Unit Cell Constants Research Articles

Orientational and crystallographic relationships in thin films of yttrium orthoferrite on sapphire substrates.

An algorithm is proposed for determining the orientational relationships and crystal unit-cell parameters of thin films using a laboratory X-ray diffractometer and stereographic projections. It is illustrated by the treatment of experimental data obtained for yttrium orthoferrite YFeO3 films on single crystalline sapphire (Al2O3) substrates for film thicknesses in the range from 100 to 7000 Å. Precise determination of unit-cell constants and angles is possible by combining the results of X-ray measurements made in the in-plane and out-of-plane geometries. The unit-cell unit parameters and orientation relationships for thin films were determined. For the studied films, typical errors in determining unit-cell parameters and angles are better than 0.17 Å and 0.17°, respectively.

Parametric Modelling of the Crystalline Microstructure of the MCM41-Type Mesoporous Silica Modified with Derivatives of Alkyls.

A siliceous material in which a framework order was established with a surfactant with sixteen carbon atoms in alkyl chains, MCM-41-C16, was synthesised, surface-modified, and tested regarding the selected physical properties. The pristine material was extracted in an acidic aqueous alcohol and then lined with different surface groups. The properties of four adsorbents were investigated using XRD, X-ray photoelectron spectroscopy, and N2 physisorption techniques. The unit-cell constant was determined from X-ray diffractograms, being in fixed relation to the edge length of the hexagonal frame. The specific surface areas of mesopores and whole crystallites were determined from low-temperature N2-physisorption isotherms. The novelty of this work is a mathematical model of a crystalline microstructure explaining the sizes and shapes of crystalline grains in relation to adsorption features, proposed and successfully tested with the aforementioned experimental data. The roughness of the surface is different from one that is necessary to explain the experimental characteristics quantitatively.

Synthesis, X-Ray, Spectral Characterization, DFT, and Molecular Docking Calculations of 2-(5-Nitro-1-H-Indazol-1-yl) Acetic Acid

In this work, theoretical and experimental studies of a new Indazole derivative named 2-(5-nitro-1-H-indazol-1-yl) acetic acid (3), including the synthesis and characterization by 1H and 13C-NMR, FT-IR, UV spectroscopies are reported together with its X-ray crystal structure. The compound crystallizes in the monoclinic crystal system of P21/c space group and unit cell constants: a = 7.8541(10) Å, b = 7.9274(11) Å, c = 15.877(2) Å, β = 101.149(5)°. In the crystal, O–H···N and C–H···O hydrogen bonds form a 3-D network structure containing small channels running parallel to the b-axis. B3LYP/6-311++G** calculations in the gas phase and ethanol solution suggest the existence of C1 and C2 conformers where the structure of C1 in both media is in agreement with that observed by X-ray diffraction. Probably, the high values observed in the dipole moments of C1 justify its presence in gas and solution phases. The stabilities of both forms were justified by NBO and AIM calculations where C1 is more stable than C2. C1 shows a higher solvation energy, dipole moment, and higher hydration than C2 while the frontier orbitals suggest a higher reactivity of C1 over C2. Force fields and complete vibrational assignments were performed for the C1 conformer because it was detected in the solid phase. Scaled force constants for both forms are also reported. Calculated chemical shifts for (3) are consistent with the experimental 1H and 13C-NMR spectra in the DMSO-d6 solution. The anti-COVID activity of 3 is investigated by its molecular docking into the binding site of SARS CoV-2 3CLpro (3 C-like protease). It shows a moderate binding affinity into the binding site of 3 C-like protease with a maximum binding energy of −5.57 kcal mol−1.

Design of compact and broadband filtering balun based on N-shaped spoof surface plasmon polaritons

This paper presents a novel compact and broadband filtering balun using N-shaped spoof surface plasmon polaritons (SSPPs). The N-shaped SSPP unit cell’s lateral size has a 48% reduction compared to the rectangle-shaped counterpart. The proposed filtering balun is constructed by periodically etching N-shaped and mode-matching SSPP unit cells into the slotline balun consisting of the microstrip-to-slotline transition (MST) structures. The combination of the N-shaped SSPP unit cells and slotline balun realize the compactness and the broadband bandpass filtering response. Moreover, we can individually adjust the passband’s lower and upper cut-off frequencies. Due to the larger phase constant of the N-shaped SSPP unit cell, the field-confined ability of the proposed filtering balun is enhanced. The proposed design is fabricated and measured. It has advantages in bandwidth, stopband performance, size, and degree of design freedom compared with existing SSPP filtering baluns.

