Local distortions and reduction in Tc in the ceramic superconductor La1.8Sr0.2Cu1-xAgxO4.

Abstract

Substitution of Ag for Cu in the high-${T}_{c}$ ceramic superconductor ${\mathrm{La}}_{1.8}$${\mathrm{Sr}}_{0.2}$Cu${\mathrm{O}}_{4}$ has been found to reduce ${T}_{c}$. The infrared absorption spectra of these superconducting systems show that the vibrational mode, which disappears at $x\ensuremath{\sim}0.15$ for ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}$, appears at a reduced frequency in the Ag-substituted systems. It is argued that the local distortions around the Ag sites result in both the reduction of ${T}_{c}$ as well as the appearance of the absorption peak at 630 ${\mathrm{cm}}^{\ensuremath{-}1}$.