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An atomic-scale understanding of the role of strain on the microstructural properties of nanoscale precipitates will be helpful to explore the precipitation behavior as well as the structure-property relationships in crystalline multi-phase systems. Nanoscale Si precipitates are formed in Al-based alloys prepared by selective laser melting. The phase structure and the nature of heterointerface have been characterized using advanced electron microscopy. The nanocrystalline Si mainly contains two polymorphs, diamond-cubic Si (

Transmission electron microscopy is an indispensable tool in modern materials science. It enables the structure of materials to be studied with high spatial resolution, and thus makes a decisive contribution to the fact that it is now possible to understand the microstructure-related physical and chemical characteristics and to correlate these with the macroscopic materials properties. It was tantamount to a paradigm shift when electron microscopy reached atomic resolution in the late 1990s due to the invention of aberration-corrected electron optics. It is now generally accepted practice to perform picometer-scale measurements and chemical analyses with reference to single atomic units. This review has three objectives. Microscopy in atomic dimensions is applied quantum physics. The consequences of this for practical work and for the understanding and application of the results shall be worked out. Typical applications in materials science will be used to show what can be done with this kind of microscopy and where its limitations lie. In the absence of relevant monographs, the aim is to provide an introduction to this new type of electron microscopy and to enable the reader to access the literature in which special issues are addressed. The paper begins with a brief presentation of the principles of optical aberration correction. It then discusses the fundamentals of atomic imaging and covers typical examples of practical applications to problems in modern materials science. It is emphasized that in atomic-resolution electron microscopy the quantitative interpretation of the images must always be based on the solution of the quantum physical and optical problem on a computer.

An atomic-scale understanding of nanoscale precipitates in thermoelectric materials will help us explore their microstructure-property relationship, providing a strategy to optimize their thermoelectric properties. In thermoelectric β-SnTe, using advanced electron microscopy techniques, self-aligned nanoscale precipitates have been identified as γ-SnTe ultrathin nanosheets that induce anisotropic strain in the β-SnTe matrix. The interlayer van der Waals interactions occur across the interface of γ-SnTe ultrathin nanosheets and the β-SnTe matrix. The phase transition from γ-SnTe ultrathin nanosheets to β-SnTe can be accomplished by in situ electron-beam irradiation that lays out an approach for tuning the properties of SnTe-based thermoelectric materials.

Heteroepitaxial oxide-based nanocomposite films possessing a variety of functional properties have attracted tremendous research interest. Here, self-assembled vertically aligned nanocomposite (Pr0.5Ba0.5MnO3)1-x:(CeO2)x (x = 0.2 and 0.5) films have been successfully grown on single-crystalline (001) (La,Sr)(Al,Ta)O3 substrates by the pulsed laser deposition technique. Self-assembling behavior of the nanocomposite films and atomic-scale interface structure between Pr0.5Ba0.5MnO3 matrix and CeO2 nanopillars have been investigated by advanced electron microscopy techniques. Two different orientation relationships, (001)[100]Pr0.5Ba0.5MnO3//(001)[1-10]CeO2 and (001)[100]Pr0.5Ba0.5MnO3//(110)[1-10]CeO2, form between Pr0.5Ba0.5MnO3 and CeO2 in the (Pr0.5Ba0.5MnO3)0.8:(CeO2)0.2 film along the film growth direction, which is essentially different from vertically aligned nanocomposite (Pr0.5Ba0.5MnO3)0.5:(CeO2)0.5 films having only (001)[100]Pr0.5Ba0.5MnO3//(001)[1-10]CeO2 orientation relationship. Both coherent and semi-coherent Pr0.5Ba0.5MnO3/CeO2 interface appear in the films. In contrast to semi-coherent interface with regular distribution of interfacial dislocations, interface reconstruction occurs at the coherent Pr0.5Ba0.5MnO3/CeO2 interface. Our findings indicate that epitaxial strain imposed by the concentration of CeO2 in the nanocomposite films affects the self-assembling behavior of the vertically aligned nanocomposite (Pr0.5Ba0.5MnO3)1-x:(CeO2)x films.

Metal-doped zeolitic imidazolate framework-8 (ZIF-8)-derived carbon materials are attractive for the electrocatalytic reduction of CO2 into CO. In such carbon materials, due to the fusion and aggre...

Electrochemically converting CO2 into fuels or high value-added chemicals hold a great promise for the utilization of emitted CO2 in the future. Metal-nitrogen active sites (such as Fe–N, Co–N and Ni–N) are supposed to be effective for the electrochemical reduction of CO2 to CO, whereas their catalytic activities are largely dependent on the dispersibility and bonding structures of the catalytically active metals. In this work, we develop atomically dispersed Fe, N-codoped sandwich-like porous carbon sheets using Fe-containing zeolitic imidazolate framework-8 and graphene oxide as precursors and polyvinyl pyrrolidone (PVP) as a mediator. Compared to catalysts without PVP or with another mediator (i.e. polyetherimide), the PVP-mediated carbon sheets show a porous morphology with a higher specific surface area and a more exposed number of Fe–N active sites. Benefiting from this favourable structure, the resultant Fe, N-codoped porous carbon sheets show higher current densities and improved faradaic efficiencies up to 98.6% at −0.62 V (vs. the reversible hydrogen electrode, RHE) for the electrochemical reduction of CO2 to CO. This PVP-mediated strategy could be applied to the fabrication of other metal/nitrogen codoped carbon materials for electrocatalysis.

