Raman scattering of Nd 0.9 Ca 0.1 Ba 2 Cu 3 O 7−δ with different oxygen contents

A series of Nd 0.9 Ca 0.1 Ba 2 Cu 3 O 7−δ samples with different oxygen contents were fabricated by the solid‐state reaction method and thermally treated under different conditions. The superconducting transition temperatures T c 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.