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Rare earth (RE) addition to steels to produce RE steels has been widely applied when aiming to improve steel properties. However, RE steels have exhibited extremely variable mechanical performances, which has become a bottleneck in the past few decades for their production, utilization and related study. Here in this work, we discovered that the property variation of RE steels stems from the presence of oxygen-based inclusions. We proposed a dual low-oxygen technology, and keeping low levels of oxygen content in steel melts and particularly in the raw RE materials, which have long been ignored, to achieve impressively stable and favourable RE effects. The fatigue life is greatly improved by only parts-per-million-level RE addition, with a 40-fold improvement for the tension-compression fatigue life and a 40% enhancement of the rolling contact fatigue life. We find that RE appears to act by lowering the carbon diffusion rate and by retarding ferrite nucleation at the austenite grain boundaries. Our study reveals that only under very low-oxygen conditions can RE perform a vital role in purifying, modifying and micro-alloying steels, to improve the performance of RE steels.

Revealing the magnetic coupling nature of boundary defects is crucial for in-depth understanding of the behavior and properties of magnetic materials and devices. Here, magnetite (i.e., Fe3O4) thin films were grown epitaxially on (100) SrTiO3 single-crystal substrates by pulsed laser deposition. Atomic-scale scanning transmission electron microscopy characterizations reveal that three types of antiphase boundaries (APBs) are formed in the Fe3O4 thin film. They are the (100) APB that is formed on the (100) plane with a crystal translation of (1/4)a[01 1 ¯ ], the type I and type II (110) APBs that are both formed on the (110) plane with the same crystal translation of (1/4)a[101] but different terminated atomic planes. The type I (110) APB is terminated at the atomic plane with mixed tetrahedral- and octahedral-sites Fe atoms, the type II (110) APB is terminated at the octahedral-site Fe plane. First-principles calculations reveal that the (100) APB and the type I (110) APB tend to form the ferromagnetic coupling that will not decrease the spin polarization of Fe3O4 films, while the type II (110) APB prefers to form the antiferromagnetic coupling that will degrade the magnetic properties. The magnetic coupling modes of the APBs are closely related to the Fe-O-Fe bond angles across the boundaries.

Screw dislocation is important not only for understanding plastic deformation of crystals but also for optical and electrical properties of materials. However, characterizations of screw dislocations are still challenging since there is almost no atom distortion when viewed along the dislocation line. In particular, although it is theoretically known that shear strains in heteroepitaxy systems may be relaxed via screw dislocation grids, the specific structures and thickness-dependent evolutions of these grids are still largely unknown. Here, by using orthorhombic [001]-oriented DyScO

Cold-drawn pearlitic steel wire is irreplaceably used in industry owing to its outstanding mechanical property which is dominated by the cementite/ferrite (Fe3C/Fe) interfaces in the material. However, the fine structures of the Fe3C/Fe interfaces in the deformed wires are less known to date. In this work, transmission electron microscopic investigation was performed on the atomic structures of the interfaces with the Isaichev orientation relationship (OR) in the wires with progressive deformation strains. In addition to the effect of the dislocation/interface interactions, this work revealed that the deformation-induced partial decomposition of cementite plays an important role in the interface reconstruction during deformation. The interfacial carbon vacancies generated by cementite decomposition and particularly, the amorphization of cementite layers in the sample with e > 1 could effectively annihilated the interfacial dislocations and consequently relaxed the interfacial stress. The correlations between the interface structure changes and the mechanical properties of the wires were discussed.

Flexoelectricity is an effective tool in modulating the crystallographic structures and properties of oxides for multifunctional applications. However, engineering the nonuniform strain to obtain tunable flexoelectric behaviors at the atomic scale remains an ongoing challenge in conventional substrate-imposed ferroelectric films. Here, the regulatable flexoelectric behaviors are demonstrated at atomic scale in [110]-oriented BiFeO3 thin films, which are triggered by the strain-field coupling of high-density interfacial dislocations. Using aberration-corrected scanning transmission electron microscopy, the asymmetric polarization rotation around the single dislocation is revealed, which is induced by the gradient strain fields of the single dislocation. These strain fields are highly correlated to generate huge strain gradients between neighboring dislocations, and thereby, serial flexoelectric responses are engineered as a function of dislocation spacings in thicker BiFeO3 films. This work opens a pathway for the modulation of flexoelectric responses in ferroelectrics, which could be extended to other functional materials to create exotic phenomena.

