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Lecture

WEB A transmission electron microscopy study of the domain morphology and phase assemblage in quenched versus furnace cooled lead-free Na0.5Bi0.5TiO3-BaTiO3



Growing concerns about the toxicity of lead and related environmental hazards has driven researchers to look for lead-free alternatives to replace lead-containing ferroelectrics. After about two decades of research in this direction, select material systems have been singled out for specific applications. Lead-free (1-x)(Na0.5Bi0.5)TiO3-xBaTiO3 (NBT-BT) is identified to be a suitable replacement for lead-containing materials in high power ultrasonic applications. However, this material class exhibits lower thermal stability. Recently, quenching these ceramics from sintering temperatures has been shown to overcome the limitations in the operational range of temperatures. Upon quenching, the thermal depolarization temperature, Td is enhanced and a stabilization of ferroelectric order is observed. In order to derive structure-property correlations, microstructural features related to ferroelectric domains and polar nanoregions (PNRs) are characterised using transmission electron microscopy. A comparative investigation into the domain morphology and crystal symmetry is presented for furnace cooled and quenched samples of NBT with 3, 6, 9 and 12 mol.% BT. Bright and dark field imaging is used to visualize changes in domain structure, such as the transition from a complex square-net domain pattern in NBT-3BT, to faint domain contrast in NBT-6BT, to lamellar grain-traversing domains in NBT-9BT and NBT-12BT furnace cooled samples. Selected area electron diffraction (SAED) patterns are used to obtain information about coexisting phases. Moreover, based on the occurrence and intensity of ½ {ooo} and ½ {ooe} superlattice reflections indicating octahedral tilting, conclusions about the presence of rhombohedral (a-a-a- tilt system) versus tetragonal (a0a0c+ tilt system) phases were made for furnace cooled and quenched NBT-BT samples.

Speaker:
Ann-Katrin Fetzer
Technische Universität Darmstadt
Additional Authors:
  • Andreas Wohninsland
    Technical University of Darmstadt
  • Prof. Dr. Hans-Joachim Kleebe
    Technical University of Darmstadt
  • Dr. Lalitha Kodumudi Venkataraman
    Technical University of Darmstadt