The structure of sodium silicate glass from neutron diffraction and modeling of oxygen-oxygen correlations (original) (raw)
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Cationic environment in silicate glasses studied by neutron diffraction with isotopic substitution
Chemical Geology, 2001
The method of neutron diffraction coupled with isotopic substitution is presented and recent investigations on the Ž. Ž environment around cations in silicate Ti in K O P TiO P 2SiO , Ca and Ni in 2CaO P NiO P 3SiO and aluminosilicate Li 2 2 2 2. in Li O P Al O P 2SiO glasses are reviewed. The examination of the cation-centered pairs obtained from the first 2 2 3 2 difference function presents striking similarities for all investigated cations. These functions indicate a well-defined shortand medium-range environment around cations. The local site generally presents a lower coordination number than that found in the crystals of similar composition. The environment around Ti in vitreous K O P TiO P 2SiO corresponds to a 2 2 2 square-based pyramid and direct TiO-TiO linkages were observed experimentally in the second difference function, 5 5 contrary to crystals. A detailed description of the cation site distortion for Li and Ca may be given by this method. The distribution of cations at medium range, which can be extracted by the double difference method, reveals the presence of cation-rich regions in silicate glasses. The cation-cation distances often indicate a two-dimensional character in the cationic organization. On the contrary, Li-aluminosilicate glass shows a more homogeneous cation distribution, in relation with the charge-compensating role of Li in this glass. This non-homogeneous distribution of cations may be related to the nano-inhomogeneities proposed in the models of supercooled liquids.
Short- and medium-range structural order around cations in glasses: a multidisciplinary approach
Comptes Rendus de l'Académie des Sciences - Series IV - Physics, 2001
The structural environment of cations at a short-and medium-range scale may be investigated either by spectroscopic methods or by radiation diffraction giving either a description of the geometry and symmetry of the cationic site, including the nature of the chemical bond, or a chemically resolved radial distribution function. Cations exhibit several original structural properties in oxide glasses. Short-range order is characterized by unusual coordination numbers, such as five-coordinated sites or tetrahedral sites which are in a network forming position, with the relative proportion of these sites depending on glass composition. Oxide glasses can also exhibit elements with unusual oxidation states, such as pentavalent uranium. The determination of the sites occupied by the elements in their different oxidation states allows to rationalize the chemical dependence of redox equilibria, which is the way to predict Fe behavior in magmatic silicate systems. Several experimental data lend support that cations are located in domains extending up to more than 8 Å radius, in which cationic polyhedra may be linked together either by edges or by corners. In low alkali borate glasses, transition elements such as Co, Ni, Zn exist in peculiar highly ordered domains corresponding to the presence of rigid borate units. Strong differences are observed between modifying and charge compensating cations, either concerning site geometry or medium-range organization. The use of numerical models for experimental data inversion allows to rationalize the structural behavior of the various glass components. 2001 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS glasses / glass structure / solid state spectroscopy / diffraction / cations Ordre local à courte et moyenne distance autour des cations dans les verres : une approche pluridisciplinaire Résumé. L'environnement structural des cations à courte et à moyenne distance peut être étudié par des méthodes spectroscopiques ou par diffraction des rayonnements, permettant d'avoir accès à une distribution radiale résolue chimiquement ou à la géométrie et à la symétrie du site cationique ainsi qu'à la nature de la liaison chimique. Les cations possèdent plusieurs propriétés structurales remarquables dans les verres oxydes. On observe des nombres de coordination inhabituels ou peu répandus dans les cristaux, comme la coordinence Note présentée par Guy LAVAL.
