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Auteur : Grafiati
Publié le 14 mars 2023

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1

Dovesi, Roberto, Roberto Orlando, Alessandro Erba, Claudio M. Zicovich-Wilson, Bartolomeo Civalleri, Silvia Casassa, Lorenzo Maschio et al. « CRYSTAL14 : A program for the ab initio investigation of crystalline solids ». International Journal of Quantum Chemistry 114, no 19 (11 mars 2014) : 1287–317. http://dx.doi.org/10.1002/qua.24658.

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Noël, Yves, Marco De La Pierre, Claudio M. Zicovich-Wilson, Roberto Orlando et Roberto Dovesi. « Structural, electronic and energetic properties of giant icosahedral fullerenes up to C6000 : insights from an ab initio hybrid DFT study ». Phys. Chem. Chem. Phys. 16, no 26 (2014) : 13390–401. http://dx.doi.org/10.1039/c4cp01442a.

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3

Чернышев, В. А., В. С. Рюмшин et П. А. Агзамова. « Структура и динамика решетки MeF-=SUB=-2-=/SUB=- (Me=Ca, Sr, Ba, Pb) в кубической и орто-фазах : ab initio расчет ». Физика твердого тела 61, no 1 (2019) : 137. http://dx.doi.org/10.21883/ftt.2019.01.46904.188.

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AbstractThe MF_2 (M = Ca, Sr, Ba, Pb) crystals undergo a structural phase transition from the cubic to the orthorhombic phase in a range of 1–10 GPa. Although the cubic fluorites are well studied experimentally, there has been almost no information on their orthorhombic phase to date. Despite a few data on the Raman spectra available in the literature, there is still a lack of IR spectra of these structures. In this respect, this work aims to study the crystal structure and the phonon spectrum of MF_2 crystals (M = Ca, Sr, Ba, Pb) in both the cubic and orthorhombic phases, using the MO LKAO approach with hybrid DFT functionals that take the contribution of nonlocal exchange in the Hartree—Fock formalism into account. The frequencies and types of fundamental IR and Raman vibrations, as well as the frequencies of “silent” modes, are found. The calculations of elastic constants for the orthorombic phase have been performed at the first time. The program CRYSTAL14 intended for simulation of periodic structures within the MO LKAO approach was used for the calculations.
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Reid, Joel W., James A. Kaduk et Jeremy A. Olson. « The crystal structure of Na(NH4)Mo3O10·H2O ». Powder Diffraction 32, no 2 (juin 2017) : 140–47. http://dx.doi.org/10.1017/s0885715617000380.

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The crystal structure of Na(NH4)Mo3O10·H2O has been solved by parallel tempering using the FOX software package with synchrotron powder diffraction data obtained from beamline 08B1-1 at the Canadian Light Source. Rietveld refinement, performed with the software package GSAS, yielded orthorhombic lattice parameters of a = 13.549 82(10), b = 7.618 50(6), and c = 9.302 74(7) Å (Z = 4, space group Pnma). The structure is composed of molybdate chains running parallel to the b-axis. The Rietveld refinement results were compared with density functional theory calculations performed with CRYSTAL14, and show excellent agreement with the calculated structure.
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Reid, Joel W., James A. Kaduk et Martin Vickers. « The crystal structure of trandolapril, C24H34N2O5 : an example of the utility of raw data deposition in the powder diffraction file ». Powder Diffraction 31, no 3 (14 juin 2016) : 205–10. http://dx.doi.org/10.1017/s0885715616000294.

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The crystal structure of trandolapril has been solved by parallel tempering using the FOX software package with laboratory powder diffraction data submitted to and published in the Powder Diffraction File. Rietveld refinement was performed with the software package GSAS yielding orthorhombic lattice parameters of a = 19.7685(4), b = 15.0697(4), and c = 7.6704(2) Å (C24H34N2O5, Z = 4, space group P212121). The Rietveld refinement results were compared with density functional theory (DFT) calculations performed with CRYSTAL14. While the structures are similar, discrepancies are observed in the configuration of the octahydroindole ring between the Rietveld and DFT structures, suggesting the refined and calculated molecules are diastereomers.
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Reid, Joel W., James A. Kaduk et Lidia Matei. « The crystal structure of MoO2(O2)H2O ». Powder Diffraction 33, no 1 (14 février 2018) : 49–54. http://dx.doi.org/10.1017/s0885715618000118.

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The crystal structure of MoO2(O2)H2O has been solved by analogy with the WO2(O2)H2O structure and refined with synchrotron powder diffraction data obtained from beamline 08B1-1 at the Canadian Light Source. Rietveld refinement, performed with the software package GSAS, yielded monoclinic lattice parameters of a = 12.0417(4) Å, b = 3.87003(14) Å, c = 7.38390(24) Å, and β = 78.0843(11)° (Z = 4, space group P21/n). The structure is composed of double zigzag molybdate chains running parallel to the b-axis. The Rietveld refined structure was compared with density functional theory (DFT) calculations performed with CRYSTAL14, and show strong agreement with the DFT optimized structure.
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7

Saleev, Vladimir, et Alexandra Shipilova. « First-principles calculations of LiNbO3 optical properties : From far-infrared to ultraviolet ». Modern Physics Letters B 32, no 05 (20 février 2018) : 1850063. http://dx.doi.org/10.1142/s021798491850063x.