SrTiO3 is generally paraelectric with centrosymmetric structure exhibiting unique quantum fluctuation related ferroelectricity. Here we reveal highly polar and periodic polarization waves in SrTiO3 at room temperature, which is stabilized by periodic tensile strains in a sandwiched PbTiO3/SrTiO3/PbTiO3 structure. Scanning transmission electron microscopy reveals that periodic a/c domain structures in PbTiO3 layers exert unique periodic tensile strains in the ultrathin SrTiO3 layer and consequently make the highly polar and periodic states of SrTiO3. The as-received polar SrTiO3 layer features peak polar ion displacement of ∼0.01 nm and peak tetragonality of ∼1.07. These peak values are larger than previous results, which are comparable to that of bulk ferroelectric PbTiO3. Our results suggest that it is possible to integrate large and periodic strain state in oxide films with exotic properties, which in turn could be useful in optical applications and information addressing when used as memory unit.

Crystal defects play an important role in the degradation and failure of semiconductor materials and devices. Direct determination of band gap of defects is a critical step for clarifying how the defects affect the physical properties of semiconductors. Here, high-quality aluminum nitride (AlN) thin films were grown epitaxially on single-crystal Al

ε-Fe

Dislocations often exhibit unique physical properties distinct from those of the bulk material. However, functional applications of dislocations are challenging due to difficulties in the construction of high-performance devices of dislocations. Here we demonstrate unidirectional single-dislocation Schottky diode arrays in a Fe2O3 thin film on Nb-doped SrTiO3 substrates. Conductivity measurements using conductive atomic force microscopy indicate that a net current will flow through individual dislocation Schottky diodes under forward bias and disappear under reverse bias. Under cyclic bias voltages, the single-dislocation Schottky diodes exhibit a distinct resistive switching behavior containing low-resistance and high-resistance states with a high resistance ratio of ∼103. A combined study of transmission electron microscopy and first-principles calculations reveals that the Fe2O3 dislocations comprise mixed Fe2+ and Fe3+ ions due to O deficiency and exhibit a one-dimensional electrical conductivity. The single-dislocation Schottky diodes may find applications for developing ultrahigh-density electronic and memory devices.

Recently, the eutectic high-entropy alloy (EHEA), AlCoCrFeNi2.1, can reach a good balance of strength and ductility. The dual-phase alloy exhibits a eutectic lamellar microstructure with large numbers of interfaces. However, the role of the interfaces in plastic deformation have not been revealed deeply. In the present work, the orientation relationship (OR) of the interfaces has been clarified as the Kurdjumov-Sachs (KS) interfaces presenting 111 B 2 | | 110 F C C and 110 B 2 | | 111 F C C independent of their morphologies. There exist three kinds of interfaces in the EHEA, namely, (321)B2||(112)FCC, (01 1 ¯ )B2||(33 2 ¯ )FCC, and (23 1 ¯ )B2||(552)FCC. The dominating (321)B2||(112)FCC interface and the secondary (01 1 ¯ )B2||(33 2 ¯ )FCC interface are both non-slip planes and atomistic-scale faceted, facilitating the nucleation and slip transmission of the dislocations. The formation mechanism of the preferred interfaces is revealed using the atomistic geometrical analysis according to the criteria of the low interfacial energy based on the coincidence-site lattice (CSL) theory. In particular, the ductility of the dual-phase alloy originates from the KS interface-induced slip continuity across interfaces, which provides a high slip-transfer geometric factor. Moreover, the strengthening effect can be attributed to the interface resistance for the dislocation transmission due to the mismatches of the moduli and lattice parameters at the interfaces.

Understanding the interface between strengthening precipitates and matrix in alloys, especially at the atomic level, is a critical issue for tailoring the precipitate strengthening to achieve desired mechanical properties. Using high-resolution scanning transmission electron microscopy, we here clarify the semi-coherent interfaces between the matrix and long-period stacking ordered (LPSO) phases, including 18R and 14H, in Mg–Zn–Y alloys. The LPSO/Mg interface features the unique configuration of the Shockley partial dislocations, which produces a near zero macroscopic strain because the net Burgers vectors equal zero. The 18R/Mg interface characterizes a dissociated structure that can be described as a narrow slab of 54R. There are two dislocation arrays accompanied to the 18R/54R and 54R/Mg interface, resulting a slight deviation (about 2.3°). The 14R/Mg interface exhibits the dislocation pairs associated with solute atoms. We further evaluate the stability and morphology of the corresponding interfaces based on elastic interaction, via calculating the mutual strong interactions between dislocation arrays, as well as that between the dislocations and solute atoms. The synchronized migration of interfacial dislocations and solute atoms, like move-drag behavior, dominates the lateral growth of LPSO phases in Mg alloys.

