Modern Functional Materials Research Articles

Highly Anisotropic Tip-Induced Domain Growth in Polydomain Triglycine Sulfate

Ferroelectrics are widely used as modern functional materials for nonlinear optics, optoelectronics, nonvolatile data storage, and nanoelectronics. Most of these applications require creation of precise micron-scale domain patterns. We have studied the current limited wall motion regime driven by anisotropic bulk screening processes during local switching in polydomain triglycine sulfate single crystals. The field application using a conductive tip of a scanning probe microscope (SPM) in a dry atmosphere resulted in formation of a partially switched area, strongly elongated in the c crystallographic direction. At the same time, switching at high humidity led to a circular shape of the area. The calculation of the spatial distribution of the external field demonstrated the possibility of domain wall shift at distances up to hundreds of microns from the SPM tip. However, after external field switch-off the depolarization field in nonscreened areas led to reverse domain wall motion. Thus, the domain wall stabilization is possible only in the regions with sufficient screening of the depolarization field. We have shown that the growth of the area size with time obeys the same current-limited wall motion expressions that were derived previously for domain growth during local switching by a highly resistive electrode. The change in the area shape with humidity was attributed to the change in the governing screening mechanism from anisotropic bulk conductivity to isotropic surface conductivity through an adsorbed water layer. The obtained results demonstrate the essential role of the screening processes during periodical poling and pave the way for further improvement of the domain engineering methods.

Hidden Local Symmetry Breaking in a Kagome-Lattice Magnetic Weyl Semimetal.

Exploring the relationship between intriguing physical properties and structural complexity is a central topic in studying modern functional materials. Co3Sn2S2, a newly discovered kagome-lattice magnetic Weyl semimetal, has triggered intense interest owing to the intimate coupling between topological semimetallic states and peculiar magnetic properties. However, the origins of the magnetic phase separation and spin glass state below TC in this ordered compound are two unresolved yet important puzzles in understanding its magnetism. Here, we report the discovery of local symmetry breaking surprisingly co-emerges with the onset of ferromagnetic order in Co3Sn2S2, by a combined use of neutron total scattering and half-polarized neutron diffraction. An anisotropic distortion of the cobalt kagome lattice at the atomic/nano level is also found, with distinct distortion directions among the two Co1 and four Co2 atoms. The mismatch of local and average symmetries occurs below TC, indicating that Co3Sn2S2 evolves to an intrinsically lattice disordered system when the ferromagnetic order is established. The local symmetry breaking with intrinsic lattice disorder provides new understanding of the puzzling magnetic properties. Our density functional theory (DFT) calculation indicates that the local symmetry breaking is expected to reorient local ferromagnetic moments, unveiling the existence of the ferromagnetic instability associated with the lattice instability. Furthermore, DFT calculation unveils that the local symmetry breaking could affect the Weyl property by breaking the mirror plane. Our findings highlight the fundamentally important role that the local symmetry breaking plays in advancing our understanding on the magnetic and topological properties in Co3Sn2S2, which may draw attention to explore the overlooked local symmetry breaking in Co3Sn2S2, its derivatives and more broadly in other topological Dirac/Weyl semimetals and kagome-lattice magnets.

Synthesis of Semiconductor Nanosized Composite Photocatalyst

Every day, composites become an important part of modern functional materials not only due to their complex structure, but also unique new properties. Nanoarchitectonics is a new field that concerns the design and transformation of nanostructures into functional materials at the nanoscale level [1-3]. A composite material is a combination of two or more materials that provides better properties than its individual components [4-5].This paper presents the results of the synthesis of the TiO2-ZnO nanocomposite, as well as the experimental results of the study of some of its properties. The method of precipitation using a reducing agent with intermediate precipitation of zinc hydroxides on the surface of industrial titanium (IV) oxide and their subsequent heat treatment was used for the synthesis of TiO2-ZnO (1:3).The obtained SEM image is presented in Fig and shows that the particles of the synthesized TiO2-ZnO composite have the shape of flakes, which are easily agglomerated into aggregates of complex shapes and different sizes. The electronic image also shows that the individual separated particles have the size which is less than 0.1μm (100 nm), i.e. are in the nanometer range.In order to determine the optical band gap, the obtained TiO2-ZnO nanocomposite powder was dispersed in distilled water by ultrasound to form a suspension, for which the absorption spectrum was then taken. The obtained data were calculated using the Kubelkа-Munch formula and constructed the dependence. Іt can be stated from the data presented that the optical band gap of the obtained powder is ~2.4 eV.

