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1.
  • Halldin Stenlid, Joakim, 1987-, et al. (author)
  • σ-Holes on Transition Metal Nanoclusters and Their Influence on the Local Lewis Acidity
  • 2017
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 7
  • Journal article (peer-reviewed)abstract
    • Understanding the molecular interaction behavior of transition metal nanoclusters lies at the heart of their efficient use in, e.g., heterogeneous catalysis, medical therapy and solar energy harvesting. For this purpose, we have evaluated the applicability of the surface electrostatic potential [VS(r)] and the local surface electron attachment energy [ES(r)] properties for characterizing the local Lewis acidity of a series of low-energy TM13 transition metal nanoclusters (TM = Au, Cu, Ru, Rh, Pd, Ir, Pt, Co), including also Pt7Cu6. The clusters have been studied using hybrid Kohn–Sham density functional theory (DFT) calculations. The VS(r) and ES(r), evaluated at 0.001 a.u. isodensity contours, are used to analyze the interactions with H2O. We find that the maxima of VS(r), σ-holes, are either localized or diffuse. This is rationalized in terms of the nanocluster geometry and occupation of the clusters’s, p and d valence orbitals. Our findings motivate a new scheme for characterizing σ-holes as σs (diffuse), σp (localized) or σd (localized) depending on their electronic origin. The positions of the maxima in VS(r) (and minima in ES(r)) are found to coincide with O-down adsorption sites of H2O, whereas minima in VS(r) leads to H-down adsorption. Linear relationships between VS,max (and ES,min) and H2O interaction energies are further discussed.
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2.
  • Jha, Piyush Kumar, et al. (author)
  • An Overview on Magnetic Field and Electric Field interactions with Ice crystalization; Application in case of frozen food
  • 2017
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 7:10
  • Research review (peer-reviewed)abstract
    • Ice nucleation is a stochastic process and it is very difficult to be controlled. Freezing technologies and more specifically crystallisation assisted by magnetic, electric and electromagnetic fields have the capability to interact with nucleation. Static magnetic field (SMF) may affect matter crystallisation; however, this is still under debate in the literature. Static electric field (SEF) has a significant effect on crystallisation; this has been evidenced experimentally and confirmed by the theory. Oscillating magnetic field induces an oscillating electric field and is also expected to interact with water crystallisation. Oscillating electromagnetic fields interact with water, perturb and even disrupt hydrogen bonds, which in turn are thought to increase the degree of supercooling and to generate numerous fine ice crystals. Based on the literature, it seems that the frequency has an influence on the above-mentioned phenomena. This review article summarizes the fundamentals of freezing under magnetic, electric and electromagnetic fields, as well as their applicability and potentials within the food industry.
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3.
  • Ali, Sk Imran, et al. (author)
  • Crystal Structure of the Disordered Non-Centrosymmetric Compound Fe0.43Mo2.56SbO9.5
  • 2019
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 9:1
  • Journal article (peer-reviewed)abstract
    • Single crystals of Fe0.43Mo2.56SbO9.5 were obtained by hydrothermal techniques at 230 degrees C. The crystal structure was determined from single crystal X-ray diffraction data. The compound crystallizes in the non-centrosymmetric space group Pc with unit cell parameters a = 4.0003(2) angstrom, b = 7.3355(3) angstrom, c = 12.6985(6) angstrom, = 90 degrees. The crystal structure comprises five crystallographically independent M atoms and one Sb3+ atom, M atoms are of two kinds of partially occupied sites Mo6+ and Fe3+. The building blocks consist of [SbO3O0.5O0.5E] octahedra (E = lone electron pair) and [(Mo/Fe)O-6] octahedra. The M = (Mo, Fe) and O atoms are arranged in a distorted hexagonal 2D-net, not the Sb atoms. The distortion of the net and consequently the symmetry reduction results mainly from the location of the Sb atoms. Disorder manifests itself as a splitting of the metal sites and as a consequent shortening of the Mo-Fe distances. Six (Mo/Fe)O-6 octahedra are connected to form a pseudohexagonal channel. The Sb3+ atom is displaced from the pseudo-six-fold axis.
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4.
  • B. Brant Carvalho, Paulo H., et al. (author)
  • Exploring High-Pressure Transformations in Low-Z (H2, Ne) Hydrates at Low Temperatures
  • 2022
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 12:1
  • Journal article (peer-reviewed)abstract
    • The high pressure structural behavior of H-2 and Ne clathrate hydrates with approximate composition H-2/Ne center dot~4H(2)O and featuring cubic structure II (CS-II) was investigated by neutron powder diffraction using the deuterated analogues at ~95 K. CS-II hydrogen hydrate transforms gradually to isocompositional C-1 phase (filled ice II) at around 1.1 GPa but may be metastably retained up to 2.2 GPa. Above 3 GPa a gradual decomposition into C-2 phase (H-2 center dot H2O, filled ice I-c) and ice VIII' takes place. Upon heating to 200 K the CS-II to C-1 transition completes instantly whereas C-1 decomposition appears sluggish also at 200 K. C-1 was observed metastably up to 8 GPa. At 95 K C-1 and C-2 hydrogen hydrate can be retained below 1 GPa and yield ice II and ice I-c, respectively, upon complete release of pressure. In contrast, CS-II neon hydrate undergoes pressure-induced amorphization at 1.9 GPa, thus following the general trend for noble gas clathrate hydrates. Upon heating to 200 K amorphous Ne hydrate crystallizes as a mixture of previously unreported C-2 hydrate and ice VIII'.
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5.
  • Bikondoa, Oier, et al. (author)
  • X-ray photon correlation spectroscopy with coherent nanobeams : A numerical study
  • 2020
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 10:9
  • Journal article (peer-reviewed)abstract
    • X-ray photon correlation spectroscopy accesses a wide variety of dynamic phenomena at the nanoscale by studying the temporal correlations among photons that are scattered by a material in dynamical equilibrium when it is illuminated with a coherent X-ray beam. The information that is obtained is averaged over the illuminated area, which is generally of the order of several square microns. We propose here that more local information can be obtained by using nanobeams with great potential for the study of heterogeneous systems and show the feasibility of this approach with the support of numerical simulations.
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6.
  • Bildirir, Hakan, 1985 (author)
  • Have covalent organic framework films revealed their full potential?
  • 2021
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 11:7
  • Research review (peer-reviewed)abstract
    • Porous organic polymers provide high accessible surface areas, which make them attrac-tive for gas storage, separation, and catalysis. In addition to those classical usage areas, such compounds are particularly interesting for electronic applications since their high dimensional, electron-rich backbone provides advanced electronic and photophysical properties. However, their non-sol-uble nature is a challenge for their processability, especially in the case of film formation, hence their limited utilization in organic electronic devices so far. Nevertheless, there are several techniques presented in the literature to overcome that issue, most of which were on the crystalline porous organic polymers, namely covalent organic frameworks (COFs). In this perspective, the develop-ments on COF film formation and prospects for the improvements are discussed with suggestions to further their performances in organic electronics.
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7.
