Showing papers on "Phase (matter) published in 2013"
TL;DR: The controlled vapour phase synthesis of molybdenum disulphide atomic layers is reported and a fundamental mechanism for the nucleation, growth, and grain boundary formation in its crystalline monolayers is elucidated.
Abstract: Single-layered molybdenum disulphide with a direct bandgap is a promising two-dimensional material that goes beyond graphene for the next generation of nanoelectronics. Here, we report the controlled vapour phase synthesis of molybdenum disulphide atomic layers and elucidate a fundamental mechanism for the nucleation, growth, and grain boundary formation in its crystalline monolayers. Furthermore, a nucleation-controlled strategy is established to systematically promote the formation of large-area, single- and few-layered films. Using high-resolution electron microscopy imaging, the atomic structure and morphology of the grains and their boundaries in the polycrystalline molybdenum disulphide atomic layers are examined, and the primary mechanisms for grain boundary formation are evaluated. Grain boundaries consisting of 5- and 7- member rings are directly observed with atomic resolution, and their energy landscape is investigated via first-principles calculations. The uniformity in thickness, large grain sizes, and excellent electrical performance signify the high quality and scalable synthesis of the molybdenum disulphide atomic layers.
1,645 citations
TL;DR: A (quasi-)two-dimensional colloidal suspension of self-propelled spherical particles propelled due to diffusiophoresis in a near-critical water-lutidine mixture finds that the driving stabilizes small clusters and undergoes a phase separation into large clusters and a dilute gas phase.
Abstract: We study experimentally and numerically a (quasi-)two-dimensional colloidal suspension of self-propelled spherical particles. The particles are carbon-coated Janus particles, which are propelled due to diffusiophoresis in a near-critical water-lutidine mixture. At low densities, we find that the driving stabilizes small clusters. At higher densities, the suspension undergoes a phase separation into large clusters and a dilute gas phase. The same qualitative behavior is observed in simulations of a minimal model for repulsive self-propelled particles lacking any alignment interactions. The observed behavior is rationalized in terms of a dynamical instability due to the self-trapping of self-propelled particles.
1,004 citations
TL;DR: It is found that electrolyte gating of epitaxial thin films of VO2 suppresses the metal-to-insulator transition and stabilizes the metallic phase to temperatures below 5 kelvin, even after the ionic liquid is completely removed.
Abstract: Electrolyte gating with ionic liquids is a powerful tool for inducing novel conducting phases in correlated insulators. An archetypal correlated material is vanadium dioxide (VO2), which is insulating only at temperatures below a characteristic phase transition temperature. We show that electrolyte gating of epitaxial thin films of VO2 suppresses the metal-to-insulator transition and stabilizes the metallic phase to temperatures below 5 kelvin, even after the ionic liquid is completely removed. We found that electrolyte gating of VO2 leads not to electrostatically induced carriers but instead to the electric field–induced creation of oxygen vacancies, with consequent migration of oxygen from the oxide film into the ionic liquid. This mechanism should be taken into account in the interpretation of ionic liquid gating experiments.
957 citations
TL;DR: A new synthetic strategy capable of metallating MOFs from the gas phase: atomic layer deposition (ALD) is introduced.
Abstract: Metal–organic frameworks (MOFs) have received attention for a myriad of potential applications including catalysis, gas storage, and gas separation. Coordinatively unsaturated metal ions often enable key functional behavior of these materials. Most commonly, MOFs have been metalated from the condensed phase (i.e., from solution). Here we introduce a new synthetic strategy capable of metallating MOFs from the gas phase: atomic layer deposition (ALD). Key to enabling metalation by ALD In MOFs (AIM) was the synthesis of NU-1000, a new, thermally stable, Zr-based MOF with spatially oriented −OH groups and large 1D mesopores and apertures.
737 citations
TL;DR: It is shown that the equilibrium quantum phase transition and the dynamical phase transition in the transverse-field Ising model are intimately related.
