The formation process of complex lead-containing niobates

Abstract

The sequence of phases formed during the solid state reaction in oxide mixtures from 500 to 900°C has been studied by x-ray diffraction in ternary system PbO:Nb₂O₅:X, where X = MgO, ZnO, Sc₂O₃ or In₂O₃. The following compositions have been investigated: 3PbO:2Nb₂O₅:X, 2PbO:Nb₂O₅:X, 5PbO:2Nb₂O₅:X, 3PbO:Nb₂O₅:X and 4PbO:Nb₂O₅:X, the concentration of X phase being taken from 0 to 1.2 molar parts.

The perovskite structure Pb(Mg_1/3Nb_2/3)O₃, Pb(Sc_1/2Nb_1/2)O₃, Pb(In_1/2Nb_1/2)O₃ is found to be formed in a complicated multistage process with several intermediate products during the reaction. The end product is sintered at temperatures beyond 800°C in a reaction between two phases with a pyrochlore structure: Pb₅·Nb₄O₁₅ and Pb₃Nb₂O₈. The diagrams of forming the end products during reactions (perovskite and pyrochlore—cubic) are proposed.