Occupation Of Voids Research Articles

Molecular Engineering Regulation Achieving Out‐of‐Plane Polarization in Rare‐Earth Hybrid Double Perovskites for Ferroelectrics and Circularly Polarized Luminescence

AbstractOut‐of‐plane polarization is a highly desired property of two‐dimensional (2D) ferroelectrics for application in vertical sandwich‐type photoferroelectric devices, especially in ultrathin ferroelectronic devices. Nevertheless, despite great advances that have been made in recent years, out‐of‐plane polarization remains unrealized in the 2D hybrid double perovskite ferroelectric family. Here, from our previous work 2D hybrid double perovskite HQERN ((S3HQ)4EuRb(NO3)8, S3HQ=S‐3‐hydroxylquinuclidinium), we designed a molecular strategy of F‐substitution on organic component to successfully obtain FQERN ((S3FQ)4EuRb(NO3)8, S3FQ=S‐3‐fluoroquinuclidinium) showing circularly polarized luminescence (CPL) response. Remarkably, compared to the monopolar axis ferroelectric HQERN, FQERN not only shows multiferroicity with the coexistence of multipolar axis ferroelectricity and ferroelasticity but also realizes out‐of‐plane ferroelectric polarization and a dramatic enhancement of Curie temperature of 94 K. This is mainly due to the introduction of F‐substituted organic cations, which leads to a change in orientation and a reduction in crystal lattice void occupancy. Our study demonstrates that F‐substitution is an efficient strategy to realize and optimize ferroelectric functional characteristics, giving more possibility of 2D ferroelectric materials for applications in micro‐nano optoelectronic devices.

Molecular Engineering Regulation Achieving Out-of-Plane Polarization in Rare-Earth Hybrid Double Perovskites for Ferroelectrics and Circularly Polarized Luminescence.

Out-of-plane polarization is a highly desired property of two-dimensional (2D) ferroelectrics for application in vertical sandwich-type photoferroelectric devices, especially in ultrathin ferroelectronic devices. Nevertheless, despite great advances that have been made in recent years, out-of-plane polarization remains unrealized in the 2D hybrid double perovskite ferroelectric family. Here, from our previous work 2D hybrid double perovskite HQERN ((S3HQ)4EuRb(NO3)8, S3HQ=S-3-hydroxylquinuclidinium), we designed a molecular strategy of F-substitution on organic component to successfully obtain FQERN ((S3FQ)4EuRb(NO3)8, S3FQ=S-3-fluoroquinuclidinium) showing circularly polarized luminescence (CPL) response. Remarkably, compared to the monopolar axis ferroelectric HQERN, FQERN not only shows multiferroicity with the coexistence of multipolar axis ferroelectricity and ferroelasticity but also realizes out-of-plane ferroelectric polarization and a dramatic enhancement of Curie temperature of 94 K. This is mainly due to the introduction of F-substituted organic cations, which leads to a change in orientation and a reduction in crystal lattice void occupancy. Our study demonstrates that F-substitution is an efficient strategy to realize and optimize ferroelectric functional characteristics, giving more possibility of 2D ferroelectric materials for applications in micro-nano optoelectronic devices.

Evaluation of Spatiotemporal Characteristics of Lane-Changing at the Freeway Weaving Area from Trajectory Data

Intensive lane-changing (LC) events are one of the great causes that make freeway weaving areas become bottlenecks. This study proposes an approach using vehicle trajectory data to investigate the spatiotemporal distributions of the number of LC events, void occupancies, and throughput variations at the freeway weaving area. Firstly, all LC events are extracted from the cleaned dataset and classified into four types according to the LC vehicles’ origin–destination lanes and LC directions. Secondly, the time and space void occupancies are calculated using the kinematic theory. Thirdly, the throughput variations are identified with the oblique N-curve method. Finally, the spatial and temporal distributions of the LC events, void occupancies, and throughput variations are plotted to analyze their characteristics and relationships. The spatial distributions of different types of LC events indicate that most LC events occur at the surrounding area of the on-ramp entrance. Spatial distributions of time void occupancies show that the time void in the original lanes is quite small while that in the target lanes is much larger. Furthermore, the time void occupancies amplify downstream when considering vehicles traveling on the road. By comparing the temporal distributions of LC events, void occupancies, and throughput variations, there is a lag effect between the large value occurrences of space void occupancy and throughput reduction and that of the LC events, which can conclude a causal relationship between LC events and the occurrences of the space void occupancies and throughput reductions.