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We perform first-principles calculations of optical properties for ferroelectric phase of LiNbO3 crystal using density functional theory (DFT) for wide range of wavelengths, from far-infrared (IR) to ultraviolet. We study frequency dependence of complex dielectric tensor and related quantities, such as refractive and reflection indices, absorption coefficients, etc. Our calculation incorporates advantages of numerical approaches based on atomic-orbital all-electron Gaussian-type basis sets, as it is realized in CRYSTAL14 program. We compared predictions obtained in general-gradient approach with PBESOL exchange-correlation functional and in hybrid approach with PBESOL0 functional, and we have found that hybrid PBESOL0 functional is more applicable to describe the wide set of the experimental data.
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8

Suzuki, Kosuke, Ayumu Terasaka, Tomoya Abe et Hiroshi Sakurai. « Modification of Electronic Structures with Lithium Intercalation in LixMn2O4 (x = 0 and 1) Studied by CRYSTAL14 Calculation Code ». Key Engineering Materials 790 (novembre 2018) : 15–19. http://dx.doi.org/10.4028/www.scientific.net/kem.790.15.

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In this study, we calculate electronic structures for Mn2O4 and LiMn2O4 by using CRYSTAL14 ab-initio calculation code in order to understand electrode reaction mechanism of LixMn2O4 by lithiation/delithiation. Mulliken population analysis for all electrons show that the redox orbitals with lithiation and delithiation is O 2p orbitals. However, difference charge densities between majority and minority electrons indicate the change of distribution in Mn 3d orbitals by lithiation. This modification of distribution in Mn 3d orbitals suggests the change of electron configuration because the number of electrons at Mn atom is almost constant in Mulliken population analysis for all electrons. As a result, this modification of distribution in Mn 3d orbitals improves electron conductivity of this material.
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9

Reid, Joel W., James A. Kaduk et Lidia Matei. « The crystal structure of MoO2(O2)(H2O)·H2O ». Powder Diffraction 34, no 1 (7 février 2019) : 44–49. http://dx.doi.org/10.1017/s0885715619000095.

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The crystal structure of MoO2(O2)(H2O)·H2O has been solved using parallel tempering with the FOX software package and refined using synchrotron powder diffraction data obtained from beamline 08B1-1 at the Canadian Light Source. Rietveld refinement, performed with the software package GSAS, yielded monoclinic lattice parameters of a = 17.3355(5) Å, b = 3.83342(10) Å, c = 6.55760(18) Å, and β = 91.2114(27)° (Z = 4, space group I2/m). The structure is composed of double zigzag molybdate chains running parallel to the b-axis. The Rietveld refined structure was compared with density functional theory (DFT) calculations performed with CRYSTAL14, and shows comparable agreement with two DFT optimized structures of similar energy, which differ by the location of the molybdate coordinated water molecule. The true structure is likely a disordered combination of the two DFT optimized structures.
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10

Mesquita, Weber D., Maria R. C. Santos, Mario G. Junior, Sérgio H. B. S. Leal, José W. M. Espinosa, Elson Longo et Maria F. C. Gurgel. « Efeito do Substituinte Sr na Transição de Fase do PT : Correlação Teórica e Experimental das Propriedades Eletrônicas e Estruturais ». Revista Processos Químicos 13, no 26 (9 mars 2020) : 73–80. http://dx.doi.org/10.19142/rpq.v13i26.542.

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A transição de fase dos compostos PT, PST e ST, sintetizados pelo Método dos Precursores Poliméricos, foram estudados através da correlação teórica e experimental empregando DFT, utilizando o pacote computacional CRYSTAL14. Os modelos foram construídos em uma supercela 1x1x2 utilizando dados do refiamento de Rietveld. Os resultados foram interpretados em termos de Estrutura de Bandas, Densidade de Estados, evolução estrutural e valor de gap. Nestes modelos, foram possíveis a identifiação e a compreensão da transição de fase e redução na relação c/a concluindo que os modelos sofrem transição de fase conforme aumenta-se a concentração de substituinte Sr na matriz do PT.
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11

Saleev, Vladimir, et Alexandra Shipilova. « Ab initio study of optical and bulk properties of cesium lead halide perovskite solid solutions ». Modern Physics Letters B 33, no 31 (10 novembre 2019) : 1950386. http://dx.doi.org/10.1142/s021798491950386x.

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The first-principles calculations of band gaps and bulk moduli of cesium lead halide perovskite solid solutions, [Formula: see text] and [Formula: see text], are performed at the level of general gradient approximation of the density functional theory. We use supercell approach for computational modeling of disordered systems, which gives a description of the properties of the structure baasing on the average over a set of multiple configurations, namely distributions of different species over a given set of atomic positions. The calculations were performed with the CRYSTAL14 program package. The dependence of the band gap and bulk modulus on the content [Formula: see text] are investigated over the whole range [Formula: see text].
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12

Lei, Lin. « Bowlic Liquid Crystalsl ». Molecular Crystals and Liquid Crystals 146, no 1 (mai 1987) : 41–54. http://dx.doi.org/10.1080/00268948708071801.

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13

Francis, Carl A. « Gold CrystalsA Primer ». Rocks & ; Minerals 79, no 1 (février 2004) : 24–29. http://dx.doi.org/10.1080/00357529.2004.9925671.

