Articoli di riviste: "Metal crystals"

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Shao, Lixiong, Jiang Diao, Wang Zhou, Tao Zhang e Bing Xie. "Non-isothermal crystallization behavior of spinel crystals in FeO-SiO2-TiO2-V2O3-Cr2O3 slag". Metallurgical Research & Technology 116, n. 1 (18 dicembre 2018): 110. http://dx.doi.org/10.1051/metal/2018033.

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The growth behaviour of spinel crystals in vanadium slag with high Cr2O3 content was investigated and clarified by statistical analyses based on the Crystal Size Distribution (CSD) theory. The results indicate that low cooling rate and Cr2O3 content benefit the growth of spinel crystals. The chromium spinel crystals firstly precipitated and then acted as the heterogeneous nuclei of vanadium and titanium spinel crystals. The growth mechanisms of the spinel crystals at the cooling rate of 5 K/min consist two regimes: firstly, nucleation control in the temperature range of 1873 to 1773 K, in which the shapes of CSD curves are asymptotic; secondly, surface and supply control within the temperature range of 1773 to 1473 K, in which the shapes of CSD curves are lognormal. The mean diameter of spinel crystals increases from 3.97 to 52.21 µm with the decrease of temperature from 1873 to 1473 K.

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Zhou, Wu Zong. "Mesoporous Crystals of Transition Metal Oxides". Solid State Phenomena 140 (ottobre 2008): 37–46. http://dx.doi.org/10.4028/www.scientific.net/ssp.140.37.

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Using mesoporous silicas as hard templates and facilitating crystal growth of transition metal oxides inside the pores, some mesoporous crystals can be produced after removing the templates. This paper gives a brief review of the research of mesoporous crystals of transition metal oxides in the last five years, including the technical development and potential applications of the new form of oxides.

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JIA, JIN-FENG, X. LIU, S. C. LI, J. Z. WANG, J. L. LI, H. LIU, M. H. PAN et al. "ARTIFICIAL METAL NANOCLUSTER CRYSTALS". Modern Physics Letters B 16, n. 23n24 (20 ottobre 2002): 889–94. http://dx.doi.org/10.1142/s0217984902004408.

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Artificial metal nanocluster crystals, (i.e. periodic lattices consisting of identical metal nanoclusters) were fabricated using a novel technique in which surface mediated magic clustering was used to achieve identical cluster size, while the Si(111)-7 × 7 surface was used as a template for ordering the clusters. The universality of this strategy was demonstrated by fabricating more than 10 different nanocluster arrays with different metals and alloys. The atomic structures, formation mechanism and stability of the nanoclusters were studied with in situ scanning tunneling microscopy combined with first-principles total energy calculations. Our study shows that delicate control of growth kinetics is extremely important for cluster crystal fabrication.

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Jiao, Benqi, Weizhong Han, Wen Zhang, Zhongwu Hu e Jianfeng Li. "Preparation, Deformation Behavior and Irradiation Damage of Refractory Metal Single Crystals for Nuclear Applications: A Review". Materials 17, n. 14 (10 luglio 2024): 3417. http://dx.doi.org/10.3390/ma17143417.

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Refractory metal single crystals have been applied in key high-temperature structural components of advanced nuclear reactor power systems, due to their excellent high-temperature properties and outstanding compatibility with nuclear fuels. Although electron beam floating zone melting and plasma arc melting techniques can prepare large-size oriented refractory metals and their alloy single crystals, both have difficulty producing perfect defect-free single crystals because of the high-temperature gradient. The mechanical properties of refractory metal single crystals under different loads all exhibit strong temperature and crystal orientation dependence. Slip and twinning are the two basic deformation mechanisms of refractory metal single crystals, in which low temperatures or high strain rates are more likely to induce twinning. Recrystallization is always induced by the combined action of deformation and annealing, exhibiting a strong crystal orientation dependence. The irradiation hardening and neutron embrittlement appear after exposure to irradiation damage and degrade the material properties, attributed to vacancies, dislocation loops, precipitates, and other irradiation defects, hindering dislocation motion. This paper reviews the research progress of refractory metal single crystals from three aspects, preparation technology, deformation behavior, and irradiation damage, and highlights key directions for future research. Finally, future research directions are prospected to provide a reference for the design and development of refractory metal single crystals for nuclear applications.

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KIRUBAVATHI, K., K. SELVARAJU e S. KUMARARAMAN. "STUDIES ON GROWTH AND CHARACTERIZATION OF BIS THIOUREA LEAD CHLORIDE: A NOVEL NONLINEAR OPTICAL CRYSTAL". Journal of Nonlinear Optical Physics & Materials 18, n. 01 (marzo 2009): 153–59. http://dx.doi.org/10.1142/s0218863509004531.

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Single crystals of the metal-organic nonlinear optical material bis thiourea lead chloride were grown from solution growth technique for the first time. The grown crystals were characterized by single crystal X-ray diffraction analysis to confirm the crystal structure. The presence of various functional groups and the coordination of metal ions to thiourea were confirmed by Fourier transform infrared analysis. UV-Vis. spectrum was recorded to study the optical transparency of the grown crystals. The second order nonlinear optical property of the grown crystal was examined by Kurtz powder technique and mechanical behavior was studied by Vickers micro hardness test.

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Øien-Ødegaard, Sigurd, e Karl Lillerud. "Twinning in Zr-Based Metal-Organic Framework Crystals". Chemistry 2, n. 3 (16 settembre 2020): 777–86. http://dx.doi.org/10.3390/chemistry2030050.

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Ab initio structure determination of new metal-organic framework (MOF) compounds is generally done by single crystal X-ray diffraction, but this technique can yield incorrect crystal structures if crystal twinning is overlooked. Herein, the crystal structures of three Zirconium-based MOFs, that are especially prone to twinning, have been determined from twinned crystals. These twin laws (and others) could potentially occur in many MOFs or related network structures, and the methods and tools described herein to detect and treat twinning could be useful to resolve the structures of affected crystals. Our results highlight the prevalence (and sometimes inevitability) of twinning in certain Zr-MOFs. Of special importance are the works of Howard Flack which, in addition to fundamental advances in crystallography, provide accessible tools for inexperienced crystallographers to take twinning into account in structure elucidation.

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Sreenivasan, R. S., N. Kanagathara, G. Ezhamani, N. G. Renganathan e G. Anbalagan. "Effect of Metal Dopant on Ninhydrin—Organic Nonlinear Optical Single Crystals". Journal of Spectroscopy 2013 (2013): 1–5. http://dx.doi.org/10.1155/2013/386024.

