Inelastic Light Scattering Study of Ferroelectric Sodium
Potasium Niobate Crystals
Takuma Ariizumi1*, Junta Zushi1, Ryu Ohta1, Yuji Noguchi2, Masaru Miyayama2,
and Seiji Kojima1
1
Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573,
Japan
2
Institute of Industrial Science, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo
153-8505, Japan
Among perovdkite oxide ferroelectrics, the lead free potassium sodium niobate, (K1-xNax)NbO3
(KNN) is one of the most promising candidates of piezoelectric materials. However, the basic
physical properties related to a successive phase transition are not yet clarified. Recently the single
crystals of (K0.5Na0.5)NbO3 (KNN50) were successfully grown by a flux method (Y. Kizaki et al.,
Appl. Phys. Lett. 84, 142901 (2006).). The KNN50 undergoes a cubic to tetragonal phase transition
at TC-T =400 oC, and a tetragonal to rhombohedral phase transition at TT-R =190 oC. The lattice
instability of KNN50 crystals are studied by low-frequency Raman scattering. In the rhombohedral
ferroelectric phase, the lowest A1(z) symmetry mode at 60 cm-1 is clearly observed at room
temperature, 293 K. On heating this mode shows remarkable softening towards TT-R. Just above TT-R,
the very intense central peak (CP) appears and its intensity gradually decreases for further heating.
*Presenting author’s email: usen1230@gmail.com