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 “columbite” 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 °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 °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.