Research of the stress-strain state of a workpiece under the double bending by the pulse loading

The object of research is the technology of metal processing by high-speed and high-energy methods, plastic deformation of layered metal compositions. Theoretical studies are based on the main provisions of the theory of joining metals in the solid phase, the theory of plasticity, explosion welding technology, plastic deformation of layered metal compositions, and their heat treatment. The main problem of creating layered metal compositions using explosion energy, including wear and corrosion resistant, electrical, materials with high ballistic resistance, etc., is that they have not yet taken their rightful place in the range of modern structural and functional materials. This can be explained by the limited application of this process, as well as the lagging behind the theory and experimental base in the field of joining various metals in the solid phase and providing the necessary performance properties according to the needs of modern industry. The process of deformation of the cladding blank during the explosion welding is considered. The process of the workpiece collision is considered in three stages: the movement of the element of the cladding workpiece before the collision, its inertial movement and deformation. The equations of motion and equilibrium of the elements of the workpiece are described. A joint solution of the equations of plasticity and equilibrium of the blank element in the double inflection zone is presented. The work is devoted to solving the problem of increasing the level of production and economic indicators of the manufacture of layered metal compositions through the development of methods for calculating and optimizing the technological parameters. Explosion welding, as the most versatile, promising, and economical method, which still has many possibilities for the application of mathematical modeling and process optimization, has been investigated for the production and subsequent processing of the main groups of industrial metal compositions. This makes it possible to solve the problem of replacing traditional materials with layered metal compositions. The results obtained are important from the point of view of the application of cost-effective materials with high mechanical, operational, and technological properties.

Research of Hardness of Polymer Composite Materials Based on Silicone and Aluminium Hydroxide with Various Mechanical-Chemical Processing

Polymer composites are one of the types of modern functional materials. This class includes many different in structure and field of application materials, including dispersed-filled polymer composites [1]. Such materials are made by mixing a polymer matrix in a fluid state with a powder filler and then curing. The properties of the resulting materials are influenced by a variety of factors, including the nature of the preliminary (prior to addition to the mixture with the polymer) mechanical-chemical processing of the filler.

Bridging Structural Inhomogeneity to Functionality: Pair Distribution Function Methods for Functional Materials Development.

The correlation between structure and function lies at the heart of materials science and engineering. Especially, modern functional materials usually contain inhomogeneities at an atomic level, endowing them with interesting properties regarding electrons, phonons, and magnetic moments. Over the past few decades, many of the key developments in functional materials have been driven by the rapid advances in short‐range crystallographic techniques. Among them, pair distribution function (PDF) technique, capable of utilizing the entire Bragg and diffuse scattering signals, stands out as a powerful tool for detecting local structure away from average. With the advent of synchrotron X‐rays, spallation neutrons, and advanced computing power, the PDF can quantitatively encode a local structure and in turn guide atomic‐scale engineering in the functional materials. Here, the PDF investigations in a range of functional materials are reviewed, including ferroelectrics/thermoelectrics, colossal magnetoresistance (CMR) magnets, high‐temperature superconductors (HTSC), quantum dots (QDs), nano‐catalysts, and energy storage materials, where the links between functions and structural inhomogeneities are prominent. For each application, a brief description of the structure‐function coupling will be given, followed by selected cases of PDF investigations. Before that, an overview of the theory, methodology, and unique power of the PDF method will be also presented.

Micromechanics of defects in functional materials

We report on the unified approach to the classification of defects in continuum-based analysis of the defect self-distortions. Defects of various dimensionality including point, linear, surface, and volume defects are considered depending on the domain of self-distortion definition. The results of analytical calculations of elastic fields and the energies of dislocations, disclinations, and inclusions in bodies of various geometries with internal and external boundaries are considered. Examples of defects in modern functional materials, e.g., graphene, are given. It is discussed how the presence of defects and associated elastic fields affects the properties of modern functional materials and the characteristics of devices based on them.

Physically inspired deep learning of molecular excitations and photoemission spectra.

