Intrinsic-strain-induced ferroelectric order and ultrafine nanodomains in SrTiO3.

Nano ferroelectrics holds the potential application promise in information storage, electro-mechanical transformation, and novel catalysts but encounters a huge challenge of size limitation and manufacture complexity on the creation of long-range ferroelectric ordering. Herein, as an incipient ferroelectric, nanosized SrTiO3 was indued with polarized ordering at room temperature from the nonpolar cubic structure, driven by the intrinsic three-dimensional (3D) tensile strain. The ferroelectric behavior can be confirmed by piezoelectric force microscopy and the ferroelectric TO1 soft mode was verified with the temperature stability to 500 K. Its structural origin comes from the off-center shift of Ti atom to oxygen octahedron and forms the ultrafine head-to-tail connected 90° nanodomains about 2 to 3 nm, resulting in an overall spontaneous polarization toward the short edges of nanoparticles. According to the density functional theory calculations and phase-field simulations, the 3D strain-related dipole displacement transformed from [001] to [111] and segmentation effect on the ferroelectric domain were further proved. The topological ferroelectric order induced by intrinsic 3D tensile strain shows a unique approach to get over the nanosized limitation in nanodevices and construct the strong strain-polarization coupling, paving the way for the design of high-performance and free-assembled ferroelectric devices.

Decoding Active Sites for Highly Efficient Semihydrogenation of Acetylene in Palladium-Copper Nanoalloys.

Accurately decoding the three-dimensional atomic structure of surface active sites is essential yet challenging for a rational catalyst design. Here, we used comprehensive techniques combining the pair distribution function and reverse Monte Carlo simulation to reveal the surficial distribution of Pd active sites and adjacent coordination environment in palladium-copper nanoalloys. After the fine-tuning of the atomic arrangement, excellent catalytic performance with 98% ethylene selectivity at complete acetylene conversion was obtained in the Pd34Cu66 nanocatalysts, outperforming most of the reported advanced catalysts. The quantitative deciphering shows a large number of active sites with a Pd-Pd coordination number of 3 distributed on the surface of Pd34Cu66 nanoalloys, which play a decisive role in highly efficient semihydrogenation. This finding not only opens the way for guiding the precise design of bimetal nanocatalysts from atomic-level insight but also provides a method to resolve the spatial structure of active sites.

High-Entropy Magnet Enabling Distinctive Thermal Expansions in Intermetallic Compounds.

The high-entropy strategy has gained increasing popularity in the design of functional materials due to its four core effects. In this study, we introduce the concept of a "high-entropy magnet (HEM)", which integrates diverse magnetic compounds within a single phase and is anticipated to demonstrate unique magnetism-related properties beyond that of its individual components. This concept is exemplified in AB2-type layered Kagome intermetallic compounds (Ti,Zr,Hf,Nb,Fe)Fe2. It is revealed that the competition among individual magnetic states and the presence of magnetic Fe in originally nonmagnetic high-entropy sites lead to intricate magnetic transitions with temperature. Consequently, unusual transformations in thermal expansion property (from positive to zero, negative, and back to near zero) are observed. Specifically, a near-zero thermal expansion is achieved over a wide temperature range (10-360 K, αv = -0.62 × 10-6 K-1) in the A-site equal-atomic ratio (Ti1/5Zr1/5Hf1/5Nb1/5Fe1/5)Fe2 compound, which is associated with successive deflection of average Fe moments. The HEM strategy holds promise for discovering new functionalities in solid materials.

Advances on T cell immunity in bone remodeling and bone regeneration. / Tç»†èƒžå ç–«åœ¨éª¨é‡å»ºå’Œéª¨å†ç”Ÿä¸­çš„ç ”ç©¶è¿›å±•.

Bone remodeling and bone regeneration are essential for preserving skeletal integrity and maintaining mineral homeostasis. T cells, as key members of adaptive immunity, play a pivotal role in bone remodeling and bone regeneration by producing a range of cytokines and growth factors. In the physiological state, T cells are involved in the maintenance of bone homeostasis through interactions with mesenchymal stem cells, osteoblasts, and osteoclasts. In pathological states, T cells participate in the pathological process of different types of osteoporosis through interaction with estrogen, glucocorticoids, and parathyroid hormone. During fracture healing for post-injury repair, T cells play different roles during the inflammatory hematoma phase, the bone callus formation phase and the bone remodeling phase. Targeting T cells thus emerges as a potential strategy for regulating bone homeostasis. This article reviews the research progress on related mechanisms of T cells immunity involved in bone remodeling and bone regeneration, with a view to providing a scientific basis for targeting T cells to regulate bone remodeling and bone regeneration.