High-performance dielectric capacitors are in high demand for advanced electronics and electric power systems. They possess high power density (on the order of Megawatt) and exhibit ultrafast charge/discharge capability (on a microsecond scale) and long-term storage lifetime1-5, and thus they are particularly demanded in pulse power systems such as high-power microwaves, hybrid electric vehicles, and high-frequency inverters. However, their relatively low operating temperature limits their widespread applications6-9. Here, guided by phase-field simulations, we synthesized capacitors with an energy storage density of 55.4 joules per cubic centimeter, energy efficiency of over 82%, and superior thermal stability and fatigue properties at record high operating temperature of 400°C. These ultrahigh-temperature performances are achieved through a relatively simple method of introduction and engineering of interfaces within the capacitors, which greatly improve their high-temperature stability, relaxation behavior, and breakdown strength. Our work not only successfully fabricated capacitors with potential applications in high-temperature electric power systems and electronic technologies but also opens up a promising and general route for designing high-performance electrostatic capacitors through interface engineering.

Pyrochlore-type (Ca,Ti) 2 (Nb,Ti) 2 O 7 thin film has been successfully prepared on (0 0 1)-oriented SrTiO 3 substrate. The atomic-scale microstructure properties of the heterostructure have been investigated by advanced electron microscopy techniques. It is found that the (Ca,Ti) 2 (Nb,Ti) 2 O 7 thin film is polycrystalline and an intermediate layer of perovskite-type Ca(Nb,Ti)O 3 with a few unit cell thicknesses forms at the (Ca,Ti) 2 (Nb,Ti) 2 O 7 /SrTiO 3 interface. In the (Ca,Ti) 2 (Nb,Ti) 2 O 7 thin film, planar defects including {1 1 1}-type stacking faults, reflection twin and glide-reflection twin appear. The stacking faults have a projected displacement vector of ( a /8)〈112〉. Cation segregation and boundary reconstruction occur at the twin boundaries and the stacking faults, which cause the change of the local stoichiometry and are believed to affect the electrical properties of the film.

Antiphase boundaries in spinel ferrites have been considered as the functional elements with great potential for applications in spintronic devices. Engineering the antiphase boundaries is a big challenge in experiments. Here, we report on that a high density of antiphase boundaries in CuFe2O4 films have been prepared on rough surface of MgAl2O4 (001) substrates. By means of advanced electron microscopy these antiphase boundaries are found to be of {011} 1 4 〈011〉-type and bound by interfacial dislocations with Burgers vector of a/4〈011〉 that contribute to relaxation of in-plane and out-of-plane lattice strain in the heterostructure. Our results provide evidence that the rough substrate surface can be applied for the formation of antiphase boundaries in the CuFe2O4/MgAl2O4 system to tune the magnetic and electrical transport properties of epitaxial spinel ferrite films.

Epitaxial c-axis-oriented (Pr, Sr)2CoO4 thin films have been successfully prepared on single-crystalline SrTiO3 (0 0 1) substrates by pulsed laser deposition technique. By using advanced imaging techniques and energy-dispersive X-ray spectroscopy mapping, the atomic-scale structural properties of interface and planar faults have been investigated in the (Pr, Sr)2CoO4/SrTiO3 (0 0 1) system. Two types of interface structure have been characterized in the heterostructure. The coalescence of different types of interface results in the formation of interfacial dislocations and nano-scale twin lamellae in the films, which in accompany with misfit dislocation contribute to strain relaxation in the heterostructure. In addition, the perovskite (Pr, Sr)CoO3 slabs in the films lead to the formation of complex planar faults, which disturb the square-lattice CoO2 sheets of the (Pr, Sr)2CoO4 films. The findings obtained in the (Pr, Sr)2CoO4/SrTiO3 (0 0 1) system could be applicable to other Ruddlesden-Popper phases in the form of thin films.

The development of lead-free ceramics for electrostatic energy storage has attracted great interest because of the growing environmental concerns. Despite the extensive exploration, the unsuccess in synergistically optimizing both energy density and efficiency of polycrystalline materials is the major hurdle for their practical applications. Herein, Bi(Mg0.5Zr0.5)O3-modified BaTiO3 lead-free relaxor ferroelectric ceramics are demonstrated to be viable candidates for energy storage. The materials can simultaneously deliver a high recoverable energy density of 2.9 J cm−3 and a high energy efficiency of 86.8%, which are enhanced by 625% and 156% over those of unmodified BaTiO3, while keeping insensitive to thermal stimulus over 30–150 °C. It is unveiled that the incorporation of Bi(Mg0.5Zr0.5)O3 favors the formation of polar nanoregions (PNRs), as evidenced by transmission electron microscope and piezoresponse force microscopy, which increases the threshold field to induce long range order and decreases the stability thereof, contributing to the more linear-towards polarization behavior. The dynamic PNRs along with the decreased grain size, increased bulk density, and consequently enhanced dielectric breakdown strength (301.4 kV cm−1) are responsible for the superior energy storage performance of Bi(Mg0.5Zr0.5)O3-modified BaTiO3 ceramics. This work opens up a new avenue to tailor lead-free dielectrics toward high energy storage performance for electrical energy storage.