Programming nonreciprocity and harmonic beam steering via a digitally space-time-coded metamaterial antenna

Recent advancement in digital coding metasurfaces incorporating spatial and temporal modulation has enabled simultaneous control of electromagnetic (EM) waves in both space and frequency domains by manipulating incident EM waves in a transmissive or reflective fashion, resulting in time-reversal asymmetry. Here we show in theory and experiment that a digitally space-time-coded metamaterial (MTM) antenna with spatiotemporal modulation at its unit cell level can be regarded as a radiating counterpart of such digital metasurface, which will enable nonreciprocal EM wave transmission and reception via surface-to-leaky-wave transformation and harmonic frequency generation. Operating in the fast wave (radiation) region, the space-time-coded MTM antenna is tailored in a way such that the propagation constant of each programmable unit cell embedded with varactor diodes can toggle between positive and negative phases, which is done through providing digital sequences by using a field-programmable gate array (FPGA). Owing to the time-varying coding sequence, harmonic frequencies are generated with different main beam directions. Furthermore, the space time modulation of the digitally coded MTM antenna allows for nonreciprocal transmission and reception of EM waves by breaking the time-reversal symmetry, which may enable many applications, such as simultaneous transmitting and receiving, unidirectional transmission, radar sensing, and multiple-input and multiple-output (MIMO) beamformer.

Exploring the Decreasing Coercivity Properties of Aluminum Cobalt Ferrites Prepared by Coprecipitation Method

Cobalt aluminum ferrites were synthesized by coprecipitation method at 1000 ºC. XRD studies pointed out the employed samples (Fe2+Al2 3+O42−, Fe0.25Co0.75Al2O4 and Fe0.75Co0.25Al2O4) were crystallized in a single phase cubic spinel form. The synthesized samples were calculated structural parameters such as crystallitesize (D: 17 nm), X-ray density (Dx: 3.97 to 4.15 g/cm3), volume of the unit cell (V: 583.64 to 586.58 Å), lattice strain (ε: 6.9 × 10-3), dislocation density (δ: 3.3 × 10-3) and lattice constant (a: 8.357 to 8.371 Å). The FE-SEM microstructure confirmed that various concentrations result in different particle sizes (5 μm to 500 nm). The magnetic characteristics were investigated by VSM and magnetic parameters like saturation magnetization (Ms: 4.82 × 10-3 to 0.673 emu/g), retentivity (Mr: 1.545 × 10-3 to 0.229 emu/g), coercivity (Hc: 775.45 to 2212.8 Oe), magnetic moment (μB: 1.57 × 10-4 to 2.108 × 10-2), remnant ratio (R: 0.32 to 0.357 no unit) and anisotropy constant (K: 3.418 to 177.57 J/m3) were calculated. High coercivity materials are ideal for use in magnetic recording media, permanent magnets and microwave devices since they possess a high degree of resistance to an external magnetic force.

Effect of Fe-Doping on Thermal Expansion and Stability of Bismuth Magnesium Tantalate Pyrochlorere.

A continuous series of solid solutions (Bi1.5Mg0.75-xFexTa1.5O7±Δ (x = 0-0.75)) with the pyrochlore structure were synthesized with the solid-phase method. It was shown that iron, like magnesium, is concentrated in the structure in the octahedral position of tantalum. Doping with iron atoms led to an increase in the upper limit of the thermal stability interval of magnesium-containing pyrochlore from 1050 °C (x = 0) up to a temperature of 1140 °C (x = 1). The unit cell constant a and thermal expansion coefficient (TEC) increase uniformly slightly from 10.5018 Å up to 10.5761 Å and from 3.6 up to 9.3 × 10-6 °C-1 in the temperature range 30-1100 °C. The effect of iron(III) ions on the thermal stability and thermal expansion of solid solutions was revealed. It has been established that the thermal stability of iron-containing solid solutions correlates with the unit cell parameter, and the lower the parameter, the more stable the compound. The TEC value, on the contrary, is inversely proportional to the cell constant.

