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Published on: June 1, 2016
Nanoscale phase boundaries: a new twist to novel functionalities.
1Department of Physics, University of California, Berkeley, California 94720, USA. jxzhang@bnu.edu.cn
Nanoscale
|September 6, 2012
Summary
Nanoscale phase boundaries in bismuth ferrite (BiFeO3) thin films enable exotic multiferroic properties. Mechanical strain induces phase transitions, creating novel functionalities at these boundaries, not in parent phases.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nanotechnology
Background:
- Nanoscale phase boundaries in functional materials exhibit unique phenomena absent in parent phases.
- Complex oxides, including multiferroic bismuth ferrite (BiFeO3), show key roles of nanoscale inhomogeneities in controlling electronic and ionic structures.
- BiFeO3 exhibits room-temperature multiferroicity, with a unique ability to alter its ground state under mechanical strain.
Purpose of the Study:
- To review progress in understanding the novel functionalities arising from strain-induced phase transitions in BiFeO3 thin films.
- To explore the role of nanoscale phase boundaries in controlling electromechanical and magnetic properties.
- To propose origins for enhanced piezoelectric and magnetic responses at phase boundaries.
Main Methods:
- Epitaxial strain engineering of BiFeO3 thin films on substrates.
- Investigation of phase transformations from rhombohedral to tetragonal-like structures under compressive strain.
- Analysis of mixed-phase states formed by nanoscale rhombohedral and tetragonal-like phases.
- Characterization of electromechanical response and magnetic properties.
Main Results:
- Compressive strain (~4-5%) transforms the BiFeO3 ground state from rhombohedral to a tetragonal-like phase (c/a ratio ~1.26).
- Partial relaxation of strain leads to a mixed-phase state with nanoscale rhombohedral and tetragonal-like phase admixtures.
- Novel functionalities, including giant piezoelectric response and enhanced magnetic moment, are observed at these phase boundaries.
- These functionalities are attributed to flexoelectric and flexomagnetic effects at the boundaries.
Conclusions:
- Nanoscale phase boundaries in strained BiFeO3 are crucial for novel electromechanical and magnetic functionalities.
- Strain-induced phase morphing provides a pathway to explore unique phenomena in constrained dimensions.
- Flexoelectric and flexomagnetic effects offer a potential explanation for the enhanced properties observed at phase boundaries.
