Abstract

Raman spectra of high-temperature superconducting materials comprised of Y-Ba-Cu-O compounds are reported. These spectra show numerous lattice modes which are attributed to both the superconducting phase YBa₂Cu₃O₇ and also impurity phases of BaCuO₂ and Y₂BaCuO₅. Ten Raman active modes are observed in the superconducting material with frequencies of 153, 217, 291, 309, 335, 441, 493, 507, 601, and 640 cm^–1. The temperature dependence of these spectra has been measured, and the 337-cn^–1 mode shows anomalous behavior. Above T_c it increases in frequency on cooling, but below T_c its frequency shift changes sign as the mode begins to soften. This very interesting anomaly may suggest the possibility of larger changes in the phonon spectra occurring at nonzero wave vectors. Raman spectroscopy has been shown to be a sensitive probe of both the structure of the superconducting phase and of impurity phases in the material.

© 1987 Optical Society of America