Raman scattering of Nd0.9Ca0.1Ba2Cu3O7−δ with different oxygen contents

A series of Nd0.9Ca0.1Ba2Cu3O7−δ samples with different oxygen contents were fabricated by the solid‐state reaction method and thermally treated under different conditions. The superconducting transition temperatures Tc were measured to be above liquid nitrogen temperature. The measurements of the thermopower S showed a monotonic decrease with increasing oxygen content. The Raman peak of the apical oxygen O(4) stretching vibration shifts to higher wavenumber, which also shows a monotonic increase in oxygen content. Two modes at 224 and 597 cm−1 are assigned to the disorder‐induced stretching vibrations of copper and oxygen atoms, respectively. They arise from symmetry breaking from short‐chain fragments and are not due to impurity phases. Copyright © 2001 John Wiley & Sons, Ltd.