Exotic domain-wall phenomena make ferroelectrics the candidates for nanoelectronics. The local symmetry and structure anomalies at domain walls have raised interest in the unusual functionalities, such as domain wall chirality and conductivity. Especially, the spontaneous lattice distortion and symmetry breaking at domain walls activate them as the location of structural transformation. However, the routes to achieve ferroelectric-antiferroelectric phase transition via ferroelectric domain walls remain challenging, which are important to develop materials for energy storage and conversion. Here, we have observed stepwise antiferroelectric phase transition in strained pure BiFeO3 ultrathin films derived from ferroelectric domain walls. Aberration-corrected transmission electron microscopy observation reveals that the resultant phase transition is mediated by dense 180° domain walls via providing the antiparallel cation displacement, cooperating with the enhanced interfacial oxygen octahedral clamping. First-principles calculations further confirm the critical role of interfacial oxygen octahedral coupling during this transition. These findings report an alternative route for antiferroelectric phase transition. Besides, our results provide fresh insights into functionalities of ferroelectric domain walls and open a venue for developing energy-storage materials based on domain engineering.

High-entropy alloys (HEAs) have displayed numerous unique features, however, high strength and high ductility are still the urgently desired mechanical property. The current study reports an outstanding combination of high strength and excellent ductility achieved in a eutectic high-entropy alloy (EHEA) AlCoCrFeNi2.1. The great achievement relays on a dual-phase heterogeneous structure strengthened with nano-precipitates. The heterogeneous structure provides the alloy a good combination of strength and ductility, and nano-precipitates in both of the face-centered cubic (FCC) and B2 phases generate an extra significant contribution to strength.

Retention failure is deleterious on ferroelectric domain stability, resulting in data loss in ferroelectric memories. However, the understanding of the origin of retention failure remains a challenge for the lack of a direct experimental evidence. Here, using a combination of piezoelectric force microscopy, atomic-scale scanning transmission electron microscopy and reciprocal space mapping, we report that the polarization retention failure is caused by a strain gradient induced flexoelectric field in tetragonal ferroelectric films. Atomic imaging reveals that the strain gradient is introduced by tensile strains, which is resultant from the vertically distributed Pb-rich anti-phase domains. This strain gradient couples with polarizations and results in flexoelectric fields in the films, leading to the retention failure in the films. Our study directly underlines the atomic mechanisms behind the strain gradient induced macroscopic retention failure behavior and clarifies the effect of local strain state on domain relaxation processes, thus can shed light on further understanding and improving the retention properties of oxide ferroelectrics.

Impurity defects are often involved in the growth of thin films by pulsed laser deposition (PLD), which is intrinsically a non-equilibrium process governed by competition between kinetics and therm...

Phase coexistence in ferroelectric oxide films displays complex phase competitions and transformation which suggest new multiple-coupled properties. Here we have successfully engineered the coexistence of flux-closure and a1/a2 phases in tensile-strained PbTiO3 films sandwiched between GdScO3 substrate and a SrTiO3 layer. Moreover, by using in-situ electron beam illumination, the unusual transformation from a1/a2 phase to the flux-closure phase was directly observed. In detail, there are two types of transformations: One is the nucleation, growth, and expansion of the flux-closure phase from the internal region of the a1/a2 phase. The other feature is a “dislocation gliding” like behavior: a thin lamella of a1/a2 shrinks like “partial dislocation pairs” and finally the gradually disappeared a1/a2 lamella forms a “perfect dislocation” in the flux-closure domain matrix. Phase-field simulations suggest that the a1/a2 to flux-closure transition is induced by the decrease of the depolarization field, which is screened by the injected electrons from electron beam irradiation. These results directly confirm the phase interconversion under an external stimulus at the nanometer scale, which shed new light on the fabrication of new polar textures.

