The occurrence of interpenetration in metal–organic and inorganic networks has been investigated by a systematic analysis of the CSD and ICSD structural databases. For this purpose, a novel version of TOPOS (a program package for multipurpose crystallochemical analysis) has been employed, where the procedure of recognition of interpenetrating nets is based on the representation of a crystal structure as a finite reduced graph. In this paper we report a comprehensive list (301 Refcodes) of interpenetrating metal–organic 3D structures from CSD, that are analyzed on the basis of their topologies. Interesting trends and novel features have been observed and distinct classes of interpenetrating nets have been envisaged, depending on the relationships of the individual motifs.

Interpenetrating metal–organic and inorganic 3D networks: a computer-aided systematic investigation. Part I. Analysis of the Cambridge structural database

Mullite has achieved outstanding importance as a material for both traditional and advanced ceramics because of its favourable thermal and mechanical properties. Mullite displays various Al to Si ratios referring to the solid solution Al 4+2 x Si 2−2 x O 10− x , with x ranging between about 0.2 and 0.9 (about 55 to 90 mol% Al 2 O 3 ). Depending on the synthesis temperature and atmosphere mullite is able to incorporate a number of transition metal cations and other foreign atoms. The crystal structure of mullite is closely related to that of sillimanite, which is characterized by chains of edge-connected AlO 6 octahedra running parallel to the crystallographic c -axis. These very stiff chains are cross-linked by tetrahedral chains consisting of (Al,Si)O 4 tetrahedra. In more detail: Parallel to a the tetrahedra are linked to the relatively short more stiff Al–O(A, B) bonds, whereas parallel b they are linked parallel to the relatively long more compliant Al–O(D) bonds. In mullite some of the oxygen atoms bridging the tetrahedra are removed for charge compensation. This gives rise to the formation of oxygen vacancies and of T 3 O groups (so-called tetrahedral triclusters). The anisotropy of the bonding system of mullite has a major influence on the anisotropy of its physical properties. For example: • the highest longitudinal elastic stiffness is observed parallel c , but lower ones parallel a and especially parallel b , • the maximum of the thermal conductivity occurs parallel c , but maller ones parallel a and especially parallel b , • large thermal expansion especially parallel b , • fastest crystal growth and highest corrosion parallel c . Heat capacity and thermal expansion measurements of mullite display reversible anomalies in the temperature range between about 1000 and 1200 °C. It is believed that tetrahedral cations, bridging O atoms, and O vacancies undergo dynamical site exchange processes at high temperatures. At lower temperatures the dynamic disorder may transform to a static one. Diffraction experiments revealed that also partially ordered states may exist.

Structure and properties of mullite—A review

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment: Editorial

We review the various kinds of symbols used to characterize the topology of vertices in 3-periodic nets, tiles and polyhedra, and symbols for tilings, making a recommendation for uniform nomenclature where there is some confusion and misapplication of terminology.

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Vertex-, face-, point-, Schläfli-, and Delaney-symbols in nets, polyhedra and tilings: recommended terminology

During the last century, inorganic oxide compounds laid foundations for materials synthesis, characterization, and technology translation by adding new functions into devices previously dominated by main-group element semiconductor compounds. Today, compounds with multiple anions beyond the single-oxide ion, such as oxyhalides and oxyhydrides, offer a new materials platform from which superior functionality may arise. Here we review the recent progress, status, and future prospects and challenges facing the development and deployment of mixed-anion compounds, focusing mainly on oxide-derived materials. We devote attention to the crucial roles that multiple anions play during synthesis, characterization, and in the physical properties of these materials. We discuss the opportunities enabled by recent advances in synthetic approaches for design of both local and overall structure, state-of-the-art characterization techniques to distinguish unique structural and chemical states, and chemical/physical properties emerging from the synergy of multiple anions for catalysis, energy conversion, and electronic materials.

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Expanding frontiers in materials chemistry and physics with multiple anions

The refractive indices of 509 oxides and 55 fluorides were analyzed using two forms of a one-term Sellmeier equation: (1) 1/(n2−1)=−A/λ2+B, where A, the slope of the plot of (n2−1)−1 versus λ−2 in units of 10−16 m2, gives a measure of dispersion and B, the intercept of the plot at λ=∞, gives n∞=(1+1/B)1/2 and (2) n2−1=EdEo/(Eo2−(ℏω)2), where ℏω=the photon energy, Eo=the average single oscillator (Sellmeier) energy gap, and Ed=the average oscillator strength, which measures the strength of interband optical transitions. Form (1) was used to calculate n at λ=589.3 nm (nD) and n at λ=∞ (n∞), and the dispersion constant A. The total mean polarizabilility for each compound was calculated using the Lorenz–Lorentz equation: αe=3/4π [(Vm) (n∞2−1)/(n∞2+2)], where Vm is the molar volume in A3. Provided for each compound are: nD, n∞, Vm, 〈αe〉, 〈A〉, 〈B〉, 〈Ed〉, 〈Eo〉, the literature reference, the method of measurement of n and estimated errors in n. Results obtained by prism, infrared reflectivity, ellipsometry, and i...

