Lead magnesium niobate ceramic dielectrics having low sintering temperatures

Claim 1

A lead magnesium niobate perovskite-rich dielectric material which is capable of being formed from a mixture of oxide powders which is sintered at relatively low temperatures, comprising: (a) lead-containing oxide component (expressed in terms of oxides) consisting essentially of 2 to 5 weight percent MgO, 15 to 30 weight percent Nb 2 O 5 , 0.5 to 7 weight percent Fe 2 O 3 , 0.5 to 5 weight percent WO 3 and PbO wherein the amount of lead (based on the total lead in the dielectric material) is between about 85 to 110 atomic percent of that required on a stoichiometric basis to satisfy the relationship: xPb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3.yPb(Fe.sub.1/2 Nb.sub.1/2)O.sub.3. zPb(Fe.sub.2/3 W.sub.1/3)O.sub.3 (based on the total iron and niobium in the dielectric material) wherein x is between about 0.8 and 0.92, y is between about 0.005 and 0.165 and z is between about 0.035 and 0.075; wherein the atomic ratio of tungsten to iron (based on the total tungsten and iron in the dielectric material) is less than about 0.49:1; and wherein the atomic ratio of magnesium to niobium (based on the total magnesium and niobium in the dielectric material) is between about 0.55:1 and 0.42:1, (b) cadmium component (expressed in terms of CdO) in an amount of about 1 to 5 weight percent based on the dielectric material, (c) transition metal component (expressed in terms of oxides) of at least one of TiO 2 , ZrO 2 and HfO 2 , said transition metal component being in an amount sufficient to increase the insulation resistance of an otherwise identical material but not containing the transition metal component, and (d) sintering aid residue (expressed in terms of oxides) in an amount of about 0.2 to 2 weight percent based on the total weight of the material, said sintering aid residue comprising one or more of GeO 2 , SiO 2 , Bi 2 O 3 , ZnO, Al 2 O 3 , CuO and B 2 O 3 , which as the sintering aid are provided in combination with PbO such that the sintering aid has a melting point of between about 650° and 900° C.