Calcination of the Precursors of Perovskites in the Ternary System of MgO-Fe_2O_3-Nb_2O_5

The phase development in the calcination of the precursors for the pseudo-binary system of PFN-PMN was investigated systematically by XRD method. During the calcination of Mg-rich mixtures, a kind of Mg-rich niobate, Mg4Nb2O9 forms along with the major phase MgNb2O6 (MN), whereas in the calcination of Fe-rich mixture, there is no Mg4Nb2O9 formed, indicating Fe2O3 (or FeNbO4) may inhibit the formation of Mg4Nb2O9. The appearance of Mg4Nb2O9 is directly related to the formation of pyrochlore in the calcinations of perovskite. MN starts to form at a temperature as low as 650℃, a temperature much lower than its ferric counterpart FN. Therefore the reactivity of Fe2O3 is inferior to that of MgO in the low temperature region.