Effect of MnO2, Bi2O3, and ZnO additions on the electrical properties of lead zirconate titanate piezoceramics

The effect of manganese dioxide additions on the electrical properties of lead zirconate titanate (PZT) piezoceramics has been investigated. The results demonstrate that, taken alone, manganese dioxide does not ensure the formation of hard PZT. The valence state of manganese in the piezoceramics is shown to be 4+ if no other dopants are present and 3+ if manganese is introduced in combination with Bi and Zn. Microstructural examination indicates that the grain size of the singly doped ceramics is 5-15 mu m, while that of the codoped ceramics is 1-3 mu m. The polarization current curves of the piezoceramics containing manganese, bis-muth, and zinc oxides have extra maxima, which points to significant internal fields. The manganese is shown to reside at grain boundaries. The conclusion is made that it is the composition of Mn-containing intergranular phases. rather than the presence of manganese ions, that plays a key role in the formation of hard piezoceramics.