The formation of silica nano- and microparticles has been studied during growth by the modified Stöber-Fink-Bohn (SFB) method. It has been experimentally found that the density and fractal structure of particles vary with size as they grow from 70 to 2200 nm. We propose a model of particle structure which is a dense primary particle core and is composed of concentric secondary particle shells terminating in dense primary particle layers.

Scheelite-type compounds with the general formula (A1,A2)(n)[(B1,B2)O(4)](m) (2/3 ≤ n/m ≤ 3/2) are the subject of large interest owing to their stability, relatively simple preparation, and optical properties. The creation of cation vacancies (□) in the scheelite-type framework and the ordering of A cations and vacancies can be a new factor in controlling the scheelite-type structure and properties. For a long time, cation-deficient Nd(3+):M(2/7)Gd(4/7)□(1/7)MoO(4) (M = Li, Na) compounds were considered as potential lasers with diode pumping. They have a defect scheelite-type 3D structure (space group I4(1)/a) with a random distribution of Li(+)(Na(+)), Gd(3+), and vacancies in the crystal. A Na(2/7)Gd(4/7)MoO(4) single crystal with scheelite-type structure has been grown by the Czochralski method. Transmission electron microscopy revealed that Na(2/7)Gd(4/7)MoO(4) has a (3 + 2)D incommensurately modulated structure. The (3 + 2)D incommensurately modulated scheelite-type cation-deficient structure of Na(2/7)Gd(4/7)MoO(4) [super space group I4 (α-β0,βα0)00] has been solved from single-crystal diffraction data. The solution of the (3 + 2)D incommensurately modulated structure revealed the partially disordered distribution of vacancies and Na and Gd cations. High-temperature conductivity measurements performed along the [100] and [001] orientation of the single crystal revealed that the conductivity of Na(2/7)Gd(4/7)MoO(4) at T = 973 K equals σ = 1.13 × 10(-5) Ω(-1) cm(-1).

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SiC nanowires (NWs) with diameters of 20-200 nm and lengths from tens to hundreds of micrometers have been synthesized by the carbothermal reduction of colloidal silica. The morphology and microstructure of NWs have been studied in detail by electron microscopy techniques. SiC NWs have been found to be hexagonal prisms, ''bamboo-like'' nanorods and nanobelts. The NWs with a [111] growth axis are hexagonal prism nanorods, while the nanobelts have growth directions varying from [110] to [113]. It has been found that NW growth proceeds in two stages. Initially, SiC crystallites grow on the carbon fiber surface. These crystallites serve as seeds, on which the SiC NWs nucleate and grow. The crystallites containing microtwins and stacking faults (SFs) with a preferential [111] growth direction give rise to the growth of nanorods, while the nanobelts start growing on the (111) facets of relatively perfect crystallites. Wires with core (SiC)-shell (SiO 2 ) structure have been obtained under special temperature treatment in air. The core-shell structure has been confirmed by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX) mapping techniques.