LATTICE-VIBRATIONS OF Y1-XPRXBA2CU3O7 - THEORY AND EXPERIMENT

We report measurements of the far-infrared reflectance of Y1-xPrxBa2Cu3O7 thin films. Detailed understanding of the experimental lineshapes is achieved with the proper treatment of the SrTiO3 Substrate, the finite film thicknesses, the background contribution of free carriers and the mid-infrared band, and the phonon modes. Shell-model calculations predict the frequencies of the infrared-active phonons to be very similar for YBa2Cu3O7 and PrBa2Cu3O7 with the exception of rare-earth-related vibrations. The experimental frequencies of the in-plane as well as z-polarized infrared-active phonons of PrBa2Cu3O7 agree satisfactorily with the calculated ones. An in-plane phonon mode at 270 cm-1, assigned to vibrations confined to the Y/Pr and neighboring oxygen ions, is found to be sensitive to the rare-earth-ion substitution. We report also the frequencies of the Raman-active B2g and B3g phonons of PrBa2Cu3O7, thus giving a nearly complete picture of all k = 0 eigenmode frequencies in the RBa2Cu3O7 crystal structure.