Abstract: A phase transition indicates a sudden change in the properties of a large system. For temperature-driven phase transitions this is related to nonanalytic behavior of the free energy density at the critical temperature: The knowledge of the free energy density in one phase is insufficient to predict the properties of the other phase. In this Letter we show that a close analogue of this behavior can occur in the real time evolution of quantum systems, namely nonanalytic behavior at a critical time. We denote such behavior a dynamical phase transition and explore its properties in the transverse-field Ising model. Specifically, we show that the equilibrium quantum phase transition and the dynamical phase transition in this model are intimately related.
663 citations
TL;DR: In this article, the authors examined a minimal model for an active colloidal fluid in the form of self-propelled Brownian spheres that interact purely through excluded volume with no aligning interaction.
Abstract: We examine a minimal model for an active colloidal fluid in the form of self-propelled Brownian spheres that interact purely through excluded volume with no aligning interaction. Using simulations and analytic modeling, we quantify the phase diagram and separation kinetics. We show that this nonequilibrium active system undergoes an analog of an equilibrium continuous phase transition, with a binodal curve beneath which the system separates into dense and dilute phases whose concentrations depend only on activity. The dense phase is a unique material that we call an active solid, which exhibits the structural signatures of a crystalline solid near the crystal-hexatic transition point, and anomalous dynamics including superdiffusive motion on intermediate time scales.
661 citations
TL;DR: In this article, resonant X-ray scattering and microscopy are combined to quantitatively measure the nanoscale domain size, distribution and composition in high efficiency solar cells based on PTB7 and PC71BM.
Abstract: The importance of morphology to organic solar cell performance is well known, but to date, the lack of quantitative, nanoscale and statistical morphological information has hindered obtaining direct links to device function. Here resonant X-ray scattering and microscopy are combined to quantitatively measure the nanoscale domain size, distribution and composition in high efficiency solar cells based on PTB7 and PC71BM. The results show that the solvent additive diiodooctane dramatically shrinks the domain size of pure fullerene agglomerates that are embedded in a polymer-rich 70/30 wt.% molecularly mixed matrix, while preserving the domain composition relative to additive-free devices. The fundamental miscibility between the species – measured to be equal to the device's matrix composition – is likely the dominant factor behind the overall morphology with the additive affecting the dispersion of excess fullerene. As even the molecular ordering measured by X-ray diffraction is unchanged between the two processing routes the change in the distribution of domain size and therefore increased domain interface is primarily responsible for the dramatic increase in device performance. While fullerene exciton harvesting is clearly one significant cause of the increase owing to smaller domains, a measured increase in harvesting from the polymer species indicates that the molecular mixing is not the reason for the high efficiency in this system. Rather, excitations in the polymer likely require proximity to a pure fullerene phase for efficient charge separation and transport. Furthermore, in contrast to previous measurements on a PTB7-based system, a hierarchical morphology was not observed, indicating that it is not necessary for high performance.
621 citations
TL;DR: In condensed matter, strong interactions alter chemical activities and create variations that can dramatically affect the reaction rate as mentioned in this paper, and the extreme case is that of a reaction coupled to a phase transformation whose kinetics must depend not only on the order parameter but also on its gradients at phase boundaries.
Abstract: Advances in the fields of catalysis and electrochemical energy conversion often involve nanoparticles, which can have kinetics surprisingly different from the bulk material. Classical theories of chemical kinetics assume independent reactions in dilute solutions, whose rates are determined by mean concentrations. In condensed matter, strong interactions alter chemical activities and create variations that can dramatically affect the reaction rate. The extreme case is that of a reaction coupled to a phase transformation, whose kinetics must depend not only on the order parameter but also on its gradients at phase boundaries. Reaction-driven phase transformations are common in electrochemistry, when charge transfer is accompanied by ion intercalation or deposition in a solid phase. Examples abound in Li-ion, metal–air, and lead–acid batteries, as well as metal electrodeposition–dissolution. Despite complex thermodynamics, however, the standard kinetic model is the Butler–Volmer equation, based on a dilute s...
497 citations
TL;DR: It is demonstrated that the crystal downsizing of twofold interpenetrated frameworks of [Cu2(dicarboxylate)2(amine)]n regulates the structural flexibility and induces a shape-memory effect in the coordination frameworks.