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In the present work, metal (Cu2+)-substituted ninhydrin single crystals were grown by slow evaporation method. The grown crystals have been subjected to single crystal XRD, powder X-ray diffraction, FTIR, dielectric and SHG studies. Single crystal X-ray diffraction analysis reveals that the compound crystallizes in monoclinic system with noncentrosymmetric space group P21 with lattice parametersa=11.28 Å,b=5.98 Å,c=5.71 Å,α=90∘,β=98.57,γ=90∘, andV=381 (Å)3, which agrees very well with the reported value. The sharp and strong peaks in the powder X-ray diffraction pattern confirm the good crystallinity of the grown crystals. The presence of dopants marginally altered the lattice parameters without affecting the basic structure of the crystal. The UV-Vis transmittance spectrum shows that the crystal has a good optical transmittance in the entire visible region with lower cutoff wavelength 314 nm. The vibrational frequencies of various functional groups in the crystals have been derived from FT-IR analysis. Based on the shifts in the vibrations, the presence of copper in the lattice of the grown crystal is clearly established from the pure ninhydrin crystals. Both dielectric constant and dielectric loss decrease with the increase in frequency. The second harmonic generation efficiency was measured by employing powder Kurtz method.

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Hayashi, Tomohiro, Hidemoto Shiga, Masayoshi Sadakata, Tatsuya Okubo e Masahiro Yoshimura. "Hydrothermal growth of millimeter-sized aluminosilicate sodalite single crystals in noble metal capsules". Journal of Materials Research 13, n. 4 (aprile 1998): 891–95. http://dx.doi.org/10.1557/jmr.1998.0120.

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Aluminosilicate sodalite Na8[SiAlO4]6Cl2 single crystals are synthesized by hydrothermal processing at 873–973 K and 100–150 MPa in noble metal capsules to avoid contamination. The starting material is aluminosilicate gel, and spontaneous nucleation followed by its growth takes place. The largest size of the single crystals obtained is 1 mm across. Longer aging and heating result in larger single crystals. It is also found that the aluminum source in the synthesis gel and the element used in the noble metal capsules influence the single crystal growth. Judging from x-ray diffraction (XRD) (powder and single-crystal), optical microscopy, and thermogravimetry and differential thermal analysis (TG-DTA), the sodalite single crystals grown have good quality compared with the conventional powder.

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Kobayashi, Jun, Keisuke Shimura, Keisuke Mikurube, Saki Otobe, Takashi Matsumoto, Eri Ishikawa, Haruo Naruke e Takeru Ito. "Polyoxomolybdate Layered Crystals Constructed from a Heterocyclic Surfactant: Syntheses, Pseudopolymorphism and Introduction of Metal Cations". Materials 15, n. 7 (25 marzo 2022): 2429. http://dx.doi.org/10.3390/ma15072429.

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Crystals with layered structures are crucial for the construction of functional materials exhibiting intercalation, ionic conductivity, or emission properties. Polyoxometalate crystals hybridized with surfactant cations have distinct layered packings due to the surfactants which can form lamellar structures. Introducing metal cations into such polyoxometalate-surfactant hybrid crystals is significant for the addition of specific functions. Here, polyoxomolybdate–surfactant hybrid crystals were synthesized as single crystals, and unambiguously characterized by X-ray structure analyses. Octamolybdate ([Mo8O26]4–, Mo8) and heterocyclic surfactant of 1-dodecylpyridinium (C12py) were employed. The hybrid crystals were composed of α-type and β-type Mo8 isomers. Two crystalline phases containing α-type Mo8 were obtained as pseudopolymorphs depending on the crystallization conditions. Crystallization with the presence of rubidium and cesium cations caused the formation of metal cation-introduced hybrid crystals comprising β-Mo8 (C12py-Rb-Mo8 and C12py-Cs-Mo8). The yield of the C12py-Rb-Mo8 hybrid crystal was almost constant within crystallization temperatures of 279–303 K, while that of C12py-Cs-Mo8 decreased over 288 K. This means that the C12py-Mo8 hybrid crystal can capture Rb+ and Cs+ from the solution phase into the solids as the C12py-Rb-Mo8 and C12py-Cs-Mo8 hybrid crystals. The C12py-Mo8 hybrid crystals could be applied to ion-capturing materials for heavy metal cation removal.

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Wade, Colin, Nicolas Barrière, Lorraine Hanlon, Pierre Bastie, Gerard Fitzpatrick, Michael Jentschel, Gilles Roudil e Peter Von Ballmoos. "Laue diffraction behaviour in silver mosaic crystals at several gamma-ray energies and orientations". Journal of Applied Crystallography 49, n. 2 (24 marzo 2016): 606–15. http://dx.doi.org/10.1107/s1600576716002880.

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The Laue lens is an emerging technology that uses crystal diffraction to concentrate gamma-rays. The Darwin model describes diffraction in mosaic crystals at high energies (>50 keV) and is the basis for assessing the throughput of a Laue lens. While the Darwin model has been used successfully to describe binary alloys, it has shown inconsistencies when applied to diffraction with pure-metal crystals. This paper presents a systematic study of diffraction in pure-metal silver mosaic crystals and the performance of the Darwin model when applied to the data. Two cut silver crystals were tested at the Institute Laue–Langevin facility at three gamma-ray energies and at three different crystallographic orientations. The rocking curves were fitted using the Darwin model. A single Gaussian for the distribution of crystallite orientations leads to poor quality fits. A crystallite distribution that is the sum of two Gaussians gives improved fits. However, for each crystal, the Darwin model gives mosaicities and crystallite sizes that are not consistent with one another as a function either of energy or of crystallographic orientation, despite these being physical properties of the materials. Without an adequate model to describe diffraction in pure-metal crystals, either a Laue lens design must severely limit its catalogue of usable materials or each crystal in the design must be tested at the exact energy at which it is to be used. A more general theory to describe hard X-ray diffraction using pure-metal mosaic crystals, possibly involving a distribution of crystallite sizes, is therefore required.

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Chen, Chen, Xiao-Tong He, Dan-Li Hong, Jing-Wen Wang, Yang-Hui Luo e Bai-Wang Sun. "Tuning the crystal structures of metal-tetraphenylporphines via a magnetic field". New Journal of Chemistry 42, n. 15 (2018): 12570–75. http://dx.doi.org/10.1039/c8nj01882k.

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In this work, two new single crystals of copper-tetraphenylporphine (Cu-TPP) (crystals 2 and 3), which were induced by external magnetic fields with strengths of 0.5 and 0.8 T, respectively, have been prepared and characterized by single-crystal X-ray diffraction and Hirshfeld surface analysis.

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Radka, Christopher D., Lawrence J. DeLucas, Landon S. Wilson, Matthew B. Lawrenz, Robert D. Perry e Stephen G. Aller. "Crystal structure ofYersinia pestisvirulence factor YfeA reveals two polyspecific metal-binding sites". Acta Crystallographica Section D Structural Biology 73, n. 7 (30 giugno 2017): 557–72. http://dx.doi.org/10.1107/s2059798317006349.

