The Phase Transitions of KNbO₃ Under High Pressure

A ferroelectric KNbO ₃ has been investigated to 11.4 GPa at room temperature by angle-dispersive powder diffraction with diamond anvil cell using synchrotron radiation, which was performed by a high-resolution evaluation setting. KNbO ₃ transforms from orthorhombic to tetragonal lattice at around 6 GPa, and further transforms to a cubic lattice at about 9.2 GPa. Single-crystal X-ray diffraction studies under pressures clarified the space groups of the three phases and their lattice constants. The extinction rule of the observed reflections and diffraction intensity distribution proved Cm2m, P4mm and Pm3m for orthorhombic, tetragonal and cubic polymorphs, respectively.

Keywords:

• Perovskite
• KNbO₃
• X-ray diffraction

Acknowledgment

The present investigation was performed under the auspice of KEK proposals of 2004G252, 2002G199 for powder experiment.

Paper originally presented at IMF-11, Iguassu Falls, Brazil, September 5–9, 2005