  • Caleman, Carl, et al. (author)
  • A Perspective on Molecular Structure and Bond-Breaking in Radiation Damage in Serial Femtosecond Crystallography
  • 2020
  • In: Crystals. - : MDPI. - 2073-4352. ; 10:7
  • Journal article (peer-reviewed)abstract
    • X-ray free-electron lasers (XFELs) have a unique capability for time-resolved studies of protein dynamics and conformational changes on femto- and pico-second time scales. The extreme intensity of X-ray pulses can potentially cause significant modifications to the sample structure during exposure. Successful time-resolved XFEL crystallography depends on the unambiguous interpretation of the protein dynamics of interest from the effects of radiation damage. Proteins containing relatively heavy elements, such as sulfur or metals, have a higher risk for radiation damage. In metaloenzymes, for example, the dynamics of interest usually occur at the metal centers, which are also hotspots for damage due to the higher atomic number of the elements they contain. An ongoing challenge with such local damage is to understand the residual bonding in these locally ionized systems and bond-breaking dynamics. Here, we present a perspective on radiation damage in XFEL experiments with a particular focus on the impacts for time-resolved protein crystallography. We discuss recent experimental and modelling results of bond-breaking and ion motion at disulfide bonding sites in protein crystals.
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8.
  • Chayanun, Lert, et al. (author)
  • Combining Nanofocused X-Rays with Electrical Measurements at the NanoMAX Beamline
  • 2019
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 9:8
  • Journal article (peer-reviewed)abstract
    • The advent of nanofocused X-ray beams has allowed the study of single nanocrystals and complete nanoscale devices in a nondestructive manner, using techniques such as scanning transmission X-ray microscopy (STXM), X-ray fluorescence (XRF) and X-ray diffraction (XRD). Further insight into semiconductor devices can be achieved by combining these techniques with simultaneous electrical measurements. Here, we present a system for electrical biasing and current measurement of single nanostructure devices, which has been developed for the NanoMAX beamline at the fourth-generation synchrotron, MAX IV, Sweden. The system was tested on single InP nanowire devices. The mechanical stability was sufficient to collect scanning XRD and XRF maps with a 50 nm diameter focus. The dark noise of the current measurement system was about 3 fA, which allowed fly scan measurements of X-ray beam induced current (XBIC) in single nanowire devices.
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9.
  • Dai, Jing, et al. (author)
  • Molecular and Segmental Orientational Order in a Smectic Mesophase of a Thermotropic Ionic Liquid Crystal
  • 2019
  • In: Crystals. - : MDPI. - 2073-4352. ; 9:1
  • Journal article (peer-reviewed)abstract
    • We investigate conformational dynamics in the smectic A phase formed by the mesogenic ionic liquid 1-tetradecyl-3-methylimidazolium nitrate. Solid-state high-resolution C-13 nuclear magnetic resonance (NMR) spectra are recorded in the sample with the mesophase director aligned in the magnetic field of the NMR spectrometer. The applied NMR method, proton encoded local field spectroscopy, delivers heteronuclear dipolar couplings of each C-13 spin to its H-1 neighbours. From the analysis of the dipolar couplings, orientational order parameters of the C-H bonds along the hydrocarbon chain were determined. The estimated value of the molecular order parameter S is significantly lower compared to that in smectic phases of conventional non-ionic liquid crystals.
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10.
  • Dai, Jing, et al. (author)
  • NMR Spectroscopic Study of Orientational Order in Imidazolium-Based Ionic Liquid Crystals
  • 2019
  • In: Crystals. - : MDPI. - 2073-4352. ; 9:10
  • Journal article (peer-reviewed)abstract
    • We report on molecular and local orientational order of a series of imidazolium-based ionic liquid crystals exhibiting layered smectic A mesophase. Materials constituting of 1-dodecyl-3-methylimidazolium cation, and different counter-ions, were investigated. We apply two-dimensional C-13-H-1 dipolar NMR spectroscopy to quantify orientational order of C-H bonds of the organic cation. The experimental data supported the structural model of the interdigitated chains aligned with the smectic layer normal. Molecular order parameter S was found to increase in the anion sequence BF4- < I- < Br- < Cl-. This trend correlates well with ionic radius, negative charge delocalization, and hydrogen-bonding properties of the anions.
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11.
  • Dorn, Katharina, et al. (author)
  • Press to Success : Gd5FW3O16-The First Gadolinium(III) Fluoride Oxidotungstate(VI)
  • 2019
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 9:8
  • Journal article (peer-reviewed)abstract
    • The gadolinium(III) fluoride oxidotungstate(VI), with the formula Gd5FW3O16, represents the first published fluoride-derivative of a rare-earth metal oxidotungstate. It is synthesized by a mixture of GdF3, Gd2O3, and WO3 at 800 degrees C and a pressure of 2 GPa with the help of a belt press. The title compound crystallizes in the monoclinic space group P2(1)/c (no. 14) with four formula units per unit cell and the following lattice parameters: a = 539.29 (4), b = 1556.41 (12), c = 1522.66 (11) pm, and beta = 93.452 (4). The crystal structure comprises five crystallographically distinguishable Gd3+ cations, which are surrounded by either oxide and fluoride anions (Gd1-3) or by oxide anions only (Gd4, Gd5), with coordination numbers ranging between seven and nine. The fluoride anions are trigonal non-planar coordinated by three Gd3+ cations (Gd1-3). The distorted [WO6](6-) octahedra in this structure form isolates edge- and vertex-connected entities of the compositions [W2O10](8-) and [W2O11](10-), respectively. According to the presented units, a structured formula can be written as Gd-4[FGd3](2)[W2O10][W2O11](2). The single-crystal Raman spectrum reveals the typical symmetric stretching vibration mode of octahedral oxidotungstate(VI) units at about 871 cm(-1).
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12.
  • Esmaeildoost, Niloofar, et al. (author)
  • Heterogeneous Ice Growth in Micron-Sized Water Droplets Due to Spontaneous Freezing
  • 2022
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 12:1
  • Journal article (peer-reviewed)abstract
    • Understanding how ice nucleates and grows into larger crystals is of crucial importance for many research fields. The purpose of this study was to shed light on the phase and structure of ice once a nucleus is formed inside a metastable water droplet. Wide-angle X-ray scattering (WAXS) was performed on micron-sized droplets evaporatively cooled to temperatures where homogeneous nucleation occurs. We found that for our weak hits ice grows more cubic compared to the strong hits that are completely hexagonal. Due to efficient heat removal caused by evaporation, we propose that the cubicity of ice at the vicinity of the droplet’s surface is higher than for ice formed within the bulk of the droplet. Moreover, the Bragg peaks were classified based on their geometrical shapes and positions in reciprocal space, which showed that ice grows heterogeneously with a significant population of peaks indicative of truncation rods and crystal defects. Frequent occurrences of the (100) reflection with extended in-planar structure suggested that large planar ice crystals form at the droplet surface, then fracture into smaller domains to accommodate to the curvature of the droplets. Planar faulting due to misaligned domains would explain the increased cubicity close to the droplet surface.
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13.
  • Faniayeu, Ihar, et al. (author)
  • Polarization Control with Helical Metasurfaces
  • 2020
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 10:9
  • Journal article (peer-reviewed)abstract
    • The ability to fully control the polarization of light using chiral metadevices has drawn considerable attention in various applications of integrated photonics, communication systems, and life sciences. In this work, we propose a comprehensive approach for the design of metasurfaces with desired polarization properties for reflected and transmitted waves based on the proper spatial arrangement of chiral inclusions in the unit cell. Polarization conversion is achieved by engineering induced electric and magnetic dipole moments of the metasurface inclusions. We show that under a proper arrangement, the same inclusion can be used as a building block of metasurfaces with drastically different wave-transformation functionalities. The horizontally and vertically oriented metallic helices were used as simplest chiral inclusions, which can be manufactured by the established 3D fabrication techniques from THz up to the visible spectral range. The proposed metadevices provide a deep understanding of the light-matter interaction for polarization conversions with helix-based structures and opens the way to new possibilities of electromagnetic polarization control with advanced chiral metadevices in communication and imaging systems.
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14.