Quantitative principles of silicate glass chemistry
Solid State Communications, 2000
The optimal compositions of many commercial glasses (such as window glass) are close to the ternary 74SiO 2 ±16Na 2 O± 10CaO. Constraint theory determines the contributions of the modi®ers Na 2 O and CaO to network formation. Unexpectedly, the mechanical aspects of ionic oxide glasses are found to be quite similar to those of covalent chalcogenide glasses, which consist of network formers alone. The theory identi®es old critical experiments and predicts new ones. It correctly determines the composition of window glass, one of nature's most remarkable materials, without adjustable parameters. q
Physical Review B, 2005
The structures of mixed alkali/alkaline-earth silicate glasses containing Na, Ca, and Sr ͓xNa2O-͑3−x͒CaO-4SiO2 with x =0, 0.4, 1.0, 1.5, and Na 2 O-yCaO-͑2− y͒SrO-4SiO 2 with y =0, 1, 2͔ were investigated in order to understand the ion conduction properties, particularly the dependencies of cation activation energies on composition. Neutron diffraction, reverse Monte Carlo ͑RMC͒ modeling, and vibrational spectroscopy ͑Raman and specular reflection infrared spectroscopy͒ techniques were employed. The results show that the cations are dispersed within the Si-O network, which consists of SiO 4 tetrahedrons that are mainly Q 2 and Q 3 . The local environments of Na and Ca are quite similar, but different from that of Sr. The structural results suggest that the replacement of Ca by Na in the Na-Ca series of glasses opens up the structure and allows the formation of diffusion pathways, thus enhancing the diffusion of both Na and Ca, since Ca cations may make use of empty Na sites.
Structures of Sodium Silicate Glass
2021
The structural model of sodium silicate glass plays a crucial role in understanding the properties and the nature of binary glass and other more complicated silicate glasses. This work proposes a structural model for sodium silicate glass based on the medium-range ordering structure of silica glass and the information found from the Na2O-SiO2 phase diagram. This new model is different from previous ones. First, the sodium silica glass is both structurally and chemically heterogeneous on the nanometer scale. Secondly, the sodium cation distribution is Na2O concentration-dependent. In order to reflect the structural change with Na2O concentration, it requires two different schematic graphs to present the glass structure. The model can be extended to other binary and multiple component silicate glasses and can be experimentally verified
2008
The local structural environment and the spatial distribution of iron and aluminum ions in sodosilicate glasses with composition NaFe x Al 1-x Si 2 O 6 (x = 1, 0.8, 0.5 and 0) is studied by highresolution neutron diffraction combined with structural modeling using the Empirical Potential Structure Refinement (EPSR) code. This work gives evidence of differences in the structural behavior of Al 3+ and Fe 3+ , which are both often considered to act as network formers in chargebalanced compositions. The short-range environment and the structural role of the two cations are not composition dependent, and hence the structure of intermediate glasses can then be seen as a mixture of the structures of the two end-members. All Al 3+ is 4-coordinated for a distance ! d [ 4] Al 3+ "O = 1.76 ± 0.01Å. The high-resolution neutron data allows deciphering between two populations of Fe. The majority of Fe 3+ is 4-coordinated (! d [ 4] Fe 3+ "O = 1.87 ± 0.01Å) while the remaining Fe 3+ and all Fe 2+ (∼12% of total Fe) are 5-coordinated (! d [ 5] Fe"O = 2.01± 0.01Å). Both AlO 4 and FeO 4 are randomly distributed and connected with the silicate network in which they share corners with SiO 4 tetrahedra, in agreement with a network-forming role of those species. On the contrary FeO 5 tends to form clusters and to share edges with each other. 5-coordinated Fe is interpreted as network modifier and it turns out that, even if this coordination number is rare in crystals, it is more common in glasses in which they can have a key role on physical properties.
Neutron-and high-energy synchrotron x-ray diffraction experiments have been performed on the (75−x)SiO 2 -xB 2 O 3 -25Na 2 O x=5, 10, 15 and 20 mol% glasses. The structure factor has been measured over a broad momentum transfer range, between 0.4 and 22 Å −1 . For data analyses and modelling the Fourier transformation and the reverse Monte Carlo simulation techniques have been applied. The partial atomic pair correlation functions, the nearest neighbour distances, coordination number distributions and average coordination number values and three-particle bond angle distributions have been revealed. The Si-O network proved to be highly stable consisting of SiO 4 tetrahedral units with characteristic distances at r Si-O =1.60 Å and r Si-Si =3.0(5) Å. The behaviour of network forming boron atoms proved to be more complex. The first neighbour B-O distances show two distinct values at 1.30 Å and a characteristic peak at 1.5 (5) Å and, both trigonal BO 3 and tetrahedral BO 4 units are present. The relative abundance of BO 4 and BO 3 units depend on the boron content, and with increasing boron content the number of BO 4 is decreasing, while BO 3 is increasing.
