Anomalous dispersion of LO phonon branches in Ba0.6K0.4BiO3 M. Braden, W. Reichardt, A. S. Ivanov and A. Yu. Rumiantsev Europhys. Lett., 34 7 (1996) 531-536 Published online: 01 September 2002 DOI: 10.1209/epl/i1996-00490-0