Crystalline Configuration Research Articles

Molecular Dynamics Simulations of PtTi High-Temperature Shape Memory Alloys Based on a Modified Embedded-Atom Method Interatomic Potential.

A new second nearest-neighbor modified embedded-atom model-based PtTi binary interatomic potential was developed by improving the pure Pt unary descriptions of the pre-existing interatomic potential. Specifically, the interatomic potential was developed focusing on the shape memory-associated phenomena and the properties of equiatomic PtTi, which has potential applications as a high-temperature shape memory alloy. The simulations using the developed interatomic potential reproduced the physical properties of the equiatomic PtTi and various intermetallic compound/alloy compositions and structures. Large-scale molecular dynamic simulations of single crystalline and nanocrystalline configurations were performed to examine the temperature- and stress-induced martensitic transformations. The results show good consistency with the experiments and demonstrate the reversible phase transformation of PtTi SMA between the cubic B2 austenite and the orthorhombic B19 martensite phases. In addition, the importance of anisotropy, constraint and the orientation of grains on the transformation temperature, mechanical response, and microstructure of SMA are presented.

Electrochemical properties of modified poly(4-aminothiophenol)-Zn-Ni MOF-reduced graphene oxide nanocomposite for high-performance supercapacitors

Metal-organic frameworks (MOFs) have escalated much attention as innovative electrode materials for supercapacitors applications due to their high porosity, adequate active sites, and tunable structures. However, most MOFs show low capacitance, which limits their application in energy storage devices. In this study, a new MOF composite containing poly(4-aminothiophenol) (PAT), Zn, Ni, and reduced graphene oxide (rGO), abbreviated as PATZ1N2G2-MOF, was fabricated by a one-step simple hydrothermal method and its electrochemical characteristics for supercapacitor applications were examined. The structural characterization of the proposed MOF exhibited successful synthesis of a highly porous and nanoscale crystalline spherical PATZ1N2G2-MOF configuration mainly spread on extra thin nano-sheets of rGO. The convenient mixed spherical structure of PATZ1N2-MOF and rGO Nano-sheets facilitates more electrochemically active regions and more accessible routes for charge and mass transfer, developing a specific capacitance as high as 1230.23F g−1 at a current density of 1.0 A g−1 as well as excellent capacitance retention of 89.8% after 3000 repetitive cycles. Moreover, the capacity of the modified positive electrode for the 2-electrode setup was obtained to be 93.31F g−1, producing a high energy and power density of 33.17 Wh kg−1 and 188.35 W kg−1, respectively. The experimental results revealed the superior supercapacitive behavior of the PATZ1N2G2-MOF/NF electrode.

First-principles simulations to understand the structural and electrolyte properties of idealized Li7.5B10S18X1.5 (X=Cl, Br, I)

Recently, researchers at the University of Waterloo (Canada) and Oak Ridge National Laboratory (Oak Ridge, TN) reported a new family of lithium thioborate halide electrolytes with the composition ${\mathrm{Li}}_{7.5}{\mathrm{B}}_{10}{\mathrm{S}}_{18}{X}_{1.5}$ $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I})$ having very impressive ionic room-temperature conductivity of magnitude $\ensuremath{\sigma}=1 \mathrm{mS}/\mathrm{cm}$. The researchers characterized the structures of the three materials in terms of a well-defined thioborate framework with a void structure containing fractionally occupied Li and X sites. The space group of the materials was identified to be monoclinic ($C2/c$, No. 15). We report the results of first-principles simulations of these materials focusing on understanding the idealized ground-state structures, the mechanisms of Li ion migration, and the overall stability of the materials. A systematic search of many possible stoichiometric crystalline configurations found ordered ground-state realizations of the materials for each of the three halides, $X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I}$. Molecular dynamics simulations based on the initially ordered structures at various temperatures show significant Li ion hopping within the void channels of the structures at temperatures as low as T = 400 K. Simulations of possible decomposition products suggest that these electrolytes are also chemically stable. Overall, the simulations are consistent with the experimentally reported findings indicating that these materials are very promising solid electrolytes for possible use in solid-state Li ion batteries.