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Gram-negative bacteria use siderophores, outer membrane receptors, inner membrane transporters and substrate-binding proteins (SBPs) to transport transition metals through the periplasm. The SBPs share a similar protein fold that has undergone significant structural evolution to communicate with a variety of differentially regulated transporters in the cell. InYersinia pestis, the causative agent of plague, YfeA (YPO2439, y1897), an SBP, is important for full virulence during mammalian infection. To better understand the role of YfeA in infection, crystal structures were determined under several environmental conditions with respect to transition-metal levels. Energy-dispersive X-ray spectroscopy and anomalous X-ray scattering data show that YfeA is polyspecific and can alter its substrate specificity. In minimal-media experiments, YfeA crystals grown after iron supplementation showed a threefold increase in iron fluorescence emission over the iron fluorescence emission from YfeA crystals grown from nutrient-rich conditions, and YfeA crystals grown after manganese supplementation during overexpression showed a fivefold increase in manganese fluorescence emission over the manganese fluorescence emission from YfeA crystals grown from nutrient-rich conditions. In all experiments, the YfeA crystals produced the strongest fluorescence emission from zinc and could not be manipulated otherwise. Additionally, this report documents the discovery of a novel surface metal-binding site that prefers to chelate zinc but can also bind manganese. Flexibility across YfeA crystal forms in three loops and a helix near the buried metal-binding site suggest that a structural rearrangement is required for metal loading and unloading.

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Chen, Xin, Zhi-Yuan Yao, Chen Xue, Zhu-Xi Yang, Jian-Lan Liu e Xiao-Ming Ren. "Novel isomorphism of two hexagonal non-centrosymmetric hybrid crystals of M(en)3Ag2I4 (M = transition metal Mn2+ or main-group metal Mg2+; en = ethylenediamine)". CrystEngComm 20, n. 3 (2018): 356–61. http://dx.doi.org/10.1039/c7ce02005h.

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For the first time, a main-group metal complex is used as a template for the formation of hybrid crystal structures and isomorphic hybrid crystals are obtained using transition and main-group metal complexes.

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Yu, Shimo, Xiang Wang, Xiuling Jiao, Cheng Li e Dairong Chen. "Polyhedral metal–organic framework monolayer colloidal crystals with sharpened and crystal facet-dependent selectivity for organic vapor sensing". Journal of Materials Chemistry C 9, n. 16 (2021): 5379–86. http://dx.doi.org/10.1039/d1tc00810b.

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Polyhedral metal–organic framework monolayer colloidal crystals demonstrate sharpened and crystal facet-dependent selectivity for organic vapors by eliminating grain boundaries and randomly exposed crystal surfaces.

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Daeges, J., H. Gleiter e J. H. Perepezko. "Superheating of metal crystals". Physics Letters A 119, n. 2 (dicembre 1986): 79–82. http://dx.doi.org/10.1016/0375-9601(86)90418-4.

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Krasavin, V. V., e A. V. Krasavin. "Study of the elastic properties of hexagonal metal single crystals". Industrial laboratory. Diagnostics of materials 85, n. 9 (28 settembre 2019): 29–35. http://dx.doi.org/10.26896/1028-6861-2019-85-9-29-35.

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Hexagonal metals (e.g., Be, Zr, Ti) are widely used in the nuclear industry, space and aircraft engineering (in manufacturing of the structural elements operating under extreme conditions). A promising way to improve the quality of products made of them is to improve the physical properties of materials using the natural anisotropy of metal single crystals. The results of studying anisotropy and a comparative analysis of the technical characteristics of the elastic properties of single crystals of hexagonal metals are presented. The equations of the elastic compliance matrix components are derived in the explicit form for arbitrary crystallographic direction proceeding from transformations of the elastic compliance tensor in the principal axes to a new arbitrary coordinate system with a subsequent use of Euler angles. Analytical expressions are presented for the technical characteristics of the elastic properties (shear and Young's moduli, Poisson's ratio) of the single crystals of 10 hep metals for an arbitrary crystallographic direction. The axial symmetry of the characteristics about the hexagonal axis is revealed. The sums of the elastic compliance coefficients which determine the shear moduli and the Poisson's ratios in two mutually perpendicular directions are constant in any crystallographic plane of the single crystal. A comparative analysis of the anisotropy of the elastic properties of single crystals of the studied group of metals revealed auxetic properties of Zn and Be single crystals and the region of crystallographic directions of uniaxia tension, leading to an auxetic effect The auxetic effect in Zn was observed under tension in the directions of the plane perpendicular to the hexagonal axis of the single crystal. The planes of the auxetic effect manifestation in Be single crystals are perpendicular to the directions making an angle of 45° with the hexagonal axis.

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D. S., Christy, Sahaya Shajan X. e Mahadevan C. K. "Study of Physico-Chemical Properties and Growth Dimension Augmentation of Barium Succinate Single Crystals Grown by Slow Evaporation Technique". Journal of Physical Science 33, n. 1 (25 aprile 2022): 29–49. http://dx.doi.org/10.21315/jps2022.33.1.3.

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Slow evaporation method was adopted to grow barium succinate (BS) single crystals for the first time and diamond shape crystals were successfully synthesised with dimension 14 mm3 × 17 mm3 × 4 mm3. Single crystal x-ray diffraction studies show that the crystal system is monoclinic. Powder x-ray diffraction studies confirmed the crystallinity of the grown BS crystal. From energy dispersive x-ray spectroscopy (EDS) analysis the presence of barium metal was confirmed. The functional group of the BS crystal was confirmed from fourier transform infrared (FTIR) spectrum. The crystals were found to be hydrated and thermally stable up to 150°C. BS crystal possesses good transmittance in the wavelength range 250 nm–1200 nm and it is non-linear optical (NLO) active material. The BS crystals have mechanical softness and normal dielectric behaviour.

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Horichok, Ihor, Myroslava Shevchuk, Taras Parashchuk e Mar’jan Galushchak. "INTRINSIC POINT DEFECTS OF SAMARIUM MONOSULPHIDE CRYSTALS IN METAL PHASE". Chemistry & Chemical Technology 11, n. 3 (28 agosto 2017): 319–26. http://dx.doi.org/10.23939/chcht11.03.319.

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Jackson, Michael R., e Thomas L. Selby. "Crystallization, optimization and preliminary X-ray characterization of a metal-dependent PI-PLC fromStreptomyces antibioticus". Acta Crystallographica Section F Structural Biology and Crystallization Communications 68, n. 11 (30 ottobre 2012): 1378–86. http://dx.doi.org/10.1107/s1744309112041371.

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A recombinant metal-dependent phosphatidylinositol-specific phospholipase C (PI-PLC) fromStreptomyces antibioticushas been crystallized by the hanging-drop method with and without heavy metals. The native crystals belonged to the orthorhombic space groupP222, with unit-cell parametersa= 41.26,b= 51.86,c = 154.78 Å. The X-ray diffraction results showed significant differences in the crystal quality of samples soaked with heavy atoms. Additionally, drop pinning, which increases the surface area of the drops, was also used to improve crystal growth and quality. The combination of heavy-metal soaks and drop pinning was found to be critical for producing high-quality crystals that diffracted to 1.23 Å resolution.