Interplanar Ferromagnetism Enhanced Ultrawide Zero Thermal Expansion in Kagome Cubic Intermetallic (Zr,Nb)Fe2.

A cubic metal exhibiting zero thermal expansion (ZTE) over a wide temperature window demonstrates significant applications in a broad range of advanced technologies but is extremely rare in nature. Here, enabled by high-temperature synthesis, we realize tunable thermal expansion via magnetic doping in the class of kagome cubic (Fd-3m) intermetallic (Zr,Nb)Fe2. A remarkably isotropic ZTE is achieved with a negligible coefficient of thermal expansion (+0.47 × 10-6 K-1) from 4 to 425 K, almost wider than most ZTE in metals available. A combined in situ magnetization, neutron powder diffraction, and hyperfine Mössbauer spectrum analysis reveals that interplanar ferromagnetic ordering contributes to a large magnetic compensation for normal lattice contraction upon cooling. Trace Fe-doping introduces extra magnetic exchange interactions that distinctly enhance the ferromagnetism and magnetic ordering temperature, thus engendering such an ultrawide ZTE. This work presents a promising ZTE in kagome metallic materials.

Ferroelectric Ordering in Nanosized PbTiO3.

The insight into the three-dimensional configuration of ferroelectric ordering in ferroelectric nanomaterials is motivated by the application of the development of functional nanodevices and the structural designing. However, the atomic deciphering of the spatial distribution of ordered structure remains challenging for the limitation of dimension and probing techniques. In this paper, a neutron pair distribution function (nPDF) was utilized to analyze the spontaneous polarization distribution of zero-dimensional PbTiO3 nanoparticles in three dimensions, via the application of reverse Monte Carlo (RMC) modeling. The comprehensive identification with transmission electron microscopy verified the linear characteristics of polarization along the c-axis in the main body, while electric polarization distribution on the surface was enhanced abnormally. In addition, the correlation of dipole vectors extending to three unit cells below the surface is retained. This work shows an application of the micro/macroscale information to effectively decode the polarization structure of nanoferroelectrics, providing new views of designing nanoferroelectric devices.

Local Structure Insight into Hydrogen Evolution Reaction with Bimetal Nanocatalysts.

The revelation of the atomic 3D structure of sub-5 nm bimetal nanocatalysts challenges the limitations of conventional methods. Notably, the identification of the cooperative relationship between the active sites and nearby coordination environment during catalytic reactions depends on the stereo distribution of local phases and chemical composition within a short range. As a model nanocatalyst in our investigation, we studied the ordered PtFe bimetals in hydrogen evolution reactions (HER). By combining pair distribution functions with reverse Monte Carlo, local-range phase symmetry, chemical composition, and atom distribution were determined. The segregation of local phase segments as disordered Pt-rich A1 and Pt3Fe L12 phases can be attributed to the marked improvement of HER activity and stability in Pt56Fe44. Following the etching of the outermost-surface Fe, the remaining disordered segregation offered a large number of active Pt sites for discharge and electrochemical desorption reactions. It resulted in local-bonding Pt pairs that made it easier for adsorbed hydrogen atoms to recombine. The current research will provide structural insight into the local range for bimetal nanocatalysts and be valuable for the creation of new, low-cost nanocatalysts.

Effects of Subsurface Oxide on Cu1/CeO2 Single-Atom Catalysts for CO Oxidation: A Theoretical Investigation.

Supported atomic dispersion metals are of great interest, and the interfacial effect between isolated metal atoms and supports is crucial in heterogeneous catalysis. Herein, the behavior of single-atom Cu catalysts dispersed on CeO2 (100), (110), and (111) surfaces has been studied by DFT + U calculations. The interactions between ceria crystal planes and isolated Cu atoms together with their corresponding catalytic activities for CO oxidation are investigated. The CeO2 (100) and (111) surfaces can stabilize active Cu+ species, while Cu exists as Cu2+ on the (110) surface. Cu+ is certified as the most active site for CO adsorption, which can promote the formation of the reaction intermediates and reduce reaction energy barriers. For the CeO2 (100) surface, the interaction between CO and Cu is weak and the CO adsorbate is more likely to activate the subsurface oxygen. The catalytic performance is closely related to the binding strength of CO to the active Cu single atoms on the different subsurfaces. These results bring a significant insight into the rational design of single metal atoms on ceria and other reducible oxides.