Heteroepitaxial CoFe2O4:MgO nanocomposite films were grown on single-crystalline MgAl2O4(0 0 1) substrates by the pulsed laser deposition technique. The effect of post-annealing on microstructural and magnetic properties of the nanocomposite films has been systematically investigated. In the heterosystems, misfit dislocations bounding anti-phase domain boundaries release the epitaxial strain between the nanocomposite films and the substrates. Compared with the as-grown films, the Co distribution and the epitaxial strain state change in the post-annealed nanocomposite films. Additionally, the in-plane saturation magnetization (Ms) and coercivity (Hc) decrease, while Ms decreases but Hc increases along the out-of-plane direction of the post-annealed nanocomposite films. Our findings indicate that a feasible strategy to change the physical properties of the single-phase film by post-annealing can be applied to the nanocomposite films containing spinel ferrites.

The formation of hydrides challenges the integrity of zirconium (Zr) fuel cladding in nuclear reactors. The dynamics of hydride precipitation are complex. Especially, the formation of the butterfly or bird-nest configurations of dislocation structures around hydride is rather intriguing. By in-situ transmission electron microscopy experiments and density functional theory simulations, it is discovered that hydride growth is a hybrid displacive-diffusive process, which is regulated by intermittent dislocation emissions. A strong tensile stress field around the hydride tip increases the solubility of hydrogen in Zr matrix, which prevents hydride growth. Punching-out dislocations reduces the tensile stress surrounding the hydride, decreases hydrogen solubility, reboots the hydride precipitation and accelerates the growth of the hydride. The emission of dislocations mediates hydride growth, and finally, the consecutively emitted dislocations evolve into a butterfly or bird-nest configuration around the hydride.

Nanoscaled HfO2-based ferroelectric thin films are a favored candidate for the integration of next-generation memory and logic devices. The unique advantage is ferroelectric polarization becomes more robust than the traditional perovskite ferroelectrics as the size is reduced. Understanding and controlling the ferroelectricity requires high-quality epitaxial thin films to explore intrinsic ferroelectric mechanism and evaluate device applications. Here, we report a semicoherent growth of ITO as a bottom electrode that enables genuine ultrathin epitaxial films of Si-doped HfO2 on YSZ[001]/[110]/[111] substrates. The films, which are under epitaxial compressive strain, display large ferroelectric polarization values up to 42 μC/cm2 and do not need wake-up cycling. Structural characterization reveals the presence of crystalline domains with short axis of the tetragonal structure oriented perpendicular to the substrate. Using piezoforce microscopy, polar domains can be written and read and are reversibly switched with a phase change of 180o. Ferroelectric polarization can be controlled by ITO surface polarity which easily exploiting the interfacial valance mismatch to influence the electrostatic potential across the interface. These findings have implications for our understanding of ferroelectric switching and offer easy method to manipulate domain reversal state in HfO2-based ferroelectric materials.

Microstructural properties of spinel LiFe5O8 (LFO) films grown on (001)-oriented SrTiO3 (STO) substrates have been investigated at the atomic-scale by advanced electron microscopy techniques. Two types of orientation relationship (OR) between the LFO films and the STO substrates have been determined, cube-on-cube and (111)[ 1 ¯ 10]LFO//(111)[1 1 ¯ 0]STO. Antiphase boundaries (APBs) and three types of twin boundaries (TBs) form within the LFO films, and the propagation of TBs and APBs results in their complex interactions. In most cases, interactions between TBs and APBs change the type of TBs and terminate the propagation of APBs since the APBs introduce a displacement vector of (a/4)〈110〉 into the TBs. In addition, the interactions between two coherent TBs are observed to generate the incoherent TB. The epitaxial strain of the LFO/STO (001) heterosystem can be released by the formation of TBs and APBs in the films and misfit dislocations at the interface. Considering that the magnetic coupling across the APBs and TBs can lead to novel physical properties, the appearance of APBs and TBs with a high density in the LFO films would affect the magnetic properties of the films.

The wide applications of Ni-rich LiNi1- x-y Cox Mny O2 cathodes are severely limited by capacity fading and voltage fading during the cycling process resulting from the pulverization of particles, interfacial side reactions, and phase transformation. The canonical surface modification approach can improve the stability to a certain extent; however, it fails to resolve the key bottlenecks. The preparation of Li(Ni0.4 Co0.2 Mn0.4 )1- x Tix O2 on the surface of LiNi0.8 Co0.1 Mn0.1 O2 particles with a coprecipitation method is reported. After sintering, Ti diffuses into the interior and mainly distributes along surface and grain boundaries. A strong surface and grain boundary strengthening are simultaneously achieved. The pristine particles are fully pulverized into first particles due to mechanical instability and high strains, which results in serious capacity fading. In contrast, the strong surface and the grain boundary strengthening can maintain the structural integrity, and therefore significantly improve the cycle stability. A general and simple strategy for the design of high-performance Ni-rich LiNi1- x - y Cox Mny O2 cathode is provided and is applicable to surface modification and grain-boundary regulation of other advanced cathodes for batteries.

To address the volume-change-induced pulverization problems of electrode materials, we propose a “silica reinforcement” concept, following which silica-reinforced carbon nanofibers with encapsulated Sb nanoparticles (denoted as SiO2/Sb@CNFs) are fabricated via an electrospinning method. In this composite structure, insulating silica fillers not only reinforce the overall structure but also contribute to additional lithium storage capacity; encapsulation of Sb nanoparticles into the carbon–silica matrices efficiently buffers the volume changes during Li–Sb alloying–dealloying processes upon cycling and alleviates the mechanical stress; the porous carbon nanofiber framework allows for fast charge transfer and electrolyte diffusion. These advantageous characteristics synergistically contribute to the superior lithium storage performance of SiO2/Sb@CNF electrodes, which demonstrate excellent cycling stability and rate capability, delivering reversible discharge capacities of 700 mA h/g at 200 mA/g, 572 mA h/g...