Abstract: Flexible porous coordination polymers change their structure in response to molecular incorporation but recover their original configuration after the guest has been removed. We demonstrated that the crystal downsizing of twofold interpenetrated frameworks of [Cu2(dicarboxylate)2(amine)]n regulates the structural flexibility and induces a shape-memory effect in the coordination frameworks. In addition to the two structures that contribute to the sorption process (that is, a nonporous closed phase and a guest-included open phase), we isolated an unusual, metastable open dried phase when downsizing the crystals to the mesoscale, and the closed phase was recovered by thermal treatment. Crystal downsizing suppressed the structural mobility and stabilized the open dried phase. The successful isolation of two interconvertible empty phases, the closed phase and the open dried phase, provided switchable sorption properties with or without gate-opening behavior.
432 citations
TL;DR: An implementation of a Gaussian-based approach to deliver the dielectric constant distribution throughout the protein and surrounding water phase by utilizing the 3D structure of the corresponding macromolecule is reported.
Abstract: Implicit methods for modeling protein electrostatics require dielectric properties of the system to be known, in particular, the value of the dielectric constant of protein. While numerous values of the internal protein dielectric constant were reported in the literature, still there is no consensus of what the optimal value is. Perhaps this is due to the fact that the protein dielectric constant is not a "constant" but is a complex function reflecting the properties of the protein's structure and sequence. Here, we report an implementation of a Gaussian-based approach to deliver the dielectric constant distribution throughout the protein and surrounding water phase by utilizing the 3D structure of the corresponding macromolecule. In contrast to previous reports, we construct a smooth dielectric function throughout the space of the system to be modeled rather than just constructing a "Gaussian surface" or smoothing molecule-water boundary. Analysis on a large set of proteins shows that (a) the average dielectric constant inside the protein is relatively low, about 6-7, and reaches a value of about 20-30 at the protein's surface, and (b) high average local dielectric constant values are associated with charged residues while low dielectric constant values are automatically assigned to the regions occupied by hydrophobic residues. In terms of energetics, a benchmarking test was carried out against the experimental pKa's of 89 residues in staphylococcal nuclease (SNase) and showed that it results in a much better RMSD (= 1.77 pK) than the corresponding calculations done with a homogeneous high dielectric constant with an optimal value of 10 (RMSD = 2.43 pK).
429 citations
TL;DR: In this article, a 3-fold increase in the decolorization rate using BaTiO3 with a high tetragonal content compared to predominantly cubic material was reported, ascribed to the ferroelectricity of the tetragonal phase.
Abstract: BaTiO3 is used as a target catalyst to probe the influence of ferroelectricity on the decolorization of a typical dye molecule—Rhodamine B—under simulated solar light. We show that there is a 3-fold increase in the decolorization rate using BaTiO3 with a high tetragonal content compared to predominantly cubic material. This is ascribed to the ferroelectricity of the tetragonal phase. The influence of ferroelectricity ensures a tightly bound layer of dye molecule and also acts to separate the photoexcited carriers due to the internal space charge layer. Both of these features act to enhance the catalytic performance. When nanostructured Ag is photochemically deposited on the surface of the BaTiO3, we find a further increase in the reaction rate that gives complete decolorization of the dye in around 45 min.
TL;DR: It is shown that studying single-crystal VO2 nanobeams in a purpose-built nanomechanical strain apparatus allows investigation of this prototypical phase transition with unprecedented control and precision, and the striking finding that the triple point of the metallic phase and two insulating phases is at the transition temperature.
