Improved Aging and Switching of Lead Zirconate-Lead Titanate Ceramics with Indium Electrodes

Abstract

After repeated switching, ferroelectric ceramic plates will exhibit aging evident in hysteresis loops as a marked decrease in remanent polarization (Pr) and an increase in coercive field (Ec). A hot-pressed ceramic having a composition of 65% lead zirconate-35% lead titanate with 2 at.% lanthanum and having a grain size 2 μ or less was used to study the effects of various electrode materials. The source disks were polished down to a thickness of 25, 37, or 63 μ and square plates 2.5 mm on edge were cut for testing. Prior to the application of the electrodes, the square plates were annealed in air at 700°C for 10 min and cooled slowly to room temperature. Electrodes were then applied as opposing disks 1.5 mm in diameter on the surfaces of the plates. A Sawyer-Tower circuit was used to observe hysteresis loops formed on an oscilloscope at a frequency of 60 Hz, and occasionally at 600 Hz. Maximum applied voltage corresponded to approximately 3Ec. Results were obtained for vapor plated electrodes of Al, Cr–Au, Pb, PbO–Ag, Sn–Ag, Ag, Ga, and In. For all but the In electrodes, a large decrease of Pr was evident by 107 cycles. The In electrodes yielded lower values of Ec (approximately 8 kV/cm) and the value of Ec did not increase appreciably over the test period. After 109 cycles, Pr had decreased by only 14% for the In electrodes.