The Al–Co–Cr alloy system was studied by scanning and transmission electron microscopy, powder X-ray diffraction and differential thermal analysis. Partial isothermal sections of Al–Co–Cr were determined at 1150, 1100, 1000, 900, 800 and 700 °C. The region of the βCo-phase extends towards γCr up to ∼18.5 at.% Cr and ∼57 at.% Al. The solubility of Cr in HCo, MCo and Al9Co2 reaches ∼11.0, 6.0 and 1.5 at.%, respectively, while θCr-phase, μCr and γCr dissolve up to ∼3.0, 1.0 and 6.0 at.% Co, respectively. The ηCr phase extends up to ∼ Al74.5Co4Cr21.5. No ternary phases were revealed in Al–Co–Cr at 1100–1150 °C. Five ternary phases designated ζ1, O1, ν, ϕ and π were revealed. The ϕ-phase (P21 or P21/m, a ≈ 1.35, b ≈ 1.27, c ≈ 1.45 nm, β ≈ 100°) is formed between ∼ Al70.5Co8.0Cr21.5 and Al77.0Co7.5Cr15.5. The π-phase (C-center monocl., a ≈ 3.28, b ≈ 1.24, c ≈ 2.43 nm, β ≈ 108°) is formed between ∼ Al75.0Co11.5Cr13.5 and Al79.0Co11.5Cr9.5. The O1-phase (B-center orth., a ≈ 3.318, b ≈ 1.255, c ≈ 2.412 nm) is formed in a small region around ∼ Al72.5Co5.0Cr22.5. The ν-phase (P63/m, a = 4.0630, c = 1.2496 nm) is formed between ∼ Al75.5Co5.5Cr19 and Al81Co5.0Cr14. The ζ1-phase ( R 3 ¯ or R3, a ≈ 1.75, c ≈ 8.0 nm) is formed in a small region around ∼ Al80.5Co3.5Cr16.0.

Epitaxial thin films of (Ca,Ti) 2 (Nb,Ti) 2 O 7 with pyrochlore structure have been successfully fabricated on orthorhombic (1 1 0) NdGaO 3 substrates by a magnetron sputtering system. By analysis of selected-area electron diffraction patterns, the film-substrate orientation relationship is determined to be 〈0 0 1〉{1 0 0} film //[0 0 1](1 1 0) substrate . Atomic-scale structure investigations of the heterointerface by means of advanced electron microscopy reveal that a perovskite-type Ca(Ti,Nb)O 3 layer with a thickness of several unit cells forms between the (Ca,Ti) 2 (Nb,Ti) 2 O 7 films and the NdGaO 3 substrates. The formation of the Ca(Ti,Nb)O 3 layer results from the demand for accommodation of the crystal structure mismatching between the pyrochlore film and the perovskite-type substrate, which favors the epitaxial growth of the (Ca,Ti) 2 (Nb,Ti) 2 O 7 films on the NdGaO 3 substrates.

Epitaxial (Pr0.5Ba0.5MnO3)1−x:(CeO2)x (PBMO:CeO2, x = 0, 10%, 20%, 35%, and 50% stands for the molar ratio of the CeO2 secondary phase) vertically aligned nanocomposite (VAN) thin films were successfully fabricated on single crystalline (001) (La,Sr)(Al,Ta)O3 substrates by pulsed laser deposition. With increasing x, a structural transition induced by the vertical strain from the CeO2 secondary phase was observed at 20% ≤ x ≤ 35% by reciprocal space mapping. What's more, it is not only the enhancement of magnetoresistance that was observed but also the increasing magnetization. The maximum magnetization and magnetoresistance were achieved at x = 35%, which are almost 4.7 times (at 20 K) and 1.6 times (at 110 K) as high as those at x = 0%, respectively. Such great enhancement of magnetization can be attributed to the vertical strain induced structural transition. Our research indicates that the structural transition induced by the introduction of secondary phase CeO2 plays an important role in improving the magnetic and transport properties of VAN thin films.

Epitaxial Pr0.5Sr0.5CoO3 thin films have been grown on single-crystalline (La0.289Sr0.712)(Al0.633Ta0.356)O3(001) substrates by the pulsed laser deposition technique. The magnetic properties and microstructure of these films are investigated. It is found that Ruddlesden-Popper faults (RP faults) can be introduced in the films by changing the laser repetition rate. The segregation of Pr at the RP faults is characterized by atomic-resolution chemical mapping. The formation of the RP faults not only contributes to the epitaxial strain relaxation but also significantly decreases the ferromagnetic long-range order of the films, resulting in lower magnetizations than those of the fault-free films. Our results provide a strategy for tuning the magnetic properties of cobalt-based perovskite films by modifying the microstructure through the film growth process.

(In + Nb) co-doped TiO2 (TINO) films with a rutile structure have been prepared on m-plane sapphire substrates using a pulsed laser deposition method. The film growth mode and the atomic-scale microstructure of the TINO/sapphire heterostructure have been investigated by advanced electron microscopy techniques. The crystallographic orientation relationship of (001)[010]rutile//( 1 1 ¯ 00 )[0001]sapphire between the TINO films and the m-plane sapphire substrates has been determined. Across the TINO/sapphire interface, Ti(In,Nb)O6−octahedra connect AlO6−octahedra through either edge-sharing or corner-sharing. Misfit dislocations appear at the TINO/sapphire interface and contribute to epitaxial strain relaxation in the heterosystem. Additionally, two types of twins, (011)[100] and (031)[100], form within the films. Cation segregation occurs at the twin boundary and the TINO grain boundary. The findings here may provide a better understanding of the growth behaviors of the (In + Nb) co-doped rutile TiO2 films prepared on other types of substrates.

