Mullite is certainly one of the most important oxide materials for both conventional and advanced ceramics. Mullite belongs to the compositional series of orthorhombic aluminosilicates with the general composition Al 2 (Al 2+2x Si 2-2x )O 10-x . Main members are sillimanite (x = 0), stoichiometric 3/2-mullite (x = 0.25), 2/1-mullite (x = 0.40), and the SiO 2 -free phase ι-alumina (x = 1, crystal structure not known). This study gives an overview on the present state of research regarding single crystal mullite. Following a short introduction, the second part of the review focuses on the crystal structure of mullite. In particular, the characteristic mullite-type structural backbone of parallel chains consisting of edge-sharing MO 6 octahedra and their specific cross-linkage by TO 4 tetrahedra is explained in detail, the role of cation disorder and structural oxygen vacancies is addressed, and the possibility of cation substitution on different sites is discussed. The third part of the study deals with physical properties being relevant for technical applications of mullite and includes mechanical properties (e.g., elasticity, compressibility, strength, toughness, creep), thermal properties (e.g., thermal expansion, heat capacity, atomic diffusion, thermal conductivity), electrical conductivity, and optical properties. Special emphasis is put on structure-property relationships which allow for interpretation of corresponding experimental data and offer in turn the possibility to tailor new mullite materials with improved properties. Finally, the reported anomalies and discontinuities in the evolution of certain physical properties with temperature are summarized and critically discussed.

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The refractive indices of 509 oxides and 55 fluorides were analyzed using two forms of a one-term Sellmeier equation: ͑1͒ 1/(n 2 Ϫ1)ϭϪA/ 2 ϩB, where A, the slope of the plot of (n 2 Ϫ1) Ϫ1 versus Ϫ2 in units of 10 Ϫ16 m 2 , gives a measure of dispersion and B, the intercept of the plot at ϭϱ, gives n ϱ ϭ(1ϩ1/B) 1/2 and ͑2͒ n 2 Ϫ1ϭE d E o /(E o 2 Ϫ(ប) 2), where បϭthe photon energy, E o ϭthe average single oscillator ͑Sellmeier͒ energy gap, and E d ϭthe average oscillator strength, which measures the strength of interband optical transitions. Form ͑1͒ was used to calculate n at ϭ589.3 nm (n D) and n at ϭϱ (n ϱ), and the dispersion constant A. The total mean polarizabilility for each compound was calculated using the Lorenz-Lorentz equation: ␣ e ϭ3/4 ͓(V m) (n ϱ 2 Ϫ1)/(n ϱ 2 ϩ2)], where V m is the molar volume in Å 3. Provided for each compound are: n D , n ϱ , V m , ͗␣ e ͘, ͗A͘, ͗B͘, ͗E d ͘, ͗E o ͘, the literature reference, the method of measurement of n and estimated errors in n. Results obtained by prism, infrared reflectivity, ellipsometry, and interference methods are compared. Consistency of dispersion values among like compounds and structural families is used to evaluate the accuracy of refractive index data. Dispersion values range from 40 to 260ϫ10 Ϫ16 m 2 with the majority of values in the range of 60-100ϫ10 Ϫ16 m 2. High dispersion is associated with s 2 , p 6 , d 10 , and transition metal ions, H 2 O, and crystalline hydrates, whereas normal dispersion values are found in borates, aluminates, gallates, silicates, germanates, phosphates, and sulfates not containing H 2 O or any of the above ions. Exceptionally high dispersion is observed in liquid H

The synthesis of host-guest composites consisting of entrapped strands of poly(methylmethacrylate) (PMMA) within the pores of inorganic hosts is described. Methyl methacrylate was adsorbed into microporous hosts including zeolite NaY, mordenite, beta, and ZSM-5 and then polymerized. Adsorption and polymerization was also performed in the mesoporous materials MCM-41 and MCM-48. The adsorption of methyl methacrylate (MMA) and its conversion to PMMA was followed by FTIR spectroscopy. Nitrogen sorption isotherms confirm the filling of the micro-and mesopores with the polymer. Thermogravimetry (TGA) shows that the polymer content of the composites increases with increasing pore volume, while no polymer deposition on the external host surface is detected with scanning and transmission electron microscopy. The polymers confined in the 6-35 Å diameter channels of the hosts do not show characteristic bulk behavior with respect to their glass transition temperature.