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14

Nelson, J. « Growth-deviation model to understand the perceived variety of falling snow ». Atmospheric Chemistry and Physics Discussions 8, no 2 (4 mars 2008) : 4407–37. http://dx.doi.org/10.5194/acpd-8-4407-2008.

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Abstract. What is the source of snow-crystal variety? This question is answered using a model of snow-crystal growth in a cloud. In the model, crystals start under various initial cloud-crystal conditions, and then encounter growth perturbations from random air-temperature deviations along simple crystal trajectories. To obtain distributions of these deviations, I analyzed recent high-resolution measurements of cloud updrafts and temperatures. The trajectories and distributions are used to estimate the number of possible snow crystal shapes, to a given viewing resolution, from a range of initial conditions. The logarithm of this number, defined here as the perceived shape variety or "diversity", is dominated not by the range of conditions, but rather by the air-temperature deviations along a trajectory. This qualitative result is independent of the viewing resolution. Thus, temperature deviations are the main source of crystal diversity. When plotted against the crystal's initial temperature (here –11 to –19°C), the curve is mitten-shaped, with a main peak at –15.4°C and a smaller, sharper peak near –14.4°C. The mitten shape arises from temperature trends in the crystal's terminal fallspeed and prism-face growth rate. Specifically, the two diversity peaks are due to maxima in growth-rate sensitivity to temperature near –15.4 and –14.0°C. Applying the results to all snow crystals ever formed, then, to 1-μm resolution, all crystals that began near –15°C would appear unique, but some that began near –11°C would not.
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15

Tipaldi, C. F., et J. Gabrusenoks. « Lattice Dynamics Calculations for Mg1-XZnxO Solid Solutions ». Latvian Journal of Physics and Technical Sciences 59, no 2 (1 avril 2022) : 3–11. http://dx.doi.org/10.2478/lpts-2022-0007.

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Abstract In this study, Mg1-xZnxO solid solutions are studied by modelling lattice dynamics, using the methods of classical molecular dynamics. These time-efficient methods are of great interest since they allow using large crystallic structures, which reduce artificial defect periodicity. The main program used is General Utility Lattice Program (GULP). The Buckingham potential is used for modelling interatomic forces. The parameters for this potential are found for different effective ionic charges by using lattice parameters and vibrational frequencies obtained from ab initio calculations performed in the program CRYSTAL14. With these potentials, the dispersion relations and densities of states have been calculated for MgO, ZnO and Mg1-xZnxO. Calculations have been made for different Mg and Zn contents in the wurtzite and cubic phase solid solutions, respectively, using the supercell method and a large number of Brillouin zone sampling points. New interatomic potentials for interactions Mg-O, O-O, Zn-O have been obtained. These potential parameters have been verified and the phonon dispersion curves and DOS for MgO and ZnO utilising these potential parameters have been compared to other studies, both experimental and theoretical. By adding more Zn in the cubic phase (c-MgO) solution, no local vibrational modes are observed; however, there is a clear spectral widening and a noticeable change in the low frequency region (100–300 cm−1) of the DOS. Adding more Mg in wurtzite phase (w-ZnO) solution, on the other hand, results in local vibrational modes in the mid (350 cm−1) and high frequency (650 cm−1) regions.
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16

Knepp, T. N., T. L. Renkens et P. B. Shepson. « Measurement of acidic ions and their qualitative effects on snow crystal morphology and the quasi-liquid layer ». Atmospheric Chemistry and Physics Discussions 9, no 1 (9 janvier 2009) : 735–66. http://dx.doi.org/10.5194/acpd-9-735-2009.

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Abstract. A chamber was constructed within which snow crystals were grown on a string at various temperatures, relative humidities, and acetic acid gas phase mole fraction. The temperature, relative humidity, and acid mole fraction were measured for the first time at the point of crystal growth. Snow crystal morphological transition temperature shifts were recorded as a function of acid mole fraction, and interpreted according to the calculated acid concentration in the crystal's quasi-liquid layer, which increased in thickness as a function of acid mole fraction, thereby affecting the crystal's morphology according to the hypothesis of Kuroda and Lacmann. Deficiencies in the understanding of the quasi-liquid layer and its role in determining snow crystal morphology are briefly discussed.
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17

Janulis, Eugene P., James C. Novack, George A. Papapolymerou, Miguel Tristani-Kendra et William A. Huffman. « Fluorinated ferroelectric liquid crystals1 ». Ferroelectrics 85, no 1 (septembre 1988) : 375–84. http://dx.doi.org/10.1080/00150198808007670.

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18

JIN, D. Z., et D. H. E. DUBIN. « Two-Dimensional Vortex Crystalsa ». Annals of the New York Academy of Sciences 848, no 1 LONG-RANGE CO (mai 1998) : 18–25. http://dx.doi.org/10.1111/j.1749-6632.1998.tb08954.x.

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19

Morozov, M. M., A. I. Potekaev, A. A. Klopotov, T. N. Markova et V. D. Klopotov. « ALLOYS ON THE BASIS OF PALLADIUM. CRYSTALLO-GEOMETRICAL AND CRYSTALLO-CHEMICAL PARAMETERS ». Izvestiya Visshikh Uchebnykh Zavedenii. Chernaya Metallurgiya = Izvestiya. Ferrous Metallurgy 57, no 12 (1 avril 2015) : 42. http://dx.doi.org/10.17073/0368-0797-2014-12-42-49.