Enhancement of polarization and magnetization in polycrystalline magnetoelectric composite

Electrical control of magnetization or magnetic control of polarization offers an extra degree of freedom in materials possessing both electric and magnetic dipole moments, viz., magnetoelectric (ME) multiferroics. A microstructure with polycrystalline configurations that enhances the overall polarization/magnetization and that outperforms single crystalline configurations is identified in a 1–3 CoFe2O4–BaTiO3 (or CFO–BTO) composite. The characterization of local fields corresponding to the polycrystal configuration underlines a nontrivial role played by randomness in better cross coupling mediated by anisotropic and asymmetric strains. The microscopic field (local field) profile of the composite provides rich information regarding the distribution of key parameters central to the magnetoelectric effect. The differential contractual stress level observed in the local stress profile of CFO–BTO composite upon applying an external magnetic field conforms with the previous experimental magnetostriction observed in CFO. The role played by residual stresses stemming from misalignment of the polarization in the neighboring grains in enhancing the ME coupling is briefly discussed.

Interfacial electronic structure modulation of Pt-MoS2 heterostructure for enhancing electrocatalytic hydrogen evolution reaction

The electronic metal-support interaction (EMSI) of heterogenous catalysts has attracted much attention for its enhancing electrocatalytic efficiency by impacting adsorption and desorption energy of reaction intermediates. Herein, we synthesize the monodispersed single-crystal Pt nanoparticles (~3 nm) decorated on MoS2 nanosheets with 2 H phase (Pt-MoS2) by a universal wet chemical method. The morphology and structure characterizations show that the loaded Pt single-crystals are approximately half truncated octahedral shapes enclosed by {1 1 1} and {2 0 0} facets. Benefitting from interfacial electronic structure modulation, the Pt-MoS2 exhibits a lower overpotential (67.4 mV at the current desity of 10 mA·cm−2), smaller Tafel slope (76.2 mV·dec−1), and robuster HER durability than those of pristine MoS2 nanosheets and prepared Pt NPs. The theoretical simulations further reveal that the Pt atom at the interface, which belong to {2 0 0} facets and adjoin S atoms, own the smallest hydrogen adsorption free energy by manipulating the d-band center of the Pt metal surface. This work provides crystalline structure and electronic configuration engineering strategy towards to design and develop of metal-support heterostructure with high HER activity and stability.

First Principles Simulations to Understand the Structural and Electrolyte Properties of Idealized Li7.5B10S18X1.5 (X = Cl, Br, I) Li Superionic Conductors Recently Identified in the Experimental Literature

Recently, researchers at the University of Waterloo (Canada) and Oak Ridge National Laboratory (USA) reported a new family of lithium thioborate halide electrolytes which have the composition Li7.5B10S18X1.5 (X = Cl, Br, I) and which are very impressive ionic conductors with \U0001d782=10-3 S/cm measured at room temperature [1]. The researchers identified the crystal structure of the three materials with the monoclinic space group C2/c (No. 15) having highly disordered Li and X sites. In this presentation, we report the results of first-principles simulations of these materials, focusing on understanding the mechanisms of Li ion migration and the overall stability of the materials. By optimizing many possible stoichiometric crystalline configurations, we found ordered ground state realizations of the materials for the three halides X = Cl, Br, and I. Molecular dynamics simulations based on the initially ordered structures at various temperatures show significant Li ion hopping within the void channels of the structures at temperatures as low as T = 600 K. Simulations of possible decomposition products suggest that these electrolytes are also chemically stable. Overall, the preliminary simulations are consistent with the experimental findings of Ref. [1], indicating that these materials are very promising solid electrolytes for possible use in solid state Li ion batteries.------------------------------------------[1] K. Kaup, A. Assoud, J. Liu, and L. F. Nazar, Fast Li-ion conductivity in superadamantanoid lithium thioborate halides, Angewandte Chimie, 133, 7051-7056 (2020) doi.org/10.002/anie.202013339.------------------------------------------Acknowledgements -- This work was supported by NSF grant DMR-1940324. Computations were performed on the Wake Forest University DEAC cluster, a centrally managed resource with support provided in part by the university.

