Rod-shaped PZT specimens were sintered with 1 w/o and 5 w/o PbO additives. ZrO/sub 2/ segregations were found in the 1% PbO specimen, and higher PbO segregations were found along the grain boundaries and at grain boundary with no ZrO/sub 2/ segregations in the 5% PbO specimen. On the basis of these microstructural observations and preliminary poling studies sintered thin disc specimens with a 3 w/o PbO additive were prepared for extensive poling studies. It was found that the breakdown limit of a specimen depends strongly on the porosity and the pore distribution. The best specimen (3 w/o PbO) could be poled at a field of 6 kV/mm, a temperature of 100/sup 0/C and a time of 10 minutes without breakdown. The planar coupling coefficient, K/sub p/, under these conditions was immediately after poling equal to 0.62. This value is the highest among the reported K/sub p/ values for pure PZT. Within the breakdown limit, K/sub p/ increases with increase of poling field, temperature and time in a regular manner so that K/sub p/ values for other conditions can be predicted. It was found that the specimen became unstable above 125/sup 0/C even when poled at low fields for shortmore » times. It was also found that a high saturated K/sub p/ value could not be reached at temperatures below 50/sup 0/C even when poled for long times. « less