Abstract: The precise location of a solid-state triple point, at which three solid phases coexist in thermal equilibrium, has been determined by controlling the stress and temperature in a nanobeam of vanadium dioxide near its metal–insulator transition Vanadium dioxide (VO2) is of interest in ultrafast optical and electrical switching applications thanks to the material's unique phase transition between metallic and insulating states involving several competing phases This study of single-crystal VO2 nanobeams in a system in which the metal–insulator transition is finely controlled by adjusting temperature and strain pinpoints the previously elusive 'triple point' — the transition temperature at which one metallic and two insulating phases can coexist — as 65 °C Other so-called correlated materials, including manganites and pnictides, also have poorly understood strain-critical phase transitions involving multiple components, and this work demonstrates a method that should be widely applicable in such situations First-order phase transitions in solids are notoriously challenging to study The combination of change in unit cell shape, long range of elastic distortion and flow of latent heat leads to large energy barriers resulting in domain structure, hysteresis and cracking The situation is worse near a triple point, where more than two phases are involved The well-known metal–insulator transition in vanadium dioxide1, a popular candidate for ultrafast optical and electrical switching applications, is a case in point Even though VO2 is one of the simplest strongly correlated materials, experimental difficulties posed by the first-order nature of the metal–insulator transition as well as the involvement of at least two competing insulating phases have led to persistent controversy about its nature1,2,3,4 Here we show that studying single-crystal VO2 nanobeams5,6,7,8,9,10,11,12,13,14,15,16 in a purpose-built nanomechanical strain apparatus allows investigation of this prototypical phase transition with unprecedented control and precision Our results include the striking finding that the triple point of the metallic phase and two insulating phases is at the transition temperature, Ttr = Tc, which we determine to be 650 ± 01 °C The findings have profound implications for the mechanism of the metal–insulator transition in VO2, but they also demonstrate the importance of this approach for mastering phase transitions in many other strongly correlated materials, such as manganites17 and iron-based superconductors18
TL;DR: It is proposed that this two-step process to create CNC HIPEs relies on a swelling process of the droplets that does not desorb the CNCs from the interface, decreasing the coverage ratio of theDroplets and leading to coalescence.
TL;DR: A simple analytical model for the defect dynamics is developed which reproduces the key features of both the numerical solutions and recent experiments on microtubule-kinesin assemblies.
Abstract: Liquid crystals inevitably possess topological defect excitations generated through boundary conditions, through applied fields, or in quenches to the ordered phase. In equilibrium, pairs of defects coarsen and annihilate as the uniform ground state is approached. Here we show that defects in active liquid crystals exhibit profoundly different behavior, depending on the degree of activity and its contractile or extensile character. While contractile systems enhance the annihilation dynamics of passive systems, extensile systems act to drive defects apart so that they swarm around in the manner of topologically well-characterized self-propelled particles. We develop a simple analytical model for the defect dynamics which reproduces the key features of both the numerical solutions and recent experiments on microtubule-kinesin assemblies.
TL;DR: This research shows that the addition of silica-alumina nanoparticles has a significant potential for enhancing the thermal storage characteristics of the NaNO3-KNO3 binary salt.
Abstract: In this study, different nanofluids with phase change behavior were developed by mixing a molten salt base fluid (selected as phase change material) with nanoparticles using the direct-synthesis method. The thermal properties of the nanofluids obtained were investigated. These nanofluids can be used in concentrating solar plants with a reduction of storage material if an improvement in the specific heat is achieved. The base salt mixture was a NaNO3-KNO3 (60:40 ratio) binary salt. The nanoparticles used were silica (SiO2), alumina (Al2O3), titania (TiO2), and a mix of silica-alumina (SiO2-Al2O3). Three weight fractions were evaluated: 0.5, 1.0, and 1.5 wt.%. Each nanofluid was prepared in water solution, sonicated, and evaporated. Measurements on thermophysical properties were performed by differential scanning calorimetry analysis and the dispersion of the nanoparticles was analyzed by scanning electron microscopy (SEM). The results obtained show that the addition of 1.0 wt.% of nanoparticles to the base salt increases the specific heat of 15% to 57% in the solid phase and of 1% to 22% in the liquid phase. In particular, this research shows that the addition of silica-alumina nanoparticles has a significant potential for enhancing the thermal storage characteristics of the NaNO3-KNO3 binary salt. These results deviated from the predictions of the theoretical model used. SEM suggests a greater interaction between these nanoparticles and the salt.