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20

Zhang, Fei Hu, Shao Long Guo, Yong Zhang et Dian Rong Luan. « Research on the Material Removal Mechanism in Deliquescent Polishing of KDP Crystals ». Key Engineering Materials 416 (septembre 2009) : 487–91. http://dx.doi.org/10.4028/www.scientific.net/kem.416.487.

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A new ultraprecision machining technology for KDP crystals, deliquescent polishing technology for KDP crystals, is presented. On the basis of analyzing the definitions of deliquescence, the dissolution experiment of KDP crystal’s surface was conducted. Through the experiment, the material removal mechanism in deliquescent polishing of KDP crystals is proposed, and the deliquescent polishing device for KDP crystals is described. Based on the material removal mechanism in deliquescent polishing of KDP crystals, the deliquescent polishing experiment of KDP crystal was carried out, the experimental result has verified the validity, feasibility and effectiveness of the material removal mechanism.
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21

Knepp, T. N., T. L. Renkens et P. B. Shepson. « Gas phase acetic acid and its qualitative effects on snow crystal morphology and the quasi-liquid layer ». Atmospheric Chemistry and Physics 9, no 20 (16 octobre 2009) : 7679–90. http://dx.doi.org/10.5194/acp-9-7679-2009.

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Abstract. A chamber was constructed within which snow crystals were grown on a string at various temperatures, relative humidities, and acetic acid gas phase mole fractions. The temperature, relative humidity, and acid mole fraction were measured for the first time at the point of crystal growth. Snow crystal morphological transition temperature shifts were recorded as a function of acid mole fraction, and interpreted according to the calculated acid concentration in the crystal's quasi-liquid layer, which is believed to have increased in thickness as a function of acid mole fraction, thereby affecting the crystal's morphology consistent with the hypothesis of Kuroda and Lacmann. Deficiencies in the understanding of the quasi-liquid layer and its role in determining snow crystal morphology are briefly discussed.
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22

Senthamizhan, A., K. Sambathkumar, S. Nithiyanantham et A. A. Alagiriswamy. « Electrical, Optical, Structural Properties with Some Physico-Mechanical of Pure and La3+ Doped L-Alanine Acetate Single Crystals ». Sensor Letters 18, no 12 (1 décembre 2020) : 894–99. http://dx.doi.org/10.1166/sl.2020.4307.

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Slow evaporation was used to successfully generate single crystals of pure and La3+ doped L-alanine acetate from aqueous solution. The structural, vibrational, chemical analysis carried out through XRD, UV, FTIR with FTRaman Analysis. The Nd: YAG laser was used to confirm and estimate the sample’s Second Harmonic Generation (SHG). The growing crystal’s laser damage threshold was also discovered. Thermogravimetic (TG) and Differential theromogravimetric (DTA) studies were used to measure the thermal stability of the formed crystal. The generated LAlA crystals were also subjected to dielectric and photoconductivity tests. The dopant has boosted the efficiency of the L-alanine acetate crystal, according to nonlinear optical studies.
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23

McPherson, Alexander. « pH and Redox Induced Color Changes in Protein Crystals Suffused with Dyes ». Crystals 9, no 3 (1 mars 2019) : 126. http://dx.doi.org/10.3390/cryst9030126.

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Protein crystals, otherwise usually colorless, can be stained a variety of hues by saturating them with dyes, by diffusion from the mother liquor or co-crystallization. The colors assumed by dyes are a function of chemical factors, particularly pH and redox potential. Protein crystals saturated with a pH sensitive dye, initially at one pH, can be exposed to the mother liquor at a second pH and the crystal will change color over time as H3O+ ions diffuse through the crystal. This allows diffusion rates of H3O+ through the crystal to be measured. Diffusion fronts are often clearly delineated. Similar experiments can be carried out with redox sensitive dyes by adding reductants, such as ascorbic acid or dithionite, or oxidants such as H2O2, to the crystal’s mother liquor. Presented here are a number of experiments using pH or redox sensitive dye-saturated protein crystals, and some experiments using double dye, sequential redox–pH changes.
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24

Gunter, Mickey E., et F. Donald Bloss. « The spindle stage : A powerful optical tool ». Proceedings, annual meeting, Electron Microscopy Society of America 46 (1988) : 52–53. http://dx.doi.org/10.1017/s0424820100102341.

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A single, reasonably homogeneous, nonopaque 30-to-300 μm crystal, mounted on a spindle stage and studied by immersion methods under a polarizing microscope, yields optical data frequently sufficient to identify and characterize a substance unequivocally. The data obtainable include (1) the orientation of the crystal's principal vibration axes and (2) its principal refractive indices, to within 0.0002 if desired, for light vibrating along these principal vibration axes. Spindle stages tend to be simple and relatively inexpensive, some costing less than $50. They permit rotation of the crystal about a single axis which is parallel to the microscope stage. This spindle or S-axis is thus perpendicular to the M-axis, namely the microscope stage's axis of rotation.A spindle stage excels when studying anisotropic crystals. It orients uniaxial crystals within minutes and biaxial crystals almost as quickly so that their principal refractive indices - ɛ and ω (uniaxial); α, β and γ (biaxial) - can be determined without significant error from crystal misorientation.
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25

Wang, Zhifeng, Yuquan Gan, Qianqian Du, Shuhong Li, Yunlong Liu et Wenjun Wang. « Morphology-Dependent Optoelectronic Properties of Pentacene Nanoribbon and Nanosheet Crystallite ». Materials 16, no 2 (6 janvier 2023) : 557. http://dx.doi.org/10.3390/ma16020557.

