Effect of composition and temperature on electric fatigue of La-doped lead zirconate titanate ceramics

Abstract

Composition and temperature of ferroelectric La-doped lead zirconate titanate ceramics influence its electric fatigue behavior, defined as the degradation of the electrical properties under the action of an ac field applied for a long time. Compositions of rhombohedral symmetry exhibit little or no fatigue compared with those of tetragonal and orthorhombic symmetry. At temperatures higher than the dielectric maximum, no fatigue effect was detected. Compositions close to phase boundaries (FE-AFE, FE-FE, or FE-PE) display significant fatigue behavior. Electric fatigue arises from the pinning of domains by space charges or injected carriers or from microcracking. The former (which are charge related) is accompanied by smaller strains and is recoverable by thermal and electrical treatment, while the latter (arising from microcracking) arises from large incompatible stresses between grains and is a permanent damage. The understanding of the mechanism of electric fatigue gained in the present study provides guidelines for enhancing the long-term reliability of devices based on ferroic materials.

Elastic aging from coexistence and transformations of ferroelectric and antiferroelectric states in PZT

“…It is usually found that the AFE materials withstand repetitive electric cycling better than the FE materials 26,33 with some compositions withstanding 10 7 cycles before appreciable decrease in the saturation polarization and strain. Yet, the Young's modulus of AFE PZT may suffer huge softenings, up to a factor of 1/4, simply upon aging at room temperature few weeks with few thermally induced AFE/FE transitions.…”

“…The accommodation of the misfit strain has been proposed to cause broken and dangling bonds 9 and to promote the migration of the larger Zr 4+ cations to the AFE domains and smaller Ti 4+ and La 3+ cations to the FE domains 24 . Also microcracking can be found in fatigued FE and AFE ceramics 26,27 , but neither microcracking nor a large/small cation imbalance should be the cause of the elastic aging discussed here, because they are not expected to be recovered by mild annealing well below the sintering temperature. In fact, the strong electric and elastic fields that might possibly promote the cation migration during the coexistence of the AFE and FE domains are missing in the C-PE phase, and under such conditions the cation migration occurs only at the sintering temperature.…”

Phenomenological description of polarization switching in ferroelectric semiconductors with charged defects

“…In such case the inner field in the bulk of the sample is the sum of the external field and predetermined depolarization field originated from displacement screening [30]. In contrast to this at δρ s ≠0 the inner field δE contains the random component dependent over δρ s (r) and δD in accordance with (9)- (10).…”

“…The system of equations (9)- (12) is complete, because the quantities E δ δ , n can be expressed via the fluctuations of displacement δD and δρ s (r) allowing for (9), (10). System (9)-(12) determines the spatial-temporal evolution of the displacement in the bulk sample and has to be supplemented by the initial distributions of all variables.…”

“…Constricted hysteresis loops similar to observed by authors of ref. [9] were found in the La-doped lead zirconate titanate ceramics with composition near the morphotropic boundaries between ferroelectric tetragonal, rhombohedral and antiferroelectric phases [10].…”