FORMATION OF LEAD MAGNESIUM NIOBATE PEROVSKITE FROM NIOBATE PRECURSORS HAVING VARYING MAGNESIUM CONTENT

Formation of lead magnesium niobate (PMN) perovskite phase using a col umbite type of precursor together with the addition of excess MgO has been investigated, When MgO and Nb2O5 are reacted with 1:1 stoichiomet ry, a minor amount (similar to 2%) of Mg4Nb2O9 is formed along with th e columbite-type phase which in turn could lead to the formation of a minor amount of ''free Nb2O5'' in the precursor This may be the reason for the formation of small amounts of pyrachlore phase during the syn thesis of PMN perovskite from the stoichiometric I:1 precursor, Howeve r, it has been found that the perovskite phase can easily be stabilize d by the addition of a large excess of MgO in the precursor, although this leads to additional Mg-Nb-O phase Mg4Nb2O9, besides the columbite -type phase MgNb2O6. It has been shown that, after this precursor reac ts with PbO to form the PMN perovskite, the excess Mg present in the M g-rich niobate precursor separates out as MgO, as evidenced by X-ray d iffraction, which can be removed by leaching with dilute nitric acid, thus forming pure PMN.