A high Mg-content AlSiMg1.4 alloy was designed for selective laser melting (SLM) processing. The SLMed AlSiMg1.4 alloy exhibits a high yield strength of 341±14 MPa and a high ultimate tensile strength of 518±6 MPa, along with a total elongation of 7.1±0.4%. The composition profile in the α-Al matrix of the alloy manifests in-phase concentration fluctuations of Mg and Si. The presence of high density Mg-Si atomic clusters as strong obstacles to dislocation gliding is suggested to provide an additional strengthening mechanism for the SLMed Al-Si-Mg alloy.

Nanoscaled HfO2-based ferroelectric thin films are a favored candidate for the integration of next-generation memory and logic devices. The unique advantage is that the ferroelectric polarization becomes more robust than the traditional perovskite ferroelectrics when the size is reduced. Understanding and controlling the ferroelectricity requires high-quality epitaxial thin films to explore intrinsic ferroelectric mechanism and evaluate device applications. Here, we report a semicoherent growth of ITO as a bottom electrode that enables genuine ultrathin epitaxial films of Si-doped HfO2 on YSZ[001]/[110]/[111] substrates. The deposited films, which are under epitaxial compressive strain, display large ferroelectric polarization values up to 42 μC/cm2 and do not need wake-up cycling. Structural characterization reveals the presence of crystalline domains with short axes of the tetragonal structure oriented perpendicular to the substrate. Using piezoforce microscopy, polar domains can be written and read and can be reversibly switched with a phase change of 180o. Ferroelectric polarization can be controlled by ITO surface polarity which can easily exploit the interfacial valance mismatch to influence the electrostatic potential across the interface. These findings have implications for our understanding of ferroelectric switching and offer easy method to manipulate domain reversal state in HfO2-based ferroelectric materials.

Pyrochlore-type (Ca,Ti)2(Nb,Ti)2O7 thin films have been grown on single-crystalline LaAlO3 and yttria-stabilized zirconia substrates by a magnetron sputtering system. Atomic-scale interface structure and growth mode of the (Ca,Ti)2(Nb,Ti)2O7 films on the substrates with different crystal structures have been investigated by advanced electron microscopy techniques. In both heterosystems, the film/substrate orientation relationship of [100](001)film//[100](001)substrate has been determined. In the heterosystem of (Ca,Ti)2(Nb,Ti)2O7/yttria-stabilized zirconia, the films directly grow on the substrates. In contrast, in the (Ca,Ti)2(Nb,Ti)2O7/LaAlO3 heterosystem, a perovskite-type Ca1-□(Ti,Nb)O3 interlayer with a few unit cells in thickness forms at the interface and interfacial reconstruction occurs at the (Ca,Ti)2(Nb,Ti)2O7/Ca1-□(Ti,Nb)O3 interface. Our findings indicate that the formation of the interlayer and the (Ca,Ti)2(Nb,Ti)2O7/Ca1-□(Ti,Nb)O3 interface reconstruction can accommodate the film/substrate dissimilarities in the crystal structures and facilitate the growth of single-crystalline pyrochlore-type films on the perovskite-type substrates.

Epitaxial films composed of (Y,Sr)CoO 3-δ and nano-scale Y 2 O 3 columns are successfully grown on (La 0.289 Sr 0.712 )(Al 0.633 Ta 0.356 )O 3 (001) substrates at 900 °C. The microstructural and electrical properties of the composite films are investigated and compared with those of the single-phase films prepared at 800 °C. In the composite films oxygen vacancies are detectable, which occur alternately in the stacking CoO 2-δ planes of (Y,Sr)CoO 3-δ . In addition, it is found that a large number of misfit dislocations distribute at the interfaces between the Y 2 O 3 columns and the (Y,Sr)CoO 3-δ film matrix. The measured resistivity of the composite films is significantly lower than that of the (Y,Sr)CoO 3-δ single-phase films. Our results indicate that the electrical properties of the perovskite-based cobaltates films can be tuned by changing the microstructure through controlling the film-growth temperature.

The occurrence of antiferromagnetic coupling at antiphase domain boundaries (APBs) of ferromagnetic materials holds potential applications for room-temperature spintronic devices. Here, we report formation mechanism and atomic-scale structure properties of APBs in α-Li 0.5 Fe 2.5 O 4 thin films on MgAl 2 O 4 (001) substrates investigated by means of aberration-corrected scanning transmission electron microscopy. The APBs in the α-Li 0.5 Fe 2.5 O 4 films are either conservative or non-conservative. Across the APBs the oxygen sublattice in α-Li 0.5 Fe 2.5 O 4 is maintained, while the stacking sequence of the cation sublattice is interrupted. The propagation of APBs is found to occur in a complex way within the ferromagnetic films, including the dissociation of APBs and the formation of kinks. Importantly, the density of APBs can be tuned by controlling the thickness of the α-Li 0.5 Fe 2.5 O 4 films since the APBs bound interfacial dislocations contributing to film-substrate strain relaxation. Our results evidence that the nano-scale APBs in the α-Li 0.5 Fe 2.5 O 4 films are controllable and stable, which could be promising candidates for applications in nano-spintronic devices.

