Unit Cell Dimensions Research Articles

Specialty topological fiber using periodic lattice geometries

Topological photonics provides a new platform to control and manipulate the flow of light in photonic devices that exhibit topological phase transitions. One way to introduce such transition of geometric phases in photonic waveguides is to modulate the structure of the photonic crystals, array waveguides, or the metamaterials in such a way that it eventually changes the bulk topology. Such topological waveguides localize the light at the boundary of the two distinct bulk systems with different topological invariant. Based on this fundamental physics, we demonstrate a robust and controlled propagation of light in a class of specialty optical fiber which exhibits the topological phase transition between a nontrivial one-dimensional (1D) periodic cylinder and its topologically trivial counterpart. The key idea is to explore the possibility of topological phase transition of 1D photonic bands over the momentum space by tuning the unit-cell dimension and its individual thicknesses. We have systematically computed the trivial and the nontrivial topological invariants, the Zak phase, of designed cylindrical 1D lattices with inversion symmetry over the first Brillouin zone. To establish the presence and the robustness of the localized edge mode, we have studied the reflectance of the geometry in the presence of disorder. Also, the simulated field profile and the back-reflectionless propagation of the edge mode through the fiber have been shown. Besides conventional fibers, such topological optical fibers are definitely a waveguide geometry for robust delivery of light and thus would be very significant to open up a new paradigm in guided wave photonics.

Structural and spectral studies of hydrated hexaamminecobalt(III)–hexafluororhenate(IV)

The crystal structure of the [Co(NH3)6]2[ReF6]3·3H2O (I) salt is reported. The salt crystallizes in the trigonal space group P31m with the following unit cell dimensions: a = 15.8714(4) Å, b = 15.8714(4) Å, and c = 9.8657(4) Å. The structure of (I) consists of [Co(NH3)6]3+ cations, [ReF6]2− anions, and co-crystallized water molecules which are linked by hydrogen bonding. In (I), independent [ReF6]2− anions and [Co(NH3)6]3+ cations octahedron are slightly distorted. Characteristic vibration bands of the [Co(NH3)6]3+ cation, [ReF6]2− anion as well as the co-crystallized H2O molecules are observed in the infrared spectra of (I). UV-Visible analyses in water showed that the absorption of the [Co(NH3)6]3+ cation predominate the spectra of (I).

Using Successive Self-Nucleation and Annealing to Detect the Solid–Solid Transitions in Poly(hexamethylene carbonate) and Poly(octamethylene carbonate)

Solid–solid transitions in poly(hexamethylene carbonate) (PC6) and poly(octamethylene carbonate) (PC8), denoted the δ to α transition, have been investigated, using self-nucleation and the successive self-nucleation and annealing (SSA) technique. The SSA protocol was performed in situ for thermal (differential scanning calorimetry (DSC)), structural (wide-angle X-ray scattering (WAXS)), and conformational (Fourier transform infrared spectroscopy (FT-IR)) characterization. The final heating after SSA fractionation displayed an enhanced (compared to a standard second DSC heating scan) endothermic and unfractionated peak signal at low temperatures corresponding to the δ to α transition. The improved (i.e., higher enthalpy and temperature than in other crystallization conditions) δ to α transition signal is produced by annealing the thickest lamellae made up by α and β phase crystals after SSA treatment. As thicker lamellae are annealed, more significant changes are produced in the δ to α transition, demonstrating the transition dependence on crystal stability and, thus, on the crystallization conditions. The ability of SSA to significantly enhance the observed solid–solid transitions makes it an ideal tool to detect and study these types of transitions. In situ WAXS reveals that the δ to α transition corresponds to a change in the unit cell dimensions, evidenced by an increase in the d-spacing. This implies a more efficient chain packing in the crystal, for both samples, in the δ phase (lower d-spacing at low temperatures) than in the α phase (higher d-spacing at high temperatures). The chain packing differences are explained through in situ FT-IR measurements that show the transition from ordered (δ phase) to disordered (α phase) methylene chain conformations.

