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 ((MgONb2O5)-Nb-.) phase was prepared by calcining a homogeneous mixture of magnesium oxalate and niobium oxide powder in the temperature range of 1000-1050 degrees 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 degrees 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. (c) 2005 Elsevier B.V. All rights reserved.