Modern functional materials consist of large molecular building blocks with significant chemical complexity which limits spectroscopic property prediction with accurate first-principles methods. Consequently, a targeted design of materials with tailored optoelectronic properties by high-throughput screening is bound to fail without efficient methods to predict molecular excited-state properties across chemical space. In this work, we present a deep neural network that predicts charged quasiparticle excitations for large and complex organic molecules with a rich elemental diversity and a size well out of reach of accurate many body perturbation theory calculations. The model exploits the fundamental underlying physics of molecular resonances as eigenvalues of a latent Hamiltonian matrix and is thus able to accurately describe multiple resonances simultaneously. The performance of this model is demonstrated for a range of organic molecules across chemical composition space and configuration space. We further showcase the model capabilities by predicting photoemission spectra at the level of the GW approximation for previously unseen conjugated molecules.

Tailoring the phase diagram of discotic mesogens.

The computational modelling of discotic molecules is a central topic in colloid science that is key for the smart design of a broad range of modern functional materials. This work lays out a versatile interaction model capable of exposing the rich mesogenic behaviour of discotics. A single coarse-grained spheroplatelet core framework is employed to generate a variety of pair interaction anisotropy classes, favouring specific relative orientations of the particles (stacked, side-side, crossed, T-shaped). This paves the way for the systematic tailoring of the discotic liquid phase diagram. Monte Carlo simulations are performed for an ensemble of case studies to illustrate the correlation between the topology of the interaction and the formation of stable nematic, smectic and columnar phases, as well as of less common cubatic, uniaxial and biaxial columnar domains.

Modern functional materials for promoting cutaneous wound healing

With the development of biomedicine and material science, more and more new multifunctional materials or dressings were developed through interdisciplinary integration and applied in repair of cutaneous wounds, thereby providing new strategies, methods, and tools for treating cutaneous wounds. This article summarizes some achievements in this field.

Anharmonicity measure for materials

Theoretical frameworks used to qualitatively and quantitatively describe nuclear dynamics in solids are often based on the harmonic approximation. However, this approximation is known to become inaccurate or to break down completely in many modern functional materials. Interestingly, there is no reliable measure to quantify anharmonicity so far. Thus, a systematic classification of materials in terms of anharmonicity and a benchmark of methodologies that may be appropriate for different strengths of anharmonicity is currently impossible. In this work, we derive and discuss a statistical measure that reliably classifies compounds across temperature regimes and material classes by their "degree of anharmonicity". This enables us to distinguish "harmonic" materials, for which anharmonic effects constitute a small perturbation on top of the harmonic approximation, from strongly "anharmonic" materials, for which anharmonic effects become significant or even dominant and the treatment of anharmonicity in terms of perturbation theory is more than questionable. We show that the analysis of this measure in real and reciprocal space is able to shed light on the underlying microscopic mechanisms, even at conditions close to, e.g., phase transitions or defect formation. Eventually, we demonstrate that the developed approach is computationally efficient and enables rapid high-throughput searches by scanning over a set of several hundred binary solids. The results show that strong anharmonic effects beyond the perturbative limit are not only active in complex materials or close to phase transitions, but already at moderate temperatures in simple binary compounds.

Multiscale Tomographic Analysis for Micron-Sized Particulate Samples.

The three-dimensional characterization of distributed particle properties in the micro- and nanometer range is essential to describe and understand highly specific separation processes in terms of selectivity and yield. Both performance measures play a decisive role in the development and improvement of modern functional materials. In this study, we mixed spherical glass particles (0.4–5.8 μm diameter) with glass fibers (diameter 10 μm, length 18–660 μm) to investigate a borderline case of maximum difference in the aspect ratio and a significant difference in the characteristic length to characterize the system over several size scales. We immobilized the particles within a wax matrix and created sample volumes suitable for computed tomographic (CT) measurements at two different magnification scales (X-ray micro- and nano-CT). Fiber diameter and length could be described well on the basis of the low-resolution micro-CT measurements on the entire sample volume. In contrast, the spherical particle system could only be described with sufficient accuracy by combining micro-CT with high-resolution nano-CT measurements on subvolumes of reduced sample size. We modeled the joint (bivariate) distribution of fiber length and diameter with a parametric copula as a basic example, which is equally suitable for more complex distributions of irregularly shaped particles. This enables us to capture the multidimensional correlation structure of particle systems with statistically representative quantities.

