Preparation of pyrochlore-free PMN powder by semi-wet chemical route

Wet chemical route was used to prepare lead magnesium niobate (PMN)powders by both the direct and the quot;columbitequot; methods. The columbite (MgO.Nb2O5) phase was prepared by calcining a homogeneous mixture of magnesium oxalate and niobium oxide powder in the temperature range of 1000-1050 deg C Three different lead precursors, i.e., lead hydroxide, lead acetate and lead formate were investigated. In some cases, 3% excess MgO was also added. Pyrochlore-free PMN powder was obtained only in the case of formate precursors with 3% excess MgO processed via the columbite route. The phase pure powder was compacted, sintered at 1150 deg C for 2 h in a lead rich atmosphere and dielectric constant of the sintered body was measured. The dielectric constant was measured to be 10,335 at room temperature and at a frequency of 100 Hz. The maximum dielectric constant was found to be 79,100 at 4.18 MHz