Effects of dopants on PbO–MgO–Nb2O5 ceramics near the Pb(Mg⅓Nb⅔)O3 composition

Abstract

We studied the effects of 15 dopants on the dielectric properties of the Pb1–x–yMgxNb2yO1+4y perovskite system. The investigated dopants are Ba, Ag, La, Bi, and Nd, which substitute in the Pb sublattice, and Co, Ni, Zn, Mn, Cr, Dy, Al, Fe, Zr, and Ti, which substitute in the sublattice occupied by Mg and Nb. While the dielectric constants of Pb1−x–yMgxNb2yO1+4y) are not affected by Al, Zr, and Ni dopants, their dielectric constants are increased by Ti dopant and decreased by other dopants. The rates of change in the Curie temperatures of Pb1–x–y MgxNb2yO1+4y with different dopant concentrations were quantitatively measured. The relative effectiveness of these dopants in altering the Curie temperature is correlated to the bond strengths between oxygen and the dopants in either the Pb sublattice or the Mg/Nb sublattice. The effects of these dopants on the dissipation factors and electrical resistivities were investigated. Cobalt and manganese oxides were identified as the most effective dopants in reducing the dissipation factor and lanthanum and barium oxides are effective in increasing the resistivity. We have also observed that zinc oxide promotes densification and reduces the temperature coefficient of capacitance in these compositions. Ternary and quaternary systems based on selected combinations of these dopants were prepared and characterized. Compositions in the Pb(Zn⅓Nb⅔)O3 + Pb(Co⅓Nb⅔O3 + PbTiO3 + Pb1–x–yMgxNb2yO1+4y quaternary systems were shown to be promising candidates for capacitor applications. Furthermore, multilayer capacitors of these promising compositions were fabricated and they were shown to have favorable device properties.