We report a giant strain (0.72%) with a low degree of hysteresis (ca. 36.2%) and a giant Smax/Emax ratio (916 pm V−1, Smax and Emax denote the maximum strain and the corresponding electric field, respectively) for lead-free (1−x)(0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3)-xSr0.8Bi0.1□0.1Ti0.8Zr0.2O2.95 piezoceramics with x = 0.06. The giant strain originates from a reversible transition between the ergodic relaxor and ferroelectric states under applied electric fields. A-site vacancies (VA) and oxygen vacancies (VO), deliberately introduced to the system, induce a randomly distributed local polarization field. The local field induces embryonic polarization domains that have a broad distribution of maturity and thus smears the transition between the ferroelectric and relaxor states. This leads to a narrow hysteresis loop. The poling field required for the relaxor-to-ferroelectric transition is reduced significantly, due to the remanent ferroelectric phase at zero field acting as the seed, and the point defects synergistically facilitating the nucleation and growth of the ferroelectric phase. Our work provides a novel route for designing piezoelectric materials with both a giant strain and a narrow hysteresis for practical actuator applications.

The Al–Cu–Mn alloy system was studied above 45 at.% Al between 550 and 910 °C by scanning electron microscopy, powder X-ray diffraction and differential thermal analysis. A wide ternary region of the so-called β-phase extending along ∼50 at.% Al was confirmed. It has a CsCl-type structure with a ≈ 0.292–0.298 nm. The total γ 1 /γ 2 -region extends from Al–Mn up to ∼17 at.% Cu and the high-temperature T-Al 3 Mn phase ( Pnma , a ≈ 1.48, b ≈ 1.24, c ≈ 1.25 nm) extends up to ∼15 at.% Cu. The so-called R-phase ( Bbmm , a ≈ 2.41, b ≈ 1.25, c ≈ 0.76 nm) was found to exist in a compositional region of Al 74-80 Cu 5-12.5 Mn 12.5-18 . The ternary phase earlier reported at Al 57.9 Cu 26.3 Mn 15.8 was confirmed. It exists below 697 °C in a compositional region of Al 55-58 Cu 29-37 Mn 7.5-14 . The decagonal D 3 -phase was concluded to be stable in a compositional region of Al 61.5-68.5 Cu 19-29.5 Mn 9-16 . Below 631 °C an fcc phase ( a = 0.5814 nm) was revealed around ∼ Al 60 Cu 36.5 Mn 3.5 . Partial isothermal sections at 550, 600, 650, 750, 850 and 910 °C were constructed.

Whether or not the 3-dimensional surface morphologies of a crystal sample can be reconstructed at atomic-scale from a single 2-dimensional image becomes an interesting issue in high-resolution transmission electron microscopy, after the work by Jia et al. [1] . Here we propose an improved and self-validated algorithm to enhance such an electron tomography method and to make it applicable to more general crystal surfaces even with thin amorphous layers. Our study shows that a resolution in the beam (z) direction and a confidence level have to be defined and estimated after performing tomographic reconstruction in order to evaluate the quality and the reliability of its result. Applying the proposed procedure to the Si[110] image to recover the surface morphologies of a silicon crystal with amorphous contamination, the obtained results show that an atomic-resolution of 0.384 nm in the z-direction and a high confidence level of 95% are achieved for imaging the Si-surface structures, quantitatively described by tomographic parameters, i.e., the height (defocus) and the thickness (atom number) of Si-atomic columns.

The Al Mn alloy system contains complex intermetallics in its Al-rich part, and this was the first system where quasiperiodic structures were recognized. In the present work, the solubility of TMs (TM = Fe, Co, Ni, Cu, Zn and Pd) in the stable binaries, the stabilization effect of these elements on the metastable binaries and the formation of ternary compounds are specified and compared. While the solubility of all these TMs in hexagonal μ-Al 4 Mn and λ-Al 4 Mn is low, the high-temperature orthorhombic T-Al 3 Mn dissolves up to at least 14.5, 12, 16 and 7.5 at.% Fe, Cu, Zn and Pd, respectively. The metastable hexagonal φ-Al 10 Mn 3 is stabilized by Fe, Co and Ni in wide ternary compositional regions, and in Al Co Mn such a region propagates up to Al 5 Co 2 . In alloys with Fe, Co and Ni, a ternary hexagonal phase isostructural to the Al Cr Ni ζ-phase ( P 6 3 / m , a ≈ 1.76, c ≈ 1.25 nm) is formed along ∼80 at.% Al, while in alloys with Cu and Pd the orthorhombic so-called R-phase ( Bbmm , a ≈ 2.41, b ≈ 1.25, c ≈ 0.76 nm) was found at similar compositions. This structure is also known in Al Zn Mn but at much lower-Al Al 68 Zn 14.5 Mn 17.5 , while in the range of 75–80 at.% Al a monoclinic phase isostructural to η-Al 11 Cr 2 ( C 2/ c , a ≈ 1.76, b ≈ 3.04, c ≈ 1.76 nm, β ≈ 90°) is formed. In addition to the stable decagonal D 3 -phase in Al Fe Mn and Al Pd Mn reported earlier, the stabilization of binary Al Mn D 3 -phase was revealed around Al 64 Cu 20 Mn 16 .