Effect of loading rates on the in-plane compressive properties of additively manufactured ABS and PLA-based hexagonal honeycomb structures

Honeycomb structures find numerous applications in automotive, aerospace, sports, and other similar engineering fields. Such incorporation is made possible by the excellent crushing resistance and specific energy absorption capabilities. However, manufacturing such structures through conventional processes is highly laborious and expensive. Such a drawback can be largely mitigated by the adoption of additive manufacturing (AM) processes. Consequently, in this study, hexagonal honeycomb structures are subjected to experimental tests to determine their compressive strength under different loading rates. In addition to this, attempts have also been made to evaluate the effect of different materials and the unit cell dimensions on the compressive properties. The test specimens of different wall thicknesses are manufactured by fused deposition modelling (FDM) using PLA and ABS as the base materials. The samples are then subjected to compressive tests using a standard UTM to quantify the effect of the cell geometrical parameters and the loading rate on the overall compressive nature of the structures. The results show that the compression properties are primarily affected by the loading rate, material properties and the cell-wall thickness of the structures. The initial compressive yield stress and plateau stress generally increase up to a given value of loading rate, after which the strength decline. The cell-wall thickness of the structure influences the threshold loading rate. Therefore, this study provides a preliminary understanding of the compressive properties of AM hexagonal honeycomb structures to analyse the prospects for application in real-world engineering applications. It is proposed that such structures find profound applications in structural components of aerospace equipment, automotive parts, sports gear, and other similar areas of interest where high strength and energy absorption are of predominant importance.

Intergrowth of Graphite‐Like Crystals in Hard Carbon for Highly Reversible Na‐Ion Storage

AbstractHard carbon usually refers to non‐graphitizable carbon, which does not transform into a crystal structure even at high temperatures. Although hard carbon is considered as the most promising anode material for Na‐ion batteries (NIBs), its practical application is still hindered by its low initial coulombic efficiency (ICE). Here, the intergrowth of large area graphite‐like crystals in hard carbon is reported using cotton as precursor and graphite as crystal template by calcination under their intimate contact condition. Extensive characterizations provide abundant evidence that graphite‐like crystal is a new carbon allotrope belonging to the hexagonal system (a = b = 3.528 Å, c = 9.6 Å, α = β = 90°, γ = 120°) with d‐spacing of 4.8 Å for (002) plane. Its unit cell dimensions and d‐spacing of (002) plane are all enlarged by the same factor of 1.428 compared to those of the graphite phase. When applied in NIBs, the hard carbon with graphite‐like crystals shows an extremely high ICE of 95.0% with a large reversible capacity of 343 mAh g−1, which reaches the same level as graphite used in Li‐ion batteries. The graphite‐like crystal breaks the traditional concept of hard carbon, while the graphite‐template induced epitaxial growth mechanism may provide a new way for obtaining novel crystalline carbon allotropes.

Design of frequency selective surface based on Minkowski fractal and interdigital capacitance

In this paper, the Minkowski fractal is used to design the geometry of a frequency selective surface (FSS) unit cell, which resembles the shapes found in nature. The proposed FSS unit cell has both angular and polarization stabilities of incident wave. For the miniaturization of FSS and decrease of resonance frequency, interdigital capacitances (IDCs) are devised in the FSS structure, which do not eliminate angular and polarization stabilities. The dimensions of the unit cell are 5 mm × 5 mm and miniaturized 0.095λ0×0.095λ0. The resonance frequency is specified as 5.75 GHz with 155 MHz bandwidth. An equivalent circuit is derived for the unit cell to evaluate its frequency responses. The effects of variations of the geometrical dimensions of the FSS unit cell on its performance are studied. A prototype model of proposed FSS is fabricated and measured. The performance of its full-wave computer simulation results and measured data are compared and are shown to be in good agreement.

