Phase Evolvement in the Calcination of Lead Magnesium Niobate and Lead Iron Niobate Powders

The phase evolvement in the process of calcination of the mixtures of MgNb₂O₆/Pb₃O₄ and FeNbO₄/Pb₃O₄ and MgNb₂O₆-FeNbO₄/Pb₃O₄ was investigated by using X-ray diffraction analysis. The mechanisms involved are found to be different for the pyrochlore phases during the calcination of lead magnesium niobate and lead iron niobate powders. In the calcination of PFN, it undergoes a sequence of the decomposition of the precursor FeNbO₄ at a lower temperature, formation of a pyrochlore phase and later the transformation from pyrochlore to perovskite phase. In the case of PMN, the formation of pyrochlore is more likely related to the residual Nb₂O₅ inherited from the precursor of MgNb₂O₆. The possible reaction sequences are proposed in this letter.