  • Fischer, Tim, et al. (author)
  • Morphological and Crystallographic Effects in the Laser Powder-Bed Fused Stainless Steel Microstructure
  • 2021
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 11:6, s. 672-
  • Journal article (peer-reviewed)abstract
    • One of the key aspects in additive manufacturing of stainless steels is the relationship between process parameters and the resulting microstructure. The selected process parameters typically cause a rapid solidification of the material, which leads to a microstructure that is highly textured both morphologically and crystallographically. While the morphological texture is characterised by a mainly columnar shape of the grains, the crystallographic texture is marked by a preferred grain orientation in the direction (fibre texture). Due to the texture effects, pronounced anisotropic mechanical properties are present in the material. In this report, a series of virtual microstructures with different morphological and crystallographic features are generated to develop a fundamental understanding of the individual texture effects on the mechanical properties. The grain morphology is based on Voronoi tessellations, and the crystallographic texture is captured with crystal plasticity. Furthermore, the numerical predictions are compared with experimental studies. The mechanical properties predicted on the basis of the virtual microstructures show that the crystallographic effect is much more dominant than the morphology of the individual grains. Consistent with the experiments, the highest load-bearing capacity of the material occurs when the macroscopic loading acts under an angle of 45 degrees to the preferred orientation of the crystals.
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15.
  • Fredrickson, Daniel C., et al. (author)
  • Bonding schemes for polar intermetallics through molecular orbital models : Ca-supported Pt-Pt Bonds in Ca10Pt7Si3
  • 2013
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 3:3, s. 504-516
  • Journal article (peer-reviewed)abstract
    • Exploratory synthesis in the area of polar intermetallics has yielded a rich variety of structures that offer clues into the transition in bonding between Zintl and Hume-Rothery phases. In this article, we present a bonding analysis of one such compound, Ca10Pt7Si3, whose large Ca content offers the potential for negative formal oxidation states on the Pt. The structure can be divided into a sublattice of Ca cations and a Pt-Si polyanionic network built from Pt7Si3 trefoil units linked through Pt-Pt contacts of 3.14 Å. DFT-calibrated Hückel models reveal that the compound adheres well to a Zintl-like electron counting scheme, in which the Pt-Si and Pt-Pt contacts are equated with two-center two-electron bonds. The experimental electron count is in excess of that predicted by 2%, a discrepancy which is attributed to the electron transfer from the Ca to the Pt-Si network being incomplete. For the Pt-Pt contacts, the occupancy of the bonding orbitals is dependent on the participation of the surrounding Ca atoms in bridging interactions. This use of multi-center interactions isolobal to classical two-center two-electron bonds may illustrate one path by which the bonds delocalize as one moves from the Zintl phases toward the Hume-Rothery domain.
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16.
  • Ge, Meng, et al. (author)
  • Three-Dimensional Electron Diffraction for Structural Analysis of Beam-Sensitive Metal-Organic Frameworks
  • 2021
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 11:3
  • Research review (peer-reviewed)abstract
    • Electrons interact strongly with matter, which makes it possible to obtain high-resolution electron diffraction data from nano- and submicron-sized crystals. Using electron beam as a radiation source in a transmission electron microscope (TEM), ab initio structure determination can be conducted from crystals that are 6-7 orders of magnitude smaller than using X-rays. The rapid development of three-dimensional electron diffraction (3DED) techniques has attracted increasing interests in the field of metal-organic frameworks (MOFs), where it is often difficult to obtain large and high-quality crystals for single-crystal X-ray diffraction. Nowadays, a 3DED dataset can be acquired in 15-250 s by applying continuous crystal rotation, and the required electron dose rate can be very low (<0.1 e s(-1) angstrom(-2)). In this review, we describe the evolution of 3DED data collection techniques and how the recent development of continuous rotation electron diffraction techniques improves data quality. We further describe the structure elucidation of MOFs using 3DED techniques, showing examples of using both low- and high-resolution 3DED data. With an improved data quality, 3DED can achieve a high accuracy, and reveal more structural details of MOFs. Because the physical and chemical properties of MOFs are closely associated with their crystal structures, we believe 3DED will only increase its importance in developing MOF materials.
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17.
  • Goerigk, Felix C., et al. (author)
  • Synthesis and Crystal Structure of the Short LnSb(2)O(4)Br Series (Ln = Eu-Tb) and Luminescence Properties of Eu3+-Doped Samples
  • 2020
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 10:12
  • Journal article (peer-reviewed)abstract
    • Pale yellow crystals of LnSb(2)O(4)Br (Ln = Eu-Tb) were synthesized via high temperature solid-state reactions from antimony sesquioxide, the respective lanthanoid sesquioxides and tribromides. Single-crystal X-ray diffraction studies revealed a layered structure in the monoclinic space group P2(1)/c. In contrast to hitherto reported quaternary lanthanoid(III) halide oxoantimonates(III), in LnSb(2)O(4)Br the lanthanoid(III) cations are exclusively coordinated by oxygen atoms in the form of square hemiprisms. These [LnO(8)](13-) polyhedra form layers parallel to (100) by sharing common edges. All antimony(III) cations are coordinated by three oxygen atoms forming psi(1)-tetrahedral [SbO3](3-) units, which have oxygen atoms in common building up meandering strands along [001] according to {[SbO2/2vO1/1t]-}infinity 1 (v = vertex-sharing, t = terminal). The bromide anions are located between two layers of these parallel running oxoantimonate(III) strands and have no bonding contacts with the Ln(3+) cations. Since Sb3+ is known to be an efficient sensitizer for Ln(3+) emission, photoluminescence studies were carried out to characterize the optical properties and assess their suitability as light phosphors. Indeed, for both, GdSb2O4Br and TbSb2O4Br doped with about 1.0-1.5 at-% Eu3+ efficient sensitization of the Eu3+ emission could be detected. For TbSb2O4Br, in addition, a remarkably high energy transfer from Tb3+ to Eu3+ could be detected that leads to a substantially increased Eu3+ emission intensity, rendering it an efficient red light emitting material.
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18.
  • Gradisek, Anton, et al. (author)
  • Study of Liquid Crystals Showing Two Isotropic Phases by H-1 NMR Diffusometry and H-1 NMR Relaxometry
  • 2019
  • In: CRYSTALS. - : MDPI. - 2073-4352. ; 9:3
  • Journal article (peer-reviewed)abstract
    • In this work, we report a study of two thermotropic liquid crystalline samples showing a not common mesophase behavior. The samples, namely a di-benzyloxy biphenyl derivative labelled 9/2 RS/RS, and a bimesogenic liquid crystal labelled L1, show a direct transition between two isotropic phases followed, at lower temperatures, by the optically isotropic, 3D structured, cubic phase. These systems have been investigated by means of H-1 NMR diffusometry and H-1 NMR relaxometry in order to characterize their isotropic-isotropic'-cubic mesophase behavior, mainly on the dynamic point of view. In particular, the temperature trend of the self-diffusion coefficients measured for both samples allowed us to significantly distinguish between the two isotropic phases, while the temperature dependence of the H-1 spin-lattice relaxation time (T-1) did not show significant discontinuities at the isotropic-isotropic' phase transition. A preliminary analysis of the frequency-dependence of H-1 T-1 at different temperatures gives information about the main motional processes active in the isotropic mesophases.
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19.