Synthesis and Characterization of Novel Fe3O4/PVA/Eggshell Hybrid Nanocomposite for Photodegradation and Antibacterial Activity

In the 21st century, hybrid nanocomposites were widely used in bioelectronic, biosensing, photocatalytic, and biomedical applications. In the present study, we fabricated a novel Fe3O4/PVA/Eggshell hybrid nanocomposite and physicochemically characterized it using powder XRD, EDS, FTIR, VSM, and HR-TEM analysis. The XRD spectrum revealed the crystalline and FCC configuration of Fe3O4 NPs with average crystal size of 16.28 nm, and the HRTEM image indicates the prepared hybrid nanocomposite is of spherical shape with less agglomeration. This hybrid nanocomposite showed a significant photodegradation property in degrading organic pollutants such as congo red and crystal violet dyes under the sunlight irradiation. In addition, the hybrid nanocomposite also displayed a potent antibacterial property against different Gram +ve and Gram −ve bacterial pathogens. This study provides a significant example in the overview of fabrication of cost effectively, eco-friendly, and multiple-application hybrid nanocomposites through eggshell membrane fibers.

Nuclear pasta structures and symmetry energy

In the framework of the relativistic mean field model with Thomas-Fermi approximation, we study the structures of low density nuclear matter in a three-dimensional geometry with reflection symmetry. The numerical accuracy and efficiency are improved by expanding the mean fields according to fast cosine transformation and considering only one octant of the unit cell. The effect of finite cell size is treated carefully by searching for the optimum cell size. Typical pasta structures (droplet, rod, slab, tube, and bubble) arranged in various crystalline configurations are obtained for both fixed proton fractions and $\beta$-equilibration. It is found that the properties of droplets/bubbles are similar in body-centered cubic (BCC) and face-centered cubic (FCC) lattices, where the FCC lattice generally becomes more stable than BCC lattice as density increases. For the rod/tube phases, the honeycomb lattice is always more stable than the simple one. By introducing an $\omega$-$\rho$ cross coupling term, we further examine the pasta structures with a smaller slope of symmetry energy $L = 41.34$ MeV, which predicts larger onset densities for core-crust transition and non-spherical nuclei. Such a variation due to the reduction of $L$ is expected to have impacts on various properties in neutron stars, supernova dynamics, and binary neutron star mergers.

Groundwater resources exploration of Harrat Khaybar area, northwest Saudi Arabia, using electrical resistivity tomography

Two-dimensional (2D) electrical resistivity tomography (ERT) survey has been conducted in the Harrat Khaybar volcanic field, northeast of Al Madinah Al Munawwarah, Saudi Arabia, to assess the presence of groundwater resources. For this purpose, eleven ERT profiles were generated at six sites oriented north–south and east–west at various lengths between 590 m and 890 m. The ERT data were collected using the Syscal Pro multinode resistivity imaging system with a dipole–dipole array and 5 m of electrode separation. Then, these data have been processed using RES2DINV software to get 2D geoelectric cross-sections. The interpreted 2D geoelectric cross-sections clarified that the Harrat Khaybar occupied by sheets of lava flows underlain by alluvial deposits of gravelly sand and clay. These deposits rest on a Precambrian crystalline rock configuration that has the potential to provide groundwater to the region. Promising water-bearing formations were detected within sub-basaltic alluvial sediments and basaltic flows as well. Moreover, the reported water table in the area has 47 m depth in average with thickness varies between 6 and 200 m. These results correlate well with those of previous hydrogeological studies conducted in Harrat Khaybar. These results are very important for the residents in Harat Khaybar, where enables them to benefit from the groundwater resources in the area for domestic and agricultural purposes.

