No abstract

Several compounds with m = 2,3,4, and 5 in the general formula (Mez'0z)2+ (Me7,L--l R, 03m+l)zwere synthesized, a number of them for the first time. They possess a layer-type crystal structure. Bi3+ may be the only suitable ion for the Me' sites; R may be Gas+, Ti4+, Nb5+, or Ta". The restrictions on the size of Me ions increases with increasing value of m. Lattice parameter data for the compounds and indexed X-ray powder patterns for m = 5 compounds are presented.

No 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.