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Kobayashi, Hiroyuki, Yoshinori Ikumura, Chang-Hyoun Lee e Akiko Hori. "Co-Crystallization and Structural Studies of Benzophenone Recognized by Positively Shifted ESPs of Perfluorinated β-Diketonate Complexes (M = Cu, Pd, Pt)". Crystals 14, n. 7 (27 giugno 2024): 593. http://dx.doi.org/10.3390/cryst14070593.

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Benzophenone was encapsulated in molecular crystals of fully fluorinated coordination complexes, [ML2] [1, M = Cu2+ and Pd2+, L = bis(pentafluorobenzoyl)-methanido−], forming a unique chiral co-crystal with a ratio of [ML2]:benzophenone = 2:3, while no encapsulation was observed in the corresponding non-fluorinated complexes [M(dbm)2] (dbm = dibenzoylmethanido−). Notable π-hole···π and metal(M)···π interactions were detected between the complex and the adapted orientation of benzophenone in the co-crystals. Analyses from crystal structures and thermogravimetric (TG) results indicated that the encapsulation and thermal stability of benzophenone in these molecular crystals correlate well with the electrophilic characteristics shown by the electrostatic potential (ESP) at the metal centers, which is enhanced by fluorination: Cu2+ > Pd2+ >> Pt2+. The recognition of benzophenone is driven by π-holes created by the electron-withdrawing nature of fluorine atoms and the electron-deficient metal ion enhanced by the aromatic fluorine, demonstrating that the effect of electrostatic molecular recognition is as significant as oxygen coordination, as shown in comparative studies with 1,1-diphenylethylene.

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Vasilyeva, Natalie, Marina Grigorieva, Alexander Antipin, Natalia Sorokina e Alexey Voloshin. "Growth and structure of K2CoxNi(1-x)(SO4)2·6H2O mixed single crystals". Acta Crystallographica Section A Foundations and Advances 70, a1 (5 agosto 2014): C1029. http://dx.doi.org/10.1107/s2053273314089700.

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To date, crystals of Tutton salts with the general formula (M+)2M2+(SO4)2*6N2O (where M+- alkali metal or ammonium, M2+ - bivalent metal - Co2+, Ni2+) are used as a materials for ultraviolet (UV) filters. Only in recent year effort of ternary crystal growth has been taken. The main problem of mixed crystal growth from liquid solution is high level of the crystal inhomogeneity, which leads to generation of the elastic stress, inclusion trapping and micro- and macrocrack formation in the bulk crystal. For the first time the optically homogeneous mixed K2CoxNi(1 – x)(SO4)2 · 6H2O (KCNSH) large single crystals have been grown from solutions of different compositions by the temperature-reduction technique. Precise X-ray experiment of three mixed crystals was carried out by four-circle diffractometer CAD-4F and XcaliburS diffractometer with two-dimensional CCD detector at the room temperature. KCNSH crystals belong to the monoclinic space group P2(1)/c. Each Co2+ or Ni2+ ion is coordinated with six H2O molecules, forming a distorted octahedral (Co(H2O)6)2+ and (Ni(H2O)6)2+ unit. With increasing content of nickel ions in the crystal, the octahedral unit is narrowed and the unit cell volume is decreased. Chemical formulas refined using diffraction data are K2Co0.657Ni0.343(SO4)2·6H2O, K2Co0.226Ni0.774(SO4)2·6H2O and K2Co0.216Ni0.784(SO4)2·6H2O. Ratios of isomorphic cobalt and nickel components in the mixed crystals are conformed to data obtained by atomic emission spectroscopy. Effect of the Co2+ and Ni2+ ion ratio in KCNSH single crystal to crystal quality is considered.

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Mulijanto, Caroline Evania, Hong Sheng Quah, Geok Kheng Tan, Bruno Donnadieu e Jagadese J. Vittal. "Curved crystal morphology, photoreactivity and photosalient behaviour of mononuclear Zn(II) complexes". IUCrJ 4, n. 1 (1 gennaio 2017): 65–71. http://dx.doi.org/10.1107/s2052252516019072.

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A dramatic effect of crystal morphology, photoreactivity and photosalient property is observed in a zinc(II) complex due to solvent effects and fluorine substitution at the backbone of the ligand. Of the two crystal forms with a 3-fluoro derivative, one yielded a curved morphology of single crystals and the second form shows photoreactivity in the solid state, whereas crystals of the 2-fluoro derivative pop during the [2 + 2] photocycloaddition reaction. This is the first report documenting curved single crystals of metal complexes obtained naturally during crystallization, although such bent crystals have been observed in extended solids naturally, or bent by mechanical force or by UV irradiation.

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Choudhury, Tanushree H., Xiaotian Zhang, Zakaria Y. Al Balushi, Mikhail Chubarov e Joan M. Redwing. "Epitaxial Growth of Two-Dimensional Layered Transition Metal Dichalcogenides". Annual Review of Materials Research 50, n. 1 (1 luglio 2020): 155–77. http://dx.doi.org/10.1146/annurev-matsci-090519-113456.

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Transition metal dichalcogenide (TMD) monolayers and heterostructures have emerged as a compelling class of materials with transformative properties that may be harnessed for novel device technologies. These materials are commonly fabricated by exfoliation of flakes from bulk crystals, but wafer-scale epitaxy of single-crystal films is required to advance the field. This article reviews the fundamental aspects of epitaxial growth of van der Waals–bonded crystals specific to TMD films. The structural and electronic properties of TMD crystals are initially described along with sources and methods used for vapor phase deposition. Issues specific to TMD epitaxy are critically reviewed, including substrate properties and film-substrate orientation and bonding. The current status of TMD epitaxy on different substrate types is discussed along with characterization techniques for large-areaepitaxial films. Future directions are proposed, including developments in substrates, in situ and full-wafer characterization techniques, and heterostructure growth.

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Chen, Li, e Yanan Wang. "Doping of metal into transition metal dichalcogenides PdTe₂". Journal of Physics: Conference Series 2713, n. 1 (1 febbraio 2024): 012025. http://dx.doi.org/10.1088/1742-6596/2713/1/012025.

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Abstract Rh-doped PdTe2 single crystals were successfully prepared using the solid-state reaction. The change of lattice constants and T c with increasing Rh content were studied and investigated. It was found that there is a very slight increase of lattice constant c with increasing Rh content. The values of T c were above 2 K when Rh content is equal to 0.05 and 0.1. The largest T c was~2.7 K for Rh0.05PdTe2 single crystal. T c does not increase with increasing x from 0.05 to 0.1. M-T measurement of Rh0.05PdTe2 single crystal with applied magnetic field H perpendicular to the c axis and along and c axis gives evidence of type II superconducting behavior. This study shows Rh doping is a promising method to increase T c and investigate SC in PdTe2.

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Kousaka, Yusuke, Satoshi Iwasaki, Taisei Sayo, Hiroshi Tanida, Takeshi Matsumura, Shingo Araki, Jun Akimitsu e Yoshihiko Togawa. "Chirality-controlled enantiopure crystal growth of a transition metal monosilicide by a floating zone method". Japanese Journal of Applied Physics 61, n. 4 (16 marzo 2022): 045501. http://dx.doi.org/10.35848/1347-4065/ac4e2f.

