5-coordinated Silicon Research Articles

Reversible and irreversible photon-absorption in amorphous SiO2 revealed by deep potential

Understanding the kinetic balance between reversible and irreversible photon-absorption (IPA/RPA) in amorphous-SiO2 (a-SiO2) is crucial for mitigating optical damage and assessing the lifetime of irradiated optics. Experimental work has placed some thermodynamic bounds on the formation of defects from damage precursor, but the formation kinetics and underlying microscopic mechanisms are yet to be elucidated. Here, by employing deep neural network potential, we find that the formation of defects are temperature-dependent and density-dependent, where competitions between IPA and RPA take place. The IPA prevails in the early formation of E’-center, and the ratio of IPA/RPA is related to the strained bonds, SiSi bonds and 5-coordinated silicon (Si5). Furthermore, the Si5 is critical to the propagation of E’-center and densification of a-SiO2. Additionally, we develop quantitative models of defects in regard with irradiation temperature of specified temperature and irradiation photon-energy, respectively.

In English

Oxides of tetravalent elements are well known to have a lot of crystalline modifications. For example, most of silica polymorphs are characterized by tetrahedral coordination environment of silicon atoms. On the contrary, crystals of stishovite and of some silicate minerals have their silicon atoms in octahedral coordination spheres. It has been found experimentally that the phase transitions between silica polymorphs accompanied by a rearrangement of silica-oxygen tetrahedrons into octahedra require an energy income (preference energy) of 54 kJ/mol. When increasing the atomic mass of the oxide forming element, the former decreases extremely and for tin dioxide is equal to -59 kJ/mol. These values can be reproduced in a theoretical way, within the frameworks of modern quantum chemical methods and periodic models. High disperse silica nanoparticles (as well as those for other oxides) have only the nearest order of atomic stationing, so that theoretical approaches developed for crystals cannot be applied to small particles. These particles can be transformed into stishovite form under hydrothermal conditions. Such a process can be simulated within cluster approximation by use of molecular models. This work is devoted to quantum chemical simulation of formation of the fragments with hexa-coordinated atoms of silicon and of its analogs in the structure of oxane dendrimers. A row of high symmetry models was examined containing two, three, five, and seventeen atoms of silicon and of germanium, titanium and tin, terminated with hydroxyl groups. These structures can be rearranged into another ones including oxide forming atoms with elevated (equal to 5 or 6) coordination number, so mimicking the rutile-like structure. Such models let it possible to fulfill the procedure of transformation without rupturing siloxane bonds, so remaining within a deformation approach. Another advantage is the exclusion of the basis set superposition error due to use of molecular models of the same total formula for all the coordination states. All calculations were carried out by Hartree-Fock and density functional theory methods with the all-electron (3-21G*) and valent (SBKJC) basis sets by means of the GAMESS program. Models of various size have been examined, in particular, disiloxane (HO)3Si-O-Si(OH)3 witch can be transformed into a self-coordinated form where one of silicon atoms becomes a five-coordinated; trisiloxane (HO)3Si-O-Si(OH)2-O-Si(OH)3 can be rearranged into symmetric isomer with one hexa-coordinated silicon atom. Pentasiloxane with neo-structure of [(HO)3Si-O]4Si forms three coordination structures, the most stable of them mimicking the stishovite crystal; it contains one 6-coordinated and two 5-coordinated silicon atoms. Siloxane containing 17 silicon atoms has a super-neo-structure of {[(HO)3Si-O]3Si-O}4Si; it includes seven six-coordinated and four five-coordinated silicon atoms. Relative models for silicon analogs have been also examined. When analyzing a dependence of the energy differences between open and coordinated oxane structures on the number of atoms of the oxide forming element in the cluster, one can jump to the conclusion that the specific value of this characteristic monotonously decreases with the increase in the number of atoms of the molecular model, so becoming close to the experimental data.

Size-Dependent Mechanical Properties of Amorphous SiO2 Nanowires: A Molecular Dynamics Study.