Converse flexoelectricity is the mechanical strain induced by electric polarization gradients, which is largely omitted compared with the relatively well-known direct flexoelectricity. Thoroughly understanding the converse effect may not only explain peculiar structures generated by electric polarization or field gradients, but also stimulate new ideas to the design of novel electromechanical devices. In this work, the converse flexoelectricity around ferroelectric domain walls has been studied elaborately by synergetically integrating the aberration-corrected transmission electron microscope (TEM), first-principles calculations, and the Landau-Ginzburg-Devonshire (LGD) theory, taking prototypical tetragonal ferroelectric PbTiO3 as an example. We not only uncovered the important role of converse flexoelectricity on the asymmetric structure around 90° domain walls, but also quantified the flexoelectric coefficients. This quantification is deterministic in both the magnitude and sign of flexoelectric coefficients, by the mutual verification of the atomic mapping and first-principles calculations. Our results suggest that the converse flexoelectricity cannot be neglected for understanding ferroelectric DWs and other boundaries in ferroelectric materials.

A topological meron features a non-coplanar structure, whose order parameters in the core region are perpendicular to those near the perimeter. A meron is half of a skyrmion, and both have potential applications for information carrying and storage. Although merons and skyrmions in ferromagnetic materials can be readily obtained via inter-spin interactions, their behaviour and even existence in ferroelectric materials are still elusive. Here we observe using electron microscopy not only the atomic morphology of merons with a topological charge of 1/2, but also a periodic meron lattice in ultrathin PbTiO3 films under tensile epitaxial strain on a SmScO3 substrate. Phase-field simulations rationalize the formation of merons for which an epitaxial strain, as a single alterable parameter, plays a critical role in the coupling of lattice and charge. This study suggests that by engineering strain at the nanoscale it should be possible to fabricate topological polar textures, which in turn could facilitate the development of nanoscale ferroelectric devices. Merons are topological structures, but these have yet to be directly observed in ferroelectrics. Here, by epitaxially straining PbTiO3 on a SmScO3 substrate, electron microscopy and phase-field modelling allow the morphology and distribution of merons to be observed.

The physical properties of perovskite oxides are very sensitive to oxygen vacancy structures, and an unambiguous acquaintance of vacancy structures of thin films is the precondition for application...

Voids, helium bubbles and stacking fault tetrahedra (SFTs) are common irradiation-induced defects in face-centered cubic (FCC) metals and their alloys that have detrimental effects on their deformation behavior and lifetime. The formation mechanisms of voids and SFTs have been investigated in single crystals but the potential augmentation of these mechanisms by a heterophase interface has not been well studied. Here, using transmission electron microscopy (TEM), we report on the stability of both SFTs and voids at interfaces in an irradiated Cu/Ag nanolayered composite. With atomistic simulations, we show that the heterophase interface can promote the transformation of voids (

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

Multiferroic materials with multifunctional characteristics play a critical role in the field of microelectronics. In a perovskite oxide, ferroelectric polarization and ferromagnetism usually cannot coexist in a single-phase material at the same time. In this work, we design a superlattice structure composed of alternating BiFeO3 and BiMnO3 layers and illustrate how tuning the supercell size of epitaxial BiFeO3/BiMnO3 superlattices facilitates ferroelectric polarization while maintaining relatively strong ferromagnetism. A comprehensive investigation reveals that the enhanced ferroelectric polarization of BiMnO3 layers originates from the induction effect induced by a strong polarization field generated by the adjacent ferroelectric BiFeO3 layers. For the magnetic behavior, we consider the existence of interfacial antiferromagnetic superexchange interaction of Fe-O-Mn between BiFeO3 and BiMnO3 layers in our superlattices. This modulation effect of artificial superlattices provides a platform to accurately control the multiple order parameters in a multiferroic oxide system.

Significance Nacre exhibits outstanding mechanical performance, which results from coordinated deformation mechanisms synergistically working in characteristic microstructures at multiple length scales. A comprehensive understanding of crystal defects within aragonite is critical for discussing the deformation behavior of nacre on microstructure at the nanoscale through atomic scale. By integrating aberration-corrected transmission electron microscopy, crystallographic analysis, and theoretical calculations, we reveal various crystal defects within aragonite at atomic scale and discuss their potential effects on deformation. Our work will serve as cornerstones for modeling analysis and in-depth discussions on nanoscale deformation mechanisms within nacre. Additionally, these atomic-scale insights will benefit theoretical evaluation of the environmental effect on defect formation, enabling defect control in synthetic aragonite and designing of stronger and tougher bioengineering materials.