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Organic, single crystals have emerged as unique optoelectrical materials due to their highly ordered structure and low defects. In this work, pentacene nanoribbons and nanosheets were selectively fabricated by controlling their growth temperature. The results show that their photoluminescence (PL) activity and electrical properties were strongly dependent on their geometrical morphology and molecular stacking mode such as the degree of π-orbital overlap and intermolecular interaction. The pentacene nanoribbon crystal exhibited a higher PL intensity compared with the nanosheet configuration; conversely, its electrical conductivity was poor. The low-temperature PL measurement indicated that there are stronger π–π stacking interactions in the nanosheet crystal than in the nanoribbon crystal, leading to exciton quenching and higher conductivity. Our study demonstrated that a unique optoelectronic property of organic crystals can be obtained by controlling the crystal’s morphology, which offers potential guidance for the future design and development of organic crystal optoelectronics.
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26

Zhong, Z., M. Hasnah, A. Broadbent, E. Dooryhee et M. Lucas. « Phase-space matching between bent Laue and flat Bragg crystals ». Journal of Synchrotron Radiation 26, no 6 (23 octobre 2019) : 1917–23. http://dx.doi.org/10.1107/s1600577519010774.

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Through phase-space analysis of Dumond diagrams for a flat Bragg crystal, a single bent Laue crystal and a monochromator consisting of double-bent Laue crystals, this work shows that it is possible to match the flat Bragg crystal to both the single-crystal and double-crystal Laue monochromators. The matched system has the advantage that the phase space of the bent crystal's output beam is much larger than that of the flat crystal, making the combined system stable. Here it is suggested that such a matched system can be used at synchrotron facilities to realize X-ray dark-field imaging, analyzer-based imaging and diffraction-enhanced imaging at beamlines using double-Laue monochromators.
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27

Dokou, Christina. « Londino-lstanbul by Crystalli Glyniadaki ». World Literature Today 85, no 2 (2011) : 71–72. http://dx.doi.org/10.1353/wlt.2011.0149.

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28

Schmidt, Tracy Smith. « The crystal's in the mail... » Nature 423, no 6942 (juin 2003) : 799–800. http://dx.doi.org/10.1038/423799a.

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29

Mueck, Leonie. « Imagine a crystal's inner life ». Nature 511, S7509 (17 juillet 2014) : 5. http://dx.doi.org/10.1038/nature13349.

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30

Praefcke, Klaus, Dirk Blunk et Joachim Hempel. « News on Inositol Liquid Crystals1 ». Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals 243, no 1 (mars 1994) : 323–52. http://dx.doi.org/10.1080/10587259408037774.

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31

Marei, Ahmed Hassan, et Isao Furuta. « Crystallo-integration in dental implantation ». Oral Surgery, Oral Medicine, Oral Pathology 78, no 2 (août 1994) : 136. http://dx.doi.org/10.1016/0030-4220(94)90131-7.

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32

Martínez-González, José, Javier Navarro-Ruiz et Albert Rimola. « Multiscale Computational Simulation of Amorphous Silicates’ Structural, Dielectric, and Vibrational Spectroscopic Properties ». Minerals 8, no 8 (15 août 2018) : 353. http://dx.doi.org/10.3390/min8080353.

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Silicates are among the most abundant and important inorganic materials, not only in the Earth’s crust, but also in the interstellar medium in the form of micro/nanoparticles or embedded in the matrices of comets, meteorites, and other asteroidal bodies. Although the crystalline phases of silicates are indeed present in nature, amorphous forms are also highly abundant. Here, we report a theoretical investigation of the structural, dielectric, and vibrational properties of the amorphous bulk for forsterite (Mg2SiO4) as a silicate test case by a combined approach of classical molecular dynamics (MD) simulations for structure evolution and periodic quantum mechanical Density Functional Theory (DFT) calculations for electronic structure analysis. Using classical MD based on an empirical partial charge rigid ionic model within a melt-quenching scheme at different temperatures performed with the GULP 4.0 code, amorphous bulk structures for Mg2SiO4 were generated using the crystalline phase as the initial guess. This has been done for bulk structures with three different unit cell sizes, adopting a super-cell approach; that is, 1 × 1 × 2, 2 × 1 × 2, and 2 × 2 × 2. The radial distribution functions indicated a good degree of amorphization of the structures. Periodic B3LYP-geometry optimizations performed with the CRYSTAL14 code on the generated amorphous systems were used to analyze their structure; to calculate their high-frequency dielectric constants (ε∞); and to simulate their IR, Raman, and reflectance spectra, which were compared with the experimental and theoretical crystalline Mg2SiO4. The most significant changes of the physicochemical properties of the amorphous systems compared to the crystalline ones are presented and discussed (e.g., larger deviations in the bond distances and angles, broadening of the IR bands, etc.), which are consistent with their disordered nature. It is also shown that by increasing the unit cell size, the bulk structures present a larger degree of amorphization.
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Polino, M., H. S. Rho, M. P. Pina, R. Mallada, A. L. Carvalho, M. J. Romão, Isabel Coelhoso, J. G. E. Gardeniers, J. G. Crespo et Carla A. M. Portugal. « Protein Crystallization in a Microfluidic Contactor with Nafion®117 Membranes ». Membranes 11, no 8 (21 juillet 2021) : 549. http://dx.doi.org/10.3390/membranes11080549.