Development of Intranasal Levothyroxine Powder Delivery for Hypothyroidism

Background: Hypothyroidism affects 3-5% of the general population with oral levothyroxine (LT4) being the predominant replacement therapy. However, significant proportion of hypothyroid patients are unable to absorb oral replacement leading to therapeutic failure and may require injectable thyroxine. Objectives: To develop non-invasive, less costly, and patient-friendly LT4 nasal delivery alternative using mucoadhesive polymers: chitosan and hydroxypropylmethylcellulose (HPMC). Methods: Six nasal LT4 formulations were developed with either chitosan or hydroxypropyl methylcellulose as mucoadhesive. The formulations were prepared through freeze-drying by varying the drug to polymer ratio (1:1, 1:3, and 1:5). The percentage drug yield was calculated by analyzing the weight of the formulation pre- and post-freeze drying. HPLC analysis was conducted to determine the amount of LT4 loaded in each formulation. Furthermore, the surface morphology, particle size, zeta potential, differential scanning calorimetry, X-ray diffraction as well as the in vitro release were assessed to determine the physicochemical properties and release characteristics of the formulations, respectively. Results: Both percentage drug loading and yield were > 70% for all the formulations. The freeze-dried formulations displayed a compact needle-like surface morphology. LT4-chitosan formulations, 1:1, 1:3, and 1:5 had mean particle size of 2.45 ± 0.88 µm, 2.76 ± 1.38 µm, and 1.59 ± 0.27 µm, respectively. Mean particle sizes for 1:1, 1:3, and 1:5 LT4-HPMC formulations were 0.56 ± 0.02 µm, 0.22 ± 0.06 µm, and 0.46 ± 0.04 µm. Zeta potential for LT4-chitosan formulation 1:1, 1:3, and 1:5 were -18.7 ± 1.00 mV, -16.2 ± 0.79 mV, and -19.17 ± 1.01 mV, respectively. LT4-HPMC 1:1, 1:3, and 1:5 formulations had zeta charges of -11.66 ± 3.16 mV, -6.06 ± 3.92 mV, and -9.53 ± 1.68 mV, respectively. Differential calorimetric analysis confirmed drug-polymer integration in all formulations, and X-ray powder diffraction showed both chitosan and HPMC formulations as crystalline configuration. The formulations with the highest in vitro release were LT4-HPMC 1:3 and LT4-chitosan 1:5. Conclusions: Results of this study suggest that both chitosan and HPMC can be used as sustained release polymers for the intranasal delivery of LT4.

Structural investigations on inorganic Al2O3–ZnO composites

The present work deals with the preparation and characterization of Al2O3/ZnO composites under the effect of structural and temperature changes. A sol–gel method of preparing Al2O3/ZnO composites with different concentrations of ZnO and Al2O3 was used. Materials with the extremely high Al2O3 concentration (80 mol%) have been simply prepared by the sol–gel technique. 27Al NMR spectroscopy, X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM) examined the structural features of all the samples. 27Al NMR showed a significant improvement in the product composition with the change of the Al2O3 to ZnO molar ratios. The main units that existed in the Al2O3 rich sample (80 mol%) are the structured groups AlO6, AlO5 and AlO4. The main unit in the lower Al2O3 concentration (20 mol%) is only AlO4 coordination. Through adding Al2O3, the crystalline configuration in the pure ZnO matrix is fully transformed into one of the amorphous forms. The amorphous composition of Al2O3/ZnO is retransformed into crystalline forms after calcination. The presence of different Al2O3 coordination such as AlO6, AlO5 and AlO4 is considered as the main cause for mismatching between different structural units that leads to transformation of crystalline into non-crystalline structure.

Structure engineering of Ni2P by Mo doping for robust electrocatalytic water and methanol oxidation reactions

Structure engineering via foreign element doping is an efficient method to modulate the electronic and crystalline structures of electrocatalysts. Herein, regulating the crystalline structure and electronic configuration of Ni2P was proposed and realized by introducing foreign Mo element to reinforce the catalytic property for oxygen evolution reaction (OER) and methanol oxidation reaction (MOR). Doping high-valence Mo created more structural defects as the catalytic sites and regulated d-band structure of Ni with higher oxidation state for better adsorption of oxygen intermediates. As the result, electrochemical performances suggested the great improvement in OER and MOR in alkali for Mo-doped Ni2P with lower overpotentials and higher current densities, more active Ni sites and better conductivity, as compared with undoped Ni2P. Therefore, the regulation of structure and improvement in electrocatalytic activity demonstrated that this highly-efficient Mo-doped Ni2P is expected as a robust electrocatalyst for practical applications of water splitting and methanol fuel cell.

