Infrared and Raman spectra of the new superconducting cuprate perovskites MBa 2Cu 3O 7, M =Nd, Dy, Er, Tm

Abstract

We report far-infrared and Raman studies of several ceramic superconducting cuprate perovskites MBa 2Cu 3O 7 with M=Nd, Dy, Er, Tm. Systematic studies of the phonon-related peaks show that the frequencies of optical phonons related to vibrations of M atoms decrease slightly with increasing atomic number of the rare earth, thus confirming the trend observed earlier for M=Y, Sm, Eu, Gd, Ho. The temperature dependence of phonon features exhibits an anomalous behavior for the optical phonons at ∼310 cm −1 and 280 cm −1. Such anomalous temperature dependence of phonons attributed to the bond bending vibrations of Cu2O2 and Cu2O3 bonds, seems to be a universal property of all superconducting cuprates. Possible origins of the phonons softening and the systematics of the variation of phonon frequencies with the ionic radius of M are discussed.