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Protein crystallization still remains mostly an empirical science, as the production of crystals with the required quality for X-ray analysis is dependent on the intensive screening of the best protein crystallization and crystal’s derivatization conditions. Herein, this demanding step was addressed by the development of a high-throughput and low-budget microfluidic platform consisting of an ion exchange membrane (117 Nafion® membrane) sandwiched between a channel layer (stripping phase compartment) and a wells layer (feed phase compartment) forming 75 independent micro-contactors. This microfluidic device allows for a simultaneous and independent screening of multiple protein crystallization and crystal derivatization conditions, using Hen Egg White Lysozyme (HEWL) as the model protein and Hg2+ as the derivatizing agent. This microdevice offers well-regulated crystallization and subsequent crystal derivatization processes based on the controlled transport of water and ions provided by the 117 Nafion® membrane. Diffusion coefficients of water and the derivatizing agent (Hg2+) were evaluated, showing the positive influence of the protein drop volume on the number of crystals and crystal size. This microfluidic system allowed for crystals with good structural stability and high X-ray diffraction quality and, thus, it is regarded as an efficient tool that may contribute to the enhancement of the proteins’ crystals structural resolution.
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Matko, Vojko, et Miro Milanovič. « Detection Principles of Temperature Compensated Oscillators with Reactance Influence on Piezoelectric Resonator ». Sensors 20, no 3 (1 février 2020) : 802. http://dx.doi.org/10.3390/s20030802.

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This review presents various ways of detection of different physical quantities based on the frequency change of oscillators using piezoelectric crystals. These are influenced by the reactance changes modifying their electrical characteristics. Reactance in series, in parallel, or a combination of reactances can impact the electrical crystal substitute model by influencing its resonant oscillation frequency. In this way, various physical quantities near resonance can be detected with great sensitivity through a small change of capacitance or inductance. A piezoelectric crystal impedance circle and the mode of frequency changing around the resonant frequency change are shown. This review also presents the influence of reactance on the piezoelectric crystal, the way in which the capacitance lost among the crystal’s electrodes is compensated, and how the mode of oscillators’ output frequency is converted to lower frequency range (1–100 kHz). Finally, the review also explains the temperature–frequency compensation of the crystals’ characteristics in oscillators that use temperature–frequency pair of crystals and the procedure of the compensation of crystals own temperature characteristics based on the method switching between the active and reference reactance. For the latter, the experimental results of the oscillator’s output frequency stability (fout = ±0.002 ppm) at dynamical change of environment temperature (0–50 °C) are shown.
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Qin, L. C. « HREM of electron-irradiated silicas ». Proceedings, annual meeting, Electron Microscopy Society of America 51 (1 août 1993) : 1102–3. http://dx.doi.org/10.1017/s0424820100151349.

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Silica (SiO2) crystals exist in various polymorphs which have different densities and different crystal structures, such as quartz, tridymite, and cristobalite, though all of these have in common the network structure which is formed by corner-sharing of SiO4 tetranedra. All these structures are sensitive to electron irradiation. Amorphization occurs when they are irradiated by energetic electrons.In the present study three polymorphs of silica crystals, α-quartz, α-tridymite and α-cristobalite crystals2 were used as starting materials. Electron irradiation experiments were carried out in situ in the electron microscope. The structural changes of the specimens were monitored using high-resolution electron microscopy (HREM).The amorphization of α-quartz crystals was found to progress through two morphologies: (a) nucleation and growth of amorphous nuclei with a sharp boundary with the crystalline matrix (figure 1); and (b) crystallinity lost gradually and more uniformly. Figure 2 shows a series of HREM images showing the amorphization of a tridymite crystal.
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Hidayathullah, A. M., R. S. Samuel, V. Chithambaram, R. Raja et S. Janarthanan. « Investigations on the synthesis and growth and structural, spectral, optical, mechanical and thermal properties of non-linear optical single crystals of Bis-L-Seriniumoxalate Dihydrate (BLSOD) ». Journal of Ovonic Research 19, no 1 (janvier 2023) : 43–52. http://dx.doi.org/10.15251/jor.2023.191.43.

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From the raw materials L-Serine and oxalic acid, the product Bis-LSeriniumoxalatedehydrate(BLSOD) was created. By using a slow evaporation process, the individual BLSOD crystals were produced from aqueous solution. According to single crystal X-ray Diffraction investigations, the structure of the produced crystal is monoclinic. The existence of different functional groups and the chemical environment present in the synthesised material were qualitatively determined through the use of Fourier Transform Infra-Red (FTIR) and proton nuclear magnetic resonance (H1NMR) spectrum studies. The crystal's transparency in the visible and near-infra-red areas was confirmed by UV-Visible-Near infrared and photoluminescence spectrum tests, which also looked at the material's viability for device construction. To determine the crystal's machinability, the mechanical properties of the material were carefully examined using Vicker's hardness research. Thermal investigations such as Thermo gravimetric (TGA) and Differential thermal analysis (DTA) have shown the thermal stability of BLSOD and the phases of weight losses. As a function of frequency and temperature, the dielectric constant and dielectric loss of grown crystals were determined. The Kurtz-Perry powder test was used to check both the second harmonic generation (SHG) and then the NLO property of the material.
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37

Bulutoglu, Pelin Su, Conor Parks, Nandkishor K. Nere, Shailendra Bordawekar et Doraiswami Ramkrishna. « Exploring New Crystal Structures of Glycine via Electric Field-Induced Structural Transformations with Molecular Dynamics Simulations ». Processes 7, no 5 (8 mai 2019) : 268. http://dx.doi.org/10.3390/pr7050268.

