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Anomalous Behaviour of the Transverse Acoustic Phonons in KTa 1 - x Nb x O 3

1993; Institute of Physics; Volume: 23; Issue: 6 Linguagem: Inglês

10.1209/0295-5075/23/6/008

1286-4854

Marc D. Fontana, G. E. Kugel, Laurent Foussadier, W. Kress, Daniel Rytz,

Photorefractive and Nonlinear Optics

In addition to the already known softening of the lowest transverse optic mode (TO) in KTa1 - x Nbx O3 a pronounced temperature dependence of the transverse acoustic (TA) mode in the [100] direction of the Brillouin zone has been observed by inelastic-neutron-scattering measurements for Nb concentrations of x = 0.008 and 0.012. In the vicinity of the phase transition the dispersion curve of the TA branch exhibits peculiarities at small wave vectors. The observed anomalies are attributed to hybridization effects of modes belonging to the same representation and to an exchange of eigenvectors between TO and TA modes.