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Abstract We performed a crystal growth to obtain chirality-controlled enantiopure crystals using a laser-diode-heated floating zone (LDFZ) method with a composition-gradient feed rod. It has been argued that the crystal handedness of TSi (T : transition metal) is fixed depending on T in the case of the ones grown by the conventional methods. We found that right-handed single crystals of CoSi and MnSi were grown from the composition-gradient feed rods that consist of FeSi–CoSi and FeSi–MnSi, respectively. The obtained CoSi and MnSi crystals inherit the chirality from the seed part of FeSi, which grows in a right-handed structure, and thus has the chirality opposite to that for the crystals in the literature. The LDFZ method with the feed rods with various combinations of TSi compounds enables flexible control of the chirality of TSi and will be useful for clarifying the interplay between crystalline chirality and chirality-induced physical responses.

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Yurov, V. M. "ANISOTROPY OF THE SURFACE OF CUBIC BODY-CENTERED CRYSTAL LATTICES". Eurasian Physical Technical Journal 18, n. 1 (30 marzo 2021): 9–15. http://dx.doi.org/10.31489/2021no1/9-15.

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In the work of Shebzukhova and Arefieva, by the method of electronic-statistical calculation of the anisotropy of the surface energy of metals, a method for estimating the work function of electrons from a metal was determined. The surface energy and electron work function of four main faces of cadmium and zinc crystals and five faces of mercury are estimated. In the work of Bokarev, the anisotropy of the surface energy of single crystals was calculated from the model of coordination melting of crystals. Based on experimental studies and theoretical calculations, it is shown that the model of coordination melting of crystals unambiguously links the physicochemical properties of the surface of single crystals with their crystal structure. In our proposed empirical model, not only the anisotropy is calculated, but also the thickness of the surface layer of the metal. It is shown that the thickness of the surface layer is determined by one fundamental parameter - the molar (atomic) volume, which periodically changes in accordance with the table of D.I. Mendeleev. It is shown in the work that the work function of electrons changes proportionally with a change in the surface energy of the metal. This means that the device we have developed can be used to measure the state of the metal surface and its anisotropy.

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27

Makarov, Yu N., D. Litvin, A. Vasiliev e S. Nagalyuk. "Sublimation Growth of 4 and 6 Inch 4H-SiC Low Defect Bulk Crystals in Ta (TaC) Crucibles". Materials Science Forum 858 (maggio 2016): 101–4. http://dx.doi.org/10.4028/www.scientific.net/msf.858.101.

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Recently, the wide bandgap semiconductors, especially silicon carbide (SiC), have become more important due to the unique electrical and thermophysical properties that make them applicable to a variety of electronic devices (Schottky and PiN diodes, JFETs, MOSFETs, etc.). For these applications, the crystals need to be manufactured with highest possible quality, both structural and chemical, at reduced cost. This requirement places rather extreme constraints on the crystal growth as the simultaneous goals of high quality and low cost are generally incompatible.Refractory metal carbide technology, particularly, tantalum carbide (TaC), was originally developed for application in highly corrosive and reactive environments. Yu. Vodakov [1] demonstrated for the first time advantages of use of refractory metal carbides for PVT growth of SiC and later AlN bulk crystals. In the present paper we discuss the effect of refractory metal on PVT growth of large diameter 4H SiC bulk crystals.

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28

Chen, Lung-Chien, Kuan-Lin Lee, Kun-Yi Lee, Yi-Wen Huang e Ray-Ming Lin. "Study of Metal–Semiconductor–Metal CH3NH3PbBr3 Perovskite Photodetectors Prepared by Inverse Temperature Crystallization Method". Sensors 20, n. 1 (5 gennaio 2020): 297. http://dx.doi.org/10.3390/s20010297.

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Numerous studies have addressed the use of perovskite materials for fabricating a wide range of optoelectronic devices. This study employs the deposition of an electron transport layer of C60 and an Ag electrode on CH3NH3PbBr3 perovskite crystals to complete a photodetector structure, which exhibits a metal–semiconductor–metal (MSM) type structure. First, CH3NH3PbBr3 perovskite crystals were grown by inverse temperature crystallization (ITC) in a pre-heated circulator oven. This oven was able to supply uniform heat for facilitating the growth of high-quality and large-area crystals. Second, the different growth temperatures for CH3NH3PbBr3 perovskite crystals were investigated. The electrical, optical, and morphological characteristics of the perovskite crystals were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible spectroscopy, and photoluminescence (PL). Finally, the CH3NH3PbBr3 perovskite crystals were observed to form a contact with the Ag/C60 as the photodetector, which revealed a responsivity of 24.5 A/W.

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29

Yeo, Hyun Ku, Jina Kang, Young Woo Park, Jung-Suk Sung e Jae Young Lee. "Crystallization and preliminary X-ray diffraction analysis of the metalloregulatory protein DtxR fromThermoplasma acidophilum". Acta Crystallographica Section F Structural Biology and Crystallization Communications 68, n. 2 (26 gennaio 2012): 172–74. http://dx.doi.org/10.1107/s1744309111051700.

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The diphtheria toxin repressor (DtxR) is a metal-ion-dependent transcriptional regulator which regulates genes encoding proteins involved in metal-ion uptake to maintain metal-ion homeostasis. DtxR fromThermoplasma acidophilumwas cloned and overexpressed inEscherichia coli. Crystals of N-terminally His-tagged DtxR were obtained by hanging-drop vapour diffusion and diffracted to 1.8 Å resolution. DtxR was crystallized at 296 K using polyethylene glycol 4000 as a precipitant. The crystals belonged to the orthorhombic space groupP21212, with unit-cell parametersa= 61.14,b= 84.61,c= 46.91 Å, α = β = γ = 90°. The asymmetric unit contained approximately one monomer of DtxR, giving a crystal volume per mass (VM) of 2.22 Å3 Da−1and a solvent content of 44.6%.

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30

Camara-Artigas, Ana, Marina Plaza-Garrido, Sergio Martinez-Rodriguez e Julio Bacarizo. "New crystal form of human ubiquitin in the presence of magnesium". Acta Crystallographica Section F Structural Biology Communications 72, n. 1 (1 gennaio 2016): 29–35. http://dx.doi.org/10.1107/s2053230x15023390.

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Ubiquitin is a small globular protein that has a considerable number of lysine residues on its surface. This results in a high surface entropy that precludes the formation of crystal-packing interactions. To date, only a few structures of the native form of ubiquitin have been solved, and most of the crystals that led to these structures were obtained in the presence of different divalent metal cations. In this work, a new crystallographic structure of human ubiquitin solved from crystals grown in the presence of magnesium is presented. The crystals belonged to a triclinic space group, with unit-cell parametersa= 29.96,b = 30.18,c= 41.41 Å, α = 88.52, β = 79.12, γ = 67.37°. The crystal lattice is composed of stacked layers of human ubiquitin molecules with a large hydrophobic interface and a smaller polar interface in which the magnesium ion lies at the junction between adjacent layers in the crystal. The metal ion appears in a hexa-aquo coordination, which is key to facilitating the crystallization of the protein.

