Poster Session I - University of Ulsan

Poster session II
Structural study of gradient lattice distortion in BaTiO3-KNbO3 composites
with heteroepitaxial interface
Eisuke Magome 1* , Yoshihiro Kuroiwa 1 , Hironori Yoshimura 1 , Chikako Moriyoshi 1 ,
Kenta Yamashita 2 , Ichiro Fujii 2 , Kouichi Nakashima 2 ,
Nobuhiro Kumada 3 and Satoshi Wada 2
1 Graduate School of Science, Hiroshima University, Hiroshima 739-8526, Japan
2 Interdisciplinary Graduate School of Medical and Engineering, University of Yamanashi,
Yamanashi 400-8510, Japan
3 Center for Crystal Science and Technology, University of Yamanashi, Yamanashi 400-8511,
Japan
* E-mail address of the corresponding author : magome@sci.hiroshima-u.ac.jp
Lead-free ferroelectric materials are of concern due to the environmental problems, and
are anticipated to be substituted for conventional ferroelectrics such as Pb(Zr,Ti)O3 ceramics.
Recently, we have found that solvothermally synthesized BaTiO3 (BT)-KNbO3 (KN)
composites with a heteroepitaxial interface show the fairly large piezoelectric constant
compared with sintered BT-KN composites in the normal way [1]. The enhancement in the
piezoelectric response would be attributed to the distinct interface, so that we consider that
promising lead-free ferroelectric materials are emerged in the process to develop such
composites with a heteroepitaxial interface. In this study, we have carried out the structural
study of the KN-BT composites to reveal the clear relationships between the crystal structures
of the interface and the dielectric property.
KN-BT composites with the KN/BT molar ratio of 0.5 were synthesized by solvothermal
method, in which the ceramic grain with homogeneous size-distribution is configurated with a
BT particle with a radius of 150 nm at the inner core covered with KN. Synchrotron radiation
powder diffraction data were collected using the large Debye-Scherrer camera installed at
SPring-8 BL02B2. The energy of X-rays was 18.5 keV (wave length ��= 0.669 Å). We
analyzed the crystal structure of the ceramic grain on the basis of the core/multi-shell model
using the Rietveld method. It is revealed that the BT particle is significantly distorted in the
large region to form the interface with KN through the gradually distorted region from the
tetragonal structure at the core toward the cubic structure at the boundary between BT and
KN. The volume of the distorted interface region is decreased and the piezoelectric response
is suppressed by annealing the composites at 1000ºC for 10 h. These experimental results
provide an evidence that the interface controls the ferroelectric properties of the composite
ceramics.
[1] I. Fujii et al. : Appl. Phys. Lett. 99 (2011) 202902.
P- 77