Core-shell structures in pressureless-sintered undoped Pb(Fe2/3W1/3)O-3 ceramics

Citation
Ry. Yang et al., Core-shell structures in pressureless-sintered undoped Pb(Fe2/3W1/3)O-3 ceramics, ACT MATER, 49(13), 2001, pp. 2597-2607
Citations number
40
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science","Material Science & Engineering
Journal title
ACTA MATERIALIA
ISSN journal
1359-6454 → ACNP
Volume
49
Issue
13
Year of publication
2001
Pages
2597 - 2607
Database
ISI
SICI code
1359-6454(20010801)49:13<2597:CSIPUP>2.0.ZU;2-M
Abstract
Core-shell structures have been found by both scanning and transmission ele ctron microscopy in undoped Pb(Fe1/3W2/3)O-3 ceramics when a solid-state-re acted powder of stoichiometric composition was sintered at 800 degreesC. Th e presence of superlattice reflections of the {1/2 1/2 1/2}-type, often ter med F-spots, indicates that the existence of nanoscale ordered domains of 2 -5 nm size in both core and shell is due to chemical ordering of the B-site cations with alternating Fell and W6+ along the < 111 > direction. The cer amic is densified by the assistance of a low-temperature liquid eutectic at similar to 690 degreesC. A formation mechanism of core-shell structures in Pb(Fe1/3W2/3)O-3 ceramic is proposed. It can be described by solution-repr ecipitation and phase transformation subsequently to perovskite Pb(Fe1/3W2/ 3)O-3, involving at least two intermediate phases which are formed at tempe ratures below and above the low-temperature liquid eutectic point and relat ed to pyrochlore (Pb2FeWO6.5). The cores are characterised by "black dots" and contain relatively Fe-excess. The shells exhibiting featureless contras t are free of "black dots" but contain W-excess relative to the cores. Long term sintering at 800 degreesC has facilitated the inward diffusion of W6 to the grain interior when the distribution of the B-site cations is impro ved. As a result, the shell increases its size at the expense of the core. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.