Refractive Index and Dispersion of Fluorides and Oxides

We studied a set of 15 reference clays from The Clay Minerals Society (CMS) Source Clays repository. Our aim was to use them as reference materials in our version of the QUAX mineral database. The QUAX software (Quantitative Phase-Analysis with X-ray Powder Diffraction) has been used successfully at the KTB site (German Continental Deep Drillling) to determine mineral assemblages quickly, in an automatic fashion, on a large number of samples (∼40,000). It was also applied to Quaternary marine sediments of the Japan Sea. Our current research focuses on marine and lacrustrine sediments from the Arctic Ocean and Siberia. QUAX is a full-pattern method using a reference materials database. The quality of a particular quantification depends on the availability of the relevant mineral phases in the database. Our aim is to extend and improve the database continuously with new data from our current projects, particularly from clay and feldspar minerals. A reference material in the QUAX software must be monomineralic. Before X-ray diffraction (XRD) patterns of CMS clays could be added to the database, quantification of any impurities was necessary. After measuring the bulk material by XRD, the <2 µm fraction was separated because we assumed it would contain the smallest amount of impurities. Here we present grain-size data, XRD data and X-ray fluorescence (XRF) data for this clay-sized fraction. The results of chemical and mineralogical preparation techniques and (elemental) analysis methods were combined. For XRD, random and oriented clay-aggregate samples as well as pressed pellets for QUAX analysis were prepared. Semi-quantitative clay mineral determinations were run for comparison.

INVESTIGATION OF THE CLAY FRACTION (<2 μm) OF THE CLAY MINERALS SOCIETY REFERENCE CLAYS

The layered silicate (LS) modification and processing parameters applied control the morphology of the LS/polymer composites. Here, increasing the surface area of the LS particles by using alternative drying processes increases dispersion towards a more typical nanocomposite morphology, which is a basic requirement for promising flame retardancy. Nevertheless, the morphology at room temperature does not act itself with respect to flame retardancy, but serves as a prerequisite for the formation of an efficient surface protection layer during pyrolysis. The formation of this residue layer was addressed experimentally for the actual pyrolysis region of a burning nanocomposite and thus our results are valid without any assumptions or compromises on the time period, dimension, surrounding atmosphere or temperature. The formation of the inorganic-carbonaceous residue is influenced by bubbling, migration, reorientation, agglomeration, ablation, and perhaps also delamination induced thermally and by decomposition, whereas true sintering of the inorganic particles was ruled out as an important mechanism. Multiple, quite different mechanisms are relevant during the formation of the residue, and the importance of each mechanism probably differs from one nanocomposite system to another. The main fire protection effect of the surface layer in polymer nanocomposites based on non-charring or nearly non-charring polymers is the increase in surface temperature, resulting in a substantial increase in reradiated heat flux (heat shielding). Copyright © 2010 John Wiley & Sons, Ltd.

Layered silicate epoxy nanocomposites: formation of the inorganic‐carbonaceous fire protection layer

The formation of aluminum rich mullites Al4 + 2x Si2 − 2xO10 − x with x > 23 has been studied at annealing temperatures between 700 and 1650 °C. Calcination of the amorphous precursor at 700 °C yields a mullite with 88 mol% Al2O3 corresponding to an x-value of 0·809. Simultaneously, a γ-alumina phase is formed. Further increase of the annealing temperature yields an increase in the aluminum incorporation up to 92·1 mol% Al2O3 at 1000 °C derived from the refined lattice constants. This is the highest amount of Al observed so far in a mullite except the supposed end member ι-Al2O3 which, however, has not yet been established unambiguously. Above 1000 °C, the aluminum content in mullite is reduced. This is accompanied by a transformation of the spinel-type phase to a superstructure of a θ-alumina like phase. The final product at 1650 °C consists of 34 mol% of a ‘normal’ mullite with x = 0·32 and 66 mol% corundum.

