Microdomain fluctuations in lead scandium tantalate (PST) observed by high resolution transmission electron microscopy

Abstract

If a crystalline material contains a set of static or dynamic aperiodic textures on a wide range of length scales, which may be more or less strongly coupled t o the critical fluctuations required for a phase transition, then we may expect a diffuse phase transition to occur. Thus different regions of the crystal will transform with different effective Curie ternperatures, depending on the local coupling interactions. This much can be said in a perfectly general way; it is the basic approach underlying the renormalization group theory of phase transitions. The length scales involved may range from grain boundaries (˜1 μm) through ferroelectric and ferroelastic domain walls (˜ 1 nm − 0.1 μm); discommensurations (≤ 20 nm) commensurate and incommensurate superlattices (˜ 1 − 5 nm); fluctuations in occupancy of cation sites in complex oxides for example, with short-range order on the scale of 0.1 − 2nm; finally we have small (point) defects and atomic structure on the scale of 0.lnm. Striking evidence of all of these phenonema, occurring in one material, was obtained by the authors in the case of strontium barium niobate (Bursill and Peng, 1986; Bursill and Peng, 1987).