Current challenges and innovative developments in pretreatment of lignocellulosic residues for biofuel production: A review

Lignocelluloses’ pretreatment is targeted for the improvement of hydrolysis of their carbohydrates, i.e., cellulose and hemicelluloses. Modification of the hardheaded structure of lignocelluloses is a fundamental stair in biofuels and biochemicals production. The high crystalline configurations of cellulose embed with hemicelluloses and lignin, give rise to recalcitrance structure. Second-generation biofuel production processes, using lignocellulosic biomass as a feedstock, is based on a three-stage process, including pretreatment, enzymatic hydrolysis, and fermentation. The pretreatment stage is the most critical, influencing, costly stage. The perfect pretreatment process is designated to provide minimum cellulosic crystallinity with remarkable low lignin content as well as inhibitory compounds through a sustainable economical process. In the present review, advances in lignocellulosic pretreatment technologies for biofuels production are reviewed and critically discussed. The article further discusses the pros and cons of the various pretreatment methodologies as well as addresses the role and impact of different process parameters associated with the pretreatment process.

Engineering functional group decorated ZIFs to high-performance Pd@ZIF-92 nanocatalysts for C(sp2)-C(sp2) couplings in aqueous medium

Herein the first ever Pd2+-decorated ZIF-92 nanostructure is readily accessed by post-synthesis modification (PSM) of the zeolitic imidazolate framework ZIF-90. Thus, the imidazolate linker of the ZIF-90 is functionalized with the hydroxyethylimino group, followed by anchoring the palladium catalytically active sites through a tight coordination of Pd2+ ions to both the N and O atoms of ZIF-92. The acquired data (by PXRD, EDS, SEM, XPS, ICP-AES) concerning the crystalline structure, elemental mapping and network configuration of the Pd@ZIF-92 catalyst confirmed its structure, before and after the cross-coupling reactions and following recycling. The Pd@ZIF-92 showed excellent catalytic activity (>99%) and chemoselectivity in Suzuki-Miyaura coupling proceeding in neat water, at very low Pd loading (0.009 mol%). Comparison of its performance with that of many reported Pd nanocatalysts operating in aqueous/protic media testifies to its superiority. The appealing gateway to this innovative, stable, robust, easily recoverable and reusable Pd@ZIF-92 nanostructure recommends its beneficial utilization in C(sp2)-C(sp2) cross-couplings and other sustainable, environmentally-friendly processes.

Perspective on the pressure-driven evolution of the lattice and electronic structure in perovskite and double perovskite

Perovskite ABO3 as one of the most common structures has demonstrated great structural flexibility and electronic applications. Evolving from perovskite, the typical double perovskite A2BB′O6 has two element species (B/B′), where the ordered arrangements of BO6 and B′O6 octahedron provide much more tunability. Especially, by applying external pressure, the energetic order between different phases in perovskite and double perovskite materials can be notably modified with more fascinating physical properties. However, it is still a challenge to propose a general model to explain and predict the high-pressure structures and properties of various perovskites and double perovskites due to their flexibility and complexity. In this perspective, we will discuss pressure effects on the crystalline structure and electronic configurations in some perovskites and double perovskites. We then focus on a prediction method for the evolution of the lattice and electronic structure for such materials with pressure. Finally, we will give a perspective on current challenges and opportunities for controlling and optimizing structural and electronic states of a given material for optimized functionalities.

Dialdehyde Oxidation of Cross-Linked Waxy Corn Starch: Optimization, Property and Characterization

The functionalization of waxy corn starch (WCS) was better realized by combing the cross-linking of epichlorohydrin with oxidation of sodium periodate. The results indicated that the cross-linking had a greater influence on the retrogradation than the oxidation, and the oxidation worsened the freeze–thaw stability of WCS. Both cross-linking and oxidation could ameliorate the alkali and acid resistance of WCS, and enhanced its heat stability. Cross-linking weakened the absorption peak of the –OH groups according to FTIR and had a small influence on the crystalline configuration of WCS belonging to a typical A-type structure, whereas the oxidation almost entirely damaged the particle structure. After the cross-linking, the tiny pits with a diameter of around 1 μm only appeared on sides of WCS granules, and proving that the cross-linking was very unevenly completed on some of WCS particles. The pasting curve of WCS was obviously different from those of its derivatives. The combination of oxidation and cross-linking could effectively decrease the setback of WCS.

