Journal
ACTA MATERIALIA
Volume 83, Issue -, Pages 149-159Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2014.09.058
Keywords
Bismuth ferrite; Rare-earth; Synthesis-structure relationship; Electromechanical behavior
Funding
- Australian Research Council ARC [LP 0991794]
- Thales Australia
- Slovenian Research Agency Program Electronic Ceramics, Nano, 2D and 3D Structures [P2-0105]
- High-Performance Piezoelectric Materials for Sensors and Actuators in High-Temperature Applications [J2-5483]
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Solid-state (non-activated) and mechanochemical activation (activated) synthesis methods were used to produce Sm-modified BiFeO3 ceramics of composition Bi0.88Sm0.12FeO3. The first part shows that the formation of Bi0.88Sm0.12FeO3 using the two synthesis methods followed a different reaction pathway on annealing the powders. The non-activated ceramics reacted by forming two intermediate phases, isostructural to BiFeO3 and SmFeO3, and then inter-diffusing, forming the final Bi0.88Sm0.12FeO3 solid solution. Unlike the non-activated samples, the activated ceramic powders formed Bi0.88Sm0.12FeO3 phase on annealing the powders, without apparent intermediate phases. As revealed by transmission electron microscopy, the non-activated reaction pathway caused the Pbam phase to form as chemical inhomogeneous (Sm-rich) isolated nano-sized grain inclusions in the final ceramics. Conversely, the activated reaction pathway caused the Pbam phase to form chemically homogeneous nano-regions within the R3c phase grains. The results demonstrate the important role of processing in the appearance of the frequently discussed anti-polar Pbam phase in this system. In the second part, the high electric-field-induced polarization and strain behaviors of these ceramics were studied by means of polarization-electric (P-E) and strain-electric field (S-E) hysteresis loops, and the S-E loops were compared with those of unmodified BiFeO3. Bipolar S-E loops of Bi0.88Sm0.12FeO3 had a distinctive butterfly shape with less frequency dependence relative to BiFeO3 at driving-field frequencies of 0.1-100 Hz. BiFeO3 ceramics exhibite strong driving electric-field-frequency-dependent domain switching, the origins of which were previously attributed to a domain-wall pinning mechanism and hardening behavior. This study shows that Sm-modification induces a hardening-softening transition in BiFeO3 ceramics. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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