Temperature-induced frequency shift of the Raman-active CuO2 planar oxygenvibrational modes of Bi-2212 related to a change of the Cu-O bonding

A change, with temperature, of the Cu-O or Bi-O bondings was previously sug gested because irregular variations, with temperature, of the lattice param eters and of the electrical resistivity were observed in Bi-2212 crystals. To check the validity of this hypothesis, a study of the variation, with te mperature, of the positions of Raman peaks associated with vibrations of th e different kinds of O atom has been performed at room and at low temperatu re. 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 CuO2 plane, is shifted by +2 % upon decreasing from 294 K to 96 K while the 466 and 627 cm(-1) peaks (bo th A(1g)) associated with the other O atoms are not shifted. So Raman spect roscopy confirms a possible change of the Cu-O bonding, in the CuO2 plane, with temperature, while the Bi-O bonding appears to be unchanged. A hardeni ng of the Cu-O bond is observed at low temperature.