Glass formation and properties of glasses in the system SrO–B2O3–SiO2–xAl2O3 (x=0; 10 mol.%)

The paper shows the prospects of the system SrO–Al2O3–B2O3–SiO2 as a basis for the synthesis of new vitreous and glass-ceramic materials, which are widely used as electrical insulated and high-temperature coatings, for sealing of solid oxide fuel cells, and in the production of heat resistant materials. We experimentally established the conditions of glass formation, regions of glass-forming melts and properties of glasses, the chemical composition of which is limited by the following content of components (mol.%): SrO 30–80, B2O3 10–60, SiO2 10–60, and Al2O3 0–10. It is shown that during the synthesis of glasses in the corundum crucible at the temperature of 13500С the region of glass formation in the system SrO–B2O3–SiO2 is limited by the following content of components (mol.%): SrO 30–60, B2O3 10–60, and SiO2 10–50. It is found that the introduction of Al2O3 to the composition of these glasses expands the region of glass formation towards increase of the SiO2 content in the glass up to 60 mol.%. Experimentally determined values of glass properties are within the following limits: coefficient of linear thermal expansion (67–118)10–7 К–1; glass transition temperature 570–6600С; dilatometric softening point 580–7000С; and density 2.62–3.71 g cm–3. The established patterns of influence of the components and conditions of glass formation on the physical and chemical characteristics of glasses may serve as an experimental basis for designing of new materials with a complex of specified properties, which allows solving the problems of their practical use.

Thermal History Dependent Al Distribution in Aluminum Substituted Strontium Hexaferrite

Single crystals of aluminum substituted strontium hexaferrite SrFe12–xAlxO19 were grown from sodium oxide based flux. The substitution level aimed for was x = 1.2. Annealing experiments performed on single crystals show that the Al distribution on the five iron sites of the hexaferrite structure depends on the annealing time at 900 °C. Single crystal X-ray diffractometry shows that annealing a crystal after the initial synthesis has an impact on the Al content on the octahedrally and tetrahedrally coordinated sites. Furthermore, it was found that heating in a corundum crucible increases the overall Al content. Magnetic measurements show that annealing in a platinum or corundum crucible decreases coercivity and remanence while the saturation magnetization is hardly influenced.

Mn3Nb6O11 und Mg3Nb6O11 - Darstellung von Einkristallen und Strukturverfeinerung / Mn3Nb6O11 and Mg3Nb6O11 - Preparation of Single Crystals and Structure Refinement

Dark green single crystals of Mg3Nb6O11 have been prepared by heating a pellet containing MgO, Nb, Nb2O5 (15:14:8) at 1550 °C in a Nb-container. Single crystals of the isotypic Mn3Nb6O11 were formed by heating a mixture of LiF, MnF2, Mn, NbO, NbO2 (1:1:1:1:2) in a corundum crucible at 750 °C. Both compounds crystallize in the trigonal space group P3̄ m 1 (Z = 1) with a = 6.041(1), c = 7.466(1) and a = 6.080(1), c = 7.627(1), respectively. The positional parameters for Mg3Nb6O11 are in excellent agreement with those determined by Marinder from powder data.

Al7Te10 — das erste Chalcogenid mit zweiwertigem Aluminium / Al7Te10 — the First Chalcogenide of Divalent Aluminum

Al7Te10 is prepared from a melt of the elements in stoichiometric amounts in a corundum crucible contained in a sealed quartz ampoule. The ruby red cube shaped crystals are stable below 840 K. The structure of Al7Te10 (R32-D37 a = 1439.5 pm, c = 1793.2 pm, Z = 6, R = 0.03) is a distorted defect variant of a tetrahedral arrangement of the 4H-polytype. The central unit, a double barrelane [Te4Al4-Al4Te4], contains an Al -Al bond of 260 pm, which is somewhat longer (n = 0.83) than an expected single bond (250 pm, n = 1). This homopolar bond disturbs the electrostatically favorable (Al-Te-)n sequence in the structure which is compensated by the occurrence of four-membered Al2Te2 rings. Al7Te10 is a Zintl phase according to 1/2{[Al2+-Al2+][Al3+]12[Te2-]20} and exhibits semiconducting and diamagnetic behaviour.