FERROELECTRICITY IN THE SYSTEM PB1-XBAX(MG1/3NB2/3)O3

A series of ceramics of composition Pb(1-x)Ba(x)(Mg1/3Nb2/3)O3 has been prepared, with x varying in regular intervals between 0 and 1. The mixed oxide processing route to lead barium magnesium niobate (PBMN) powders involves the preparation of magnesium niobate, MgNb2O6, as an intermediate compound, in order to inhibit the formation of pyrochlore phase. All samples in the composition range are sintered by conventional methods, except the x = 1 composition, for which fast firing is used. The weak-field dielectric response has been measured for each composition, and the results interpreted in terms of the variation in chemical composition between the samples. The niobium-oxygen coordination polyhedra are considered to be the basic polar units, and the function of the Pb2+ ions is to couple the individual niobium-oxygen octahedra together to form a ferroelectric network. The effect of the Ba2+ ion is to weaken this coupling. The ferroelectric response of each composition is thought to be due to lead-rich microregions, which become progressively smaller as the relative barium content is increased. The rate of fall-off of relative permittivity with increasing barium content suggests that lead-rich ferroelectric clusters of ions persist to high values of x. An assessment is made of the contribution of this work to the development of structure-dielectric property relationships in relaxor ferroelectrics.