Temperature-induced frequency shift of the Raman-active CuO₂planar oxygen vibrational modes of Bi-2212 related to a change of the Cu-O bonding

Abstract

A change, with temperature, of the Cu-O or Bi-O bondings was previously suggested because irregular variations, with temperature, of the lattice parameters and of the electrical resistivity were observed in Bi-2212 crystals. To check the validity of this hypothesis, a study of the variation, with temperature, of the positions of Raman peaks associated with vibrations of the different kinds of O atom has been performed at room and at low temperature. It is shown here that the 285 cm −1 Raman peak (B 1g), associated with the out-of-plane vibrations of O atoms of the CuO 2 plane, is shifted by +2% upon decreasing from 294 K to 96 K while the 466 and 627 cm −1 peaks (both A 1g) associated with the other O atoms are not shifted. So Raman spectroscopy confirms a possible change of the Cu-O bonding, in the CuO 2 plane, with temperature, while the Bi-O bonding appears to be unchanged. A hardening of the Cu-O bond is observed at low temperature.

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