Coherent phase boundaries are widely expected as segregation-free boundaries due to their low interfacial energies and lack of trapping sites for impurities. Here, we report an equilibrium segregation of W atoms at fully coherent terraces of a Fe

SrTiO

Periodic arrays of electric dipole waves in ferroelectric oxides can be stabilized at room temperature by quenching., A dipole wave is composed of head-to-tail connected electric dipoles in the form of sine function. Potential applications in information carrying, transporting, and processing are expected, and logic circuits based on nonlinear wave interaction are promising for dipole waves. Although similar spin waves are well known in ferromagnetic materials for their roles in some physical essence, electric dipole wave behavior and even its existence in ferroelectric materials are still elusive. Here, we observe the atomic morphology of large-scale dipole waves in PbTiO3/SrTiO3 superlattice mediated by tensile epitaxial strains on scandate substrates. The dipole waves can be expressed in the formula of y = Asin (2πx/L) + y0, where the wave amplitude (A) and wavelength (L) correspond to 1.5 and 6.6 nm, respectively. This study suggests that by engineering strain at the nanoscale, it should be possible to fabricate unknown polar textures, which could facilitate the development of nanoscale ferroelectric devices.

B4C particulate-reinforced 6061Al composite was fabricated by powder metallurgy method. The as-rolled composite possesses high tensile strength which is comparable to that of the peak-aged 6061Al alloy. More importantly, the microstructures and mechanical properties are thermally stable during long-term holding at elevated temperature (400 °C). The microstructual contributions to the strength of the composite were discussed. Transmission electron microscopy (TEM) analysis indicates that the in-situ formed reinforcement Mg(Al)B2, as products of the interfacial reactions between B4C and the aluminum matrix, show not only good resistance to thermal coarsening but also strong pinning effect to the grain boundaries in the alloy matrix.

The multiple polarization states driven by polarization rotation could trigger giant piezoelectric responses in electromechanical sensors. Theoretically and experimentally, polarization rotation in...

Passive metals have superior resistance to general corrosion but are susceptible to pitting attack in certain aggressive media, leading to material failure with pronounced adverse economic and safety consequences. Over the past decades, the mechanism of pitting corrosion has attracted corrosion community striving to study. However, the mechanism at the pitting initiation stage is still controversy, due to the difficulty encountered in obtaining precise experimental information with enough spatial resolution. Tracking the accurate sites where initial dissolution occurs as well as the propagation of the dissolution by means of multi-scale characterization is key to deciphering the link between microstructure and corrosion at the atomic scale and clarifying the pitting initiation mechanism. Here, we review our recent progresses in this issue by summarizing the results in three representative materials of 316F, and Super 304H stainless steel as well as 2024-Al alloy, using in situ ex-environmental TEM technique.

In this work, we investigate the tensile strength and ductility of bulk Cu/Nb nanolaminates after exposure to high temperatures. We show that the interface transforms from flat to wavy at a transition temperature of 700 °C, and tensile strength is linearly proportional to H-1/2 (H = layer thickness). Moreover, the wavy interfaces give rise to a higher slope of the Hall-Petch law. This result can be attributed to greater resistance to slip transmission across wavy interfaces compared to planar interfaces. After 1000 °C for 1 h, the material still exhibits a high strength of 468 MPa and enhanced elongation.

Ferroelectric flux-closure domains have attracted great attention due to their potentials in high density data storage. For their future applications, it is important to understand their evolution with different factors, such as misfit strain. In this work, a flux-closure domain consisting of a vertical 180° domain wall with two symmetric a domains in both ends (“I” type closure) was observed in nearly unstrained SrTiO3/PbTiO3 multilayers by aberration corrected Transmission Electron Microscopy, which was speculated to be mainly induced by the strong depolarization field near the interface. With the tensile strain increasing, the small a domains in “I” type flux-closures grow gradually and eventually change to the well-known “V” type flux-closures. On the basis of a combination of experimental results and phase field simulations, the phase diagram of the stabilized domain arrays versus the strains in PbTiO3 films are established. These results provide significant information on understanding the formation mechanism of flux-closure domains and shed light on their controlled growth. In addition, it paves a way to reduce the economic cost in their commercial applications because the SrTiO3 substrate is easy to synthesize and much cheaper than scandate substrates.