The effect of heavy and light electronic bands on thermoelectric properties of Mg2Si1-xSnx alloys: Insights from an ab-initio study

Mg2X (X = Si, Sn, and Ge) based compounds have attracted great attention due to their numerous advantages in thermoelectric (TE) applications. In particular, to date, ternary Mg2X based alloys have been recognized the most extensively explored thermoelectric systems, because these compounds exhibit excellent TE properties. Using the first-principles methods, we accomplished mutual alloying of Mg2X (Si, Sn) compounds in order to develop their efficiency in expanding the range of TE applications. The electrical, structural, and thermoelectric properties of Mg2Si1-xSnx were studied. With increasing Sn content in Mg2Si1-xSnx compounds, our calculations reveal a linear increase of the unit-cell constant and a decrease of the bulk modulus. Besides, this Sn content increase also leads to a decrease in the energy gap values. Moreover, taking into account the carrier concentration impact on the TE properties, we can state that the n-type Mg2Si1-xSnx alloys reveal higher TE behavior resulting from the large effective mass m* (in terms of electron mass m0) and higher DOS at the Fermi level. In particular, the supreme ZT value is about 1.4 for n-type Mg2Si0.375Sn0.625 at 700 K with n = 4x1020 cm−3, where the combination of elevated power factor and small thermal conductivity values play a key role. The supreme value of ZT is 0.9 for p-type Mg2Si at 700 K. These results suggest that Mg2Si1-xSnx alloys could be considered exceptional TE materials for practical use due to their fair TE performance.

Correlation between linear magnetostriction and magnetocaloric effect in the Fe7Se8 single crystals

The effect of the change in size under the influence of an applied magnetic field (magnetostriction) was studied in Fe7Se8 single crystals. It was shown that a systematic change in the unit-cell constants, induced by an external magnetic field and dependent on the direction and magnitude of this field, strongly correlates with the change in the spin reorientation temperature (T SRT) and the magnetic entropy change, which is strongly dependent on T SRT and magnetization. The obtained results suggest that the relation between magnetostriction and the change in magnetic entropy (ΔS m), reported previously for different materials, seems to have universal character, and magnetostriction can be used as an indirect method to estimate the change in magnetic entropy in Fe7Se8 single crystals substituted with transition metals.

Completely crystalline carbon containing graphite-like crystal enables 99.5% initial coulombic efficiency for Na-ion batteries

Hard carbon, also known as hardly graphitizable carbon, shows great potential for Na-ion batteries (NIBs), but its practical application is greatly hindered by the low initial coulombic efficiency (ICE). Here we report the growth of the completely crystalline carbon from hard carbon precursor under sufficient graphite template-induced conditions. The most crucial growth stage is realized at the low temperature slightly higher than pyrolysis peak temperature (e.g. 380 °C for eggshell membrane), in which sufficient biomass pyrolysis is realized; graphite crystal template can efficiently induce the decomposed carbon atoms and atomic fragments orderly align in parallel fashion enabling their orderly mobility and conversion of sp3-hybridized carbon to sp2-hybridized carbon, promoting the formation of crystal structure. Further high temperature calcination (e.g. 1300 °C) is used to improve the crystal quality, leading to the formation of completely crystalline carbon. The graphite-like crystal possesses a geometrically similar unit-cell to graphite but proportionally enlarged unit-cell constants and interplanar distance of (002) plane. When used as an anode in NIBs, it achieves an ICE up to 99.5% with large reversible capacity of 321.7 mAh/g. Furthermore, it demonstrates only low-voltage plateaus below 0.5 V without high-voltage slope region, showing the same electrochemical behaviors as Li-graphite counterpart.

