ANOMALOUS BEHAVIOR OF THE TRANSVERSE ACOUSTIC PHONONS IN KTA1-XNBXO3

In addition to the already known softening of the lowest transverse op tic mode (TO) in KTa1-xNbxO3 a pronounced temperature dependence of th e transverse acoustic (TA) mode in the [100] direction of the Brilloui n zone has been observed by inelastic-neutron-scattering measurements for Nb concentrations of x = 0.008 and 0.012. In the vicinity of the p hase transition the dispersion curve of the TA branch exhibits peculia rities at small wave vectors. The observed anomalies are attributed to hybridization effects of modes belonging to the same representation a nd to an exchange of eigenvectors between TO and TA modes.