Uniaxial tension tests were performed for amorphous SiO2 nanowires using molecular dynamics simulation to probe the size effect on the mechanical properties and plastic deformation by varying the length of nanowires. The simulation results showed that the Young’s modulus of SiO2 nanowires increased with the decrease of nanowires length due to its higher surface stress. The corresponding deformation of SiO2 nanowires during tension exhibited two periods: atomic arrangement at small strain and plastic deformation at large strain. During the atomic arrangement period, the percentage variations of atom number of 2-coordinated silicon and 3-coordinated silicon (PCN2 and PCN3) decreased, while the percentage variations of atom number of 4-coordinated silicon, 5-coordinated silicon (PCN4 and PCN5) and the Si–O bond number (PCB) rose slightly with increasing strain, as the strain was less than 22%. The situation reversed at the plastic deformation period, owing to the numerous breakage of Si–O bonds as the strain grew beyond 22%. The size effect of nanowires radius was considered, finding that the Young’s modulus and fracture stress were higher for the larger nanowire because of fewer dangling bonds and coordinate defeats in the surface area. The elastic deformation occurred at a small strain for the larger nanowire, followed by the massive plastic deformation during tension. A brittle mechanism covers the fracture characteristics, irrespective of the nanowire size.

ChemInform Abstract: 5-Coordinate Si Compounds as Intermediates in the Synthesis of Silicates in Nonaqueous Media.

Sodium silicoglycolate, an organosilicon compound in which silicon is in 5-coordination with respect to oxygen, is shown to be a reaction intermediate in the synthesis of a purely siliceous sodalite with ethylene glycol as solvent. The presence of silicon-29 nuclear magnetic resonances at –105.5 ± 0.3 parts per million in solution and –102.7 parts per million in the solid state as well as x-ray powder diffraction patterns demonstrate that 5-coordinate silicon is intimately involved in the synthesis. Silicon compounds of the 5-coordinate type are highly reactive and are promising starting materials for the synthesis of novel silicone polymers, molecular sieves, glasses, semiconductors, and ceramics. We have used sodium silicoglycolate to prepare the molecular sieve silicalite as well as sodalites of different compositions.

Nuclear magnetic resonance studies of alkaline earth phosphosilicate and aluminoborosilicate glasses

The 11B, 27Al, 29Si and 31P magic angle spinning (MAS) NMR spectra of MO–P 2O 5, MO–SiO 2–P 2O 5 and MO(M ′ 2O)–SiO 2–Al 2O 3–B 2O 3 (M=Mg, Ca, Sr and Ba, M ′=Na) glasses were examined. In binary MO–P 2O 5 (M=Ca and Mg) glasses, the distributions of the phosphate sites, P(Q n ), can be expressed by a theoretical prediction that P 2O 5 reacts quantitatively with MO. In the ternary 0.30MO–0.05SiO 2–0.65P 2O 5 glasses, the 6-coordinated silicon sites were detected, whose population increases in the order of MgO<CaO<SrO≒BaO. In xCaO–0.05SiO 2–(0.95− x)P 2O 5 glasses, its population increases with an increase in f (=([P 2O 5]−[MO]−[B 2O 3]−[Na 2O])/[SiO 2]) and has maximum at f=9. The signal due to the 5-coordinated silicon atoms is also observed when x is smaller than 0.45. When three network-forming oxides such as SiO 2, Al 2O 3 and B 2O 3 coexist, Al 2O 3 reacts preferably with MO. The populations of 4-coordinated boron atoms, N 4, are expressed well with r/(1− r), where r=([Na 2O]−[Al 2O 3])/([Na 2O]−[Al 2O 3]+[B 2O 3]). The correlation of the Raman signal at 1210 and 1350 cm −1 with the NMR signal of Si(Q 6) at −215 ppm is also seen.

Silicon and Oxygen Self-Diffusivities in Silicate Liquids Measured to 15 Gigapascals and 2800 Kelvin

Mass transport properties of silicate liquids exhibit complex behavior as a function of pressure, as the tetrahedral framework structure of the liquid shifts to a more compact arrangement of atoms. For highly polymerized aluminosilicate liquids, oxygen diffusivities pass through a maximum at pressures below 10 gigapascals, whereas up to 15 gigapascals diffusivities continue to increase for sodium tetrasilicate liquid. A diffusivity maximum indicates a change in the mechanism of formation of 5-coordinated silicon or aluminum in the liquid. In the case of aluminosilicate liquids, this mechanism is restricted to aluminum sites in the network, suggesting that not only degree of polymerization, but also the ratio of aluminum to aluminum plus silicon strongly influences the behavior of magmatic processes at depth.

Hydrothermal Synthesis of Zeolites from 5-Coordinate Silicon Compounds

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHydrothermal Synthesis of Zeolites from 5-Coordinate Silicon CompoundsBruno Herreros and Jacek KlinowskiCite this: J. Phys. Chem. 1995, 99, 3, 1025–1029Publication Date (Print):January 1, 1995Publication History Published online1 May 2002Published inissue 1 January 1995https://doi.org/10.1021/j100003a027RIGHTS & PERMISSIONSArticle Views150Altmetric-Citations3LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (417 KB) Get e-Alerts

Synthesis of zeolites from sodium silicoglycolate, a 5-coordinate silicon compound

We have used sodium silicoglycolate, an organosilicon compound in which Si is in 5-coordination with respect to oxygen, to prepare the molecular sieve silicalite as well as sodalites of different compositions. The highly reactive 5-coordinate silicon compounds are promising starting materials for the synthesis of silicone polymers, molecular sieves, glasses, semiconductors and ceramics.