The structure of sodium iron silicate glass – a multi-technique approach
Journal of Non-Crystalline Solids, 1999
Sodium iron silicate glasses of formula 0.3Na 2 OÁxFe 2 O 3 Á(0.7 À x)SiO 2 (0.0 T x T 0.20) have been prepared by meltquenching and their structures have been studied using X-ray photoelectron spectroscopy (XPS), neutron diraction and M ossbauer spectroscopy. XPS of surfaces fractured in ultra-high vacuum showed the presence of both Fe 2 and Fe 3 in the glasses but the proportion of the smaller oxidation state is <20% for larger x. The O 1s spectrum can be ®tted by bridging and non-bridging oxygen contributions but properties show that this description is inadequate and there are contributions from bridging oxygens, Si±O±Si, from non-bridging oxygens, Si±O ± Na and also directionally bonded Si±O±Fe. The neutron diraction and M ossbauer data indicate that iron, irrespective of oxidation state, is 4coordinated by oxygen. The Fe±O bond length decreases and the O±O bond length increases with increasing Fe 2 O 3 content. M ossbauer spectroscopy con®rms the predominance of the Fe 3 state in these glasses and indicates smaller Fe 2 concentrations than does XPS, possibly due to restructuring at the glass fracture surfaces examined in XPS. The eective Debye temperatures for Fe 2 and Fe 3 are 258 and 312 K, respectively, a consequence of the dierent M±O bond strengths of the two oxidation states. Ó
Medium range order around cations in silicate glasses
Chemical Geology, 1996
In multicomponent silicate glasses, chemically selective techniques are needed to probe the local environment of specific cations. This paper reviews recent results obtained using three methods which give access to this chemical selectivity: extended X-ray absorption fine structure (EXAFS), anomalous wide-angle X-ray scattering (AWAXS) and neutron scattering with isotopic substitutions (NSIS) in glasses. These methods allow us to determine the relationships between cation sites and the glassy network. Scattering methods give structural information around cations up to 10 A and demonstrate the existence of a local order around densely packed cations, indicating a non-random distribution of these cations in silicate glasses. These data may be used to constrain glass structure using modified Pauling rules and aid a better understanding of the macroscopic properties of silicate glasses.
Reconciling ionic-transport properties with atomic structure in oxide glasses
Physical Review B, 1995
Structural evidence for the microsegregation of alkalis in oxide glasses is reviewed and the implications for ionic transport, viz. , nearest-neighbor hopping, cooperative and correlation effects, are considered. Distinctions are drawn between the hopping of alkalis in silicate glasses, where changes in the configurations of neighboring bridging and nonbridging oxygens are expected, and alkali hopping in fully compensated aluminosilicate glasses where nonbridging oxygens are absent and conformational changes in the network are minimized. A simple expression is introduced for the microscopic energy Generally referred to as intermediate-range order, this is the regime particularly relevant to ionic diItusion as it is oveI these distances that ions will interact and where cooperative phenomena, not least the mixed alkali e6'ect, ' will be played out. While the continuous random network (CRN) of Zachariasen continues to provide a pragmatic solution for rationalizing well-defined short-range order with the absence of atomic periodicity, the process by which glass-forming bonds become partly depolymerized in a modified glass has, until recently, proved difticult to identify, let alone characterize. Considerable advances in elucidating the structure of modified oxide glasses, however, have been made through the use of new techniques, notably x-ray-absorption finestructure (XAFS) spectroscopy, but also magic angle spinning NMR (MASNMR) (Refs. 6-9) isotopic substitution neutron scattering' as well as the traditional spectroscopies of IR, " Raman, ' and x-ray photoemission spectroscopy (XPS). ' ' Experimental findings from these studies have been corroborated by recent sophisticated molecular dynamics (MD) simulations, ' ' all of