Potassic-Hastingsite from the Kedrovy District (East Siberia, Russia): Petrographic Description, Crystal Chemistry, Spectroscopy, and Thermal Behavior

In this work we report on a petrographic, crystal-chemical, and optical characterization, obtained from different analytical methods, of amphibole species. Potassic-hastingsite, ideally AKBCa2C(Fe2+4Fe3+)T(Si6Al2)O22W(OH)2, has been found in the Kedrovy district (East Siberia, Russia). The sample occurs as well-formed and large radially radiant aggregates of dark green, almost black crystals. The unit cell dimensions are a = 9.9724(3) Å, b = 18.2968(4) Å, c = 5.3573(1) Å, β = 104.945(3)°, V = 944.44(4) Å3, Z = 2. Site populations were determined by combining single-crystal structure refinement and electron probe microanalysis, and Fe3+/Fe2+ ratio was obtained from X-ray fluorescence analysis. Infrared, diffuse light UV/Vis/NIR absorption, and electron spin resonance spectra are presented and discussed. A thermoelastic behavior of a powder of potassic-hastingsite was studied by in situ high-temperature X-ray diffraction. A thermal expansion and subsequent significant contraction in the unit cell volume during a high-temperature X-ray powder diffraction experiment is observed as a consequence of the deprotonation process, which is locally balanced via oxidation of Fe2+. According to the data obtained for potassic-hastingsite, these processes occur within 400–600 °C. The thermal expansion of the mineral is anisotropic; the thermal expansivity coefficients αa:αb:αc (×10−6) = −18.06:9.59:−1.09 at 400 °C, −26.15:−1.52:2.22 at 600 °C and 23.77:−25.06:42.08 at 750 °C.

Growing a Display Crystal of Recycled Potassium Tris(oxalato)ferrate(III) Trihydrate

Potassium tris(oxalato)ferrate(III) trihydrate is a commonly prepared coordination compound in general or upper-level chemistry laboratories and can be recycled to grow large single crystals that instructors may display when introducing the experiment to classes. Showing the crystal’s shape can also be used to briefly introduce students to X-ray crystallography, symmetry, and unit cell dimensions.

Bi8Te3, the 11-Atom Layer Member of the Tetradymite Homologous Series

Bi8Te3 is a member of the tetradymite homologous series, previously shown to be compositionally and structurally distinct from hedleyite, Bi7Te3, yet inadequately characterized structurally. The phase is identified in a sample from the Hedley district, British Columbia, Canada. Compositions are documented by electron probe microanalysis and structures are directly imaged using high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). Results confirm that Bi8Te3 has an 11-atom layer structure, in which three Bi-Bi pairs are placed adjacent to the five-atom sequence (Te-Bi-Te-Bi-Te). Bi8Te3 has trigonal symmetry (space group R3¯m) with unit cell dimensions of a = ~4.4 Å and c = ~63 Å calculated from measurements on representative electron diffraction patterns. The model is assessed by STEM simulations and EDS mapping, all displaying good agreement with the HAADF STEM imaging. Lattice-scale intergrowths are documented in phases replacing Bi8Te3, accounting for the rarity of this phase in nature. These results support prior predictions of crystal structures in the tetradymite homologous series from theoretical modeling and indicate that other phases are likely to exist for future discovery. Tetradymite homologues are mixed-layer compounds derived as one-dimensional superstructures of a basic rhombohedral sub-cell. Each member of the series has a discrete stoichiometric composition and unique crystal structure.

In situ growth of an ethyl p-hydroxybenzoate single crystal by the vertical Bridgman technique: a potential nonlinear optical material for third-harmonic generation

Optically transparent single crystals of ethyl p-hydroxybenzoate (EPHB) were successfully grown by the vertical Bridgman technique. The crystalline phase and unit-cell dimensions were obtained from powder X-ray diffraction using Rietveld analysis. The presence of defects and grain boundaries was investigated by high-resolution X-ray diffraction. The optical quality of the grown single crystal was assessed by UV–Vis and photoluminescent spectroscopies. A blue emission, with a bi-exponential decay time, was obtained from time-resolved photoluminescence upon laser excitation at 266 nm. The mechanical strength of the EPHB single crystal was studied by Vickers hardness testing. A decrease in the laser-damage threshold was observed with a nanosecond Nd:YAG laser source for increased pulse repetition rates. The third-order nonlinearity, nonlinear absorption coefficient and nonlinear refractive index were measured using the Z-scan technique with a femtosecond Ti:sapphire laser. The third-order nonlinear coefficient values for the grown crystal were compared with those of a potassium dihydrogen phosphate single crystal.

