Direct evidence of Lowenstein's rule violation in swelling high-charge micas

Pavón, Esperanza; Osuna, Francisco J.; Alba, María D.; Delevoye, Laurent

doi:10.1039/c4cc01632g

Cited by 10 publications

(8 citation statements)

References 22 publications

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“…The last oxygen environment, Al tet -O-3Mg, that is present in the structure, was previously reported considering the electronegativity only [15]. The Al tet -O-3Mg sites should feature smaller CQ and smaller isotropic chemical shift values than that of Si-O-3Mg environments.…”

Section: Resultsmentioning

confidence: 51%

“…However, in addition to being expensive, 17 O isotopic enrichment might be challenging from the synthesis point of view as it would require, in our study, 17 O enriched SiO2 and Al(OH)3 as precursors, and further heating at high temperature (900 ºC). In a recent publication, Pavón et al [15] showed that it was possible to obtain 17 Today, experimental NMR is often combined with density functional theory (DFT) calculations of parameters to obtain a deeper understanding of the relation between NMR data and the local structure and disorder. This is of great interest in the present context of natural abundance 17 O NMR spectra of low sensitivity.…”

Section: Introductionmentioning

confidence: 99%

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Natural abundance 17O MAS NMR and DFT simulations: New insights into the atomic structure of designed micas

Pavón

Osuna

Alba

et al. 2019

Solid State Nuclear Magnetic Resonance

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Combining 17 O Magic-Angle Spinning (MAS) NMR at natural abundance with DFT calculations is a promising methodology to shed light on the structure and disorder in tetrahedral sheets of designed micas with enhanced properties. Among brittle micas, synthetic mica is an important alternative to natural ones with a swelling sheet-like structure that results in many applications, by exploiting unique characteristics. Lowenstein's rule is one of the main chemical factor that determines the atomic structure of aluminosilicates and furthermore their properties. In the present article, 17 O MAS NMR spectroscopy is used to validate (or not) the agreement of the Lowenstein's rule with the distribution of Si and Al sites in the tetrahedral sheets of synthetic micas. 17 O MAS spectra of synthetic high-charged micas exhibit two regions of signals that revealed two

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Section: Resultsmentioning

confidence: 51%

Section: Introductionmentioning

confidence: 99%

Natural abundance 17O MAS NMR and DFT simulations: New insights into the atomic structure of designed micas

Pavón

Osuna

Alba

et al. 2019

Solid State Nuclear Magnetic Resonance

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“…In contrast with the correlated disorder of the ice system discussed above, where violations of the structural restrictions yield unstable and hence forbidden configurations, structures that contain Al–O–Al bonds may very well be stable, albeit energetically unfavorable. And as a matter of fact the Loewenstein’s rule is not strict and is violated in many systems [ 55 ]. The amount of violations typically increases with the synthesis temperature, which maximizes the effect of the entropy contribution to the Gibbs free energy, and with the cooling rate, which should be fast enough to limit local atomic rearrangements in the favor of Si–O–Al bonds.…”

Section: Exploring Supercell Configurations: Supercell mentioning

confidence: 99%

Supercell program: a combinatorial structure-generation approach for the local-level modeling of atomic substitutions and partial occupancies in crystals

2016

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BackgroundDisordered compounds are crucially important for fundamental science and industrial applications. Yet most available methods to explore solid-state material properties require ideal periodicity, which, strictly speaking, does not exist in this type of materials. The supercell approximation is a way to imply periodicity to disordered systems while preserving “disordered” properties at the local level. Although this approach is very common, most of the reported research still uses supercells that are constructed “by hand” and ad-hoc.ResultsThis paper describes a software named supercell, which has been designed to facilitate the construction of structural models for the description of vacancy or substitution defects in otherwise periodically-ordered (crystalline) materials. The presented software allows to apply the supercell approximation systematically with an all-in-one implementation of algorithms for structure manipulation, supercell generation, permutations of atoms and vacancies, charge balancing, detecting symmetry-equivalent structures, Coulomb energy calculations and sampling output configurations. The mathematical and physical backgrounds of the program are presented, along with an explanation of the main algorithms and relevant technical details of their implementation. Practical applications of the program to different types of solid-state materials are given to illustrate some of its potential fields of application. Comparisons of the various algorithms implemented within supercell with similar solutions are presented where possible.ConclusionsThe all-in-one approach to process point disordered structures, powerful command line interface, excellent performance, flexibility and GNU GPL license make the supercell program a versatile set of tools for disordered structures manipulations.Electronic supplementary materialThe online version of this article (doi:10.1186/s13321-016-0129-3) contains supplementary material, which is available to authorized users.

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“…However, a small number of Löwenstein-disobeying (NLöw) examples have been proposed for aluminosilicates: in the aluminate sodalites,3 zeolite stilbite,4 in bicchulite5–7 and gehlenite-type8 materials, where Si : Al ratios below 1 can be achieved, aluminosilicate glasses9,10 and metastable, disordered phases, such as cordierite11 and anorthite 12. Among related materials that have been shown to disobey Löwenstein's rule are layered Na-4-micas13 and gallobicchulite 14. Most of the analyses reporting on violations of Löwenstein's rule have been either indirect, or applied to materials generated under exotic conditions 11,12,15,16.…”

Section: Introductionmentioning

confidence: 99%