Dielectric properties due to excess PbO and MgO in lead magnesium niobate ceramics

The dielectric properties of lead magnesium niobate (PMN) have been investigated as a function of the amount of excess PbO and excess MgO in the range of 0–40 m/o and 0–150 m/o, respectively. In the case of PMN with both 40 m/o excess PbO and 5 m/o excess MgO added, the pyrochlore phase was completely eliminated. And there was great increase in grain size and dielectric constant as compared to PMN with no excess MgO. But in the range of 10–150 m/o excess MgO, the dielectric constant tended to decrease with increase in the amount of excess MgO even though no pyrochlore phase was found to be present. Also, the MgO rich second phase appeared to precipitate. These results can be explained by microstructure analysis.