Targeted regulation and optimization of multifunctional phase transition materials by novel void occupancy engineering.

As an innovative form of stimulus-response materials, organic-inorganic hybrid phase transition materials have become a wonderful contender in the field of functional electronic equipment due to their versatile structure, intensive functions and straightforward preparation. However, the targeted regulation and optimization of the electrical/optical response, along with the establishment of regular structure-performance relationships, pose significant challenges in meeting the diverse demands of practical applications over an extended period. Herein, we conducted a systematic investigation into the role of lattice void occupancy in regulating phase transition temperature (Tp) and related optical/electrical bistability. By taking hybrid material [TMEA][Cd(SCN)3] featuring a flexible ammonium cation [TMEA]+ (TMEA = ethyltrimethylammonium) as the prototype, we successfully synthesized three phase transition materials, namely [DEDMA][Cd(SCN)3], [TEMA][Cd(SCN)3] and [TEA][Cd(SCN)3] (DEDMA = diethyldimethylammonium, TEMA = triethylmethylammonium, and TEA = tetraethylammonium), and the excellent regulation of the physical properties of these compounds was achieved through subtle engineering of void occupancy. More strikingly, [TEA][Cd(SCN)3] exhibits remarkable bistable properties in terms of dielectric and nonlinear optical responses (with second-harmonic generation intensity reaching 2.5 times that of KDP). This work provides a feasible avenue to reasonably customise organic-inorganic hybrid phase transition materials and finely adjust their intriguing functionalities.

Super‐Ionic Conductivity in ω‐Li9TrP4 (Tr = Al, Ga, In) and Lithium Diffusion Pathways in Li9AlP4 Polymorphs

AbstractPhosphide‐based compounds are promising materials for solid electrolytes. In recent times, a multiplicity of compounds featuring isolated MP4 (M = Si,Ge,Sn,Al,Ga) tetrahedra as structural building units in different arrangements with superionic lithium conductivity have been discovered. ω‐Li9AlP4, ω‐Li9GaP4, and ω‐Li9InP4 are presented as new high‐temperature modifications with superionic lithium conductivity reaching 4.5 mS cm−1 at room temperature. Impedance spectroscopy and static temperature‐dependent 7Li NMR experiments reveal conductivity values in the range of 0.2 to 4.5 mS cm−1 at room temperature and low activation energies for the title compounds. X‐ray and neutron diffraction methods disclose that the phosphorus atoms form a cubic‐close packing. The triel element and Li atoms are located in tetrahedral voids, further Li atoms partially fill the octahedral voids. Temperature‐dependent neutron diffraction shows for Li9AlP4 a phase transition at 573 K that influences the occupation of voids with Li and significantly affects the Li‐ion mobility. The evaluation of nuclear scattering densities by the maximum‐entropy approach and application of the one‐particle‐potential formalism reveal 3D lithium diffusion with a low activation energy preferentially on paths of adjacent tetrahedral and octahedral voids. The investigation of different polymorphs suggests that the equilibrated filling of tetrahedral and octahedral voids is a crucial parameter for the enhancement of superionic lithium conductivity.

Macroscopic constitutive equations of thermo-poroelasticity derived using eigenstrain–eigenstress approaches

Macroscopic constitutive equations for thermoelastic processes in a fluid-saturated porous medium are re-derived using the notion of eigenstrain or, equivalently, eigenstress. The eigenstrain-stress approach is frequently used in micromechanics of solid multi-phase materials, such as composites. Simple derivations of the stress–strain constitutive relations and the void occupancy relationship are presented for both fully saturated and partially saturated porous media. Governing coupled equations for the displacement components and the fluid pressure are also obtained.