Synthesis, Crystal Structure, Hirshfeld Surface, Energy Framework and Molecular Docking of 2-(((6-Methoxy pyridin-3-yl)imino)methyl)Phenol

The structure of 2-(((6-methoxypyridin-3-yl)imino)methyl)phenol (MPIMP) (C13H12N2O2) has been determined by X-ray diffraction methods. It crystallizes in the tetragonal crystal system with space group P42/n and unit cell dimensions a = 14.2958(3) Å, b = 14.2958(3) Å, c = 11.0179(3) Å, V = 2251.73(12) Å3, Z = 8. The structure has been refined by full-matrix least square procedure to a final R-value of 0.0518(wR2= 0.1312) for 1709 observed reflections. The molecules linked via two intermolecular (C-H...N and C-H...O) hydrogen bonds. The crystal structure was further stabilized by a strong intramolecular N-H...O hydrogen bond. The Hirshfeld surface analysis reveals the interaction contacts of the molecule and the strength of molecular packing in the crystal. The energy framework has been performed through different intermolecular interaction energies for structural stability. The molecular docking of MPIMP was performed against tuberculosis enzyme Decaprenyl-phosphoryl-b-Dribose 20-epimerase (DprE1, PDB code: 4KW5) to reconnoiter the binding interactions at the active sites.

Crystal structure and heat capacity study of (C12H25NH3)2CoCl4(s) phase change material

Crystal structure of a novel complex (C12H25NH3)2CoCl4(s) has been determined by X-ray crystallography. Crystal system of the compound is monoclinic, and space group is P2(1)/c. Unit cell dimensions are a = (0.73492 ± 0.00010) nm, b = (1.02115 ± 0.00013) nm, and c = (4.2486 ± 0.0003) nm; α = 90°, β = (94.061 ± 0.002)°, γ = 90°, and Z = 4. Low-temperature heat capacities of the title compound are measured by an improved precision automated adiabatic calorimeter in the temperature range from 77 to 396 K. A solid to solid phase transition process occurs in the temperature range of 330 ∼ 365 K in the heat capacity curve, and peak temperature, molar transition enthalpy and entropy from three series of heat capacity measurements of the title compound are determined. The average phase transition temperature Ttrs, phase transition enthalpy ∆trsHm and phase transition entropy ∆trsSm from three series of experiments are (363.06 ± 0.54) K, (83.119 ± 0.197) kJ•mol−1 and (228.94 ± 0.34) J•K−1•mol−1, respectively. Experimental values of molar heat capacities in the temperature regions of 77–327 K and 367–396 K are, respectively fitted to two polynomial equations. Polynomial fitted values of molar heat capacities and fundamental thermodynamic functions of the sample relative to standard reference temperature 298.15 K are calculated and tabulated at an interval of 5 K.

ADDITIVELY MANUFACTURED Ti6Al4V LATTICE STRUCTURES FOR BIOMEDICAL APPLICATIONS

Additive Manufacturing (AM) is a rapidly developing technology which provides opportunity to build up complex geometries due to the freedom of manufacturing. Lattice structures, three-dimensional open-celled structures composed of one or more repeating unit cells, can be produced with unique mechanical, thermal, acoustic, biomedical and electrical properties by optimization of type and dimension of unit cell and additive manufacturing parameters. Lattice structures provide lightweight and porous parts which are widely preferable in biomedical applications. Different type of lattice structures have been used for obtaining bone like implant surface to accelerate osseointegration. There are many studies in this field, but the ideal designs and dimensional accuracy of the various lattice structures for biomedical field have not been completely reached. In this study, octahedral, star and dodecahedron lattice structures with thin strut diameter were manufactured by laser powder bed fusion technology (LPBF) by Ti6Al4V powder. Cubic and plate samples were built on z-direction and their top and side surfaces were inspected in terms of topographical characteristics and dimensional accuracy by scanning electron microscope.

