Thermovaporous synthesis of complicated oxides

Abstract

In this paper the results of investigations of the mechanism and kinetics of reactions of formation of fine crystalline complicated oxides in thermovaporous and solvothermal conditions are presented. The processes of formation of complicated oxides, magnesian spinel (MgAl₂O₄), aluminate of lanthanum (LaAlO₃), gahnite (ZnAl₂O₄), barium hexaferrite (BaFe₁₂O₁₉), lithium metaniobate (LiNbO₃), and yttrium-aluminum garnet (Y₃Al₅O₁₂) were studied. Synthesis of complicated oxides carried out both in solvothermal (T = 250−350°C) and in supercritical conditions (T > 380 °C) in medium of water fluid. As raw materials were intermixtures of solid simple oxides or hydroxides and, sometimes, oxides with solution of compound containing doping component. It was found that process of complicated oxides formation proceeds into solid phase. In all cases the formation of complicated oxides has gone through a stage of existence of intermediate crystalline substance with Me(OH)_n structure. The properties of synthesized complicated oxides mainly are determinated by peculiarities of this intermediate. It is possible to influence on properties of a finished product by changing conditions of formation of intermediate.