Two-Dimensional Negative Thermal Expansion in a Facile and Low-Cost Oxalate-Based Metal-Organic Framework.

Two-dimensional negative thermal expansion (NTE) is achieved in a tetragonal oxalate-based metal-organic framework (MOF), CdZrSr(C2O4)4, within a temperature range from 123 to 398 K [space group I4̅m2, αa = -2.4(7) M K-1, αc = 11.3(3) M K-1, and αV = 6.4(1) M K-1]. By combining variable-temperature X-ray diffraction, a high-resolution synchrotron X-ray pair distribution function, and thermogravimetry-differential scanning calorimetry, we shows that NTE within the ab plane derives from the oriented rotation of an oxalate ligand in zigzag chains (-CdO8-ox-ZrO8-ox-)∞. That is simplified to the Zr atom rotating with an unchanged Zr···Cd distance as the radius, which also gives rise to the deformation of a hingelike connection along the c axis and results in its positive thermal expansion. By virtue of the facile and low-cost oxalate ligand, the present NTE MOF may show application prospects in the future.

Chemical-Pressure-Modulated BaTiO3 Thin Films with Large Spontaneous Polarization and High Curie Temperature.

Although BaTiO3 is one of the most famous lead-free piezomaterials, it suffers from small spontaneous and low Curie temperature. Chemical pressure, as a mild way to modulate the structures and properties of materials by element doping, has been utilized to enhance the ferroelectricity of BaTiO3 but is not efficient enough. Here, we report a promoted chemical pressure route to prepare high-performance BaTiO3 films, achieving the highest remanent polarization, Pr (100 µC/cm2), to date and high Curie temperature, Tc (above 1000 °C). The negative chemical pressure (∼-5.7 GPa) was imposed by the coherent lattice strain from large cubic BaO to small tetragonal BaTiO3, generating high tetragonality (c/a = 1.12) and facilitating large displacements of Ti. Such negative pressure is especially significant to the bonding states, i.e., hybridization of Ba 5p-O 2p, whereas ionic bonding in bulk and strong bonding of Ti eg and O 2p, which contribute to the tremendously enhanced polarization. The promoted chemical pressure method shows general potential in improving ferroelectric and other functional materials.

Ultrawide Temperature Range Super-Invar Behavior of R_{2}(Fe,Co)_{17} Materials (R = Rare Earth).

Super Invar (SIV), i.e., zero thermal expansion of metallic materials underpinned by magnetic ordering, is of great practical merit for a wide range of high precision engineering. However, the relatively narrow temperature window of SIV in most materials restricts its potential applications in many critical fields. Here, we demonstrate the controlled design of thermal expansion in a family of R_{2}(Fe,Co)_{17} materials (R=rare Earth). We find that adjusting the Fe-Co content tunes the thermal expansion behavior and its optimization leads to a record-wide SIV with good cyclic stability from 3-461 K, almost twice the range of currently known SIV. In situ neutron diffraction, Mössbauer spectra and first-principles calculations reveal the 3d bonding state transition of the Fe-sublattice favors extra lattice stress upon magnetic ordering. On the other hand, Co content induces a dramatic enhancement of the internal molecular field, which can be manipulated to achieve "ultrawide" SIV over broad temperature, composition and magnetic field windows. These findings pave the way for exploiting thermal-expansion-control engineering and related functional materials.

Zero Thermal Expansion and Strong Covalent Binding of VB2 Compound.

Zero thermal expansion (ZTE) is an intriguing phenomenon by virtue of its peculiar lack of expansion and contraction with temperature. The achievement of ZTE in a metallic material is a desired but challenging task. Here we report the ZTE behavior of a single-phase metallic VB2 compound, stacking with the V and B atomic layers along the c direction (αV = 2.18 × 10-6 K-1, 5-150 K). Neutron powder diffraction demonstrates that the ZTE behavior is entangled in the direct blocking of the lattice expansion along all crystallographic directions with temperature. X-ray photoelectron spectroscopy and density functional theory calculations indicate that strong covalent binding adheres the nearest-neighbor B-B and V-B pairs, which is proposed to control the ZTE within both the basal plane and the c direction. An intimate correlation is revealed between the covalent binding and the lattice parameters. Our work indicates the opportunity to design metallic ZTE with strong chemical binding in the future.