Wurtzite boron nitride (w-BN) is a metastable superhard material that is a high-pressure polymorph of BN. Clarifying how the metastable high-pressure material can be stabilized at atmospheric pressure is a challenging issue of fundamental scientific importance and promising technological value. Here, we fabricate millimeter-size w-BN bulk crystals via the hexagonal-to-wurtzite phase transformation at high pressure and high temperature. By combining transmission electron microscopy and ab initio molecular dynamics simulations, we reveal a stabilization mechanism for w-BN, i.e., the metastable high-pressure phase can be stabilized by 3D networks of planar defects which are constructed by a high density of intersecting (0001) stacking faults and {10 [Formula: see text] 0} inversion domain boundaries. The 3D networks of planar defects segment the w-BN bulk crystal into numerous nanometer-size prismatic domains with the reverse crystallographic polarities. Our findings unambiguously demonstrate the retarding effect of crystal defects on the phase transformations of metastable materials, which is in contrast to the common knowledge that the crystal defects in materials will facilitate the occurrence of phase transformations.

Titanium with hexagonal close-packed (hcp) structure can undergo phase transformation to face-centered cubic (fcc) structure under mechanical straining at room temperature. In this work, we identified two orientation relationships (ORs) between fcc phase and hcp matrix in commercial pure Ti, i.e., P-type OR [ 1 ¯ 2 1 ¯ 0]hcp||[1 1 ¯ 0]fcc and (10 1 ¯ 0)hcp||(110)fcc, and B-type OR [ 1 ¯ 2 1 ¯ 0]hcp||[1 1 ¯ 0]fcc and (0001)hcp||( 1 ¯ 1 ¯ 1)fcc. The P-type interface is flat while the B-type interface is stepped, which are ascribed to the pure-shuffle mechanism and the partial gliding mechanism, respectively. Most intriguingly, the B-type fcc lamella can penetrate the P-type fcc lamella through gliding of the dislocation with Burgers vector ½[110] on (001)fcc plane.

High entropy alloys (HEAs) have presented potential applications in nuclear power plants owing to their novel atomic structure based high irradiation resistance. However, understanding of He-ion irradiation of HEAs is still lacking. In this work, we reveal He-ion irradiation resistance of HEA CrMnFeCoNi by comparison study with a pure Ni and a 304 stainless steel (304SS). It is found that the damage structure in the three materials can be characterized with He bubbles and stacking faults/stacking fault tetrahedrons ((SFs/SFTs), which show a similar depth distribution after He-ion irradiation at both RT and 450 °C. Although the He bubbles have a similar size about 2 nm after irradiation at RT, the He bubble sizes of the HEA, 304SS, and Ni increase to 4.0 ± 0.9, 5.3 ± 1.0 and 6.7 ± 1.0 nm after irradiation at 450 °C, respectively. Moreover, the density of SFs/SFTs displays in an order of Ni

Topological defects showing exotic properties and diverse functionalities provide us a potential utilization in nanoscale electronic devices. However, the formation mechanism and density manipulati...

The grain boundaries (GBs) of graphene and molybdenum disulfide have been extensively demonstrated to have a strong influence on electronic, thermal, optical, and mechanical properties. 2D transition-metal carbides (TMCs), known as MXenes, are a rapidly growing new family of 2D materials with many fascinating properties and promising applications. However, the GB structure of 2D TMCs and the influence of GB on their properties remain unknown. Here, we used aberration-corrected scanning transmission electron microscopy combined with electrical measurements to study the GB characteristic of highly crystalline 2D Mo2C superconductor, a newly emerging member of the 2D TMC family. The 2D Mo2C superconductor shows a unique tilt-angle-dependent GB structure and electronic transport properties. Different from the reported 2D materials, the GB of 2D Mo2C shows a peculiar dislocation configuration or sawtooth pattern depending on the tilt angle. More importantly, we found two new periodic GBs with different periodi...

