Effect of the Addition of Potassium or Lithium on the Columbite Precursor Microstructure

The Pechini method was used to synthesise magnesium niobate (MN) powders with stoichiometric control. K- and Li-doped MN in the range 0.1-5.0 mol% of dopants were obtained at relatively lower temperatures than is possible with the conventional mixture of oxides. Results from BET analysis indicated that the doped powders had a lower surface area and attrition milling promoted an increase in surface area values for all powders. The Rietveld method was used to calculate the mean crystallite size and the microstrain in the crystal. With additions of up to 5.0 mol% of K or 2.0 mol% of Li, it was possible to obtain MN as a solid solution. Both dopants changed the cell parameters of the columbite phase crystal, reduced the microstrain, and increased the main crystallite size. Analysis of results from SEM indicates that powders prepared with addition of dopants are more agglomerate than pure lead magnesium niobate powder. 24 refs.