Strong Second Harmonic Generation in a Tungsten Bronze Oxide by Enhancing Local Structural Distortion.

To discover the nonlinear optical (NLO) materials with strong second harmonic generation (SHG), the design of NLO-active molecular units with large polarization is considered as a common strategy. Herein, we propose that the local structural distortion induced with vacancies, apart from the NLO-active units, can be employed to improve the NLO effect in solids as well. Accordingly, a new tungsten bronze (TB) oxide, Pb2(Pb0.15Li0.7□0.15)Nb5O15 (□ representing vacancies), is successfully designed and prepared, which exhibits a strong SHG response of 39 times that of KH2PO4. The detailed analysis reveals that the local structural distortions enhanced by the vacancies in PLN strengthen the local dipole moments of neighboring NbO6 octahedra, and thus significantly prompt the SHG effect. Moreover, a series of new TB compounds with large NLO effects are discovered by this molecular design strategy, which are perspectives for new NLO materials synthesis.

Role of "Dumbbell" Pairs of Fe in Spin Alignments and Negative Thermal Expansion of Lu2Fe17-Based Intermetallic Compounds.

Knowledge of negative thermal expansion (NTE) is an interesting issue in the field of materials science and engineering. It has been proposed that the unique dumbbell pairs of Fe (dumbbells) are highly entangled in the NTE behaviors of R2Fe17 (R = rare earth) compounds but still remain controversial. Here, a facile method is employed to explore the role of dumbbells in spin alignments and NTE by the nonstoichiometric design of Lu2-xFe17 compounds. The powder synchrotron X-ray diffraction, magnetometry, and neutron powder diffraction investigations indicate that a decrease of the Lu content can enhance the dumbbell concentration and motivate an incommensurate magnetic structure simultaneously. However, increasing the dumbbell concentration makes little difference in the amplitude of the ordered magnetic moments of Fe sublattices, which reveals an equivalent NTE behavior for Lu2-xFe17 compounds. This work gives insight into the role that dumbbells played in spin alignments and NTE for Lu2Fe17-based compounds, correcting the previously proposed conjecture and probably conducive to adjusting the related magnetic performances of R2Fe17 compounds in the future.

Manipulating Spin Alignments of (Y,Lu)1.7Fe17 Intermetallic Compounds via Unusual Thermal Pressure.

External pressure has been successfully employed to achieve desirable spin alignments in the field of materials science but is seriously restricted by the difficulty of reaching high pressure with conventional methods. The search for simple and effective ways to apply pressure on the lattice is challenging but intriguing. Here we report a new strategy to manipulate the spin alignments of (Y,Lu)1.7Fe17 intermetallic compounds through unusual thermal pressure. The spin alignments of Fe initially lie parallel inside the basal plane and then turn spirally between adjacent layers with a zone axis along the c direction under higher Lu concentration. The synchrotron and neutron powder diffraction investigations clearly reveal that the direction of spin alignments is highly correlated to large lattice contraction induced by negative thermal expansion (NTE), an unusual thermal pressure, along the c direction. The critical lattice parameter c to form spiral spin alignments is determined unambiguously. This work presents a feasible way to adjust spin alignments through NTE, which might be conducive to the future design of particular spin alignments instead of physical pressure for functional magnetic materials.

Negative Thermal Expansion in (Hf,Ti)Fe2 Induced by the Ferromagnetic and Antiferromagnetic Phase Coexistence.

Negative thermal expansion (NTE) is an intriguing physical phenomenon that can be used in the applications of thermal expansion adjustment of materials. In this study, we report a NTE compound of (Hf,Ti)Fe2, while both end members of HfFe2 and TiFe2 show positive thermal expansion. The results reveal that phase coexistence is detected in the whole NTE zone, in which one phase is ferromagnetic (FM), while the other is antiferromagnetic (AFM). With increasing temperature, the FM phase is gradually transformed to the AFM one. The NTE phenomenon occurs in the present (Hf,Ti)Fe2 because of the fact that the unit cell volume of the AFM phase is smaller than that of the FM phase, and the mass fraction of the AFM phase increases with increasing temperature. The construction of phase coexistence can be a method to achieve NTE materials in future studies.