Controlling domain width, orientation, and patterns in oxide ferroelectrics are not only important for fundamental research but also for potential electronic application. Here, a series of PbTiO3 thin films under various cooling rates were deposited on (110)-oriented NdScO3 substrates by pulsed laser deposition and investigated by using conventional transmission electron microscopy, Cs-corrected scanning TEM and piezoresponse force microscopy. Contrast analysis and electron diffraction revealed that PbTiO3 films are a1/a2 domain patterns under large tensile strains with different cooling rates. The a1/a2 domains distribute periodically and the domain width increases with decrease in the cooling rates. Upon increasing the cooling rate, the domain density increases and the domain configurations become complicated. There are special square frame-like domain patterns with charged domain walls found in the PTO films with the fast cooling rate. PFM measurement shows that the PTO films with high cooling rate exhibit enhanced piezoresponse behavior which is ascribed to the high density domain/domain walls and special domain configurations. The formation mechanism of the different domain configurations is discussed in terms of the effect of cooling rates, defects and thermal kinetics. These results are expected to provide useful information for domain/domain wall control and thus facilitate further modulation of the properties for potential applications.

Common pursuits of developing nanometric logic and neuromorphic applications have motivated intensive research studies into low-dimensional resistive random-access memory (RRAM) materials. However, fabricating resistive switching medium with inherent stability and homogeneity still remains a bottleneck. Herein, we report a self-assembled uniform biphasic system, comprising low-resistance 3 nm-wide (Bi0.4,La0.6)FeO3-δ nanosheets coherently embedded in a high-resistance (Bi0.2,La0.8)FeO3-δ matrix, which were spinodally decomposed from an overall stoichiometry of the (Bi0.24,La0.76)FeO3-δ parent phase, as a promising nanocomposite to be a stable and endurable RRAM medium. The Bi-rich nanosheets accommodating high concentration of oxygen vacancies as corroborated by X-ray photoelectron spectroscopy and electron energy loss spectroscopy function as fast carrier channels, thus enabling an intrinsic electroforming-free character. Surficial electrical state and resistive switching properties are investigated using multimodal scanning probe microscopy techniques and macroscopic I-V measurements, showing high on/off ratio (∼103) and good endurance (up to 1.6 × 104 cycles). The established spinodal decomposition-driven phase-coexistence BLFO system demonstrates the merits of stability, uniformity, and endurability, which is promising for further application in RRAM devices.

Quasicrystals have special crystal structures with long-range order, but without translational symmetry. Unexpectedly, carousel-like successive flippings of groups of atoms inside the ∼2 nm decagonal structural subunits of the decagonal quasicrystal Al

Quasicrystals have special crystal structures with long-range order, but without translational symmetry. Unexpectedly, carousel-like successive flippings of groups of atoms inside the ∼2 nm decagonal structural subunits of the decagonal quasicrystal Al60Cr20Fe10Si10 were directly observed using in situ high-temperature high-resolution transmission electron microscopy imaging. The observed directionally successive phason flips occur mainly clockwise and occasionally anticlockwise. The origin of these directional phason flips is analyzed and discussed.

La2Ti2O7 has recently received extensive interest due to its attractive ferroelectric and photocatalytic properties. Here, high-quality La2Ti2O7 thin films on (110) SrTiO3 substrates are prepared via oxidation of LaTiO3 thin films that are fabricated by pulsed-laser deposition. X-ray diffraction analyses reveal that the La2Ti2O7 thin film grows epitaxially on the (110) SrTiO3 substrate and has a good crystallinity. Atomic force microscopy investigations suggest that the surface of La2Ti2O7 thin film turns into a stepped and terraced structure after the annealing. X-ray photoelectron spectroscopy analyses indicate that the La2Ti2O7 thin film has a high purity and contain only Ti4+ ions (i.e., without Ti3+ ions). The band gap of the La2Ti2O7 film is measured to be ∼ 3.2 eV by UV-visible spectra. Atomic and electronic structures of the La2Ti2O7/SrTiO3 heterointerface have been studied by a combination of transmission electron microscopy and first-principles calculations. The La2Ti2O7/SrTiO3 heterointerface is atomically abrupt and coherent. Electronically, this heterointerface contributes to the decrease of band gap in the La2Ti2O7 film. The reduction of spontaneous polarization in La2Ti2O7 is localized in two layers of TiO6 octahedra near the interface due to the discontinuous Ti-O bonds between the perovskite layers of La2Ti2O7.

Multiferroic materials with multifunctional characteristics play a critical role in the field of microelectronics. In a perovskite oxide, ferroelectric polarization and ferromagnetism usually cannot coexist in a single-phase material at the same time. In this work, we design a superlattice structure composed of alternating BiFeO