Einfluß von Instoechiometrien auf die dielektrischen Eigenschaften von Blei-Barium-Magnesium-Niobat-Keramiken

Mixtures of ferroelectric and paraelectric materials offer the possibility to develop materials with temperature directed coefficient of capacity as used in ceramic multilayer capacitors of type1. Lead- Barium-Magnesium-Niobate ceramics of the general composition Pb1-xBax(Mgy/3Nb2/3)O(8+y)/3 have been prepared to investigate the influence of composition, synthesis conditions and technological variations on structural and dielectric properties of such ceramics. A complete solid solution with perovskite structure was found in the entire compositional range. Lattice constant increases with increasing Ba2plus content. Apart from the Pb2plus/Ba2plus ratio the dielectric properties depend on Mg2plus content and sintering atmosphere. This behaviour is connected with the appearance of a pyrochlor minor phase as well as with PbO evaporation starting at 900 degree. The influence of the Mg2plus content on the occurence of pyrochlor minor phase and PbO evaporation decreases with increasing Ba2plus content. Reaction mechanism of pyrochlor minor phase formation as well as the microstructure of the sintered pellets is discussed.