Formation of aluminum rich 9:1 mullite and its transformation to low alumina mullite upon heating

An extensive set of refractive indices determined at λ = 589.3 nm ( n D ) from ~2600 measurements on 1200 minerals, 675 synthetic compounds, ~200 F-containing compounds, 65 Cl-containing compounds, 500 non-hydrogen-bonded hydroxyl-containing compounds, and ~175 moderately strong hydrogen-bonded hydroxyl-containing compounds and 35 minerals with very strong H-bonded hydroxides was used to obtain mean total polarizabilities. These data, using the Anderson-Eggleton relationship
 α T = ( n D 2 − 1 ) V m 4 π + ( 4 π 3 − c ) ( n D 2 − 1 ) where α T = the total polarizability of a mineral or compound, n D = the refractive index at λ = 589.3 nm, V m = molar volume in A 3 , and c = 2.26, in conjunction with the polarizability additivity rule and a least-squares procedure, were used to obtain 270 electronic polarizabilities for 76 cations in various coordinations, H 2 O, 5 H x O y species [(H 3 O) + , (H 5 O 2 ) + , (H 3 O 2 ) − , (H 4 O 4 ) 4− , (H 7 O 4 ) − ], NH 4 + , and 4 anions (F − , Cl − , OH − , O 2− ). Anion polarizabilities are a function of anion volume, V an , according to α − = α − 0 ⋅ 10 − N o / V an 1 . 20 where α − = anion polarizability, α − o = free-ion polarizability , and V an = anion molar volume. Cation polarizabilities depend on cation coordination according to a light-scattering (LS) model with the polarizability given by α ( C N ) = ( a 1 + a 2 C N e − a 3 C N ) − 1 where CN = number of nearest neighbor ions (cation-anion interactions), and a 1 , a 2 , and a 3 are refinable parameters. This expression allowed fitting polarizability values for Li + , Na + , K + , Rb + , Cs + , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Mn 2+ , Fe 2+ , Y 3+ , (Lu 3+ -La 3+ ), Zr 4+ , and Th 4+ . Compounds with: (1) structures containing lone-pair and uranyl ions; (2) sterically strained (SS) structures [e.g., Na 4.4 Ca 3.8 Si 6 O 18 (combeite), Δ = 6% and Ca 3 Mg 2 Si 2 O 8 (merwinite), Δ = 4%]; (3) corner-shared octahedral (CSO) network and chain structures such as perovskites, tungsten bronzes, and titanite-related structures [e.g., MTiO 3 (M = Ca, Sr, Ba), Δ = 9–12% and KNbO 3 , Δ = 10%]; (4) edge-shared Fe 3+ and Mn 3+ structures (ESO) such as goethite (FeOOH, Δ = 6%); and (5) compounds exhibiting fast-ion conductivity, showed systematic deviations between observed and calculated polarizabilities and thus were excluded from the regression analysis. The refinement for ~2600 polarizability values using 76 cation polarizabilities with values for Li + → Cs + , Ag + , Be 2+ → Ba 2+ , Mn 2+/3+ , Fe 2+/3+ , Co 2+ , Cu +/2+ , Zn 2+ , B 3+ → In 3+ , Fe 3+ , Cr 3+ , Sc 3+ , Y 3+ , Lu 3+ → La 3+ , C 4+ → Sn 4+ , Ti 3+/4+ , Zr 4+ , Hf 4+ , Th 4+ , V 5+ , Mo 6+ , and W 6+ in varying CN’s, yields a standard deviation of the least-squares fit of 0.27 (corresponding to an R 2 value of 0.9997) and no discrepancies between observed and calculated polarizabilities, Δ > 3%. Using
 n D = 4 π α ( 2 . 26 − 4 π 3 ) α + V m + 1 the mean refractive index can be calculated from the chemical composition and the polarizabilities of ions determined here. The calculated mean values of n D > for 54 common minerals and 650 minerals and synthetic compounds differ by In a comparison of polarizability analysis with 68 Gladstone-Dale compatibility index (CI) (Mandarino 1979, 1981) values rated as fair or poor, we find agreement in 32 instances. However, the remaining 36 examples show polarizability Δ values

Reinhard X. Fischer

Papers

Refractive Index and Dispersion of Fluorides and Oxides

INVESTIGATION OF THE CLAY FRACTION (<2 μm) OF THE CLAY MINERALS SOCIETY REFERENCE CLAYS

Layered silicate epoxy nanocomposites: formation of the inorganic‐carbonaceous fire protection layer

Formation of aluminum rich 9:1 mullite and its transformation to low alumina mullite upon heating

Empirical electronic polarizabilities of ions for the prediction and interpretation of refractive indices: Oxides and oxysalts