ТВЕРДІ РОЗЧИНИ ЗАМІЩЕННЯ КУПРАТУ НЕОДИМУ СУБМІКРОННОЇ ДИСПЕРСНОСТІ

High-temperature superconducting compounds based on rare-earth elements with a perovskite-like structure play an important role in the creation of modern functional materials with special magnetic, superconducting and electrophysical properties. The potential of high-temperature superconducting compounds is widely used in microelectronics, medicine, transport, telecommunications technology, energy and more. Increased functionality, performance and reliability are the driving force for the production, research and application of this class of inorganic functional materials. Solid solutions of the type NdBa2–xNdxCu3O7–δ, are structural analogues of HTSC cuprate YBa2Cu3Oy (Y123). The study of the substitution of Ba2+ atoms for Nd3+ is important for obtaining new promising materials with various electrophysical and magnetic properties, as well as improving the characteristics of existing substances. Compounds of the composition NdBa2-xNdxCu3O7–δ, where x = 0–0.9 were synthesized sol-gel method. The parameters of the crystallattice and the transition temperature to the superconducting state for the synthesized compounds are calculated. The dependence of the parameters and the type of symmetry of the crystallattice of systems on the degree of substitution of x is investigated. It was found that the samples, sol-gel method are single-phase. The unsubstituted sample of NdBa2-xNdxCu3O7–δ, is single-phase, has an orthorhombic syngony of o-Nd123 and a space group Pmmm. Within creasing degree of substitution x in solid solutions of NdBa2–xNdxCu3O7–δ, where x = 0–0.9, there is a transition from the orthorhombic to tetragonal phase (space symmetry group P4/mmm).

A New Look on Octet‐Compliant Macrocyclic Organoaluminum Carboxylates as Dormant Poly‐Lewis Acids

A more in‐depth understanding of the multi‐faceted chemistry of organoaluminum complexes is continually vital for the comprehension and development of new reagents and catalytic systems as well as molecular building blocks for modern functional materials. In this report we utilize a macrocyclic tetranuclear organoaluminum derivative of 2,3‐naphthalenedicarboxylic acid (naphtha‐H2), [(Me2Al)2(naphtha)]2, as a model complex to probe both the dormant Lewis acidity and self‐assembly processes of octet‐compliant multinuclear macrocyclic organoaluminum compounds in the presence of mono‐ or bidentate pyridine ligands. The results nicely demonstrate that multinuclear octet‐compliant organoaluminum clusters may effectively act as so‐called poly‐Lewis acids, utilizing their dormant Lewis acidity with the preservation or cleavage of the parent macrocycle depending on the character of both donor ligands and aromatic subunits of the dicarboxylate ligands.

Aerogeles – Modern Functional Materials for Chemistry Lessons?

AbstractAerogele zeichnen sich als moderne Funktionswerkstoffe durch herausragende und gezielt modifizierbare Eigenschaften aus. Diese beruhen auf ihrer spezifischen hochporösen Struktur. Die daraus resultierende Vielzahl hochinteressanter Einsatzmöglichkeiten macht die Stoffklasse zum Gegenstand intensiver Forschung. Im Beitrag wird eine an schulische Gegebenheiten angepasste Synthese und Trocknung eines organisch modifizierten Silica‐Aerogels vorgestellt. Die Charakterisierungen der so hergestellten Proben belegen die aerogeltypischen Eigenschaften des erhaltenen Materials. Abschließend werden unterrichtliche Einsatzmöglichkeiten anhand von einfachen Freihandversuchen und Überlegungen zur didaktischen Einbettung aufgezeigt.

Epitaxial strain adaptation in chemically disordered FeRh thin films

Strain and strain adaption mechanisms in modern functional materials are of crucial importance for their performance. Understanding these mechanisms will advance innovative approaches for material properties engineering. Here we study the strain adaption mechanism in a thin film model system as function of epitaxial strain. Chemically disordered FeRh thin films are deposited on W-V buffer layers, which allow for large variation of the preset lattice constants, e.g. epitaxial boundary condition. It is shown by means of high resolution X-ray reciprocal space maps and transmission electron microscopy that the system reacts with a tilting mechanism of the structural units in order to adapt to the lattice constants of the buffer layer. This response explained by density functional theory calculations, which evidence an energetic minimum for structures with a distortion of c/a =0.87. The experimentally observed tilting mechanism is induced by this energy gain and allows the system to remain in the most favorable structure. In general, it is shown that the use of epitaxial model heterostructures consisting of alloy buffer layers of fully miscible elements and the functional material of interest allows to study strain adaption behaviors in great detail. This approach makes even small secondary effects observable, such as the directional tilting of the structural domains identified in the present case study.