TL;DR: In this paper, the impact of the Cu/Li ratio on the sequence and kinetics of solid-state precipitation is studied for two recently developed Al-Cu-Li-Mg-Ag alloys: AA2198 and AA2196.
TL;DR: In this paper, high-level crystalline ZnO nanoparticles (NPs) were synthesized with zinc acetate as precursor and oxalic acid at 80°C through the simple solution phase approach.
TL;DR: In this article, the phase behavior of 8 hydrophobic poorly water-soluble drug molecules in highly supersaturated aqueous solutions was examined, and colloid formation was explained in terms of liquid-liquid phase separation (LLPS).
Abstract: Highly supersaturated aqueous drug solutions are often generated during drug testing and upon delivery to the patient. The phase behavior of such solutions appears complex and poorly understood, with the formation of colloidal drug aggregates often being reported. In this study, the phase behavior of eight hydrophobic poorly water-soluble drug molecules in highly supersaturated aqueous solutions was examined, and colloid formation was explained in terms of liquid–liquid phase separation (LLPS). A relationship was found between the concentration at which LLPS was observed and the theoretically predicted amorphous “solubility” value, where the latter was predicted based on the thermodynamic properties of the crystalline solid/supercooled liquid and solution activity coefficients. A phase diagram for the ritonavir–water system as a function of temperature was used to demonstrate that LLPS occurs in the metastable region of the phase diagram, and thus LLPS is a precursor to crystallization. Using an amorphous...
TL;DR: This work reports a general strategy for the creation of heterogeneous nanoparticle superlattices using DNA and carboxylic-based conjugation, and shows that nanoparticles with all major types of functionality--plasmonic, magnetic, catalytic, and luminescent--can be incorporated into binary systems in a rational manner.
Abstract: Nanoparticles coated with DNA molecules can be programmed to self-assemble into three-dimensional superlattices. Such superlattices can be made from nanoparticles with different functionalities and could potentially exploit the synergetic properties of the nanoscale components. However, the approach has so far been used primarily with single-component systems. Here, we report a general strategy for the creation of heterogeneous nanoparticle superlattices using DNA and carboxylic-based conjugation. We show that nanoparticles with all major types of functionality--plasmonic (gold), magnetic (Fe2O3), catalytic (palladium) and luminescent (CdSe/Te@ZnS and CdSe@ZnS)--can be incorporated into binary systems in a rational manner. We also examine the effect of nanoparticle characteristics (including size, shape, number of DNA per particle and DNA flexibility) on the phase behaviour of the heterosystems, and demonstrate that the assembled materials can have novel optical and field-responsive properties.
TL;DR: These results serve as proof that at low temperatures SmB6 has a metallic surface that surrounds an insulating bulk, paving the way for transport studies of the surface state in this proposed TKI material.
Abstract: A topological insulator (TI) is an unusual quantum state in which the insulating bulk is topologically distinct from vacuum, resulting in a unique metallic surface that is robust against time-reversal invariant perturbations. The surface transport, however, remains difficult to isolate from the bulk conduction in most existing TI crystals (particularly Bi2Se3, Bi2Te3 and Sb2Te3) due to impurity caused bulk conduction. We report in large crystals of topological Kondo insulator (TKI) candidate material SmB6 the thickness-independent surface Hall effects and non-local transport, which persist after various surface perturbations. These results serve as proof that at low temperatures SmB6 has a metallic surface that surrounds an insulating bulk, paving the way for transport studies of the surface state in this proposed TKI material.
TL;DR: In this article, the structural stability of Li7La3Zr2O12 garnets is investigated, focusing on the mechanisms that result in the transformation from tetragonal to cubic symmetry, and the natures of the high and low temperature cubic garnets are totally different: the one found above the phase transition does not involve any change in the stoichiometry, whereas the cubic phase formed at low temperature is a hydrated, lithium defective phase, due to the combined effect of water insertion into the garnet structure and the H+/Li+ exchange mechanism.
