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Successful Observation of Precessional Motion of Polarization Inside Piezoelectric Body (Press Release)

Release Date
03 Jul, 2012
  • BL02B2 (Powder Diffraction)
- Elucidation of very piezoelectric mechanism: a new way for developing lead-free materials -

Tokyo Institute of Technology
Kyoto University
Osaka Prefecture University

The dynamic precessional motion of the electric polarization*2 vector within a piezoelectric body*1 was successfully observed by a group of researchers. The study group consisted of the following researchers: Dr. Kengo Oka (extraordinary research associate at Tokyo Institute of Technology), Prof. Masaki Azuma (Tokyo Institute of Technology), two graduate students at Osaka Prefecture University (Tsukasa Koyama, Tomoatsu Ozaki), Prof. Shigeo Mori (Osaka Prefecture University) and Prof. Yuichi Shimakawa. Piezoelectric zirconate titanate (PZT) is a practically used piezoelectric material characterized by its marked piezoelectric property, and the origin of this unique property has long been considered to be linked with the precessional motion of polarization. However, the process has evaded actual observation up to the present.

Dr. Oka (extraordinary research associate) and co-workers made a close examination of the crystal structure of the monoclinic perovskite BiCo1−xFexO3 - a piezoelectric material newly developed simulating the PZT structure - and found that the directional vector of polarization makes a precession movement depending on the temperature and composition. Piezoelectric materials have found a variety of applications in electronic devices as sensors and actuators*3. The findings obtained through the observations reported here are expected to pave the way for the development of a new breed of piezoelectric materials free of environmentally hazardous lead.

The research results were published in the online version of “Angewandte Chemie International Edition” (a German scientific journal) on the 3rd of July.

Publication:
"Polarization Rotation in the Monoclinic Perovskite BiCo1−xFexO3"
Kengo Oka, Tsukasa Koyama, Tomoatsu Ozaaki, Shigeo Mori, Yuichi Shimakawa, Masaki Azuma
Angewandte Chemie International Edition, 51 (2012)

<<Figures>>

Fig.1. Lattice structures of: tetragonal (left), rhombohedral (piezoelectric body)(center), and monoclinic (right) crystals. BiCoz0.3Fe0.7O3 belongs to the monoclinic structure.
Fig.1. Lattice structures of: tetragonal (left), rhombohedral (piezoelectric body)(center),
and monoclinic (right) crystals. BiCoz0.3Fe0.7O3 belongs to the monoclinic structure.

While the direction of electric polarization (the red arrows in the figure) is fixed in tetragonal and rhombohedral structures, it can make a precessional motion in a plane (drawn in pink) in the monoclinic phase.

Fig.2. a) Synchrotron radiation X-ray diffraction profiles of BiCoz0.3Fe0.7O3 for levels of temperatures, b) the directions of electric polarization calculated from the diffraction data.
Fig.2. a) Synchrotron radiation X-ray diffraction profiles of BiCoz0.3Fe0.7O3 for levels of temperatures,
b) the directions of electric polarization calculated from the diffraction data.

The figure indicates that the directional vector makes a precessional motion with temperature.

<<Glossary>>
*1 Piezoelectric body
A class of materials characterized by the generation of surface charges when placed under mechanical stress, and deformation when placed under an external electric field. The origin of these characteristics is ascribed to electric polarization.

*2 Electric polarization
The partial separation of electric charges within a material, due to displacement of positive and negative ions from the center of neutrality.

*3 Actuator
A driving device that performs a simple mechanical movement such as elongation-contraction, bending-stretching, or rotation.


For more information, please contact:
　　Prof. Masaki Azuma (Materials & Structures Laboratory, Tokyo Institute of Technology)
　　　　E-mail :