Multi-temperature X-ray diffraction study of a reversible structural phase transition in the high-temperature polymorph of Ce2Rh2Ga compound

A recently investigated HT-Ce2Rh2Ga was found to exhibit a magnetic phase transition at 128.5 K. A comprehensive multi-temperature investigation in the 85–400 K temperature range showed that the compound undergoes a structural phase transition as well. Upon cooling below 123.2 K its crystal symmetry changes from Cmce to C2/m being accompanied by non-merohedral twinning. Both structural transformations are reversible with a small hysteresis furthermore. The temperature of the structural phase transition was detected by anomalies in temperature dependences of unit cell dimensions, interatomic distances, and atomic displacement parameters. Negative thermal expansion along the c-axis was revealed in the range 92.7–170 K. When cooled to 200 K, Ce and Rh atoms converge to a distance sufficient for structural changes to become qualitative. Upon further cooling to 145 K, this interaction affects positions of all the atoms in the structure, leading to anisotropy of earlier equivalent interatomic distances and a sharp anomalous increase in atomic displacement parameters, the dynamics of which deviates more and more from the theoretical dependences in the Einstein and Debye approximations.

Design and Analysis of a Photonic Crystal Based Planar Antenna for THz Applications

Modern advancements in wearable smart devices and ultra-high-speed terahertz (THz) communication systems require low cost, low profile, and highly efficient antenna design with high directionality to address the propagation loss at the THz range. For this purpose, a novel shape, high gain antenna for THz frequency range applications is presented in this work. The proposed antenna is based on a photonic bandgap (PBG)-based crystal polyimide substrate which gives optimum performance in terms of gain (9.45 dB), directivity (9.99 dBi), and highly satisfactory VSWR (<1) at 0.63 THz. The performance of the antenna is studied on PBGs of different geometrical configurations and the results are compared with the antenna based on the homogeneous polyimide-based substrate. The effects of variations in the dimensions of the PBG unit cells are also studied to achieve a −10 dB bandwidth of 28.97 GHz (0.616 to 0.64 THz).

Unit cell estimation of volumetrically-varying permittivity in additively-manufactured ceramic lattices with X-ray computed tomography

Additive manufacturing of ceramics is transforming electromagnetics by providing density-varying lattices and stochastic foams within arbitrary envelopes. Periodic structures can now be fabricated with zirconia which offers the highest permittivity of any 3D printable material possible to be printed with nearly-full-density. By arranging a lattice with variation in the strut and node sizings as well as unit cell dimensions, the effective density of a structure can be spatially-modulated gracefully and with unprecedented freedom. These variations in density directly translate into variations in the effective permittivity of the bulk lattice (estimated locally and globally with a combination of mixing formulas, curve fits, and capacitance models). A lattice had previously been fabricated with a rectangular envelope for evaluation of effective global permittivity of the overall structure using a network analyzer. For this work, the structure was scanned with X-ray computed tomography (CT) to capture the three dimensional density of the structure including both the solid ceramic elements as well as the interstitial space. Software was developed that reads CT scan data and provides a 3D data structure with a pointwise unit cell estimation of the effective permittivity throughout the volume - a model well suited for electromagnetic simulations to optimize advanced microwave devices. The proposed technique serves as a foundation for the non-destructive estimation of space-varying permittivity within 3D printed lattices and foams.

The molecular model of Marcellus shale kerogen: Experimental characterization and structure reconstruction