High-pressure study of hydrogen storage material ethylenediamine bisborane from first-principle calculations

Ethylenediamine bisborane (EDAB), as a hydrogen storage material, is one of the most promising possible candidates. This work reports the effects of pressure on the structural, mechanical, electronic, and vibrational behaviors of EDAB using density functional theory calculations. The predicted lattice parameters, bulk modulus B0 and its first pressure derivative B′ are in accord with available experimental data. From the unit-cell constants as a function of pressure, crystal EDAB is found to present an anisotropic compressibility. The calculated elastic properties show that the ambient phase EDAB is mechanical unstable at 3 GPa. Furthermore, the discontinuous behavior was found in the pressure dependence of crystal and electronic structure, suggesting a structural transformation occurred around 3 GPa. Finally, vibrational spectra are reported together with their infrared active modes assignment. The NH and BH stretching modes soften under compression, indicating the strengthening of hydrogen bonding, which leads to the occurrence of pressure-induced structural transformation.

A physicochemical study of a modified sol–gel derived neodymium-hydroxyapatite

Nd-doped hydroxyapatite (HANd) nanoparticles, Ca10−xNdx(PO4)6(OH)2, x = 0.1, 0.2, 0.3, 0.4 and 0.5, were obtained via the sol–gel technique. The as-prepared powders were subsequently calcined at 600 and 700 °C. X-ray diffraction (XRD) was used to investigate phase purity, crystal structure while Fourier Transform Infrared Spectroscopy (FTIR) was used to analyze the functional group of the obtained powders. The unit cell constants have also been calculated and match well with those of the hexagonal hydroxyapatite with the space group P63/m. Powders calcined at 700 °C were better crystallized than at 600 °C, which was furthermore confirmed by the IR spectra. Moreover, wettability was measured using a static sessile drop technique. All powders have shown a high hydrophilicity.

Neutron Diffraction Study of the Martensitic Transformation of Ni2.07Mn0.93Ga Heusler Alloy

The martensitic transition featuring the ternary Heusler alloy Ni2.09Mn0.91Ga was investigated by neutron diffraction. Differential scanning calorimetry indicated that structural transition starts at 230 K on cooling with a significant increase in the martensitic transformation onset compared to the classical Ni2MnGa. The low-temperature martensite presents the 5M type of modulated structure, and the structural analysis was performed by the application of the superspace approach. As already observed in Mn-rich modulated martensites, the periodical distortion corresponds to an incommensurate wave-like shift of the atomic layers. The symmetry of the modulated martensite at 220 K is orthorhombic with unit cell constants a = 4.2172(3) Å, b = 5.5482(2) Å, and c = 4.1899(2) Å; space group Immm(00γ)s00; and modulation vector q = γc* = 0.4226(5)c*. Considering the different neutron scattering lengths of the elements involved in this alloy, it was possible to ascertain that the chemical composition was Ni2.07Mn0.93Ga, close to the nominal formula. In order to characterize the martensitic transformation upon increasing the temperature, a series of neutron diffraction patterns was collected at different temperatures. The structural analysis indicated that the progressive change of the martensitic lattice is characterized by the exponential change of the c/a parameter approaching the limit value c/a = 1 of the cubic austenite.

Anomalous charge density wave state evolution and dome-like superconductivity in CuIr2Te4−x Se x chalcogenides

We report the anomalous charge density wave (CDW) state evolution and dome-like superconductivity in CuIr2Te4−x Se x (0 ⩽ x ⩽ 0.5) series. Room temperature powder x-ray diffraction (XRD) results indicate that CuIr2Te4−x Se x (0 ⩽ x ⩽ 0.5) compounds retain the same structure as the host CuIr2Te4 and the unit cell constants a and c manifest a linear decline with increasing Se content. Magnetization, resistivity and heat capacity results suggest that superconducting transition temperature (T c) exhibits a weak dome-like variation as substituting Te by Se with the maximum T c = 2.83 K for x = 0.1 followed by suppression in T c and simultaneous decrease of the superconducting volume fraction. Unexpectedly, the CDW-like transition (T CDW) is suppressed with lower Se doping (0.025 ⩽ x ⩽ 0.2) but re-emerges at higher doping (0.25 ⩽ x ⩽ 0.5). Meanwhile, the temperature-dependent XRD measurements show that the trigonal structure is stable at 20 K, 100 K and 300 K for the host sample and the doping composition with x = 0.5, thus we propose that the behavior CDW-like transition arises from the disorder effect created by chemical doping and is not related to structural transition. The lower and the upper critical fields of these compounds are also addressed.