  • Grazenaite, Egle, et al. (author)
  • Ga-Substituted Cobalt-Chromium Spinels as Ceramic Pigments Produced by Sol–Gel Synthesis
  • 2020
  • In: Crystals. - : MDPI. - 2073-4352. ; 10:12
  • Journal article (peer-reviewed)abstract
    • For the first time to the best of our knowledge, cobalt-chromium spinels CoCr2−xGaxO4 with different amounts of gallium (x = 0–2 with a step of 0.5) were synthesized via the aqueous sol–gel route as ceramic pigments. The phase composition, crystallite size, morphological features, and color parameters of new compositions and their corresponding ceramic glazes were investigated using XRD, CIELab, SEM, and optical microscopy. It was demonstrated that the formation of single-phase CoCr2−xGaxO4 samples was problematic. Full substitution of Cr3+ by Ga3+ ion in the spinel resulted in the formation of light blue powders, which yielded violetish blue color for the corresponding ceramic glaze.
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20.
  • Grishin, Alexander M. (author)
  • Hardness, Young's Modulus and Elastic Recovery in Magnetron Sputtered Amorphous AlMgB14 Films
  • 2020
  • In: Crystals. - : MDPI. - 2073-4352. ; 10:9
  • Journal article (peer-reviewed)abstract
    • We report optical and mechanical properties of hard aluminum magnesium boride films magnetron sputtered from a stoichiometric AlMgB14 ceramic target onto Corning (R) 1737 Glass and Si (100) wafers. High target sputtering rf-power and sufficiently short target-to-substrate distance appeared to be critical processing conditions. Amorphous AlMgB14 films demonstrate very strong indentation size effect (ISE): exceptionally high nanohardness H = 88 GPa and elastic Young's modulus E* = 517 GPa at 26nmof the diamond probe penetration depth and almost constant values, respectively, of about 35 GPa and 275 GPa starting at depths of about 2-3% of films' thickness. For comparative analysis of elastic strain to failure index H/E*, resistance to plastic deformation ratio H-3/E*(2) and elastic recovery ratio W-e were obtained in nanoindentation tests performed in a wide range of loading forces from 0.5 to 40 mN. High authentic numerical values of H = 50 GPa and E* = 340 GPa correlate with as low as only 10% of total energy dissipating through the plastic deformations.
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21.
  • Gunasekara, Saman Nimali, Dr. 1982-, et al. (author)
  • Thermal Energy Storage Materials (TESMs)-What Does It Take to Make Them Fly?
  • 2021
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 11:11, s. 1276-
  • Journal article (peer-reviewed)abstract
    • Thermal Energy Storage Materials (TESMs) may be the missing link to the "carbon neutral future " of our dreams. TESMs already cater to many renewable heating, cooling and thermal management applications. However, many challenges remain in finding optimal TESMs for specific requirements. Here, we combine literature, a bibliometric analysis and our experiences to elaborate on the true potential of TESMs. This starts with the evolution, fundamentals, and categorization of TESMs: phase change materials (PCMs), thermochemical heat storage materials (TCMs) and sensible thermal energy storage materials (STESMs). PCMs are the most researched, followed by STESMs and TCMs. China, the European Union (EU), the USA, India and the UK lead TESM publications globally, with Spain, France, Germany, Italy and Sweden leading in the EU. Dissemination and communication gaps on TESMs appear to hinder their deployment. Salt hydrates, alkanes, fatty acids, polyols, and esters lead amongst PCMs. Salt hydrates, hydroxides, hydrides, carbonates, ammines and composites dominate TCMs. Besides water, ceramics, rocks and molten salts lead as STESMs for large-scale applications. We discuss TESMs' trends, gaps and barriers for commercialization, plus missing links from laboratory-to-applications. In conclusion, we present research paths and tasks to make these remarkable materials fly on the market by unveiling their potential to realize a carbon neutral future.
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22.
  • Hanna, Abanoub R. N., et al. (author)
  • Single-Crystal Growth and Small Anisotropy of the Lower Critical Field in Oxypnictides : NdFeAsO1-xFx
  • 2020
  • In: Crystals. - : MDPI. - 2073-4352. ; 10:5
  • Journal article (peer-reviewed)abstract
    • High-quality single crystals of the unconventional superconductor NdFeAsO1 - xFx were grown. We developed a new optimized flux technique to overcome the difficulties in single-crystal growth and the sample quality limitations of NdFeAsO1 - xFx. The normal state of the F-doped samples exhibits simple metallic behavior upon cooling down from room temperature, followed by a sharp superconducting transition. The values of residual resistivity ratio (RRR) is 3.2, 6.4, and 10.3 for x = 0.1, 0.15, and 0.2, respectively. Both the large RRR and the narrow superconducting transition signpost the high quality of the crystals. We have examined the in- and out-of-plane lower critical fields, and the field at which vortices penetrate the sample of NdFeAsO1 - xFx (x = 0.1). The anisotropy ratio [gamma(Hc1) (0)] increased slightly with increasing temperature from 0.8 Tc to Tc. The temperature dependence of the first vortex penetration field was obtained under the static magnetic field, H, parallel to the c- and ab- axis, and pronounced changes in the H-c(1)(T) curvature were observed, which are attributed to the multi-band superconductivity.
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23.
  • He, Junjing, et al. (author)
  • Application of Fundamental Models for Creep Rupture Prediction of Sanicro 25 (23Cr25NiWCoCu)
  • 2019
  • In: Crystals. - : MDPI. - 2073-4352. ; 9:12
  • Journal article (peer-reviewed)abstract
    • Creep rupture prediction is always a critical matter for materials serving at high temperatures and stresses for a long time. Empirical models are frequently used to describe creep rupture, but the parameters of the empirical models do not have any physical meanings, and the model cannot reveal the controlling mechanisms during creep rupture. Fundamental models have been proposed where no fitting parameters are involved. Both for ductile and brittle creep rupture, fundamental creep models have been used for the austenitic stainless steel Sanicro 25 (23Cr25NiWCoCu). For ductile creep rupture, the dislocation contribution, solid solution hardening, precipitation hardening, and splitting of dislocations were considered. For brittle creep rupture, creep cavitation models were used taking grain boundary sliding, formation, and growth of creep cavities into account. All parameters in the models have been well defined and no fitting is involved. MatCalc was used for the calculation of the evolution of precipitates. Some physical parameters were obtained with first-principles methods. By combining the ductile and brittle creep rupture models, the final creep rupture prediction was made for Sanicro 25. The modeling results can predict the experiments at long-term creep exposure times in a reasonable way.
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24.
  • Johansson, Leif, et al. (author)
  • Is the Registry Between Adjacent Graphene Layers Grown on C-Face SiC Different Compared to That on Si-Face SiC
  • 2013
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 3:1, s. 1-13
  • Journal article (peer-reviewed)abstract
    • Graphene grown on C-face SiC substrates using two procedures, high and low growth temperature and different ambients, was investigated using Low Energy Electron Microscopy (LEEM), X-ray Photo Electron Electron Microscopy (XPEEM), selected area Low Energy Electron Diffraction (μ-LEED) and selected area Photo Electron Spectroscopy (μ-PES). Both types of samples showed formation of μm-sized grains of graphene. The sharp (1 × 1) μ-LEED pattern and six Dirac cones observed in constant energy photoelectron angular distribution patterns from a grain showed that adjacent layers are not rotated relative to each other, but that adjacent grains in general have different azimuthal orientations. Diffraction spots from the SiC substrate appeared in μ-LEED patterns collected at higher energies, showing that the rotation angle between graphene and SiC varied. C 1s spectra collected did not show any hint of a carbon interface layer. A hydrogen treatment applied was found to have a detrimental effect on the graphene quality for both types of samples, since the graphene domain/grain size was drastically reduced. From hydrogen treated samples, μ-LEED showed at first a clear (1 × 1) pattern, but within minutes, a pattern containing strong superstructure spots, indicating the presence of twisted graphene layers. The LEED electron beam was found to induce local desorption of hydrogen. Heating a hydrogenated C-face graphene sample did not restore the quality of the original as-grown sample.
