Soft modes and the structure of ferroelectric tetragonal potassium tantalate-niobate (I)

Publisher Website
Google Scholar
Abstract
The structure of ferroelectric tetragonal KTN (KTaxNb1 - xO3 with x = 0.56), which is isomorphous with BaTiO3, has been determined by neutron diffraction. The atomic displacements from the cubic perovskite positions are δ(K) = 0.012 ± 0.003, δ(Ta,Nb) = 0.0003, δ(O(1)) = -0.010 ± 0.001 and δ(O(2)) = δ(O(3)) = -0.011 ± 0.001 in fractions of the unit cell edge c = 4.006 Å = 1.0033a. These displacements are in fair agreement with those expected from the soft optic mode identified by inelastic neutron scattering. The essential character of this mode at q = 0 is a vibration of the oxygen atoms against the remainder, with the heavy (Ta, Nb) atoms virtually fixed at the centre of mass.