Development of PZT powders by wet chemical method and fabrication of multilayered stacks/actuators

Lead zirconate titanate (PZT) compositions near morphotropic phase boundary (MPB) Pb(Zr_xTi_1−x)O₃, 0.48≤ x ≤0.54, were prepared by wet chemical route using water soluble precursors. Compositions were prepared with donor dopants, such as La³⁺, Nd³⁺ or their combinations. The combined hydrous precursors were calcined in the temperature range of 750–900 °C. From the X-ray diffraction (XRD) patterns of calcined PZT powders, a change of tetragonal to rhombohedral phase was noticed with increase in zirconia concentration from 0.48 to 0.54 mol. Both rhombohedral and tetragonal phases were found in the composition range of 0.52–0.54 mol ratios of zirconia, therefore, this range was identified as MPB composition. Calcined PZT powders were compacted and sintered at 1250 °C/2 h in a closed lead rich atmosphere. The sintered compacts were leveled, polished, electroded and the ferroelectric and dielectric properties were measured. After poling, piezo properties were also measured. In case of undoped samples, it was observed that remnant polarization (P_r), dielectric constant (K) and piezoelectric charge constant (d₃₃) increase with zirconia concentration. In general, the above properties increase substantially by addition of dopants at low concentrations. The increase was found more for lanthanum doped samples compared to neodymium. The d₃₃ value for the combined dopants of lanthanum and neodymium was in between the values obtained for individual dopants of the same concentration. A few multilayered (25 layers) stacks were fabricated using thin strips cut from the sintered blocks of the above powders. The strips were electroded and poled in a dc field of 2 kV/mm and were laminated into multilayered stacks. The free strain of the multilayered stacks was measured by applying a dc voltage up to 650 V. The free strain was found to be linear and 0.1% of the height of the stack.