Anomalous behavior around 220 K in optimal doped YBa2Cu3O7−δ investigated by Sr substitution

Much interest has been paid to the origination of anomalous behavior around 220 K in optimal doped YBa2Cu3O7−δ (Y123). In mechanical spectroscopy, an internal friction peak (labeled as P1) was observed in this temperature range. Following a previous internal friction study of Sr substituted Y123, Raman spectroscopy was used to evaluate the structural change during Sr substitution. A clear change of Raman phonon at 340 cm−1, which corresponds to the vibrations of the oxygen atoms in two adjacent planes out of phase and out of the plane, was observed with Sr substitution. Then a correlation between internal friction P1 peak and Raman spectrum supports the close relationship between P1 with the CuO2 plane rather than CuOx chains. Furthermore, the possible relationship of P1 with the dynamical stripe scenario was discussed.