Synthesis and Characterizations of Two Tellurides β-BaGa2Te4 and Ba5Ga2Ge3Te12 with Flexible Chain Structure.

Demands for IR birefringent materials are increasing due to the rapid developments of IR laser applications. Herein, two new chain tellurides β-BaGa2Te4 and Ba5Ga2Ge3Te12 have been discovered. β-BaGa2Te4 crystallizes in the orthorhombic space group Imma (no. 74) with unit cell constants of a = 23.813(3) Å, b = 11.9673(19) Å, and c = 6.7215(9) Å, while Ba5Ga2Ge3Te12 crystallizes in the monoclinic space group P21/c (no. 14) with unit cell constants of a = 13.6540(3) Å, b = 9.6705(2) Å, and c = 23.1134(7) Å. The structure of β-BaGa2Te4 can be considered to be the antiparallel arrangement of one-dimensional (1D) [GaTe2] chains formed by edge-sharing GaTe4 tetrahedra, which are separated by Ba2+ cations. In the crystal structure of Ba5Ga2Ge3Te12, two kinds of 1D chains, namely chain 1 ∞1[(GaGe)3Te8] and chain 2 ∞1[(GaGe)2Te4], are stacked alternately and put together by the coulomb force with Ba2+ cations. In addition, First-principles calculations indicate that β-BaGa2Te4 has a large birefringence, ∼0.325 at 2050 nm, derived from the superposition of the polarizabilities of GaTe4 tetrahedra, implying that it has potential as an IR birefringent material. This work may provide some guidance for exploring new IR birefringent crystals.

“MoCl3(dme)” Revisited: Improved Synthesis, Characterization, and X-ray and Electronic Structures

"MoCl3(dme)" (dme = 1,2-dimethoxyethane) is an important precursor for midvalent molybdenum chemistry, particularly for triply Mo-Mo bonded compounds of the type Mo2X6 (X = bulky anionic ligand). However, its exact structural identity has been obscure for more than 50 years. In search of a convenient, large-scale synthesis, we have found that trans-MoCl4(Et2O)2 dissolved in dme can be cleanly reduced with dimethylphenylsilane, Me2PhSiH, to provide khaki Mo2Cl6(dme)2 in ∼90% yield. If the reduction is performed on a small scale, single crystals suitable for X-ray crystallography can be obtained. Two different crystal morphologies were identified, each belonging to the P21/n space group, but with slightly different unit cell constants. The refined structure of each form is an edge-shared bioctahedron with overall Ci symmetry and metal-metal separations on the order of 2.8 Å. The bulk material is diamagnetic as determined by both the Gouy method and SQUID magnetometry. Density functional theory calculations suggest a σ2π2δ*2 ground state for the dimer with the diamagnetism arising from a singlet diradical "broken symmetry" electronic configuration. In addition to a definitive structural assignment for "MoCl3(dme)", this work highlights the utility of organosilanes as easy to handle, alternative reductants for inorganic synthesis.

High pressure structural and vibrational properties of nitrogen-rich compound 1,5-Diamino-1H-1,2,3,4-tetrazole

Abstract 1,5-Diamino-1H-1,2,3,4-tetrazole (DAT) has attracted much attention due to its good thermal stability and high nitrogen content, as well as being a building block for a wide range of high energy density materials (HEDMs). Herein, the static compression behavior of DAT was investigated in the pressure range of 0–20 GPa using dispersion corrected density functional theory (DFT-D) calculations. The calculated crystal parameters, molecular geometry, and fundamental vibrational modes are in good agreement with those obtained experimentally at ambient condition. Furthermore, the compressibility of the unit cell constants presents an isotropic behavior. The subtle abrupt changes are observed in the lattice angle, bond lengths, dihedral angles and vibrational modes at 7 and 17 GPa, suggesting the isostructural phase transitions occurred. The Hirshfeld surfaces analysis and vibrational results suggest that the strengthening of intermolecular interactions has intensified crystal packing.