  •  
25.
  • Kamel, Mohamed, et al. (author)
  • Synthesis, Optical, Magnetic and Thermodynamic Properties of Rocksalt Li1.3Nb0.3Mn0.4O2 Cathode Material for Li-Ion Batteries
  • 2021
  • In: Crystals. - : MDPI. - 2073-4352. ; 11:7
  • Journal article (peer-reviewed)abstract
    • Since the discovery of the reversible intercalation of lithium-ion materials associated with promising electrochemical properties, lithium-containing materials have attracted attention in the research and development of effective cathode materials for lithium-ion batteries. Despite various studies on synthesis, and electrochemical properties of lithium-based materials, fairly little fundamental optical and thermodynamic studies are available in the literature. Here, we report on the structure, optical, magnetic, and thermodynamic properties of Li-excess disordered rocksalt, Li1.3Nb0.3Mn0.4O2 (LNMO) which was comprehensively studied using powder X-ray diffraction, transient absorption spectroscopy, magnetic susceptibility, and low-temperature heat capacity measurements. Charge carrier dynamics and electron-phonon coupling in LNMO were studied using ultra-fast laser spectroscopy. Magnetic susceptibility and specific heat data are consistent with the onset of long-range antiferromagnetic order at the Neel temperatures of 6.5 (1.5) K. The effective magnetic moment of LNMO is found to be 3.60 mu B. The temperature dependence of the inverse magnetic susceptibility follows the Curie-Weiss law in the high-temperature region and shows negative values of the Weiss temperature 52 K (3), confirming the strong AFM interactions.
  •  
26.
  • Khakurel, Krishna P., et al. (author)
  • Kilohertz Macromolecular Crystallography Using an EIGER Detector at Low X-ray Fluxes
  • 2020
  • In: Crystals. - : MDPI. - 2073-4352. ; 10:12
  • Journal article (peer-reviewed)abstract
    • Time-resolved in-house macromolecular crystallography is primarily limited by the capabilities of the in-house X-ray sources. These sources can only provide a time-averaged structure of the macromolecules. A significant effort has been made in the development of in-house laser-driven ultrafast X-ray sources, with one of the goals as realizing the visualization of the structural dynamics of macromolecules at a very short timescale within the laboratory-scale infrastructure. Most of such in-house ultrafast X-ray sources are operated at high repetition rates and usually deliver very low flux. Therefore, the necessity of a detector that can operate at the repetition rate of the laser and perform extremely well under low flux conditions is essential. Here, we present experimental results demonstrating the usability of the hybrid-pixel detectors, such as Eiger X 1M, and provide experimental proof that they can be successfully operated to collect macromolecular crystallographic data up to a detector frame rate of 3 kHz from synchrotron sources. Our results also show that the data reduction and structural analysis are successful at such high frame rates and fluxes as low as 10(8) photons/s, which is comparable to the values expected from a typical laser-driven X-ray source.
  •  
27.
  • Kim, Kyung Ho, 1984, et al. (author)
  • Thermal stability of epitaxial graphene electrodes for conductive polymer nanofiber devices
  • 2017
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 7:12
  • Journal article (peer-reviewed)abstract
    • We used large area, monolayer graphene epitaxially grown on SiC (0001) as contact electrodes for polymer nanofiber devices. Our fabrication process, which avoids polymer resist residues on the graphene surface, results in graphene-polyaniline nanofiber devices with Ohmic contacts and electrical conductivity comparable to that of Au-nanofiber devices. We further checked the thermal stability of the graphene contacts to polyaniline devices by annealing up to T = 800 °C, the temperature at which polyaniline nanofibers are carbonized but the graphene electrode remains intact. The thermal stability and Ohmic contact of polymer nanofibers are demonstrated here, which together with the chemical stability and atomic flatness of graphene, make epitaxial graphene on SiC an attractive contact material for future all-carbon electronic devices.
  •  
28.
  • Kong, J., et al. (author)
  • A structural study of 0.06LiNbO3-0.94K0.5Na0.5NbO3 from neutron total scattering analysis
  • 2021
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 11:4
  • Journal article (peer-reviewed)abstract
    • The structure of ferroelectric 0.06LiNbO3-0.94K0.5Na0.5NbO3 (KNNL6) was investigated by the neutron total scattering method in the temperature range of 290-773 K. The Rietveld analysis using the powder neutron diffraction data in the range of 290-773 K indicates transition from a two-phase (monoclinic and tetragonal) mixture at room temperature to tetragonal and cubic phases at higher temperatures. However, characterization of the local structure by the pair distribution function (PDF) method indicates that the local structure (r ≤ 10 Å) stays monoclinic over the same temperature range. Besides, the local oxygen octahedral distortion exhibits smaller changes with temperature than what is observed for the long-range average structure.
  •  
29.
  • Koruza, Katarina, et al. (author)
  • From initial hit to crystal optimization with microseeding of human carbonic anhydrase IX—A case study for neutron protein crystallography
  • 2018
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 8:11
  • Journal article (peer-reviewed)abstract
    • Human carbonic anhydrase IX (CA IX) is a multi-domain membrane protein that is therefore difficult to express or crystalize. To prepare crystals that are suitable for neutron studies, we are using only the catalytic domain of CA IX with six surface mutations, named surface variant (SV). The crystallization of CA IX SV, and also partly deuterated CA IX SV, was enabled by the use of microseed matrix screening (MMS). Only three drops with crystals were obtained after initial sparse matrix screening, and these were used as seeds in subsequent crystallization trials. Application of MMS, commercial screens, and refinement resulted in consistent crystallization and diffraction-quality crystals. The crystallization protocols and strategies that resulted in consistent crystallization are presented. These results demonstrate not only the use of MMS in the growth of large single crystals for neutron studies with defined conditions, but also that MMS enabled re-screening to find new conditions and consistent crystallization success.
  •  
30.
  • Larsson, Per-Lennart, 1961- (author)
  • On Plowing Frictional Behavior during Scratch Testing : A Comparison between Experimental and Theoretical/Numerical Results
  • 2019
  • In: Crystals. - : MDPI. - 2073-4352. ; 9:1
  • Journal article (peer-reviewed)abstract
    • Scratch testing is a contact mechanics based nondestructive testing method that, if correctly evaluated, can give a lot of information about the material and tribological behavior of a material. In contrast to the situation with another contact-based method, indentation testing, wear characteristics can also be investigated, for example. In order to get results of practical importance from a scratch test, it is necessary to have evaluation formulae available. Indeed, such formulae exist for scratch testing but can be substantially influenced by frictional effects. For this reason, closed-form analytical relations have been suggested for the purpose of accounting for such effects during scratching and in particular the plowing frictional effect. As a major benefit, these relations can also be of assistance during material characterization through scratch testing. However, the proposed existing relations are based solely on theoretical/numerical analyses and, remembering that the scratch test of course is an experimental approach, verification by experiments is a necessity. Such a task is performed in the present study and it is shown that, based on standard contact global properties, the relations are accurate for most polymeric materials but could also be used for some metallic ones.
  •  
31.
