Phonons in YBa2Cu3O7-δ-type materials

Abstract

We report infrared reflectivity measurements on YBa2Cu3O7-δ and SmBa2Cu3O7-δ, in the tetragonal semiconducting phase. Ten of the eleven symmetry allowed modes are seen, and the eleventh is probably observed in the Sm material. When Sm replaces Y, two of the phonons at 200 cm-1 shift to lower energy by 22 and 27 cm-1. These modes, and the two at 110 cm-1, which undoubtedly involve BA motions, are very sharp. From Sm-atom substitution, we can surmise which of the two-high-frequency Cu-against-O modes is the planar Eu mode, and which is the chain A2u mode. Surprisingly, with Sm replacing Y, the planar mode shifts down in frequency by 25 cm-1 (and the chain mode is hardly affected). Other aspects of the data are discussed. © 1988 The American Physical Society.