Macroscopic constitutive equations of thermo-poroviscoelasticity derived using eigenstrains

Macroscopic constitutive equations for thermo-viscoelastic processes in a fully saturated porous medium are re-derived from basic principles of micromechanics applicable to solid multi-phase materials such as composites. Simple derivations of the constitutive relations and the void occupancy relationship are presented. The derivations use the notion of eigenstrain or, equivalently, eigenstress applied to the separate phases of a porous medium. Governing coupled equations for the displacement components and the fluid pressure are also obtained.

Ionic compounds: applications of chemistry to mineralogy

Chapter 1. Bonding and Composition. Types of Bonding. Ionic Compounds. Types of Ions. Names of Ions. Percent Composition and Empirical Formula. The Mole. Molar Mass (Formula Weight). Calculation of Empirical Formula from Percent Composition. Use of Oxide Data. Formulas for Solid Solutions. Covalent Character in Ionic Compounds. Interactions Between Ions. Some Laws of Electrostatics. Potential Energy of Charged Particles. Lattice Energy and Its Effect on Properties. Chapter 2. Structure of Ionic Compounds: Close-packing. Closest Packing of Ions. The Holes Between the Layers. Stacking Sequences. Closest Packing for Ionic Compounds. Relationship of Formula to Occupation of Voids. Chapter 3. The Symmetry of Crystals. Symmetry Elements. Hermann-Mauguin Notation (Point Groups). Crystal Systems. Chapter 4. Structure of Some Simple Closest-packed Compounds. Symmetry of the AB and ABC Closest-Packed Arrangements. The Unit Cell. The NaCl Structure. The Sphalerite Structure. Axial Relationships. Wurtzite, a Polymorph of Sphalerite. The Fluorite Structure. The Rutile Structure, Polyhedral Coordination Models. Chapter 5. Factors that Affect the Symmetry of the Unit Cell. Effect of Cation. The Chalcopyrite Structure and Solid Solution. Effect of the Anion. Some Oxy Anions. The Pyrite Structure. The Calcite Structure. Aragonite, A Polymorph of Calcite. Several Sulfates, Anhydrite and Barite. Several Silicates, Zircon and Beryl. Effect of Temperature and Pressure. Chapter 6. Physical Properties: Morphology. Morphology. Miller indices. Forms. Habit. Deviations in Crystal Growths. Parallel Growth. Twinning. Epitaxis and Pseudomorphism. Chapter 7. Physical Properties: Color. Light and the Electromagnetic Spectrum. The Nature of Electrons. Electron Configurations. The Crystal Field Model. Colored Cations. Ion Impurities. Crystal Defects. Chapter 8. Chemical Properties. Solubility. Energetics of Dissolution. Solubility Rules. Double Salts. Reaction with Acids. Types of Chemical Reactions. Water as Both Acid and Base. Strong and Weak Acids. Conjugate Bases. Use of Chemical Reactions for Identification. Appendices. 1. The periodic chart. 2. The elements: Symbols, melting points, boiling points, densities, and electronegativities . 3. Metallic, covalent, and ionic radii. 4. Quartz. 5. Crystal system identification practice. 6. Crystal classes and point groups. 7. Additional reading and resources.

Polydimethylsiloxane at the interfaces of fumed silica and zirconia/fumed silica

Polydimethylsiloxane (PDMS)/fumed silica A-300 and PDMS/ZrO 2/A-300 were studied using adsorption, thermogravimetry, temperature-programmed desorption (TPD) mass-spectrometry, infrared spectroscopy, XRD, and broadband dielectric relaxation spectroscopy. ZrO 2 was synthesized on fumed silica with zirconium acetylacetonate in CCl 4 at 350 K for 1 h and calcinated at 773 K for 1 h (1–4 reaction cycles). PDMS (5–40 wt.%) was adsorbed onto silica and zirconia/silica from hexane solution and then dried. Grafted zirconia changes the chemistry of the surface (because of its catalytic capability) and the topology of secondary particles (because of occupation of voids in aggregates of primary silica particles by zirconia nanoparticles) responsible for the textural porosity of the powders. Therefore, many properties (such as structural characteristics of the composites, reactions on heating in air and vacuum, interfacial relaxation phenomena, hydrophobicity as a function of treatment temperature, etc.) of PDMS/zirconia/silica strongly differ from those of PDMS/A-300. Broadening of the α-relaxation of PDMS at the interfaces of disperse oxides suggests both weakening of the PDMS–PDMS interaction and strengthening of the PDMS–oxide interaction.