Hamiltonians and order parameters for crystals of orientable molecules

Many modern functional materials exhibit microscopic degrees of freedom that are difficult to describe mathematically or do not conform to conventional models in solid state physics. In this paper, we consider crystals containing orientable molecular species, which encompass the class of promising photovoltaic materials ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbX}}_{3}$. Abstracting these materials as crystals of orientable rigid rotors, we develop an effective Hamiltonian that expresses the crystal potential energy in terms of collective orientations of interacting rigid rotors. The approach is motivated by the cluster expansion framework from alloy theory and is appropriate for describing both chiral and achiral molecules. This framework utilizes a quaternion parametrization of molecular orientation and makes full use of the symmetry both of the rotors and of the crystal in order to constrain the functional form of the final Hamiltonian expression. The resulting Hamiltonian is compact, systematically improvable, and is suitable for Monte Carlo or molecular dynamics simulation. We apply this formalism to ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{PbI}}_{3}$ and report symmetry-adapted basis functions that can be used to construct order parameters or Hamiltonians that describe orientational correlation of methylammonium ions in hybrid organic-inorganic halide perovskite materials.

Selective Molecular Transport in Thermoresponsive Polymer Membranes: Role of Nanoscale Hydration and Fluctuations

For a wide range of modern soft functional materials the selective transport of sub-nanometer-sized molecules (`penetrants') through a stimuli-responsive polymeric membrane is key to the desired function. In this study, we investigate the diffusion properties of penetrants ranging from non-polar to polar molecules and ions in a matrix of collapsed Poly(N-isopropylacrylamide) (PNIPAM) polymers in water by means of extensive molecular dynamics simulations. We find that the water distributes heterogeneously in fractal-like cluster structures embedded in the nanometer-sized voids of the polymer matrix. The nano-clustered water acts as an important player in the penetrant diffusion, which proceeds via a hopping mechanism through `wet' transition states: the penetrants hop from one void to another via transient water channels opened by rare but decisive polymer fluctuations. The diffusivities of the studied penetrants extend over almost five orders of magnitude and thus enable a formulation of an analytical scaling relation with a clear non-Stokesian, exponential dependence of the diffusion coefficient on the penetrant's radius for the uncharged penetrants. Charged penetrants (ions) behave differently as they get captured in large isolated water clusters. Finally, we find large energetic activation barriers for hopping, which significantly depend on the hydration state and thereby challenge available transport theories.

Evidence for Itinerant Carriers in an Anisotropic Narrow-Gap Semiconductor by Angle-Resolved Photoemission Spectroscopy.

The ability to accurately determine the electronic structure of solids has become a key prerequisite for modern functional materials. For example, the precise determination of the electronic structure helps to balance the three thermoelectric parameters, which is the biggest challenge to design high-performance thermoelectric materials. Herein, by high-resolution, angle-resolved photoemission spectroscopy (ARPES), the itinerant carriers in CsBi4 Te6 (CBT) are revealed for the first time. CBT is a typical anisotropic, narrow-gap semiconductor used as a practical candidate for low-temperature thermoelectric applications, and p-doped CBT series show superconductivity at relatively low carrier concentrations. The ARPES results show a significantly larger bandwidth near the Fermi surface than calculations, which means the carriers transport anisotropically and itinerantly in CBT. It is reasonable to believe that these newly discovered features of carriers in narrow-gap semiconductors are promising for designing optimal thermoelectric materials and superconductors.

Atom size electron vortex beams with selectable orbital angular momentum

The decreasing size of modern functional magnetic materials and devices cause a steadily increasing demand for high resolution quantitative magnetic characterization. Transmission electron microscopy (TEM) based measurements of the electron energy-loss magnetic chiral dichroism (EMCD) may serve as the needed experimental tool. To this end, we present a reliable and robust electron-optical setup that generates and controls user-selectable single state electron vortex beams with defined orbital angular momenta. Our set-up is based on a standard high-resolution scanning TEM with probe aberration corrector, to which we added a vortex generating fork aperture and a miniaturized aperture for vortex selection. We demonstrate that atom size probes can be formed from these electron vortices and that they can be used for atomic resolution structural and spectroscopic imaging – both of which are prerequisites for future atomic EMCD investigations.