques, and report the successful direct atomic-resolution imaging of every individual atomic column in the complex fluorapatite structure of shark tooth enameloid, which can be of paramount importance for teeth in general. We demonstrate that every individual atomic column in shark tooth enameloid can be spatially resolved, and has a complex fluorapatite structure. Furthermore, ab initio calculations show that fluorine atoms can be covalently bound to the surrounding calcium atoms, which improves understanding of their caries-reducing effects in shark teeth. [ABSTRACT FROM AUTHOR]

The LiFePO4/FePO4 phase transition process is remarkable in terms of its excellent reversibility, making this redox system extremely promising for high rate lithium storage. The recent observation of ordering effects (Li0.5FePO4) during the phase transition challenges the traditional two phase models. In this work, the phenomenon of staging for LiFePO4 for different sizes (70 nm and 50 nm) by high resolution aberration corrected annular bright electron microscopy is detected, investigated, and discussed along with previous results on larger crystals. In the small crystals, staging is found throughout with a decrease of order from center to the surface. For the larger crystal, a staging phase occurs constituting the interfacial zone (width around 15 nm) between LiFePO4 and FePO4. A comparison is made to recent experiments on even larger crystals showing such an interphase of smaller extent (around 2 nm). Thus it appears that these zones narrow with increasing size. These findings are discussed in the light of phase transition thermodynamics and kinetics. In particular, the possibility is discussed that the staging interphase may constitute a low energy solution to the LiFePO4/FePO4 contact. [ABSTRACT FROM AUTHOR]

Phasen: Die Koexistenz von rhomboedrischen LiTMO2 ‐ (TM=Ni, Co, Mn) und monoklinen Strukturen vom Li2MnO3 ‐ Typ in Li1.2Mn0.567Ni0.166Co0.067O2 wird mit atomarer Auflösung direkt nachgewiesen. Die beobachtete Heterogrenzfläche entlang der [001]rh/[103]mon ‐ Zonenachsenrichtung belegt den Zweiphasencharakter dieser lithiumreichen Kathodenmaterialien. [ABSTRACT FROM AUTHOR]

Nanocrystalline tetragonal ZrO2 polycrystals ( TZP) have been fabricated by the pressureless sintering of recently developed tetragonal ZrO2 powder containing 5.69 mol% YO1.5 and 0.60 mol% AlO1.5. The average grain sizes were 160 nm in the TZP sintered at 1150°C for 10 h and 150 nm in the 0.25 mol% GeO2-doped TZP sintered at 1100°C for 100 h. The TZP and Ge4+-doped TZP-sintered bodies were essentially single-phase materials, and neither the amorphous layer nor the second-phase particle was observed along the grain boundary faces. High-resolution transmission electron microscopy ( HRTEM), scanning transmission electron microscopy ( STEM), and nanoprobe energy-dispersive X-ray spectrometer ( EDS) measurements revealed that the Y3+, Al3+ and Ge4+ cations tend to segregate in the vicinity of the grain boundaries in the TZP-sintered bodies. The TZP and Ge4+-doped TZP exhibited an elongation to failure of more than 100% in the temperature range of 1150°C-1300°C and initial strain rate range of 1.4 × 10−5 s−1 to 1.0 × 10−2 s−1. For instance, an elongation to failure in the Ge-doped TZP reached about 200% at 1150°C and 1.4 × 10−5 s−1. The nanocrystallization reduced the lower limit of the superplastic temperature of conventional, submicron-grain TZP materials by 150°C. The improved ductility of the TZP at low temperatures was essentially attributed to the reduced grain size. [ABSTRACT FROM AUTHOR]

Grinding media 1 mm in diameter, containing 0.4 and 0.7 wt% SiO2, were fabricated using Y-TZP powder prepared by the liquid-phase method. The wear resistance of media for grinding, with and without the addition of BaTiO3 powder, was evaluated at 20–80°C in water and in a nonaqueous solvent, isoparaffin. A rapid increase in the media wear rate of SiO2-undoped media at 60°C was observed using water as a solvent, but little wear was observed for isoparaffin. The operating time until a rapid increase in the wear rate was observed in water increased with the increase in the grain size of the Y-TZP media. When the media wear became stable, the media surface was observed to be smooth. This suggested that the hydration reaction of Y2O3 and/or ZrO2 by OH− was inhibited by an increase in the grain size, and as a consequence, the decay of the grain boundaries was suppressed. In contrast, several traces of grain loss from the grain boundaries were confirmed on the worn surface of the media when a rapid increase in the wear rate was observed. The wear resistance for grinding BaTiO3 powder using SiO2-doped and -undoped media was also investigated. The wear for SiO2-undoped media increased drastically with increasing slurry temperature; however, the wear for SiO2-doped media did not increase, but was low and stable, regardless of the slurry temperature. This indicated that the hydration reaction of Y2O3 and/or ZrO2 by OH− was further inhibited by the segregation of SiO2 at the grain boundaries, and hence SiO2-doped Y-TZP media have high wear resistance, even with increased slurry temperature. [ABSTRACT FROM AUTHOR]

We have investigated the deformation mechanism of ruby in a microscopic area using a femtosecond laser having a pulse width, wavelength, and repetition rate of 238 fs, 780 nm, and 1 kHz, respectively. Transmission electron microscope observation revealed that a specific oblique pattern originating from cracks having a width of approximately 10 nm formed at the focal point. The peak shift of ruby fluorescence indicated the existence of a residual stress of 0.11 GPa at the irradiated area. Considering the pattern and magnitude of the residual stress at the focal point, we suggest that the crack propagated along the rhombohedral planes and the planes by laser irradiation. [ABSTRACT FROM AUTHOR]

The isothermal sintering behavior in 3 mol% yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) was investigated to clarify phase-separation and grain-growth mechanisms during sintering. In the Y-TZP sintered at 1300°C for 2 h, the Y3+ ion distribution of grain interiors in Y-TZP was nearly homogeneous, but Y3+ ions segregated along grain boundaries within a width of about 10 nm. When the holding time increased from 2 to 50 h, the cubic-phase regions with high Y3+ ion concentrations were clearly formed in the grain interiors adjacent to the grain boundaries, though the average grain size hardly increased. This result shows that the cubic-phase regions were formed without grain growth, which can be explained by the grain-boundary segregation-induced phase transformation mechanism. In the Y-TZP sintered at 1500°C for 2 h, the cubic-phase regions were already formed, and both of the cubic-phase region and average grain size increased with increasing holding time. This grain-growth behavior can be interpreted by the third-power growth low derived based on the solute drag theory, which indicates that the cubic-phase regions do not effectively act as the pinning points. [ABSTRACT FROM AUTHOR]