Neutron Diffraction Study of Unusual Magnetic Behaviors in the Ho2Fe11Al6 Intermetallic Compound.

Knowledge of structure-property relationships is fundamental but significant in the exploitation of magnetic materials. Here we report that the high Al substitution for Fe transformed the crystal structure from a hexagonal Ho2Fe17 compound to a rhombohedral Ho2Fe11Al6 compound. Intriguingly, the latter shows unusual evolution of magnetization around 86 and 220 K compared with the former. Integrated investigations of the detailed structure analysis and magnetic performance on the Ho2Fe11Al6 compound demonstrate that the Ho2Fe11Al6 compound possesses a stable rhombohedral structure (R3̅m) from 5 to 430 K with preferred occupation of Al atoms and ferrimagnetic structure in which the magnetic moments of Ho and Fe lie antiparallel in the basal plane below the Curie temperature. The results of the temperature dependence of moments reveal that the disparate rates of change of the moments for Ho and Fe sublattices give rise to unusual evolution of magnetization around 86 and 220 K and then turn to paramagnetic above 280 K. This work provides clear structure and magnetization information on the Ho2Fe11Al6 compound, which may be beneficial to guiding the future development of magnetic materials.

Twin Crystal Induced near Zero Thermal Expansion in SnO2 Nanowires.

Knowledge of controllable thermal expansion is a fundamental issue in the field of materials science and engineering. Direct blocking of the thermal expansions in positive thermal expansion materials is a challenging but fascinating task. Here we report a near zero thermal expansion (ZTE) of SnO2 achieved from twin crystal nanowires, which is highly correlated to the twin boundaries. Local structural evolutions followed by pair distribution function revealed a remarkable thermal local distortion along the twin boundary. Lattice dynamics investigated by Raman scattering evidenced the hardening of phonon frequency induced by the twin crystal compressing, giving rise to the ZTE of SnO2 nanowires. Further DFT calculation of Grüneisen parameters confirms the key role of compressive stress on ZTE. Our results provide an insight into the thermal expansion behavior regarding to twin crystal boundaries, which could be beneficial to the applications.

Localized Symmetry Breaking for Tuning Thermal Expansion in ScF3 Nanoscale Frameworks.

The local symmetry, beyond the averaged crystallographic structure, tends to bring unusual performances. Negative thermal expansion is a peculiar physical property of solids. Here, we report the delicate design of the localized symmetry breaking to achieve controllable thermal expansion in ScF3 nanoscale frameworks. Intriguingly, an isotropic zero thermal expansion is concurrently engineered by localized symmetry breaking, with a remarkably low coefficient of thermal expansion of about +4.0 × 10-8/K up to 675 K. This mechanism is investigated by the joint analysis of atomic pair distribution function of synchrotron X-ray total scattering and extended X-ray absorption fine structure spectra. A localized rhombohedral distortion presumably plays a critical role in stiffening ScF3 nanoscale frameworks and concomitantly suppressing transverse thermal vibrations of fluorine atoms. This physical scenario is also theoretically corroborated by the extinction of phonon modes with negative Grüneisen parameters in rhombohedral ScF3. The present work opens an untraditional chemical modification route to achieve controllable thermal expansion by breaking local symmetries in materials.

A New Insight into Cross-Sensitivity to Humidity of SnO2 Sensor.

The efficiency of gas sensors varies enormously from fundamental study to practical application. This big gap comes mainly from the complex and unpredictable effect of atmospheric environment, especially in humidity. Here, the cross-sensitivity to humidity of a SnO2 sensor from local structural and lattice evolutions is studied. The sensing response of ethanol is found to be efficiently activated by adsorbing trace of water but inhibited as humidity increases. By X-ray diffraction, pair distribution function of synchrotron and ab initio calculations, the independent effect of water and ethanol on lattice and local structure are clearly revealed, which elucidate the intricate sensing reactions. The formation of hydrogen bonds and repulsion of ethoxides play key roles in the structural distortions, and also in adsorption energies that are critical to the sensitive behavior. The results show the sensor performance coupled with local structural evolution, which provides a new insight into the controversial effects of humidity on SnO2 sensors.