Thermoelectric properties of uranium filled skutterudites U y(Fe xCo 4− x)Sb 12

The filled skutterudites of the form U y Fe x Co 4− x Sb 12 were fabricated and the thermoelectric properties for certain samples studied. For samples containing 100% cobalt, uranium could not be incorporated, or ‘filled’, into the voids in the skutterudite structure. With substitution of iron for cobalt the void occupancy by uranium increased. Uranium filled samples indicated relatively large Seebeck coefficient and p-type behavior. The thermal conductivity, especially below 500 K, of U y Fe x Co 4− x Sb 12 was strongly depressed by uranium filling and iron substitution. The dimensionless thermoelectric figure of merits, ZT, were improved by uranium filling and showed a maximum value ZT = 0.55 at 800 K for U 0.2FeCo 3Sb 12 of nominal composition.

Numerical simulation of two-phase flow in conceptualized fractures

Two-phase flow in fractured rock is an important phenomenon related to a range of practical problems, including non-aqueous phase liquid contamination of groundwater. Although fractured rocks consist of fracture networks, the study of two-phase flow in a single fracture is a pre-requisite. This paper presents a conceptual and numerical model of two-phase flow in a variable fracture. The void space of the fracture is conceptualized as a system of independent channels with position-dependent apertures. Fundamental equations, governing two-phase displacement in each channel, are derived to represent the interface positions and fractional flows in the fracture. For lognormal aperture distributions, simple approximations to fractional flows are obtained in analytical form by assuming void occupancy based on a local capillary allowability criterion. The model is verified by analytical solutions including two-phase flow in a parallel-plate fracture, and used to study the impacts of aperture variation, mobility ratio and fracture orientation on properties of two-phase flow. Illustrative examples indicate that aperture variation may control the distribution of wetting and non-wetting fluids within the fracture plane and hence the ability of the fracture to transmit these fluids. The presence of wetting fluid does little to hinder non-wetting fluid flow in fractures with large aperture variations, whereas a small volume of non-wetting fluid present in the fracture can significantly reduce wetting fluid flow. Large mobility ratios and high fracture slope angles facilitates the migration of non-wetting fluid through fractures.

Cerium filling and doping of cobalt triantimonide

We have fabricated and studied the structural, magnetic, and transport properties of filled skutterudites of the form Ce{sub y}Fe{sub 4{minus}x}Co{sub x}Sb{sub 12} with 0{lt} y{lt}1 and x=3.25 and 4. For samples containing 100{percent} Co, Ce can be inserted into approximately 10{percent} of the voids in the skutterudite structure. It is shown that the rare earth is trivalent and dopes the host CoSb{sub 3} n-type. With substitution of Fe for Co the void occupancy by Ce increases. The thermal conductivity is strongly depressed even at small (5{percent}) rare-earth filling fractions, and is further degraded by substitution of Fe for Co. Although the electron mobility in n-type samples is smaller than the hole mobility in p-type samples, due to their large electron masses the Seebeck coefficient in n-type material maintains large values at high electron concentrations. {copyright} {ital 1997} {ital The American Physical Society}

The effect of moisture absorption on the thermomechanical properties of particulates

Water absorption in particulate composites at ambient temperature influences their thermomechanical properties. Second Fick's law of diffusion was used in this paper to predict the diffusion coefficient of the composite materials tested. In all cases the matrix material was a diglycidyl ether of bisphenol-A polymer cured with 8 phr triethylene tetramine and filled with iron particles with an average diameter 150 μm at five distinct volume fractionsvf=0, 0.05, 0.10, 0.16 and 0.20. The modification of the modulus of elasticity, ultimate stress, breaking strain and breaking energy due to moisture absorption was examined. Moreover, differential scanning calorimetry was used to study the influence of the time exposure into water and the filler concentration of the particulates on their glass transition temperature. Finally, the void occupancy in the composite was evaluated from free volume considerations.