The phase transitions of KNbO3 under high pressure

A ferroelectric KNbO3 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. KNbO3 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.