Thin films of lead-free piezoelectric 0.95Na 0.5 Bi 0.5 TiO 3 –0.05BaTiO 3 (0.95NBT–0.05BT) are epitaxially grown on single crystalline SrTiO 3 (001) substrates at 800 °C, 850 °C and 900 °C, respectively, by a high-pressure sputtering deposition technique. The microstructure of the thin films is investigated by means of aberration-corrected scanning transmission electron microscopy. Planar defects are observed and the density of the defects increases with the increase of the film-growth temperature. Two types of planar defects in the films are studied at the atomic scale. One consists of groups of edge-sharing TiO 6 octahedra with Bi atoms located between the TiO 6 octahedral groups, and the other exists in the form of Na/Bi(Ba) O 2 Na/Bi(Ba) layer parallel to the (010) plane of the films. Based on the structure feature of the planar defects, the propagation of the planar defects related to edge-sharing TiO 6 octahedra within the films and from the film-substrate interface is discussed. Furthermore, the ordering of the planar defects is expected to form new structures. In comparison with the microstructure of 0.95NBT–0.05BT bulk materials, the appearance of the high-density planar defects observed within the films could be considered to be responsible for the difference in the physical properties between the bulk materials and the films.

Highly epitaxial thin films of copper ferrite (CuFe2O4) have been fabricated on MgAl2O4 (001) substrates at a growth temperature of 400 °C for the first time, we believe, through a radio-frequency sputtering method. Structural analyses through high-resolution X-ray diffraction (HRXRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) all confirm the tetragonal spinel phase of CuFe2O4 epitaxial film and high tetragonal distortion (c/a = 1.08) of its unit cells. The 50 nm-thick T-CuFe2O4 epitaxial film shows unique soft magnetism with small coercivity of 23 Oe and decreased magnetization. However, a superior ferromagnetic linewidth of only ∼93 Oe in the post-annealed T-CuFe2O4 film compared with a linewidth of ∼1500 Oe in T-CuFe2O4 single crystal bulk material is also observed, which indicates that epitaxial growth of oxide thin films combined with proper heat-treatment-induced cation engineering can impose novel functionalities.

Mn-rich Mn-Si binary alloys containing the ν phase have been prepared by arc-melting and rapid-quenching methods. In comparison, twins and polytypic stacking faults (SFs) are observed in the rapidly quenched ν phase, and the atomic-scale structure properties of twins and SFs have been determined by using aberration-corrected scanning transmission electron microscopy techniques. Both twins and SFs break the crystallographic symmetry of the ν phase, and lead to reconstruction of the subunits of the ν phase at twin boundaries and SFs. On the basis of experimental results, new structural models are proposed to explain the twin and SFs formation in the rapidly quenched ν phase.

The interfaces in oxide heterostructures that bring novel physical phenomena and functionalities have attracted great attention in fundamental research and device applications. For uncovering structure–property relationships of oxide heterostructures, direct evidence of the atomic-scale structure of heterointerfaces is highly desired. Here, we report on studying the structure of interfaces between YBa2Cu3O7-δ thin films and SrTiO3 substrates by means of aberration-corrected ultrahigh-resolution electron microscopy. Employing advanced imaging and spectroscopic techniques, shifts of atoms at the interface away from the regular lattice sites are measured, leading to the interfacial polarity. The local polarization induced by the atomic shifts directs toward the cuprate films and is estimated to be about 36.1 μC/cm2. The observed interfacial polar layer is understood by the special atomic configuration across the interface, which could modulate the electrical properties in superconducting devices that are based on the ferroelectric/superconductor heterosystems.

Precipitation behavior and its effect on mechanical properties in magnesium-based alloys are necessary to be explored at the atomic scale. Here microstructural properties of as-cast, cold-rolled and post-annealed Mg88Ni5Y7 (at%) alloys containing long-period stacking ordered (LPSO) phase have been investigated by advanced electron microscopy techniques. In comparison, cold-rolling of as-cast alloys leads to form kink boundaries within LPSO phase, and post-annealing of the cold-rolled alloys at different temperatures results in the formation of different types of precipitates at the kink boundaries, which affects the mechanical properties of the LPSO phase. Our findings provide a better understanding of microstructure evolutions of the deformed Mg88Ni5Y7 (at%) alloys subjected to annealing treatment, which is of great significance for the design and optimization of the magnesium-based alloys.

Lead-free 0.95(Na0.5Bi0.5)TiO3–0.05BaTiO3 (NBT-BT) piezoelectric films have been successfully fabricated by high-pressure magnetron sputtering deposition technique on (0 0 1)-oriented MgO substrates at 800 °C and 900 °C, respectively. By advanced electron microscopy techniques, the orientation relationship of (0 0 1)[1 1 0]film//(0 0 1)[1 0 0]MgO and (0 0 1)[1 0 0]film//(0 0 1)[1 0 0]MgO is determined for the NBT-BT/MgO heterostructures prepared at 800 °C and 900 °C, respectively. In comparison, a high density of zigzag-typed planar defects appear in the film prepared at 900 °C. At the semi-coherent interfaces, periodic dislocation arrays form to relax the film-substrate misfit strain. In particular, the formation of both (a/2) 〈0 1 0〉 -type and (a/2) 〈01 1 - 〉 -type interfacial dislocations facilitates the growth of NBT-BT films on rough MgO substrates at 900 °C. Our findings indicate that the mode of film growth and microstructure for NBT-BT films prepared on MgO substrates can be tuned by the growth temperature.