A realistic three-dimensional (3D) kerogen molecular model adds significant values in petrographical evaluation in shale, especially it is essential to conduct molecular simulation for gas storage and transport behaviors in shale. In this study, the 3D kerogen molecular structure of Marcellus shale was reconstructed based on molecular simulation, and eight experimental techniques, including 13C nuclear magnetic resonance (13C NMR) spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), elemental analysis, helium porosimetry, low-pressure CO2 adsorption, and radial distribution function (RDF) obtained from synchrotron X-ray. The XPS data provides elemental compositions and the contents of functional groups of carbon, oxygen, nitrogen and sulfur on the kerogen surface. FTIR and 13C NMR spectroscopy provide the contents of aliphatic chains and aromatic rings. The two-dimensional (2D) kerogen molecular structure was initially constructed, and the connection of kerogen fragments was verified by comparing the experimental and calculated 13C NMR spectra. Then, fourteen 2D kerogen molecules were used to reconstruct the 3D kerogen molecular structure. Experimental helium density and micropore volume were used to verify the density and micropore structure of the final 3D model. Experimental RDF data were also used to analyze the spatial distribution of the kerogen atoms. The reconstructed 3D kerogen molecular structure of Marcellus shale contains 5936 atoms (C2856H2492N56O532), and the unit cell dimension is 3.755 × 3.755 × 3.755 nm. This study provides a systematic approach to establish a realistic 3D kerogen molecular model by leveraging the advantages of various techniques. The established Marcellus kerogen model lays the foundation for future fluid transport and storage studies.

Patterns in Nature—S-Layer Lattices of Bacterial and Archaeal Cells

Bacterial surface layers (S-layers) have been observed as the outermost cell envelope component in a wide range of bacteria and most archaea. S-layers are monomolecular lattices composed of a single protein or glycoprotein species and have either oblique, square or hexagonal lattice symmetry with unit cell dimensions ranging from 3 to 30 nm. They are generally 5 to 10 nm thick (up to 70 nm in archaea) and represent highly porous protein lattices (30–70% porosity) with pores of uniform size and morphology in the range of 2 to 8 nm. Since S-layers can be considered as one of the simplest protein lattices found in nature and the constituent units are probably the most abundantly expressed proteins on earth, it seems justified to briefly review the different S-layer lattice types, the need for lattice imperfections and the discussion of S-layers from the perspective of an isoporous protein network in the ultrafiltration region. Finally, basic research on S-layers laid the foundation for applications in biotechnology, synthetic biology, and biomimetics.

Crystal structure, Raman spectroscopy study and quantum chemical DFT calculations of N-phenyl -3-para nitro phenyl isoxazolidine-5-carbonitrile

N-phenyl-3-para nitro phenyl isoxazolidine-5-carbonitrile compound (C16H13N3O3) has been synthesized and characterized by single-crystal X-ray diffraction at 293 K. The title compound crystallized in the orthorhombic system (Pbca space group) with Z = 8 and the following unit cell dimensions: a = 12.9970 (9) Å, b = 7.3090 (9) Å, c = 29.658 (2) Å. Raman spectroscopy has been investigated at room temperature. Raman spectra have been measured at 647.5 nm excited laser lines in the frequency range 125–4000 cm−1. The Raman spectrum is characterized by a series of bands in the 150–3500 cm−1 spectral range. The structure of the this compound was optimized by density functional theory (DFT) using B3LYP method and shows that the calculated values obtained by B3LYP/6-31G(d,p) basis are in much better agreement with the experimental data than those obtained by B3LYP/6- 31G(d). The vibrational frequencies were evaluated using density functional theory (DFT) with the standard B3LYP/6-31G(d,p) basis. The Molecular Frontiers Orbitals (FMOS) calculation is carried out to determine the charge transfer within the molecule.

Capacity Fading Mechanisms in Ni-Rich Single-Crystal NCM Cathodes

A series of single-crystal, Ni-rich Li[NixCoyMn1–x–y]O2 (NCM) cathodes (x = 0.7, 0.8, and 0.9) with particle diameters of ∼3 μm are systematically compared with polycrystalline cathodes with corresponding Ni contents. Despite their high resistance to microcracking, the electrochemical performances of single-crystal NCM cathodes, in terms of capacity and cycling stability, are inferior to those of polycrystalline NCM cathodes. In situ XRD and TEM analyses reveal that the lithium concentrations in single-crystal NCM cathodes become spatially inhomogeneous during cycling; this phenomenon is exacerbated by high C rates and Ni contents, resulting in the coexistence of phases with widely different unit cell dimensions within a single cathode particle. This coexistence of two phases induces nonuniform stress that generates structural defects, impairing the diffusion of lithium ions and, eventually, leading to rapid capacity fading.