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Being able to control polymorphism of a crystal is of great importance to many industries, including the pharmaceutical industry, since the crystal’s structure determines significant physical properties of a material. While there are many conventional methods used to control the final crystal structure that comes out of a crystallization unit, these methods fail to go beyond a few known structures that are kinetically accessible. Recent studies have shown that externally applied fields have the potential to effectively control polymorphism and to extend the set of observable polymorphs that are not accessible through conventional methods. This computational study focuses on the application of high-intensity dc electric fields (e-fields) to induce solid-state transformation of glycine crystals to obtain new polymorphs that have not been observed via experiments. Through molecular dynamics simulations of solid-state α -, β -, and γ -glycine crystals, it has been shown that the new polymorphs sustain their structures within 125 ns after the electric field has been turned off. It was also demonstrated that strength and direction of the electric field and the initial structure of the crystal are parameters that affect the resulting polymorph. Our results showed that application of high-intensity dc electric fields on solid-state crystals can be an effective crystal structure control method for the exploration of new crystal structures of known materials and to extend the range of physical properties a material can have.
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38

Baker, Oliver. « Innovative Crystal's Got Plenty O' Nuthin' ». Science News 156, no 21 (20 novembre 1999) : 327. http://dx.doi.org/10.2307/4012011.

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39

Dorenbos, P., E. Bougrine, J. T. M. De Haas, C. W. E. Van Eijk et M. V. Korzhik. « Scintillation properties of GdAlO3:Ce crystals1 ». Radiation Effects and Defects in Solids 135, no 1-4 (décembre 1995) : 321–23. http://dx.doi.org/10.1080/10420159508229859.

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Dorenbos, P., M. Marsman, C. W. E. Van Eijk, M. V. Korzhik et B. I. Mlnkov. « Scintillation properties of Y2SiO5:Pr crystals1 ». Radiation Effects and Defects in Solids 135, no 1-4 (décembre 1995) : 325–28. http://dx.doi.org/10.1080/10420159508229860.

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41

Sunandana, C. S. « A crystallo-chemical approach to superionics ». Journal of Physics and Chemistry of Solids 58, no 9 (septembre 1997) : 1359–65. http://dx.doi.org/10.1016/s0022-3697(97)00027-9.

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42

Praefcke, K., B. Kohne, B. Gündogan, D. Singer, D. Demus, S. Diele, G. Pelzl et U. Bakowsky. « News on Nematic-Biaxial Liquid Crystals1 ». Molecular Crystals and Liquid Crystals 198, no 1 (avril 1991) : 393–405. http://dx.doi.org/10.1080/00268949108033415.

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43

Onaka, Jessica, Daisuke Koyama, Yuma Kuroda, Akira Emoto et Mami Matsukawa. « Optical evaluation of a double-layered ultrasound liquid crystal lens ». Journal of Applied Physics 131, no 19 (21 mai 2022) : 193103. http://dx.doi.org/10.1063/5.0091093.

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A method to improve the performance of an ultrasound liquid crystal lens is proposed. A double-layer-based lens model tailored based on the liquid crystal’s physical properties, e.g., its dielectric anisotropy and elastic constants, is presented as an alternative method to improve the lens’s optical performance while forming weak anchoring surfaces for nematic liquid crystals, thus promoting easier reorientation of the liquid crystal molecules. The lens configuration was simulated by finite-element analysis using Ansys software. The lens’s physical and optical characteristics were evaluated via comparison using two different liquid crystal materials: 5CB and RDP-85475. The birefringence distribution within the liquid crystal layer was investigated under ultrasound excitation, and the molecular angles of inclination were estimated. A higher birefringence distribution, greater molecular inclination, and a longer focal length were obtained for the double-layered liquid crystal lens using the 5CB material.
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44

Tian, Ruifeng, Mingyan Pan, Lu Zhang et Hongji Qi. « Crystal growth and spectral properties of (Yb0.15Lu0.85xY0.85-0.85x)3Al5O12 single crystals ». Chinese Optics Letters 20, no 12 (2022) : 121601. http://dx.doi.org/10.3788/col202220.121601.

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45

Gatta, G. D., N. Rotiroti et M. Zucali. « Plastic deformations in kyanites by tectonometamorphic processes : a single-crystal X-ray diffraction study ». Mineralogical Magazine 73, no 3 (juin 2009) : 359–71. http://dx.doi.org/10.1180/minmag.2009.073.3.359.

