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Pressure Dependence of Electron Density Distribution of Ferroielectric KNbO3 Polymorphs by Maximum Entropy Method (MEM) Using Single Crystal Diffraction Study

Published online by Cambridge University Press:  26 February 2011

Takamitsu Yamanaka ,
Taku Okada ,
Yuki Nakamoto  and
Kenji Ohi
Takamitsu Yamanaka
Affiliation:
t.yamanaka@kce.biglobe.ne.jp, Osaka University, Earth and Space Science, 1-1 Machikaneyama, Toyonaka, 560-0043, Japan, +81-45-785-7878, +81-45-785-7878
Taku Okada
Affiliation:
okatak@ess.sci.osaka-u.ac.jp, Osaka University, Earth and Space Science, 1-1 Machikaneyam, Toyonaka, 560-0043, Japan
Yuki Nakamoto
Affiliation:
nakamoto@cqst.osaka-u.ac.jp, Osaka University, Kyokugen Extreme Research Center, 1-3 Machikaneyama, Toyonaka, 560-0043, Japan
Kenji Ohi
Affiliation:
ohi@ess.sci.osaka-u.ac.jp, Osaka University, Earth and Space Science, 1-1 Machikaneyama, Toyonaka, 560-0043, Japan
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Abstract

Single-crystal structure analysis of KNbO3 has been executed under high pressure through diamond anvil cell installed in the four-circle diffractometer using synchrotron radiation at Photon Factory, KEK in order to clarify the dielectric property. KNbO3 has three structural transitions with increasing pressure at ambient temperature: from orthorhombic structure with the space group Cm2m (Amm2) to tetragonal structure (P4mm) at about 7.0 GPa, to cubic structure (Pm3m) at about 10.0 GPa. The highest-pressure cubic phase is paraelectric, and the other two phases are ferroelectric. The dielectric changes in KNbO3 are clarified by the successive pressure-change of the electron density distribution observed by maximum entropy method (MEM) using high-pressure diffraction data. The MEM electron density maps suggest that the tetragonal phase designates the largest polarization among three polymorphs. The maps also indicate that the localization of the valence electron around the cation position is more enhanced under higher pressure.

Keywords

ferroelectricphase transformationelectron-phonon interactions
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 987: Symposium PP – Materials Research at High Pressure , 2006 , 0987-PP05-03
Copyright
Copyright © Materials Research Society 2007

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