The Ferroelectric Mode In Orthorhombic Knbo3

Both Raman scattering and infrared reflectivity measurements have been performed to determine the complete optic mode spectrum of orthorhombic KNbO3 and characterize the ferroelectric modes. The low frequency, k ∼ 0 mode is quasitransverse and possesses a spacial anisotropy similar to the TA branch at finite k. Of the original cubic ferroelectric mode, the component along the remaining soft direction is found at 56 cm-1 and not overdamped (Γ/ω = 1), while the other two components have stiffened equally so that the mode is essentially isotropic in the orthogonal polarizations. © 1975.171215411543Harada, Axe, Shirane, (1971) Phys. Rev., 4 B, p. 155Nunes, Axe, Shirane, A neutron study of diffuse scattering in cubic KNbO3 (1971) Ferroelectrics, 2, p. 291Shirane, Nathans, Minkiewicz, (1967) Phys. Rev., 157, p. 396Winter, Wiesendanger, Claus, (1974) Phys. Status Solidi (b), 64, p. 95Currat, Comes, Dorner, Wiesendanger, (1974) J. Phys. C: Solid State Phys., 7, p. 2521Katz, Megaw, The structure of potassium niobate at room temperature: the solution of a pseudosymmetric structure by Fourier methods (1967) Acta Crystallographica, 22, p. 639Wiesendanger, (1974) Ferroelectrics, 6, p. 263(1975) Bull. Am. Phys. Soc., 20, p. 327. , A preliminary account can be found inBarker, Jr., Hopfield, (1964) Phys. Rev., 135, p. A1732Wemple, Didomenico, Jr., Camlibel, (1968) J. Phys. Chem. Solids, 29, p. 1797Gillis, Koehler, (1971) Phys. Rev., 4 B, p. 397