Structural Characteristics and Photoluminescence of Thin Films of Cu(In1–xgax)(Syse1–y)2 Solid Solutions

The phase composition and structural and optical characteristics of thin films of Cu(In1–xGax)(SySe1–y)2 solid solutions with the chalcopyrite structure were investigated. The unit-cell constants according to x-ray diffraction analysis were a ~ 5.720 A and c ~ 11.52 A. The elemental compositions were x = Ga/(Ga + In) ~ 0.14 and y = S/(S + Se) ~ 0.11 for Cu(In1–xGax)(S ySe1–y)2 thin films. The optical band gap of Cu(In1–xGax)(S ySe1–y)2 solid solutions determined from measurements of photoluminescence spectra and luminescence excitation spectra at ~4.2 K was Eg ~ 1.122 eV. The mechanism of radiative recombination of nonequilibrium charge carriers in thin films of Cu(In1–xGax) (S ySe1–y)2 solid solutions is discussed.

Synthesis, crystal structure, DFT calculations, Hirshfeld surface analysis, energy frameworks, molecular dynamics and docking studies of novel isoxazolequinoxaline derivative (IZQ) as anti-cancer drug

Quinoxaline derivatives with the molecular formula [C8H6N2] also named benzopyrazines, which are a valuable class of heterocyclic compounds useful for their numerous industrial and pharmaceutical applications. The new isoxazolquinoxalin (IZQ) 3-phenyl-1-((3-(p-tolyl)-4,5-dihydroisoxazol-5yl)methyl)quinoxalin-2(1H)-one (5) has been synthesized with good yield by stirring the compounds of 1-allyl-3-phenylquinoxalin-2(1H)-one (3, 3.8mmol), and (E)-4 methylbenzaldehydeoxime (4, 1.3mmol) in 20 ml of chloroform. The aqueous solution of sodium hypochlorite (10 ml of water bleach 12°) was added drop wise using bromine funnel. The mixture was stirring at 0°C temperature for 6 hours. Then it dried to obtain a crude product which on recrystallization with ethanol afforded the title compound (5) as colourless rectangular block shape crystals, and then confirmed by H NMR, LC-MS spectra. The structure of the compound has been confirmed by single crystal X-ray diffraction technique. The compound crystallizes in the monoclinic crystal system with the space group P21/c. The unit cell constants; a =15.9437(6) Å, b =16.3936(6) Å, c =7.4913(3) Å, and β =94.178(2)o. DFT calculations were carried out and HOMO-LUMO energy levels have been determined. In the structure, both Intermolecular and intramolecular hydrogen bonds of the type C-H...O were observed along with C-H...cg interactions. Hirshfeld surface studies were performed to understand the different interaction contacts of the molecule and the molecular packing strength of the crystal. Energy frameworks were constructed through different intermolecular interaction energies to investigate the stability of the compound and to know type of the dominate energy. Docking studies predicted anti-cancer activity of the title molecule against homo sapiens protein (pdb code:6HVH) and exhibited prominent interactions at active site region.

Analytical Approach to Screen Semiconducting MOFs Using Bloch Mode Analysis and Spectroscopic Measurements.

A rapid and simple analytical approach is developed to screen the semiconducting properties of metal organic frameworks (MOFs) by modeling the band structure and predicting the density of state of isoreticular MOFs (IRMOFs). One can consider the periodic arrangement of metal nodes linked by organic subunits as a 1D periodic array crystal model, which can be aligned with any unit-cell axis included in the IRMOF's primitive cubic lattice. In such a structure, each valence electron of a metal atom feels the potential field of the entire periodic array. We allocate the 1D periodic array in a crystal unit cell to three IRMOFs-n (n = 1, 8, and 10) of the Zn4O(L)3 IRMOF series and apply the model to their crystal lattices with unit-cell constants a = 25.66, 30.09, and 34.28 Å, respectively. By solving Schrödinger's equation with a Kronig-Penney periodic potential and fitting the computed energy spectra to IRMOFs' experimental spectroscopic data, we model electronic band structures and obtain densities of state. The band diagram of each IRMOF reveals the nature of its electronic structures and density of state, allowing one to identify its n- or p-type semiconducting behavior. This novel analytical approach serves as a predictive and rapid screening tool to search the MOF database to identify potential semiconducting MOFs.