Abstract: We address the controversial issue of the structural stability of Li7La3Zr2O12 garnets, focusing on the mechanisms that result in the transformation from tetragonal to cubic symmetry. We show that undoped tetragonal Li7La3Zr2O12 not exposed to humidity at any moment undergoes a reversible phase transition to cubic symmetry at Tc ≃ 645 °C that we ascribe to lithium dynamic effects. On the other hand, a close correlation has been found between the appearance of a cubic phase between 100 and 200 °C in X-ray diffractograms and the presence of water, either in the atmosphere in which experiments are performed or already in the starting material. The natures of the high and low-temperature cubic garnets are totally different: the one found above the phase transition does not involve any change in the stoichiometry, whereas the cubic phase formed at low temperature is a hydrated, lithium defective phase, due to the combined effect of water insertion into the garnet structure and the H+/Li+ exchange mechanism. Differences in the actual compositions of the samples depending on their thermal history are corroborated by TG-MS experiments. Chemical reactions and phases formed along the thermal evolution are elucidated with the help of Raman spectroscopy.
TL;DR: In this article, a one pot successive layer-by-layer (SLBL) strategy is introduced to fabricate the core/shell upconversion nanoparticles (NPs) for the first time by using high boiling-point Re-OA (rare-earth chlorides dissolved in oleic acid at 140 °C) and Na-TFA-OA as shell precursor solutions.
Abstract: One pot successive layer-by-layer (SLBL) strategy is introduced to fabricate the core/shell upconversion nanoparticles (NPs) for the first time by using high boiling-point Re-OA (rare-earth chlorides dissolved in oleic acid at 140 °C) and Na-TFA-OA (sodium trifluoroacetate dissolved in oleic acid at room temperature) as shell precursor solutions. This protocol is flexible to deposit uniform multishell on both hexagonal (β) and cubic (α) phase cores by successive introducing of the shell precursor solutions. Shell thickness of the obtained NPs with narrow size distribution (σ < 10%) can be well controlled from 1 monolayer (∼0.36 nm) to more than 20 monolayers (∼8 nm) by simply tuning the amounts of the shell precursors. Furthermore, the tunable doping positions (core doping and shell doping) can also be achieved by adjusting the species and addition sequence of the shell precursors. As a result of the high quality uniform shell and advanced core/shell structures, the optical properties of the obtained core...
TL;DR: In this paper, three classes of interacting colloidal particles, crystal, glasses, and gels, are reviewed, each of which represents fascinating properties of colloidal particle as well as a model for more general types of materials and their behavior.
Abstract: Colloidal particles are microscopic solid particles suspended in a fluid. Colloids are small enough that thermal energy drives their dynamics and ensures equilibration with the suspending fluid; they are also large enough that their positions and motions can be measured precisely using optical methods, such as light scattering and laser-scanning confocal fluorescence microscopy. Colloidal suspensions are a powerful model system for the study of other phenomena in condensed matter physics, where the collective phase behavior of the solid particles mimics that of other condensed systems. We review three classes of interacting colloidal particles, crystals, glasses, and gels, each of which represents fascinating properties of colloidal particles as well as a model for more general types of materials and their behavior.
TL;DR: In this article, the σ phase formation is directly related to the valence electron concentration (VEC) of the alloy, and the formation of σ-phase-forming VEC range was systematically studied and revealed.
Abstract: Formation of the σ phase has been observed in quite a few high-entropy alloys (HEAs) recently. The σ phase significantly enhances the hardness of the alloys but reduces their ductility. Thus, controlling the formation of σ phase through proper design is critical for HEAs. However, theories to predict the σ phase formation based on HEA composition are still not available. Here, we demonstrate that the σ phase formation is directly related to the valence electron concentration (VEC) of the alloy. The σ-phase-forming VEC range was systematically studied and revealed. Such finding is of crucial importance to the future design of HEAs.
TL;DR: In this article, the grain boundary diffusion process using an Nd70Cu30 eutectic alloy has been applied to hot-deformed anisotropic Nd-Fe-B magnets, resulting in a substantial enhancement of coercivity, at the expense of remanence.
TL;DR: In this article, a review of recent developments in research in nanostructured permanent magnets (hard magnetic materials) with emphasis on bottom-up approaches to fabrication of hard/soft nanocomposite bulk magnets is presented.
