LATTICE-DYNAMICS AND THE FAR-INFRARED SPECTRA OF PRXLN1-XBA2CU3O7-Y (LN=LANTHANIDE)

Lattice dynamical calculations on high T(c) superconductors and non su perconductors PrxLn1-xBa2Cu3O7-y (Ln=Y, Er, Ho, Dy, Gd, Sm, Nd) are st udied using the shell model. Far infrared reflection spectra of PrxLn1 -xBa2Cu3O7-y are studied for various Pr concentration x. Carrier densi ty of 4-6 x 10(20) CM-3 is shown from the infrared optical measurement to be the critical carrier concentration for the appearance of the su perconductivity for all Ln. ''Barium mode'' near 154 cm-1 has large os cillator strength for the systems studied here. The oscillator strengt h of the phonon band by the Kramers-Kronig analysis is found to depend strongly on the absolute value of the broad back ground reflection, a nd the origin of the anomalously large change of the oscillator streng th of the ''Barium mode'' near 154 cm-1 is attributed to this effect.