Syntheses and Characterization of Bis(benzene-1,2-diolato)diisothiocyanatosilicon(IV) Compounds: First Stable Bicyclic Siliconate Dianion

Syntheses of the first bicyclic dianion containing hexacoordinate silicon with several cations, [(C 6 H 4 O 2 ) 2 -Si(NCS) 2 ] 2- °B] + 2 (B=pyH (1), 3-mepyH (2), 4-mepyH (3), K (4), Na (5), NH 4 (6), Et 2 NH 2 (7)), are described. Complexes 1-3 are prepared from the reactions between benzene-1,2-diol and the appropriate cationic 5-coordinate silicon(IV) compounds 8-10. Complexes 4-6 are obtained in one-step reaction between diethoxydiisothiocyanatosilane and the diol in the presence of 1 equiv amount of NCS- anion, while 7 is formed using chemoselective metathesis of 6 with diethylamine. All the reactions occur at ambient temperature (≤25 o C)

Spectroscopic Studies of 5-Coordinate Silicon Compounds

A detailed study of the structural and chemical features of a series of novel compounds in which silicon is in 5-coordination with respect to oxygen has been carried out using XRD, FTIR, solid-state NMR, and ESCA. All compounds contain glycolate groups and different charge-balancing alkali-metal cations. NMR confirms that only 5-coordinate Si is present. There is a unique set of ESCA core level binding energies for these materials. Peak positions may be influenced by (1) the coordination number of Si, (2) the presence of organic moieties, and (3) the kind and concentration of cations. All binding energies in the 5-coordinate silicon compound with Cs + are shifted with respect to those in other compounds to suggest that effects (1) and (3) are dominant

5-Coordinate Si Compounds as Intermediates in the Synthesis of Silicates in Nonaqueous Media

Sodium silicoglycolate, an organosilicon compound in which silicon is in 5-coordination with respect to oxygen, is shown to be a reaction intermediate in the synthesis of a purely siliceous sodalite with ethylene glycol as solvent. The presence of silicon-29 nuclear magnetic resonances at -105.5 +/- 0.3 parts per million in solution and -102.7 parts per million in the solid state as well as x-ray powder diffraction patterns demonstrate that 5-coordinate silicon is intimately involved in the synthesis. Silicon compounds of the 5-coordinate type are highly reactive and are promising starting materials for the synthesis of novel silicone polymers, molecular sieves, glasses, semiconductors, and ceramics. We have used sodium silicoglycolate to prepare the molecular sieve silicalite as well as sodalites of different compositions.

Kinetic Study on the Reaction of (Arylthio)trimethylsilanes with Phenacyl Bromide Giving Aryl Phenacyl Sulfides and Bromotrimethylsilane

Abstract A kinetic study has been conducted on the reactions of (arylthio)trimethylsilanes with phenacyl bromide giving aryl phenacyl sulfides and bromotrimethylsilane. Remarkably large positive substituent effect (ρ=+2.2) and large negative entropy of activation were observed for the reaction. A mechanism involving 5-coordinated silicon intermediate prior to the rate-determining heterolysis of the Si–S bond has been suggested for the reaction based on the kinetic results.

Reactions of the ambidentate substrate chloromethyldimethylchlorosilane with amines and amides

Chloromethyldimethylchlorosilane (CMDS) reacts with diethylamine and aniline at the SiCl group to form the corresponding chloromethyldimethylsilylamines. With amides, however, substitution on CMDS occurs at the CCl bond to form compounds with a 5-membered ring containing a 5-coordinate silicon. Reaction of trimethylsilyl amides with CMDS provides the most convenient route to this ring system but with bis(trimethylsilyl) amides, RCON[Si(CH 3) 3] 2, it proceeds only when R is small. Reaction of bis(trimethylsilyl)acetamide and N-methyltrimethylsilylacetamide with a variety of substrates of the type X(CH 2) n Si(CH 3) 2Y occurs when X = Cl or Br and Y = Cl, Br or N(C 2H 5) 2 and n = 2 but not when n = 3 or Y = OC 2H 5, CH 3, CH = CH 2, or C 6H 5.