The magnetic and electrical properties of complex oxide thin films are closely related to the phase stability and cation ordering, which demands that we understand the process-structure-property relationships microscopically in functional materials research. Here we study multiferroic thin films of double-perovskite La2NiMnO6 epitaxially grown on SrTiO3, KTaO3, LaAlO3 and DyScO3 substrates by pulsed laser deposition. The effect of epitaxial strains imposed by the substrate on the microstructural properties of La2NiMnO6 has been systematically investigated by means of advanced electron microscopy. It is found that La2NiMnO6 films under tensile strain exhibit a monoclinic structure, while under compressive strain the crystal structure of La2NiMnO6 films is rhombohedral. In addition, by optimizing the film deposition conditions a long-range ordering of B-site cations in La2NiMnO6 films has been obtained in both monoclinic and rhombohedral phases. Our results not only provide a strategy for tailoring phase stability by strain engineering, but also shed light on tuning B-site ordering by controlling film growth temperature in double-perovskite La2NiMnO6 films.

In this study, the spinel solid solution ceramics (1−x)LiFe5O8–xLi2ZnTi3O8 (0 ≤ x ≤ 1) were prepared via the solid-state reaction method. The phase evolution, sintering behaviors, microstructures, magneto-dielectric properties, and microwave dielectric properties were systematically investigated. The XRD and SEM analysis indicated that the LiFe5O8 phase and the Li2ZnTi3O8 phase were almost fully soluble in each other at any proportion. Meanwhile, the evidence of ionic substitution has been directly observed at the atomic scale by means of scanning transmission electron microscopy, which is further confirmed by the Raman spectroscopy. Evidence shows that the magnetic and dielectric properties are quite sensitive to the compositions. The optimal results with remarkable magneto-dielectric properties of μ′ = 38.2, tanδμ = 0.25, e′ = 19.6, tanδe = 8 × 10−3 at 1 MHz, and e′ = 19.1, Q × f = 10 400 GHz at about 7 GHz have been obtained in 0.25LiFe5O8–0.75Li2ZnTi3O8 sample. The design of complex spinel solid solution can generate novel magneto-dielectric single-phase ceramics combining both high permeability and good dielectric properties, which provides a way in developing multifunctional materials for applications in electronic devices.

Epitaxial LiFe5O8 thin films with various thicknesses were fabricated on (001) MgAl2O4 substrates by using a high-pressure sputtering system. All the LiFe5O8 thin films have excellent epitaxial quality with ordered α-LiFe5O8 structure, and larger in-plane compressive and out-of-plane tensile strain can be obtained by decreasing the film thickness. Moreover, the in-plane compressive strain can significantly induce the enhancement of in-plane magnetization while the out-of-plane tensile strain tends to reduce the out-of-plane magnetization. It indicates that controlling the thickness of the films is an effective method to tailor the interface strain and further modify the magnetic properties of the epitaxial LiFe5O8 thin films.

We report on an investigation of state-of-the-art flux-grown multiferroic bismuth ferrite (BiFeO3; BFO) single crystals by transmission electron microscopy and electron diffraction. The crystals were pre-characterized by piezoresponse force microscopy, electrical resistance and superconducting quantum interference device magnetization measurements. The structurally highly perfect crystals show a ferroelectric stripe domain structure characterized by a domain width of 55 nm. Inside these domains an additional contiguous nanodomain substructure occurs, consisting of 180° related domains, giving rise to satellite reflections at 1 2 1 2 1 2 -type positions along 〈 1 1 0 〉 directions in the electron diffraction pattern corresponding to a characteristic length in real space of 15.5 nm. Furthermore, we present the first atomic-resolution study on the short-range order by aberration-corrected transmission electron microscopy in which all atoms including oxygen are imaged directly. By measuring the –Fe–O–Fe– atom topology, bond angles and atomic distances we derive the electrical dipole moment as well as the magnitude of the magnetic moment on the unit-cell level. The results evidence substantial atomic- to nano-scale disorder. Both the nanodomain substructure as well as the disorder should affect the subtle magnetoelectric interactions in this material and thereby impede the formation of long-range cycloidal spin ordering which up to now was considered an intrinsic feature of the magnetic properties of BiFeO3 single crystals. By Monte Carlo simulation on the basis of a state-of-the-art effective Hamiltonian we scrutinize certain aspects of the phase formation behavior in the BFO system forming the background of single-crystal growth. This study reveals a very sluggish phase evolution behavior, which should make it invariably difficult to obtain structurally fully equilibrated single crystals.

Graphene-based nanocomposites have been synthesized and tested as electrode materials for high power lithium-ion batteries. In the synthesis of such nanocomposites, graphene is generally introduced by either thermally or chemically reduced graphite oxide (GO), which has poorer electric conductivity and crystallinity than mechanically exfoliated graphene. Here, we prepare few-layer graphene sheet (FLGS) with high electric conductivity, by sonicating expanded graphite in DMF solvent, and develop a simple one-pot hydrothermal method to fabricate monodispersed and ultrasmall Co3O4 nanocubes (about 4 nm in size) on the FLGS. This composite, consisting of homogeneously assembled and high crystalline Co3O4 nanocubes on the FLGS, has shown higher capacity and much better cycling stability than counterparts synthesized using GO as a precursor. The products in different synthesis stages have been characterized by TEM, FTIR and XPS to investigate the nanocube growth mechanism. We find that Co(OH)2 initially grew homogeneously on the graphene surface, then gradually oxidized to form Co3O4 nanoparticle seeds, and finally converted to Co3O4 nanocubes with caboxylated anion as surfactant. This work explores the mechanism of nanocrystal growth and its impact on electrochemical properties to provide further insights into the development of nanostructured electrode materials for high power energy storage.