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31

Apkarian, R. P., e M. D. Gutekunst. "High-Resolution Topographic Imaging of Enamel Crystal Surfaces". Proceedings, annual meeting, Electron Microscopy Society of America 46 (1988): 188–89. http://dx.doi.org/10.1017/s0424820100103024.

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Previous interpretations of enamel crystal morphology have been handicapped by preparation techniques and the understanding of enamel crystals was derived from TEM and conventional SEM studies looking into lesion formation in enamel. Early studies focused on the demineralization and effects of mineralization on enamel structure. Enamel crystals were previously described as flattened hexagonal structures 100 μm long and 35-40 nm in diameter using conventional SEM and 47.3 nm in diameter using TEM. A methodology has been developed and employed in order to accurately image hydroxyapatite crystals in normal human teeth. The combination of an ultrathin coating of sputtered chromium (Cr) film and SE-I imaging herein provide topographic contrasts of crystal surfaces. Since the majority of the SE-I information should be produced close to the surface, the resultant image is specimen surface specific. Optimal metal coating thicknesses of low atomic number were utilized so that the generation of the SE-I signal contrast which occurs on the enamel crystal surface was used to form the image, thus avoiding image contrast contribution by electrons scattered in the metal coat.

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32

Sano, Daisuke, e Soshu Kirihara. "Fabrication of Metal Photonic Crystals with Graded Lattice Spacing by Using Micro-Stereolithography". Materials Science Forum 631-632 (ottobre 2009): 287–92. http://dx.doi.org/10.4028/www.scientific.net/msf.631-632.287.

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We designed micro-scale photonic crystal with or without graded lattice spacing composed of copper to control Terahertz (THz) waves. Designed structures were fabricated by using micro-stereolithography. By proper dewaxing and sintering process, pure copper photonic crystals were obtained. Transmission properties of THz waves propagating through the photonic crystals were measured by THz time-domain spectroscopy. Measured results showed good agreements with the simulated results.

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33

Suponitsky, Kyrill Yu, Ivan V. Fedyanin, Valentina A. Karnoukhova, Vladimir A. Zalomlenkov, Alexander A. Gidaspov, Vladimir V. Bakharev e Aleksei B. Sheremetev. "Energetic Co-Crystal of a Primary Metal-Free Explosive with BTF. Ideal Pair for Co-Crystallization". Molecules 26, n. 24 (9 dicembre 2021): 7452. http://dx.doi.org/10.3390/molecules26247452.

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Co-crystallization is an elegant technique to tune the physical properties of crystalline solids. In the field of energetic materials, co-crystallization is currently playing an important role in the engineering of crystals with improved performance. Here, based on an analysis of the structural features of the green primary explosive, tetramethylammonium salt of 7-oxo-5-(trinitromethyl)-4,5,6,7-tetrahydrotetrazolo[1,5-a][1,3,5]triazin-5-ide (1), a co-former such as the powerful secondary explosive, benzotrifuroxan (BTF, 2), has been proposed to improve it. Compared to the original 1, its co-crystal with BTF has a higher detonation pressure and velocity, as well as an initiating ability, while the impact sensitivity and thermal stability remained at about the same level. Both co-formers, 1 and 2, and co-crystal 3 were characterized by single-crystal X-ray diffraction and their crystal packing was analyzed in detail by the set of approaches, including periodic calculations. In the co-crystal 3, all intermolecular interactions were significantly redistributed. However, no new types of intermolecular interactions were formed during co-crystallization. Moreover, the interaction energies of structural units in crystals before and after co-crystallization were approximately the same. A similar trend was observed for the volumes occupied by structural units and their densifications. The similar nature of the organization of the crystals of the co-formers and the co-crystal gives grounds to assert that the selected co-formers are an ideal pair for co-crystallization, and the invariability of the organization of the crystals was probably responsible for the preservation of some of their properties.

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34

Krause, Simon, Volodymyr Bon, Hongchu Du, Rafal E. Dunin-Borkowski, Ulrich Stoeck, Irena Senkovska e Stefan Kaskel. "The impact of crystal size and temperature on the adsorption-induced flexibility of the Zr-based metal–organic framework DUT-98". Beilstein Journal of Nanotechnology 10 (20 agosto 2019): 1737–44. http://dx.doi.org/10.3762/bjnano.10.169.

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Abstract (sommario):

In this contribution we analyze the influence of adsorption cycling, crystal size, and temperature on the switching behavior of the flexible Zr-based metal–organic framework DUT-98. We observe a shift in the gate-opening pressure upon cycling of adsorption experiments for micrometer-sized crystals and assign this to a fragmentation of the crystals. In a series of samples, the average crystal size of DUT-98 crystals was varied from 120 µm to 50 nm and the obtained solids were characterized by X-ray diffraction, infrared spectroscopy, as well as scanning and transmission electron microscopy. We analyzed the adsorption behavior by nitrogen and water adsorption at 77 K and 298 K, respectively, and show that adsorption-induced flexibility is only observed for micrometer-sized crystals. Nanometer-sized crystals were found to exhibit reversible type I adsorption behavior upon adsorption of nitrogen and exhibit a crystal-size-dependent steep water uptake of up to 20 mmol g−1 at 0.5 p/p 0 with potential for water harvesting and heat pump applications. We furthermore investigate the temperature-induced structural transition by in situ powder X-ray diffraction. At temperatures beyond 110 °C, the open-pore state of the nanometer-sized DUT-98 crystals is found to irreversibly transform to a closed-pore state. The connection of crystal fragmentation upon adsorption cycling and the crystal size dependence of the adsorption-induced flexibility is an important finding for evaluation of these materials in future adsorption-based applications. This work thus extends the limited amount of studies on crystal size effects in flexible MOFs and hopefully motivates further investigations in this field.

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35

Abrahams, Brendan F., Nicholas J. FitzGerald, Timothy A. Hudson, Richard Robson e Richard D. Shalders. "Metal Exchange within a Body-Centred Cubic Hydrogen-Bonded Network". Australian Journal of Chemistry 60, n. 1 (2007): 68. http://dx.doi.org/10.1071/ch06334.

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A hydrogen bonded network of composition Zn8(C4O7)4(H2O)12·hydrate was shown to undergo a single crystal to single crystal exchange process when crystals are immersed in a concentrated aqueous solution of Ni(ii). In the exchange process, half of the zinc(ii) centres are replaced by nickel(ii) centres. The process of metal ion exchange was monitored using IR spectroscopy. Crystal structures of the transformed crystal and the product generated from a direct synthetic approach are presented.

