FABRICATION, CHARACTERIZATION AND FORMATION MECHANISM OF PB1.83MG0.29NB1.71O6.39 PYROCHLORE

Pb1.83Mg0.29Nb1.71O6.39 (PMN) pyrochlore ceramics were fabricated from solid state reaction of mixed oxides and by partial oxalate methods. For both methods the pyrochlore crystal structure was not formed direc tly but via a sequence of intermediate reactions. However, the formati on temperature of PMN pyrochlore was lower for the partial oxalate met hod due to the higher reactivity of these powders. Microstructural inv estigation of pellets produced from mixed oxides and partial oxalate p owders prepared using columbite (MgNb2O6) revealed only single-phase p yrochlore whereas those produced from partial oxalate powders made usi ng uncalcined Mg and Nb oxides contained clusters of perovskite grains with intergranular Mg-rich phases. Pyrochlore ceramics produced from partial oxalate powders showed higher dielectric constant but lot-tier dielectric loss than those produced from mixed oxides. (C) 1997 Elsev ier Science Limited.