  • Lenton, Samuel, et al. (author)
  • Structural biology of calcium phosphate nanoclusters sequestered by phosphoproteins
  • 2020
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 10:9
  • Research review (peer-reviewed)abstract
    • Biofluids that contain stable calcium phosphate nanoclusters sequestered by phosphopeptides make it possible for soft and hard tissues to co-exist in the same organism with relative ease. The stability diagram of a solution of nanocluster complexes shows how the minimum concentration of phosphopeptide needed for stability increases with pH. In the stable region, amorphous calcium phosphate cannot precipitate. Nevertheless, if the solution is brought into contact with hydroxyapatite, the crystalline phase will grow at the expense of the nanocluster complexes. The physico-chemical principles governing the formation, composition, size, structure, and stability of the complexes are described. Examples are given of complexes formed by casein, osteopontin, and recombinant phosphopeptides. Application of these principles and properties to blood serum, milk, urine, and resting saliva is described to show that under physiological conditions they are in the stable region of their stability diagram and so cannot cause soft tissue calcification. Stimulated saliva, however, is in the metastable region, consistent with its role in tooth remineralization. Destabilization of biofluids, with consequential ill-effects, can occur when there is a failure of homeostasis, such as an increase in pH without a balancing increase in the concentration of sequestering phosphopeptides.
  •  
32.
  • Li, Jiantong, et al. (author)
  • Prevention of graphene restacking for performance boost of supercapacitors-a review
  • 2013
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 3:1, s. 163-190
  • Research review (peer-reviewed)abstract
    • Graphene is a promising electrode material for supercapacitors mainly because of its large specific surface area and high conductivity. In practice, however, several fabrication issues need refinement. The restacking of graphene flakes upon being packed into supercapacitor electrodes has become a critical challenge in the full utilization of graphene's large specific surface area to further improve the device performance. In this review, a variety of recent techniques and strategies are overviewed for the prevention of graphene restacking. They have been classified into several categories to improve and facilitate the discussion on the underlying ideas. Based on the overview of the existing techniques, we discuss the trends of future research in the fields.
  •  
33.
  • Lidin, Sven, et al. (author)
  • Y 3 R u2−x -A representative of a composite modulated family of intermetallics
  • 2019
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 9:4
  • Journal article (peer-reviewed)abstract
    • The compound Y 3 R u2−x was synthesized from the elements and the structure was solved from single crystal synchrotron data. The high quality of the data allowed the determination of the incommensurate ordering of the compound, previously reported as disordered, with respect to the second subsystem. The compound crystallizes in the super space group X-3(00γ)0 with the q-vector axial along c*, q = 00γ, λ = 0.4276(7) and the centering vectors (1/3 2/3 0 1/3), (2/3 1/3 0 2/3).
  •  
34.
  • Liu, Yanrong, et al. (author)
  • Ionic Liquids/Deep Eutectic Solvents-Based Hybrid Solvents for CO2 Capture
  • 2020
  • In: Crystals. - : MDPI. - 2073-4352. ; 10:11
  • Research review (peer-reviewed)abstract
    • The CO2 solubilities (including CO2 Henry’s constants) and viscosities in ionic liquids (ILs)/deep eutectic solvents (DESs)-based hybrid solvents were comprehensively collected and summarized. The literature survey results of CO2 solubility illustrated that the addition of hybrid solvents to ILs/DESs can significantly enhance the CO2 solubility, and some of the ILs-based hybrid solvents are super to DESs-based hybrid solvents. The best hybrid solvents of IL–H2O, IL–organic, IL–amine, DES–H2O, and DES–organic are [DMAPAH][Formate] (2.5:1) + H2O (20 wt %) (4.61 mol/kg, 298 K, 0.1 MPa), [P4444][Pro] + PEG400 (70 wt %) (1.61 mol/kg, 333.15 K, 1.68 MPa), [DMAPAH][Formate] (2.0:1) + MEA (30 wt %) (6.24 mol/kg, 298 K, 0.1 MPa), [TEMA][Cl]-GLY-H2O 1:2:0.11 (0.66 mol/kg, 298 K, 1.74 MPa), and [Ch][Cl]-MEA 1:2 + DBN 1:1 (5.11 mol/kg, 298 K, 0.1 MPa), respectively. All of these best candidates show higher CO2 solubility than their used pure ILs or DESs, evidencing that IL/DES-based hybrid solvents are remarkable for CO2 capture. For the summarized viscosity results, the presence of hybrid solvents in ILs and DESs can decrease their viscosities. The lowest viscosities acquired in this work for IL–H2O, IL–amine, DES–H2O, and DES–organic hybrid solvents are [DEA][Bu] + H2O (98.78 mol%) (0.59 mPa·s, 343.15 K), [BMIM][BF4] + DETA (94.9 mol%) (2.68 mPa·s, 333.15 K), [L-Arg]-GLY 1:6 + H2O (60 wt %) (2.7 mPa·s, 353.15 K), and [MTPP][Br]-LEV-Ac 1:3:0.03 (16.16 mPa·s, 333.15 K) at 0.1 MPa, respectively.
  •  
35.
  • Music, Denis, et al. (author)
  • Theoretical and Experimental Aspects of Current and Future Research on NbO2 Thin Film Devices
  • 2021
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 11:2
  • Research review (peer-reviewed)abstract
    • The present research front of NbO2 based memory, energy generation, and storage thin film devices is reviewed. Sputtering plasmas contain NbO, NbO2, and NbO3 clusters, affecting nucleation and growth of NbO2, often leading to a formation of nanorods and nanoslices. NbO2 (I41/a) undergoes the Mott topological transition at 1081 K to rutile (P42/mnm), yielding changes in the electronic structure, which is primarily utilized in memristors. The Seebeck coefficient is a key physical parameter governing the performance of thermoelectric devices, but its temperature behavior is still controversial. Nonetheless, they perform efficiently above 900 K. There is a great potential to improve NbO2 batteries since the theoretical capacity has not been reached, which may be addressed by future diffusion studies. Thermal management of functional materials, comprising thermal stress, thermal fatigue, and thermal shock, is often overlooked even though it can lead to failure. NbO2 exhibits relatively low thermal expansion and high elastic modulus. The future for NbO2 thin film devices looks promising, but there are issues that need to be tackled, such as dependence of properties on strain and grain size, multiple interfaces with point and extended defects, and interaction with various natural and artificial environments, enabling multifunctional applications and durable performance.
  •  
36.
  • Paterlini, Veronica, et al. (author)
  • Spectroscopic and Structural Properties of β-Tricalcium Phosphates Ca9RE(PO4)7 (RE = Nd, Gd, Dy)
  • 2021
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 11:10
  • Journal article (peer-reviewed)abstract
    • Rare-earth-based Ca9RE(PO4)7 (RE = Nd, Gd, Dy) materials were synthesized by solid-state reaction at T = 1200 °C. The obtained tricalcium phosphate (TCP) materials are efficient light emitters due to the presence of RE3+ ions, although these ions are present at high concentrations. Moreover, in these host structures, these ions can be used as optical probes to study their local environments. Thus, photoluminescence (PL) emission spectra of the powder samples clearly indicated, for Dy3+ and Gd3+ ions, the presence of the RE3+ ion in low-symmetry sites with some local structural disorder, and the spectra show the presence of vibrational features (in the case of Gd3+). For the Nd3+ phase, emission bands are present around 900, 1050, and 1330 nm, originating from the 4F3/2 level. In general, these RE-TCP samples are interesting luminescent materials in the visible (Dy), UV (Gd), and NIR (Nd) regions, due to weak concentration quenching even for high concentrations of the emitting ion.
  •  
37.