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36

Lillo, Vanesa, e José Ramón Galán-Mascarós. "Transition metal complexes with oligopeptides: single crystals and crystal structures". Dalton Trans. 43, n. 26 (2014): 9821–33. http://dx.doi.org/10.1039/c4dt00650j.

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37

Tian, Yu, A. Lysyakov, Haoyu Wang e Haoyu Xie. "Development of Wide Bandgap One-dimensional MOF/TiO2 Photonic Crystal and Its Gas-sensing Properties". Bulletin of Science and Practice 10, n. 6 (14 giugno 2024): 306–16. http://dx.doi.org/10.33619/2414-2948/103/34.

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Abstract (sommario):

Metal-organic framework (MOFs) materials are a type of coordination polymer that have seen significant breakthroughs in material science over the past decade. Because of their high specific surface area and porosity, they are widely used for gas adsorption, storage, and separation. Additionally, their structural tunability allows for a wide variety of MOFs, with more remarkable properties yet to be discovered as research continues. When MOFs are applied in photonic crystals, adjustments to their structure enable them to act as specific gas-sensitive materials, causing shifts in the photonic crystal's forbidden band after gas adsorption. This generates distinguishable signals for effective sensing. In conventional single-metal MOFs, doping with another metal to prepare photonic crystals increases defect size while reducing symmetry and simplicity, leading to more pronounced forbidden bands and improved sensing. Therefore, in this thesis, we aim to partially replace the chromium in MIL-101 with magnesium and then self-assemble it with titanium dioxide to prepare photonic crystals. This approach aims to leverage the exceptional properties of MOFs, resulting in photonic crystals with improved gas-specific recognition and sensitivity, further enhancing their gas-sensing capabilities.

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38

Yang, Xue, Michel Giorgi, Hakim Karoui, Didier Gigmes, Virginie Hornebecq, Olivier Ouari, Anthony Kermagoret e David Bardelang. "A single-crystal-to-single-crystal transformation affording photochromic 3D MORF crystals". Chemical Communications 55, n. 92 (2019): 13824–27. http://dx.doi.org/10.1039/c9cc07121k.

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39

Liu, Chong, e Nathaniel L. Rosi. "Ternary gradient metal–organic frameworks". Faraday Discussions 201 (2017): 163–74. http://dx.doi.org/10.1039/c7fd00045f.

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Abstract (sommario):

Gradient MOFs contain directional gradients of either structure or functionality. We have successfully prepared two ternary gradient MOFs based on bMOF-100 analogues, namely bMOF-100/102/106 and bMOF-110/100/102, via cascade ligand exchange reactions. The cubic unit cell parameter discrepancy within an individual ternary gradient MOF crystal is as large as ∼1 nm, demonstrating the impressive compatibility and flexibility of the component MOF materials. Because of the presence of a continuum of unit cells, the pore diameters within individual crystals also change in a gradient fashion from ∼2.5 nm to ∼3.0 nm for bMOF-100/102/106, and from ∼2.2 nm to ∼2.7 nm for bMOF-110/100/102, indicating significant porosity gradients. Like previously reported binary gradient MOFs, the composition of the ternary gradient MOFs can be easily controlled by adjusting the reaction conditions. Finally, X-ray diffraction and microspectrophotometry were used to analyse fractured gradient MOF crystals by comparing unit cell parameters and absorbance spectra at different locations, thus revealing the profile of heterogeneity (i.e. gradient distribution of properties) and further confirming the formation of ternary gradient MOFs.

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40

Chen, Jing, Meng-Yao Chao, Yan Liu, Bo-Wei Xu, Wen-Hua Zhang e David J. Young. "An N,N′-diethylformamide solvent-induced conversion cascade within a metal–organic framework single crystal". Chemical Communications 56, n. 44 (2020): 5877–80. http://dx.doi.org/10.1039/d0cc02420a.

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Abstract (sommario):

A two-dimensional metal–organic framework undergoes four-step single-crystal to single-crystals conversions, including a three-step DEF-induced cascade conversion to shuttle back to its original connectivity.

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41

Perumal, R., S. Thanikaikarasan, M. Saravannan, R. Kanimozhi e S. Sudharthini. "Influence of Halogens on the Growth Aspects of Allylthiourea Cadmium Complex Nonlinear Optical Single Crystals". Journal of New Materials for Electrochemical Systems 25, n. 2 (10 giugno 2022): 110–15. http://dx.doi.org/10.14447/jnmes.v25i2.a04.

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Abstract (sommario):

Allylthiourea complex crystals is an organometallic complex, a new nonlinear optical materials with high second harmonic generation effect. Tri-allylthiourea cadmium chloride and Tri-allylthiourea cadmium bromide are the promising nonlinear optical crystals belonging to this family. Both the crystals have been grown from an aqueous solution by slow cooling technique. The solubility and growth optimization of the grown crystals in terms of pH were analyzed and the influence of the different halogen atoms on the properties of as grown single crystals was studied by conducting various characterization techniques. Powder X-ray diffraction studies revealed that both the crystals are trigonal crystal structure with R3C space group. The spectroscopic properties were investigated by recording the Fourier Transform Infra Red and UV-Visible-NIR spectroscopy. Spectrocopic study confirmed the coordination of metal and red shift of the grown crystal. Nonlinear behavior of the as grown crystals was identified by Kurtz powder technique. Thermal and electrical properties of the as grown crystals were also analyzed by thermogravimetric and dielectric studies. Influence of the halogens on the growth as well as the properties were studied.

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42

Yu, Jianyuan, Yingeng Wang, Yan Huang, Xiuwen Wang, Jing Guo, Jingkai Yang e Hongli Zhao. "Structural and electronic properties of SnO2 doped with non-metal elements". Beilstein Journal of Nanotechnology 11 (3 settembre 2020): 1321–28. http://dx.doi.org/10.3762/bjnano.11.116.

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Abstract (sommario):

Crystal structure and electronic properties of SnO2 doped with non-metal elements (F, S, C, B, and N) were studied using first-principles calculations. The theoretical results show that doping of non-metal elements cannot change the structure of SnO2 but result in a slight expansion of the lattice volume. The most obvious finding from the analysis is that F-doped SnO2 has the lowest defect binding energy. The doping with B and S introduced additional defect energy levels within the forbidden bandgap, which improved the crystal conductivity. The Fermi level shifts up due to the doping with B, F, and S, while the Fermi level of SnO2 doped with C or N has crossed the impurity level. The Fermi level of F-doped SnO2 is inside the conduction band, and the doped crystal possesses metallicity. The optical properties of SnO2 crystals doped with non-metal elements were analyzed and calculated. The SnO2 crystal doped with F had the highest reflectivity in the infrared region, and the reflectance of the crystals doped with N, C, S, and B decreased sequentially. Based on this theoretical calculations, F-doped SnO2 is found to be the best photoelectric material for preparing low-emissivity coatings.

