We report on a Raman-scattering investigation of phonons in ceramic ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_4$${\mathrm{O}}_8$ (${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$124) with x=0–1, and (${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${)}_2$${\mathrm{Ba}}_4$${\mathrm{Cu}}_7$${\mathrm{O}}_{15\mathrm{-}\mathrm{\delta }}$ (${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$247) with x=0–0.6. It is found that the ${\mathit{A}}_{\mathit{g}}$ symmetry phonons of the BaO layers and the CuO double-chain layers increase in frequency with Pr content x, while ${\mathit{B}}_{2\mathit{g}}$ and ${\mathit{B}}_{3\mathit{g}}$ symmetry phonons decrease in frequency. In the ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$247 samples we are able to identify two symmetry allowed apical oxygen ${\mathit{A}}_{\mathit{g}}$ modes. The ${\mathit{B}}_{1\mathit{g}}$-like plane oxygen phonon softens by ∼12% from x=0 to x=1, and exhibits a two-mode behavior at intermediate x in both ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$124 and ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$247. Polarized micro-Raman spectra of Pr124 crystallites show that several phonons are asymmetric, exhibiting Fano line shapes similar to what has been found in superconducting Y124. The variation in phonon frequencies with Pr content is similar to what has been reported for the single-chain cuprate ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$${\mathrm{Ba}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ (${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Pr}}_{\mathit{x}}$123), and the changes can be understood from the variation in structural parameters. We do not observe any peculiarities that can explain the disappearance of superconductivity, or the different rates of ${\mathit{T}}_{\mathit{c}}$ suppression in the three different Y-Ba-Cu-O systems, upon Pr substitution. © 1996 The American Physical Society.

• Received 30 June 1995

DOI:https://doi.org/10.1103/PhysRevB.53.3590