Dielectric, pyroelectric, electrostrictive and relaxor properties of lead-zinc-niobate - barium-titanate - lead-titanate ceramic solid solutions.

摘要

The exceptional piezoelectric properties of the morphotropic boundary compositions of Lead zinc niobate-Lead titanate (PZN-PT) single crystals are not observed in the ceramic due to the instability of the required perovskite phase. In the past, a small quantity of Barium titanate (BT) was used to stabilize the perovskite phase, and the dielectric and piezoelectric properties of the new solid solution were studied extensively. For the present study, the (1-x-Y)PZN-xBT-yPT compositions were prepared with three different aims.; 1. The electrostrictive properties of compositions in the PZN/BT/PT system with different crystal structures were characterized. Irrespective of the crystal structure, the transverse electrostrictive Q coefficients showed a relatively constant magnitude of {dollar}-{dollar}0.007 to {dollar}-{dollar}0.009 m{dollar}sp4{dollar}/C{dollar}sp2{dollar}. Among these compositions, the ceramic with 0.85PZN-0.10BT-0.05PT showed optimum properties for room temperature applications. Some of the dielectric and electrostrictive properties of this composition are: K{dollar}sb{lcub}rm RT{rcub}{dollar} = 8050; T{dollar}sb{lcub}rm max{rcub}{dollar} = 83{dollar}spcirc{dollar}C; T{dollar}sb{lcub}rm t{rcub}{dollar} = 22{dollar}spcirc{dollar}C; Q{dollar}sb{lcub}12{rcub}{dollar} = {dollar}- 0.0073{dollar} m{dollar}sp4{dollar}/C{dollar}sp2{dollar}; s{dollar}sb2{dollar} at 25 kV/cm = {dollar}-6.6 times{dollar} 10{dollar}sp{lcub}-4{rcub}{dollar}. Compared to the commercially utilized PMN/PT compositions, this material shows about 60% higher induced strain and about 60% lower room temperature dielectric constant. But it also shows a slightly larger hysteresis in P-E and s-E characteristics.; 2. When a relaxor ferroelectric forms a solid solution with a first-order ferroelectric material, the relaxor nature of the solid solution will diminish as the amount of the second phase increases. But in (1 {dollar}-{dollar} x)PZN-xBT system, enhanced relaxor characteristics were observed with BT addition. This behavior was explained by hypothesizing the formation of nonpolar BZN rich regions. The same hypothesis was used to explain the relaxor characteristics of the MPB compositions in (0.95-y)PZN-0.05BT-yPT series. Along with the normal relaxor characteristics, the MPB compositions with a tetragonal structure showed a larger thermal hysteresis in the dielectric spectrum similar to that of PLZT compositions. Since it is not possible to prepare the MPB compositions of PZN/PT ceramics, the effect of the absence of the nonpolar regions on the dielectric behavior was studied with a PMN/PT (0.65PMN-0.35PT) ceramic.; 3. The diluting effect of Ba was clearly seen by comparing the dielectric properties of different PZN/BT/PT compositions. Since it is not possible to prepare PZN ceramic, the PZN/PT powders were prepared by a modified coulumbite precursor technique. By this technique it was possible for the first time, to prepare the pure perovskite powder with only 15 mole% of PT. But since the sintered material showed only 85% of the theoretical density, a peak dielectric constant of only about 8000 was observed at 210{dollar}spcirc{dollar}C. By utilizing the same technique, a processing procedure was optimized to prepare MPB compositions with only 2 mole% BT.