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43

Lim, W. T., J. H. Jang, N. Y. Park, S. M. Paek, W. C. Kim e M. Park. "Spontaneous nanoparticle formation coupled with selective adsorption in magadiite". Journal of Materials Chemistry A 5, n. 8 (2017): 4144–49. http://dx.doi.org/10.1039/c7ta00038c.

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Abstract (sommario):

The adsorbed heavy metal cations were spontaneously and systematically transformed into the corresponding hydroxide nanoparticles exclusively on the crystal edges and the nanoparticles ultimately sprouted out of the crystals on full growth.

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44

Su, Longxing. "Growth of a Sub-Centimeter-Sized CsPbBr3 Bulk Single Crystal Using an Anti-Solvent Precipitation Method". Symmetry 16, n. 3 (9 marzo 2024): 332. http://dx.doi.org/10.3390/sym16030332.

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Abstract (sommario):

A facile and low-cost strategy to fabricate CsPbBr3 single crystals is essential for developing perovskite optoelectronic devices. Herein, we have presented a room temperature anti-solvent precipitate method for growing sub-centimeter-sized CsPbBr3 single crystals. The as-prepared CsPbBr3 single crystal has an orthorhombic structure, and phase transition occurs as the measured temperature increases. The as-grown CsPbBr3 single crystal also shows abundant surface morphologies including footsteps, precipitated crystals, cracks, and pits. Subsequently, a metal–semiconductor–metal (MSM)-structured photodetector was fabricated based on the CsPbBr3 single crystal. Under 525 nm green light illumination, the photodetector exhibits an obvious response and the photocurrent linearly increases with the increase in the light intensity. The rise time of the photodetector increases from 0.82 s to 2.19 s as the light intensity is enhanced from 15 mW/cm2 to 160 mW/cm2, indicating that more time is required to reach to a stable photocurrent. However, the decay time is as fast as ~0.82 ms, irrelevant of the light intensity. The photocurrent, under continuous light illumination, was further studied and this indicates that a stronger light intensity can accelerate the attenuation of the device.

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45

Shen, Kui, Lei Zhang, Xiaodong Chen, Lingmei Liu, Daliang Zhang, Yu Han, Junying Chen et al. "Ordered macro-microporous metal-organic framework single crystals". Science 359, n. 6372 (11 gennaio 2018): 206–10. http://dx.doi.org/10.1126/science.aao3403.

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Abstract (sommario):

We constructed highly oriented and ordered macropores within metal-organic framework (MOF) single crystals, opening up the area of three-dimensional–ordered macro-microporous materials (that is, materials containing both macro- and micropores) in single-crystalline form. Our methodology relies on the strong shaping effects of a polystyrene nanosphere monolith template and a double-solvent–induced heterogeneous nucleation approach. This process synergistically enabled the in situ growth of MOFs within ordered voids, rendering a single crystal with oriented and ordered macro-microporous structure. The improved mass diffusion properties of such hierarchical frameworks, together with their robust single-crystalline nature, endow them with superior catalytic activity and recyclability for bulky-molecule reactions, as compared with conventional, polycrystalline hollow, and disordered macroporous ZIF-8.

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46

Hans, Philipp, Berthold Stöger, Matthias Weil e Erich Zobetz. "Structure of the mixed-metal carbonate KAgCO3revisited: order–disorder (OD) polytypism and allotwinning". Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 71, n. 2 (31 marzo 2015): 194–202. http://dx.doi.org/10.1107/s2052520615004138.

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Abstract (sommario):

Crystals of KAgCO3belong to an order–disorder (OD) family of structures composed of layers of two kinds. There are two polytypes with a maximum degree of order [MDO1:Pccb; MDO2:Ibca, doubleda-axis compared with MDO1], which are both realised to a different extent in two crystals under investigation [volume fraction MDO1:MDO2in crystal (I): 0.0216:0.9784 (3) and in crystal (II): 0.9657:0.0343 (3)]. Sharp diffraction spots and the absence of diffuse scattering indicate highly ordered macroscopic domains. The structure of KAgCO3was refined concurrently against all reflections using an allotwin model (addition of the intensities of both domains). It is shown that a disorder model refined against reflections of only one domain can lead to a significant overestimation of the volume fraction of this domain.

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47

Owens-Baird, Bryan, Juliana P. S. Sousa, Yasmine Ziouani, Dmitri Y. Petrovykh, Nikolai A. Zarkevich, Duane D. Johnson, Yury V. Kolen'ko e Kirill Kovnir. "Crystallographic facet selective HER catalysis: exemplified in FeP and NiP2 single crystals". Chemical Science 11, n. 19 (2020): 5007–16. http://dx.doi.org/10.1039/d0sc00676a.

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The effect of the crystal structure of ordered transition-metal phosphide catalysts on the hydrogen-evolution reaction is investigated using single crystals of iron-phosphide (FeP) and monoclinic nickel-diphosphide (m-NiP₂).

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48

Ge, Meng, Xiaodong Zou e Zhehao Huang. "Three-Dimensional Electron Diffraction for Structural Analysis of Beam-Sensitive Metal-Organic Frameworks". Crystals 11, n. 3 (8 marzo 2021): 263. http://dx.doi.org/10.3390/cryst11030263.

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Abstract (sommario):

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 Å−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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49

Krishnamoorthy, Aravind, Lindsay Bassman, Rajiv K. Kalia, Aiichiro Nakano, Fuyuki Shimojo e Priya Vashishta. "Kinetics and Atomic Mechanisms of Structural Phase Transformations in Photoexcited Monolayer TMDCs". MRS Advances 3, n. 6-7 (2018): 345–50. http://dx.doi.org/10.1557/adv.2018.122.

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ABSTRACTRapid transitions between semiconducting and metallic phases of transition-metal dichalcogenides are of interest for 2D electronics applications. Theoretical investigations have been limited to using thermal energy, lattice strain and charge doping to induce the phase transition, but have not identified mechanisms for rapid phase transition. Here, we use density functional theory to show how optical excitation leads to the formation of a low-energy intermediate crystal structure along the semiconductor-metal phase transition pathway. This metastable crystal structure results in significantly reduced barriers for the semiconducting-metal phase transition pathway leading to rapid transition in optically excited crystals.

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Kirman, Marina, Artem Talantsev e Roman Morgunov. "Peierls “Washboard” Controls Dynamics of the Domain Walls in Molecular Ferrimagnets". Solid State Phenomena 233-234 (luglio 2015): 55–59. http://dx.doi.org/10.4028/www.scientific.net/ssp.233-234.55.

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The magnetization dynamics of metal-organic crystals has been studied in low frequency AC magnetic field. Four modes of domain wall motion (Debye relaxation, creep, slide and over - barrier motion (switching)) were distinguished in [MnII(H(R/S)-pn)(H2O)] [MnIII(CN)6]⋅2H2O crystals. Debye relaxation and creep of the domain walls are sensitive to Peierls relief configuration controlled by crystal lattice chirality. Structural defects and periodical Peierls potential compete in the damping of the domain walls. Driving factor of this competition is ratio of the domain wall width to the crystal lattice parameter.

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