Constant chemical potential, pressure and temperature profiles in liquid–vapour equilibrium obtained by spinodal decomposition

Constant chemical potential, pressure and temperature profiles across a slab of liquid in equilibrium with its vapour confirm that, the spinodal decomposition procedure carried on the NVT ensemble simulated via molecular dynamics produce an equilibrium system. An initial homogeneous crystalline configuration of fluid is kept in a cell with a parallelepiped shape at a density near the critical density and a temperature between the triple and critical temperatures, form a slab of liquid in equilibrium with its vapour by the spinodal decomposition phenomenon if the simulation is performed in the NVT ensemble. An elongated box favours the formation of two planar parallel surfaces along the largest side of the box. We show in this paper that the ‘three conditions’ for thermodynamic equilibrium: constant temperature, constant pressure and constant chemical potential are met for such a system.

Surface Enhancement and Structure Formation of Metakaolin from Thailand Kaolin on the Various Calcination Temperature

Abstract The metakaolin was chosen as a starting material for the synthesis of the zeolite because it is high crystallinity, reactivity and purity of raw material. Kaolin from Thailand which was selected from 3 different sources including Ratchaburi, Lampang, and Uttaradit were using as starting materials for synthesis of metakaolin by calcination temperature of this study were chosen in the range of 500 to 1000 °C for 2 h. Calcination temperature is significantly affect crystalline size, function group, and configuration of metakaolin by the results which obtained from X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy techniques were indicated that the best metakaolin was obtained from Uttaradit’s kaolin which was calcined at 1000 oC for 2h by it shows the lowest impurities.

Growth and characterization of Ca-Mo mixed oxide films on Mo(001).

Calcium-molybdate ultrathin films were prepared on a Mo(001) crystal and characterized by means of scanning tunneling microscopy (STM), electron diffraction, photoelectron spectroscopy, and density functional theory (DFT). The films were grown via reactive Ca deposition, followed by a vacuum annealing step to trigger Mo diffusion from the support into the Ca-O ad-layer. A series of crystalline oxide configurations was revealed that evolves from a (3 × 3) to a (4 × 4) and (6 × 6) superstructure with increasing annealing temperature and finally decays to a binary MoOx phase. The stoichiometry of the initial (3 × 3) phase was estimated to CaMo3O6, yet with decreasing Ca concentration at higher temperature. In the search for a suitable structure model for DFT calculations, we have started with a bulk CaMo5O8 configuration that was iteratively modified to match the experimental data. The optimized structure is made of regular sequences of flat-lying and upright standing Mo octahedrons, being separated from each other by Ca2+ ion rows. With decreasing Ca content, the central Mo units grow in size, which explains the observed transition from (3 × 3) to (6 × 6) superstructures upon annealing. The proposed structure model rationalizes the periodicity and corrugation of the regular oxide surface as well as the characteristic domain patterns in the film. Its electronic properties, as deduced from STM conductance spectroscopy, can be correlated with an increasing metallicity of the ad-layer upon annealing. Our work presents a facile pathway to produce high-quality ternary oxide films via interdiffusion of atoms from a suitable metal support into a binary oxide layer.

Hierarchical Cobalt Selenides as Highly Efficient Microwave Absorbers with Tunable Frequency Response.

Microwave absorbing materials have attracted much attention in solving electromagnetic interference and pollution problems. Hierarchical cobalt selenides have been obtained through a facile selenization annealing process. The as-prepared samples exhibit distinct reflection losses (RL) and frequency responses via tailoring their crystalline configurations, with excellent absorption in Ku, X, or C band. All of the samples show RL greater than or near -50 dB with effective bandwidths more than 4 GHz, indicating that they may serve as high-efficient and frequency-tunable microwave absorbers. Especially, the sample annealed at 400 °C shows a competitive RL of -62.04 dB at 9.92 GHz with a thickness of 2.25 mm; meanwhile, its effective absorption bandwidth reaches 5.36 GHz with a thickness as small as 1.56 mm. The cobalt selenides as microwave absorbers exhibit a promising prospect applied in complex electromagnetic environments.