| dc.description |
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<sup>-1</sup> Raman peak (B<sub>1g</sub>), associated with the out-of-plane vibrations of O atoms of the CuO<sub>2</sub> plane, is shifted by +2% upon decreasing from 294 K to 96 K while the 466 and 627 cm<sup>-1</sup> peaks (both A<sub>1g</sub>) associated with the other O atoms are not shifted. So Raman spectroscopy confirms a possible change of the Cu-O bonding, in the CuO<sub>2</sub> plane, with temperature, while the Bi-O bonding appears to be unchanged. A hardening of the Cu-O bond is observed at low temperature. |
