The formation process of complex lead-containing niobates

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(Mg1/3Nb2/3)O3, Pb(Sc1/2Nb1/2)O3, Pb(In1/2Nb1/2)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.