  • Penha, Frederico M., et al. (author)
  • In Situ Observation of Epitaxial Growth during Evaporative Simultaneous Crystallization from Aqueous Electrolytes in Droplets
  • 2021
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 11:9, s. 1122-1122
  • Journal article (peer-reviewed)abstract
    • In this study, crystallization phenomena were investigated by real-time in situ observation of seeded droplets under evaporation using a self-developed hot-stage platform. Ternary solutions at eutonic conditions at 25 °C were investigated for the following systems: NaCl–KCl–H2O, NaCl–CaSO4–H2O, and NaCl–Na2SO4–H2O. Evidence of epitaxial growth was found for aqueous NaCl–KCl and aqueous NaCl–Na2SO4. Sodium chloride nucleated and grew epitaxially upon the other substrates in a larger proportion compared with the inverse. This observation could be related to the higher solubility, and consequently higher residual supersaturation of NaCl regarding the other components. Hopper-like NaCl crystals developed in almost all systems. The results may help devise strategies to control particle morphologies and purity in industrial crystallization from complex systems.
  •  
38.
  • Qian, Zhao, et al. (author)
  • Atomistic Modeling of Various Doped Mg2NiH4 as Conversion Electrode Materials for Lithium Storage
  • 2019
  • In: Crystals. - : MDPI. - 2073-4352. ; 9:5
  • Journal article (peer-reviewed)abstract
    • In this work, we have compared the potential applications of nine different elements doped Mg2NiH4 as conversion-type electrode materials in Li-ion batteries by means of state-of-the-art Density functional theory calculations. The electrochemical properties, such as specific capacity, volume change and average voltage, as well as the atomic and electronic structures of different doped systems have been investigated. The Na doping can improve the electrochemical capacity of the pristine material. Si and Ti doping can reduce the band gap and benefit the electronic conductivity of electrode materials. All of the nine doping elements can help to reduce the average voltage of negative electrodes and lead to reasonable volume changes. According to the computational screening, the Na, Si and Ti doping elements are thought to be promising to enhance the comprehensive properties of pure material. This theoretical study is proposed to encourage and expedite the development of metal-hydrides based lithium-storage materials.
  •  
39.
  • Rastabi, Shahrzad Arshadi, et al. (author)
  • Synthesis of NiMoO4/3D-rGO Nanocomposite in Alkaline Environments for Supercapacitor Electrodes
  • 2019
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 9:1
  • Journal article (peer-reviewed)abstract
    • Although Graphene oxide (GO)-based materials is known as a favorable candidate for supercapacitors, its conductivity needs to be increased. Therefore, this study aimed to investigate the performance of GO-based supercapicitor with new methods. In this work, an ammonia solution has been used to remove the oxygen functional groups of GO. In addition, a facile precipitation method was performed to synthesis a NiMoO4/3D-rGO electrode with purpose of using synergistic effects of rGO conductivity properties as well as NiMoO4 pseudocapacitive behavior. The phase structure, chemical bands and morphology of the synthesized powders were investigated by X-ray diffraction (XRD), Raman spectroscopy, and field emission secondary electron microscopy (FE-SEM). The electrochemical results showed that the NiMoO4/3D-rGO(II) electrode, where ammonia has been used during the synthesis, has a capacitive performance of 932 Fg(-1). This is higher capacitance than NiMoO4/3D-rGO(I) without using ammonia. Furthermore, the NiMoO4/3D-rGO(II) electrode exhibited a power density of up to 17.5 kW kg(-1) and an energy density of 32.36 Wh kg(-1). These results showed that ammonia addition has increased the conductivity of rGO sheets, and thus it can be suggested as a new technique to improve the capacitance.
  •  
40.
  • Ravensburg, Anna L., et al. (author)
  • Experimental and Theoretical Investigation of the Elastic Properties of HfV2O7
  • 2020
  • In: Crystals. - : MDPI. - 2073-4352. ; 10:3
  • Journal article (peer-reviewed)abstract
    • We investigated the elastic properties of the HfV2O7 high-temperature phase, exhibiting negative thermal expansion, in a synergetic strategy of first-principle calculations and nanoindentation experiments performed on sputtered films. Self-consistent results were obtained for the measured elastic modulus (73 +/- 14 GPa) and dispersion-corrected density functional theory calculations. The elastic properties of HfV2O7 are affected by long-range dispersion interaction, which may be induced by severe modification in the second-nearest neighbor O-O bond distance as obtained upon compression. HfV2O7 is composed of HfO6, VO4, and V2O7 building blocks, whereby the latter is characterized by an increasing V-O(-V) bond length upon compression.
  •  
41.
  •  
42.
  • Shtepliuk, Ivan, et al. (author)
  • Role of the Potential Barrier in the Electrical Performance of the Graphene/SiC Interface
  • 2017
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 7:6
  • Research review (peer-reviewed)abstract
    • In spite of the great expectations for epitaxial graphene (EG) on silicon carbide (SiC) to be used as a next-generation high-performance component in high-power nano- and micro-electronics, there are still many technological challenges and fundamental problems that hinder the full potential of EG/SiC structures and that must be overcome. Among the existing problems, the quality of the graphene/SiC interface is one of the most critical factors that determines the electroactive behavior of this heterostructure. This paper reviews the relevant studies on the carrier transport through the graphene/SiC, discusses qualitatively the possibility of controllable tuning the potential barrier height at the heterointerface and analyses how the buffer layer formation affects the electronic properties of the combined EG/SiC system. The correlation between the sp(2)/sp(3) hybridization ratio at the interface and the barrier height is discussed. We expect that the barrier height modulation will allow realizing a monolithic electronic platform comprising different graphene interfaces including ohmic contact, Schottky contact, gate dielectric, the electrically-active counterpart in p-n junctions and quantum wells.
  •  
43.
  • Solomon, Getachew, et al. (author)
  • Microwave-Assisted vs. Conventional Hydrothermal Synthesis of MoS2 Nanosheets : Application towards Hydrogen Evolution Reaction
  • 2020
  • In: Crystals. - : MDPI. - 2073-4352. ; 10:11
  • Journal article (peer-reviewed)abstract
    • Molybdenum sulfide (MoS2) has emerged as a promising catalyst for hydrogen evolution applications. The synthesis method mainly employed is a conventional hydrothermal method. This method requires a longer time compared to other methods such as microwave synthesis methods. There is a lack of comparison of the two synthesis methods in terms of crystal morphology and its electrochemical activities. In this work, MoS2 nanosheets are synthesized using both hydrothermal (HT-MoS2) and advanced microwave methods (MW-MoS2), their crystal morphology, and catalytical efficiency towards hydrogen evolution reaction (HER) were compared. MoS2 nanosheet is obtained using microwave-assisted synthesis in a very short time (30 min) compared to the 24 h hydrothermal synthesis method. Both methods produce thin and aggregated nanosheets. However, the nanosheets synthesized by the microwave method have a less crumpled structure and smoother edges compared to the hydrothermal method. The as-prepared nanosheets are tested and used as a catalyst for hydrogen evolution results in nearly similar electrocatalytic performance. Experimental results showed that: HT-MoS2 displays a current density of 10 mA/cm2 at overpotential (−280 mV) compared to MW-MoS2 which requires −320 mV to produce a similar current density, suggesting that the HT-MoS2 more active towards hydrogen evolutions reaction.
  •  
44.