Abstract: This paper reviews recent developments in research in nanostructured permanent magnets (hard magnetic materials) with emphasis on bottom-up approaches to fabrication of hard/soft nanocomposite bulk magnets. Theoretical and experimental findings on the effects of soft phase and interface conditions on interphase exchange interactions are given. Synthesis techniques for hard magnetic nanoparticles, including chemical solution methods, surfactant-assisted ball milling and other physical deposition methods are reviewed. Processing and magnetic properties of warm compacted and plastically deformed bulk magnets with nanocrystalline morphology are discussed. Prospects of producing bulk anisotropic hard/soft nanocomposite magnets are presented.
TL;DR: In this paper, the 1H phase is the most stable one, while the metallic 1T phase, strongly unstable, undergoes a phase transition towards a metastable and insulating 1T${}^{\ensuremath{'}}$ structure composed of separated zigzag chains.
Abstract: Chemically and mechanically exfoliated MoS${}_{2}$ single-layer samples have substantially different properties. While mechanically exfoliated single-layers are monophase(1H polytype with Mo in trigonal prismatic coordination), the chemically exfoliated samples show coexistence of three different phases, 1H, 1T (Mo in octahedral coordination), and 1T${}^{\ensuremath{'}}$ (a distorted $2\ifmmode\times\else\texttimes\fi{}1$ 1T superstructure). By using first-principles calculations, we investigate the energetics and the dynamical stability of the three phases. We show that the 1H phase is the most stable one, while the metallic 1T phase, strongly unstable, undergoes a phase transition towards a metastable and insulating 1T${}^{\ensuremath{'}}$ structure composed of separated zigzag chains. We calculate electronic structure, phonon dispersion, Raman frequencies, and intensities for the 1T${}^{\ensuremath{'}}$ structure. We provide a microscopical description of the ${J}_{1}$, ${J}_{2}$, and ${J}_{3}$ Raman features that were first detected more than 20 years ago but have remained unexplained up to now. Finally, we show that H adsorbates, which are naturally present at the end of the chemical exfoliation process, stabilize the 1T${}^{\ensuremath{'}}$ over the 1H one.
TL;DR: In this paper, the effect of amorphous (am)-monoclinic (m)-and tetragonal (t -) ZrO 2 phase on the physicochemical and catalytic properties of supported Cu catalysts for ethanol conversion was studied.
TL;DR: The majority of studies on high-entropy alloys are focused on their phase, microstructure, and mechanical properties, but the physical properties of these materials are also encouraging.
Abstract: The majority of studies on high-entropy alloys are focused on their phase, microstructure, and mechanical properties. However, the physical properties of these materials are also encouraging. This paper provides a brief overview of the physical properties of high-entropy alloys. Emphasis is laid on magnetic, electrical, and thermal properties.
TL;DR: The observations, and corresponding electronic structure and quantum transport calculations, indicate the conducting character of the one-dimensional sulphur chains under ambient pressure, in stark contrast to bulk sulphur that needs ultrahigh pressures exceeding ~90 GPa to become metallic.
Abstract: Despite extensive research for more than 200 years, the experimental isolation of monatomic sulphur chains, which are believed to exhibit a conducting character, has eluded scientists. Here we report the synthesis of a previously unobserved composite material of elemental sulphur, consisting of monatomic chains stabilized in the constraining volume of a carbon nanotube. This one-dimensional phase is confirmed by high-resolution transmission electron microscopy and synchrotron X-ray diffraction. Interestingly, these one-dimensional sulphur chains exhibit long domain sizes of up to 160 nm and high thermal stability (~800 K). Synchrotron X-ray diffraction shows a sharp structural transition of the one-dimensional sulphur occurring at ~450-650 K. Our observations, and corresponding electronic structure and quantum transport calculations, indicate the conducting character of the one-dimensional sulphur chains under ambient pressure. This is in stark contrast to bulk sulphur that needs ultrahigh pressures exceeding ~90 GPa to become metallic.