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AbstractThe crystalch emistry and crystal structure of naturalky anite crystals from the Eclogitic Micaschists Complex of the Sesia-Lanzo Zone, Western Italian Alps, have been investigated by means of optical microscopy, wavelength dispersive X-ray microanalysis, and single-crystal X-ray diffraction. The association of kyanite + garnet + phengitic-mica + chloritoid suggests that the eclogite-facies stages occurred at P ≤ 2.1 GPa and T ≤ 650ºC. Kyanite grains are large (cm-sized) porphyroblasts grown dynamically during one of the deformational events related to the subduction of the Austroalpine continentalcr ust. Under the polarizing microscope, kyanite grains show almost homogeneous cores, whereas rims are sometimes symplectitic aggregates of quartz and kyanite, confirming at least two stages of growth most likely related to the multistage deformational history of these rocks. Chemical analysis shows that Fe3+ is the major substituting cation for Al3+, ranging between 0.038 and 0.067 a.p.f.u.The single-crystal X-ray diffraction investigation of the kyanites shows severely textured patterns on the (h0l)*-plane. Such evidence is not observed in the unwarped diffraction patterns on (0kl)* and (hk0)*. The most significant difference between the structuralp arameters refined in this study, with respect to those of previously published unstrained gem-quality crystals, concerns the displacement parameters. The anisotropic displacement ellipsoids of all the atomic sites are significantly larger than those previously described, and systematically oriented with the largest elliptical section almost perpendicular to [010]. The larger ellipsoids in the kyanite crystal investigated here reflect the displacement of the centre of gravity of the electron distribution, rather than an anomalous atomic thermal motion. The magnitude and orientation of the displacement parameters and the textured/strained diffraction pattern may be the result of two combined effects: (1) that the kyanite crystals are actually composed of several blocks; (2) the crystals are affected by a pervasive residual strain, as a result of tectonometamorphic plastic deformations and re-crystallization.
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46

Zakgeim, Dmitrii, Dmitrii Bauman, Dmitrii Panov, Vladislav Spiridonov, Arina Kremleva, Andrei Smirnov, Maxim Odnoblyudov, Alexey Romanov et Vladislav Bougrov. « Growing of bulk β-(Al x Ga1−x )2O3 crystals from the melt by Czochralski method and investigation of their structural and optical properties ». Applied Physics Express 15, no 2 (17 janvier 2022) : 025501. http://dx.doi.org/10.35848/1882-0786/ac44ca.

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Abstract Bulk (Al x Ga1−x )2O3 crystals with an Al fraction x in the range from 0.0 to 0.23 were successfully grown by the Czochralski method. An increase in the band gap from 4.7 to 5.1 eV with the rise of the Al content was demonstrated by analyzing optical transmission spectra. The crystal quality of the obtained samples was characterized by X-ray diffractometry. The appearance of the crystal’s mosaic blockness was found for the Al fraction x above 0.05.
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47

Yi, Chengqi. « Probing enzyme-mediated oxidation reactions in crystallo ». Pure and Applied Chemistry 83, no 12 (31 octobre 2011) : 2199–212. http://dx.doi.org/10.1351/pac-con-11-08-10.

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Reaction intermediates define the chemical steps of transformation from substrates to products, and capture of intermediates along catalytic pathways remains one focal point in the studies of enzymatic mechanisms. Performing enzymatic reactions in protein single crystals has been shown to be very effective in trapping and identifying unstable intermediates. In this critical review, we provide several examples of in crystallo approaches to trap reactive oxidation intermediates, thereby allowing the studies of enzymatic oxidation mechanisms.
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Varadachari, Chandrika, Tarit Chattopadhyay et Kunal Ghosh. « The crystallo-chemistry of oxide-humus complexes ». Soil Research 38, no 4 (2000) : 789. http://dx.doi.org/10.1071/sr99053.

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Complexation of humic substances with goethite, hematite, gibbsite, and boehmite has been explained from a viewpoint of crystal structure of the minerals. Theoretical analysis of crystal surface structures revealed the following. (i) Residual charge carried by O or OH on surfaces of gibbsite is –1/2; on boehmite it is –3/2 or –1/2; on goethite it is –4/3, –2/3, or –1/3; and on hematite it is –3/2, –1, or –1/2. Cations adsorbed to neutralise these charges can form bridging links with humic acid; higher charges form stronger links. (ii) Surfaces of goethite, hematite, and gibbsite also contain octahedral sites in which one O/OH position is vacant. These may provide centres for the formation of strong coordination bonds. (iii) Such vacant octahedral positions are absent in boehmite. It follows that in gibbsite, cation bridging links would be weak and vacant octahedral sites would be the dominant bonding sites; in goethite and hematite, both cation bridging and surface coordination sites would be present; in boehmite, cation bridging would be the only strong bonding mode. Derivations from crystallochemical analysis are supported by experimental observations. Infrared studies also show strong OH involvement in boehmite complexation in contrast to the weakness of OH involvement in gibbsite complexes.
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Chen, Fanrong, Peter C. Burns et Rodney C. Ewing. « 79Se : geochemical and crystallo-chemical retardation mechanisms ». Journal of Nuclear Materials 275, no 1 (octobre 1999) : 81–94. http://dx.doi.org/10.1016/s0022-3115(99)00105-1.

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Towler, M. J., H. G. Walton et I. W. Stewart. « Important Physical Properties of Smectic Liquid Crystals1 ». Liquid Crystals Today 8, no 1 (mars 1998) : 5–9. http://dx.doi.org/10.1080/13583149808047692.

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