  • Su, Xiaojun, et al. (author)
  • Understanding of photophysical processes in dio additive-treated ptb7:Pc71 bm solar cells
  • 2021
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 11:9
  • Journal article (peer-reviewed)abstract
    • 1,8-diiodooctane (DIO) additive is an important method for optimizing the morphology and device performance of polythieno[3,4-b]-thiophene-co-benzodithiophene (PTB7)-based polymer solar cells. However, the effect of DIO additive on charge photogeneration dynamics of PTB7-based polymer solar cells is still poorly understood. In this work, the effect of DIO additive on the carrier photogeneration dynamics, as well as device performance of PTB7: [6,6]-phenyl-C71-butyric acid methyl ester (PC71 BM) solar cells was studied. Bias-dependent photoluminescence (PL) experiments of a neat PTB7 device show that the exciton cannot be dissociated by the electric field in the device within the operating voltage range, but it can be effectively dissociated by the high electric field. PL and time-resolved PL studies show that DIO additive reduces the phase size of PTB7 in the blend film, resulting in an increased exciton dissociation efficiency. The carrier recombination processes were studied by transient absorption, which shows geminate carrier recombination was suppressed in the DIO-treated PTB7:PC71 BM device in ultrafast time scale. The increased exciton dissociation efficiency and suppressed carrier recombination in ultrafast time scale play an important role for DIO-treated PTB7:PC71 BM solar cells to attain a higher power conversion efficiency.
  •  
45.
  • Sun, Jie, 1977, et al. (author)
  • Synthesis Methods of Two-Dimensional MoS2: A Brief Review
  • 2017
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 7:7, s. Article no 198 -
  • Research review (peer-reviewed)abstract
    • Molybdenum disulfide (MoS2) is one of the most important two-dimensional materials after graphene. Monolayer MoS2 has a direct bandgap (1.9 eV) and is potentially suitable for post-silicon electronics. Among all atomically thin semiconductors, MoS2's synthesis techniques are more developed. Here, we review the recent developments in the synthesis of hexagonal MoS2, where they are categorized into top-down and bottom-up approaches. Micromechanical exfoliation is convenient for beginners and basic research. Liquid phase exfoliation and solutions for chemical processes are cheap and suitable for large-scale production; yielding materials mostly in powders with different shapes, sizes and layer numbers. MoS2 films on a substrate targeting high-end nanoelectronic applications can be produced by chemical vapor deposition, compatible with the semiconductor industry. Usually, metal catalysts are unnecessary. Unlike graphene, the transfer of atomic layers is omitted. We especially emphasize the recent advances in metalorganic chemical vapor deposition and atomic layer deposition, where gaseous precursors are used. These processes grow MoS2 with the smallest building-blocks, naturally promising higher quality and controllability. Most likely, this will be an important direction in the field. Nevertheless, today none of those methods reproducibly produces MoS2 with competitive quality. There is a long way to go for MoS2 in real-life electronic device applications.
  •  
46.
  • Wang, L, et al. (author)
  • Novel Dilute Bismide, Epitaxy, Physical Properties and Device Application
  • 2017
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 7:3, s. Article no 63 -
  • Research review (peer-reviewed)abstract
    • Dilute bismide in which a small amount of bismuth is incorporated to host III-Vs is the least studied III-V compound semiconductor and has received steadily increasing attention since 2000. In this paper, we review theoretical predictions of physical properties of bismide alloys, epitaxial growth of bismide thin films and nanostructures, surface, structural, electric, transport and optic properties of various binaries and bismide alloys, and device applications.
  •  
47.
  • Yazdi, Gholamreza, et al. (author)
  • Epitaxial Graphene on SiC: A Review of Growth and Characterization
  • 2016
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 6:5
  • Research review (peer-reviewed)abstract
    • This review is devoted to one of the most promising two-dimensional (2D) materials, graphene. Graphene can be prepared by different methods and the one discussed here is fabricated by the thermal decomposition of SiC. The aim of the paper is to overview the fabrication aspects, growth mechanisms, and structural and electronic properties of graphene on SiC and the means of their assessment. Starting from historical aspects, it is shown that the most optimal conditions resulting in a large area of one ML graphene comprise high temperature and argon ambience, which allow better controllability and reproducibility of the graphene quality. Elemental intercalation as a means to overcome the problem of substrate influence on graphene carrier mobility has been described. The most common characterization techniques used are low-energy electron microscopy (LEEM), angle-resolved photoelectron spectroscopy (ARPES), Raman spectroscopy, atomic force microscopy (AFM) in different modes, Hall measurements, etc. The main results point to the applicability of graphene on SiC in quantum metrology, and the understanding of new physics and growth phenomena of 2D materials and devices.
  •  
48.
  • Öhrström, Lars, 1963 (author)
  • Let’s talk about MOFs—Topology and terminology of metal-organic frameworks and why we need them
  • 2015
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 5:1, s. 154-162
  • Journal article (peer-reviewed)abstract
    • Recent IUPAC (The International Union for Pure and Applied Chemistry) recommendations on the terminology of metal-organic frameworks are reviewed and the background to a proposed topology classification is discussed. The various numerical designators such as point symbols, vertex symbols and transitivity are also explained and their importance elucidated.
  •  
49.
  • Bathen, M. E., et al. (author)
  • Influence of carbon cap on self-diffusion in silicon carbide
  • 2020
  • In: Crystals. - : MDPI AG. - 2073-4352. ; 10:9, s. 1-11
  • Journal article (peer-reviewed)abstract
    • Self-diffusion of carbon (12C and13C) and silicon (28Si and30Si) in 4H silicon carbide has been investigated by utilizing a structure containing an isotope purified 4H-28Si12C epitaxial layer grown on an n-type (0001) 4H-SiC substrate, and finally covered by a carbon capping layer (C-cap). The13C and30Si isotope profiles were monitored using secondary ion mass spectrometry (SIMS) following successive heat treatments performed at 2300–2450◦C in Ar atmosphere using an inductively heated furnace. The30Si profiles show little redistribution within the studied temperature range, with the extracted diffusion lengths for Si being within the error bar for surface roughening during annealing, as determined by profilometer measurements. On the other hand, a significant diffusion of13C was observed into the isotope purified layer from both the substrate and the C-cap. A diffusivity of D = 8.3 × 106 e−10.4/kBT cm2/s for13C was extracted, in contrast to previous findings that yielded lower both pre-factors and activation energies for C self-diffusion in SiC. The discrepancy between the present measurements and previous theoretical and experimental works is ascribed to the presence of the C-cap, which is responsible for continuous injection of C interstitials during annealing, and thereby suppressing the vacancy mediated diffusion.
  •  
50.
  • Burakovsky, Leonid, et al. (author)
  • Systematics of the Third Row Transition Metal Melting: The HCP Metals Rhenium and Osmium
  • 2018
  • In: Crystals. - : MDPI. - 2073-4352. ; 8:6
  • Journal article (peer-reviewed)abstract
    • The melting curves of rhenium and osmium to megabar pressures are obtained from an extensive suite of ab initio quantum molecular dynamics (QMD) simulations using the Z method. In addition, for Re, we combine QMD simulations with total free energy calculations to obtain its phase diagram. Our results indicate that Re, which generally assumes a hexagonal close-packed (hcp) structure, melts from a face-centered cubic (fcc) structure in the pressure range 20-240 GPa. We conclude that the recent DAC data on Re to 50 GPa in fact encompass both the true melting curve and the low-slope hcp-fcc phase boundary above a triple point at (20 GPa, 4240 K). A linear fit to the Re diamond anvil cell (DAC) data then results in a slope that is 2.3 times smaller than that of the actual melting curve. The phase diagram of Re is topologically equivalent to that of Pt calculated by us earlier on. Regularities in the melting curves of Re, Os, and five other 3rd-row transition metals (Ta, W, Ir, Pt, Au) form the 3rd-row transition metal melting systematics. We demonstrate how this systematics can be used to estimate the currently unknown melting curve of the eighth 3rd-row transition metal Hf.
  •  
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