Thermovaporous synthesis of complicated oxides

The mechanism and kinetics of reactions of formation of fine crystalline complex oxides under thermovaporous and solvothermal conditions were analysed. The formation of magnesian spinel (MgAl2O4), lanthanum aluminate (LaAlO3), gahnite (ZnAl2O4), barium hexaferrite (BaFe12O19), lithium metaniobate (LiNbO3), and yttrium-aluminium garnet (Y3Al5O12) was studied. The synthesis of these oxides was carried out both in solvothermal (T = 250-350 C) and supercritical conditions (T > 380 C) in aqueous media. Raw materials were intermixtures of solid simple oxides or hydroxides and, occasionally, oxides with solution of compound containing dopants. It was found that the process of complex oxide formation proceeds in the solid phase. In all cases, the formation of complex oxides involves the existence of an intermediate crystalline substance with the Me(OH)n structure. The properties of the synthesised complex oxides are mainly determined by the peculiarities of this intermediate. It is possible to influence the properties of a finished product by changing the formation conditions of the intermediate. 11 refs.